Bicycle Technology: Wheels

The typical bicycle wheel can be considered a minor technical miracle. With a minimal weight of its own, the wheel not only carries a heavy weight by comparison, it also has minimal rolling resistance arid even provides some shock absorption. Fig. 8.1 shows such a wheel, built up of hub, spokes, rim, tire and inner tube. These are the parts covered in this section.

8.1 and 8.2. Above: Parts of the wheel. Below: High flange and low flange mountain bike hubs from Campagnolo.

The Hub

The hub is the heart of the bicycle wheel, covered here only in its general form, while some special types with integrated gearing and brakes will be described in Sections 11 and 13, respectively. Since the entire wheel is removed and installed by means of the hub, this section will cover this work as well as the technical details of the hub proper.

8.3 and 8.4. Left: Cross section showing the parts of the hub. Right: Comparison between high flange and low flange hubs.

Fig. 8.3 shows a cross section through a typical hub. The two main types of attachment are by means of axle nuts and by means of a quick-release. In the latter case the hub axle is hollow, with a quick-release spindle in stalled through it. Low-end bikes usually have hubs with axle nuts, often with a tab-plate between hub and fork to prevent the wheel from falling out when the nuts are loosened. Another distinguishing factor for different hubs is based on the size of the flanges in which the spokes are attached into high and low, or big and small, flange models, as shown in Fig. 8.4. Al though structural virtues are sometimes claimed for the high flange type, low flange hubs are lighter and equally strong (except in a radially spoked wheel, described in the section The Spokes).

8.5. Hub width dimensions.

8.6. Assembly of quick-release hub.

Another myth surrounds the use of quick-releases, shown in Fig. 8.6: Hubs with them are not inherently better than those without, even though most quality hubs are made with hollow axles and quick-releases for easy installation and removal (and theft). A solid axle of the same material and the same diameter is stronger than the hollow one used with a quick-release, and its overall weight is slightly less. Early mountain bikes and all tandems come with solid axles. The best ones have axle nuts with integrated washers to reduce friction resistance and axle torque when they are tightened.

Fig. 8.5 illustrates the width of the hub. It is measured between the locknuts and must correspond to the internal dimension between the drop-outs or fork-ends of frame or fork. The over-locknut width is typically 100mm for a front wheel, 125mm for a rear wheel with

6- or 7-speed freewheel for regular drop-handlebar derailleur bikes, while hubs intended for mountain bikes and tandems tend to be wider — up to 135mm in the rear for some models. Often the use of solid axles is structurally justified, especially on the rear wheel with its greater width, which more easily leads to a broken axle. The greatest risk of breaking an axle is when the bearings lie rather far inward relative to the drop-outs or fork-ends.

Wheel Removal and Installation

The wheels have to be removed for numerous maintenance operations on the bike. Illustrated in Fig 8.7 and 8.8, this job looks easy enough. Even so, a systematic approach as described here will prevent all sorts of frustration. You may need a wrench to fit the axle nuts and a rag to hold back the chain on the rear wheel.

8.7. Installation of hub with axle nuts

Removal Procedure:

1. Remove any operating elements that may be attached to the wheel or interfere with its removal.

2. On the rear wheel of a derailleur bike, select a gear that combines the smallest sprocket in the rear with a small chain-wheel in the front while turning the cranks with the wheel lifted off the ground.

3. Untension the brake, generally with the aid of the brake quick-release. On mountain bikes or other machines with cantilever brakes, this is typically done by squeezing the brake arms in and then un hooking the transverse cable. In the case of a roller-cam brake, the cam plate must be twisted out from its rollers.

4. On a wheel with a hub brake, loosen the bolt that holds the counter lever to the frame or the fork.

5. If the hub has no quick-release, unscrew the axle nuts by about three turns each — if there is a wheel locator, far enough to allow opening the fork to free the tab.

6. On a wheel with quick-release hub, twist the lever in the open position. If this does not free the hub adequately, loosen the locknut on the other side by 1—2 turns.

7. On a rear wheel, hold back the chain by pulling the derailleur cage away from the sprocket.

8. Pull the wheel out of the bike in the direction of the slot in the drop-outs or fork-ends. If the tire should get stuck between the brake blocks, despite having released the brake, let the air out of the tire. On forks with drop-outs with a ridge that traps the axle nut or quick-release, loosen both nuts (on the former) or the thumbnut (on the latter) until they are clear of the ridge.

Installation Procedure:

1. On the rear wheel of a derailleur bike, first set the shifters in such a position that the gear with the smallest sprocket and the small chainwheel are engaged.

2. If required, release the brake as described in step 3 in the removal procedure.

3. Move any other items that may hinder installation out of the way.

4. Make sure the quick-release is in the open position or the axle nuts are undone far enough (and the lock washers are pushed up against them) to pass by the fork-ends or drop-outs.

5. On a rear wheel, hold back the derailleur with the chain so that the wheel can be moved into position.

6. Install the wheel in the fork or the frame, centering it in position by the rim and fully back in the drop outs (against the adjusters if installed), which may have to be adjusted to center the wheel correctly.

7. Tighten the quick-release or the axle nuts. If the quick-release does not hold the wheel firmly, undo it again, then turn in the locknut on the other side and try again.

8. Re-tension the brakes, making sure the brake blocks fully contact the sides of the rim when engaged — correct wheel position or brake adjustment correspondingly, if necessary.

9. Reinstall and adjust any other parts that were removed or loosened for removal or installation.

8.8. Installation of hub with quick- release.

Hub Maintenance

If the hub does not turn freely or is too loose, the problem can generally be solved with bearing adjustment. Only if adjustment does not do the trick, will a general overhaul be necessary, although this work is recommended on a yearly or even half-yearly schedule if the bike is used frequently under demanding conditions with dust and moisture.

The hub bearings must be tightened if the wheel can be moved sideways relative to the fork or the frame in the vicinity of the rim. They must be loosened if the wheel does not spin lightly, finally coming to rest alter some pendulum movement with the valve at the bottom, when allowed to turn freely. The whole thing must be overhauled if you notice rough spots or crunching noises when the wheel is turned. The same applies if adjusting for too loose a bearing results in notable tightness. Don’t think a loosely adjusted hub bearing that allows the wheel to turn freely does not offer excessive rolling resistance: it turns freely only without load, and the rolling resistance may become quite significant when the bike is loaded with the rider’s weight.

8.9. Assembly details of Maxicar sealed, adjustable bearing hub. Although generally used on fine-tuning bikes, it is equally suitable for tandems and mountain bikes.

Adjusting Hub Bearings

Since both the fixed and the rotating parts of the two bearings are connected with each other via the axle and the hub shell, respectively, it will suffice to adjust the bearing on one side (see Fig. 8.10). A hub with axle nuts can be left installed on the bike on one side, so only one axle nut must be loosened. A wheel with a quick-release hub is removed from the bike for this procedure, following the preceding instructions. You will need a cone wrench and a wrench that fits on the locknut.

8.10. Hub bearing adjustment detail

Procedure:

1. If the wheel remains in the bike (wheel with axle nuts), loosen the axle nut on one side by 2 – 3 turns. This will then be the side on which to adjust. Retighten alter completion of the adjustment 2. Loosen locknut by one turn, countering from the cone on the same side.

3. Lift the lock washer off the cone.

4. Tighten the cone by ¼ turn to correct a bearing that is too loose, or loosen it by that much to correct one that is too tight.

5. Install lock washer and tighten the locknut.

6. Check and readjust if necessary.

Overhauling Hub Bearings

The wheel must be removed for this work. Once that is done, you will need a cone wrench, a wrench to fit the locknut, rags and bearing grease.

Disassembly Procedure:

1. Loosen and remove the locknut on one side, countering at the cone on the same side. Leave the locknut on the other side installed.

2. Remove the lock washer.

3. Unscrew the cone, countering at the cone on the other side.

4. Remove the axle with the cone and locknut still installed on one side, catching the bearing balls.

Overhauling Procedure:

1. Clean and inspect all bearing parts, including the cups inside the hub. Replace the bearing balls and any parts that are damaged, pitted or corroded.

2. Replace the axle if it is not perfectly straight any more (check by rolling over a flat surface — it is bent if It seems to wobble up and down).

3. Replace the lock washer if the key does not lock in the longitudinal groove in the axle.

4. If replacement parts of a certain make or model are not available, you may sometimes get matching components of another make, providing you try them out to make sure they really fit.

5. To replace the bearing cups, special removal and installation tools are required, so it is advisable to get this done at a bike shop if you don’t want to buy such exotic tools

6. If the cone that was left on the axle has to be re placed, first measure exactly how much axle protrudes to its outside, then install the new one in that same location.

7. Fill the cleaned bearing cups with bearing grease and push the new bearing balls in, leaving just a little freedom to move.

8. Insert the axle from the side with the installed cone, making sure the bearing balls are not lost.

9. Install the cone on the free end of the axle, followed by the lock washer and the locknut, and adjust provisionally so the bearing turns freely.

10. Adjust the bearing per the preceding procedure Hub Bearing Adjustment.

8.11. SunTour low flange hubs

8.12. Shimano high flange hubs

The Tires

The tires not only cause the most misery on the bike, they also directly affect how lightly the bike runs, so it is well worth selecting and maintaining them properly. In this section we will cover both the mundane maintenance matters and the theory that determines their rolling resistance.

8.13. Top: tubular and wired-on tires with matching rims. Bottom: seating detail for different wired-on tires.

8.14. Rolling resistance is a function of the pitch-over angle, which depends on tire pressure and road surface quality.

There are two types of bicycle tire: the common wired- on type, also referred to as clincher, and the tubular tire, often called sew-up. Cross sections are illustrated in Fig. 8.13. The wired-on tire is held around a separate inner tube on a deep-bedded rim by means of metal wires (sometimes these are replaced by aramid, such as Kevlar, to save weight and provide flexibility for easy folded storage). The tubular tire is sown around the inner tube and is literally glued onto a much shallower rim.

Certainly at speeds not exceeding 16km/h (10mph), the rolling resistance plays a major part in determining how easily a bicycle runs. Only at higher speeds (or strong head winds) does wind resistance become increasingly important. But even at those elevated speeds, the rolling resistance may make the difference between comfortable cycling and plodding along — if higher speeds are ever reached at all on a bike with poor wheels. Fig. 8.14 gives a graphic representation of the differences between rolling resistance for various tires.

Rolling Resistance

Contrary to common opinion, the rolling resistance is not primarily a function of the tire width. In reality, it depends mainly on the area of deformation. The most important factor that enters into its determination is the tire pressure, and it is easier to make a tire withstand a high pressure by minimizing the cross section width, but it can be achieved with a wide tire too. On the other hand, the condition of the road also enters into the equation. Also important is the load, which is assumed to be 60% of the total weight of bike and rider in the back, 40% in the front for a conventional racing bike; on a mountain bike the figures may be 65% and 35%, respectively.

Fig. 8.16 shows the principle of the pneumatic tire as a suspension element that minimizes energy losses due to road unevennesses. The idea is to provide a very flexible layer that forms around the obstacles, balancing out the forces on either side, so no retarding component results. To approach this ideal, the tire must be both highly compressed (to minimize deformation on level ground) and highly flexible (to minimize the forces required to deform the tire around the obstacles). On an inflexible tire, the higher resistance is mainly due to the energy that goes into lifting the bike up over the obstacle. On a soft tire (or on soft ground), the energy equivalent to raising the bike over the height of the deformation is consumed with each wheel revolution.

Tire Pressure

To optimize the tires’ suspension effect, they should be inflated to the maximum pressure compatible with the road surface (hard on smooth, hard ground, softer on irregular surfaces, very soft on soft ground). Fig. 8.15 shows the effects of different road surfaces relative to the tire pressure. The pressure of front and rear tires should reflect the differences in loading, meaning that the rear tire should have about 20% more pressure than the one in front. The narrower tires do not only allow higher pressures, they usually require it, since they don’t have as much protective cushioning as the thicker ones. Just the same, in recent years mountain bike tires have been introduced that withstand quite impressive pressures without blowing off the rim.

The following values are based on the use of racing tires with a cross section of up to 25mm. For the rear tire, the optimal value for use on smooth asphalt is about 7 - 8bar (100 - 125psig). A rough asphalt or brick road surface would require 5 - 6bar (70 - 85psig), while a cobblestone road can only be mastered at any respectable speed with tires inflated to 3 - 4bar (45 - 60psig). When you get off road, soft soil, sand arid snow may require pressures as low as 1 - 2 bar (15 - 30 psi)

Only relatively fat tires, such as mountain bike versions, allow use at very low pressures. Other models do not have enough cushioning to protect the rim or pre vent the tire and the tube from getting caught between a rock and a hard spot — the rim and the road, respectively. Special tires with protective layers between the tread and the casing, usually made with aramid (Kevlar), will prevent puncturing upon impacting in the thread area, but will generally not help if the tires are so soft that the tubes get pinched.

Most people who have investigated rolling resistance under the pretense of science have done so in an in credibly incompetent manner. Rather than comparing equal tires under different circumstances or the same tire under different circumstances, they have compared different tires, each inflated to some arbitrary pressure that differed widely, all ridden on a perfectly smooth, hard surface — of course using the fanciest electronic instruments. Not surprisingly, the results simply favored whatever tire was inflated the hardest, since that is all that really counts under such favorable conditions.

8.15. Relative deformation of tire and road surface.

8.16. Principle of pneumatic tire: Balanced forces instead of reaction force in opposite direction.

8.17. Determining tire pressure. The modern designation is in bar one bar being 14.7 psi.

What’s needed is less hocus-pocus and more common sense. In a consistent series of simple comparative tests, I have established the criteria that determine the ease of rolling when all are inflated to the same pres sure. Even this is of course not the full story. Alter all, the bicycle wheel is part of the total suspension system of the bike (so the tires on a bike with suspension should only be tested in combination with it), and even the relative flexing of the frame and the steering leads to forces that retard the bike at high speeds. Even so, this simple test has brought a number of significant conclusions about the tires themselves to light:

- A cross section that minimizes the volume contained in the rim compared to the volume projecting.

- The lightest and most flexible side wall design and construction possible.

- A flexible tread surface, which can be tested as shown in Fig. 8.20.

- The use of the lightest and most flexible inner tube.

The wheel diameter also has some effect, but this factor is quite insignificant compared to the others: several speed records were established with the Moulton with its 17-inch wheels (compared to the 27-inch diameter customary on racing bikes) and dampened suspension. Fig. 8.18 illustrates the effect of the wheel size on the way the bike travels through unevennesses — unless a separate suspension is used.

8.18 and 8.19: Left: Effect of tire size on rolling resistance. Right: Effect of road surface quality on rolling resistance.

8.20. Simple check of tire flexibility.

Tire Sizing

Although it is still customary in the US to give tires sizes by some archaic method referring to inch sizes that don’t even resemble any measurable dimension, there is a more systematic and logical system in use. This is the ETRTO method of tire and rim size designation, developed by the European Tire and Rim Technical Organization, and now integrated in the internationally applicable ISO standards for bicycle components, and referred to as Universal Tire Marking Sys tem. This method is illustrated in Fig. 8.21.

8.21 and 8.22. Left: Tire size designation in accordance with the ETRTO and ISO standards for Universal Tire Marking. Below: Testing for tire rolling resistance In Raleigh’s product testing laboratory in Nottingham, England.

The ETRTO size designation applies to both rims and tires and references the rim bed, or shoulder, diameter. A second dimension quoted is the tire cross section for tires, the inside rim width for rims. Thus, the tires are identified by a code consisting of a 2-digit number followed by a 3-digit number, separated by a dash. The 2- digit number represents the inflated tire cross section, while the 3-digit number is the diameter of the rim bed in mm. Similarly, rim sizes are quoted as the same three-digit code, followed by a two-digit code referring to its inside width in mm, separated by an X. The out side diameter of a wheel is the sum of the rim bed diameter and twice the tire cross section. For mountain bikes, the usual rim size is 559mm, while it is either 622mm or 630mm for conventional derailleur bikes.

The last figures betray the absurdity of the archaic tire size designation method still generally used in the US today, because the 622mm rim used for 700mm (28- inch) tires, is smaller than the 630mm rim used on what is called a 27-inch wheel — given tires of identical cross section, the 27-inch wheel is actually bigger than the 700mm (28-inch) wheel. In the ETRTO system, within reason, any tire with 622 in its code fits any rim of that size, while any tire with 630 matches a corresponding rim size.

Tire Tread

The tread of a bicycle tire is generally profiled. Certainly in the case of high-pressure tires, this is of dubious benefit, since the idea of tread profile is strictly unique to the low-pressure condition found on cars. Car tires are inflated much less than bicycle tires for comparable road surfaces. Consequently, the contact pressure (i.e. force per unit area) is much less, which allows water to build up between tire and road when it is wet, causing aquaplaning in rainy weather on smooth asphalt.

Bicycle tires do not have this problem since they are inflated to pressures that are up to 3 times as high as car tires (at least for road use). Consequently, there is no need to remove water through channels in the tire tread. Only towards the sides of the tires, where the contact is angular in a curve, is there any justification for a rougher surface to prevent skidding when cornering in wet weather.

Tube and Valve

The inner tube used with the conventional wired-on tire is generally made of butyl, or synthetic rubber. Particularly tough tubes are made of other synthetic com pounds that are meant to resist puncturing better. The lightest and most flexible tubes, chosen to minimize rolling resistance, are of latex, i.e. pure unvulcanized rubber. This flexible material is not particularly puncture-prone either, but it allows air to pass through rather easily, and thus daily re-inflation may be required.

Butyl tires also lose air, but less so: racing bikes with butyl tires may require inflation twice a week, while mountain bike tires will go at least a week without fresh air. Depending on the material, the size of the tube must match that of the tire within certain limits. Latex tubes must match the tire dimension to within the closest tolerances, while butyl tubes can be stretched e.g. from 47mm to 54mm cross section (typical mountain bike sizes).

8.23. Mountain bike tire profiles. For road use, and for firm ground off-road, smooth tires (slicks) offer less resistance and excellent traction.

Fig. 8.24 shows three valve types, used for letting the air into the tube. In the US, only the Presta and Schrader models are commonly used: the former for racing bikes, the latter for most mountain bikes and utility machines. Each type requires a different valve hole diameter in the rim. Although Schrader valves can be inflated at a gas station, the Presta type is preferable, requiring less pressure to inflate. Tubes with this valve type are available for any tire size, although more readily so for narrow tires than for mountain bikes. Make sure the valve has a section of screw thread on the shaft, since valves without this feature tend to disappear back into the rim when you try to inflate them, making it very hard to do so.

8.24. The three most common valve types

Tire and Tube Maintenance

Of all the problems associated with the bicycle, the flat tire, or puncture, is by far the most common. Although things have greatly improved with the introduction of high-pressure tires in big sizes, such as on the mountain bike, the problem always remains. Just the same, the risk of any damage can be minimized, and it is not insignificant that experienced cyclists have far fewer punctures than inexperienced riders: it’s a matter of how you ride and how you maintain your equipment.

The tube must be protected against damage. Only careful path selection will give a safeguard against sharp objects in the road, although tires with aramid (Kevlar) liners are indeed remarkably tough in this respect. Regularly inspect the tires and remove any sharp objects that are embedded. Maintain sufficient tire pres sure and watch where you ride, avoiding potholes, rocks and debris in your path, to minimize the risk of pinching the tube and the tire sidewall between the rim and the road. Rim tape, wrapped around the rim bed, should be used to protect the tire from the spoke ends and the sharp outlines of the nipples in the rim bed.

Puncture Repair

Although many people seem to think fixing a flat by the roadside is more hassle than it is worth, it is a simple job that almost always can be carried out satisfactorily in reasonable time, even under quite adverse circumstances. If you want to pull out the old tube and install a spare, be my guest, but realize that you can’t carry unlimited spares, and sooner or later you will still be confronted with the need to patch a tire anyway. The following description can be followed either in the workshop or by the roadside.

8.26. Use of tire levers

To carry out a puncture repair, you will need a set of (usually three) tire levers, patch kit (containing patches, rubber solution, and sandpaper or a scraper). In addition, you may need whatever tools are used to remove the wheel. If wheel removal is complicated to do (e.g. on a bike with special brakes), you can just leave the wheel in the bike, merely turning the bike upside down while supporting the handlebars to protect anything mounted on them.

Procedure:

1. Remove the wheel from the bike. Follow the appropriate instructions above for wheel removal.

2. Check whether the cause is visible from the out side. In that case, remove it and mark its location, so you know where to work.

3. Remove the valve cap and the locknut, unscrew the round nut (if you have a Presta valve).

4. Push the valve body in and work one side of the tire into the deeper center of the rim, as shown in Fig. 8.25.

8.25. Pushing the tire bead into the deep center portion of the rim.

5. Put a tire lever under the bead on the side that has been freed, at some distance from the valve, then use it to lift the bead over the rim edge and hook it on a spoke, as shown in Fig. 8.26.

6. Do the same with the second tire lever two spokes to the left, and with the third one two spokes over to the right. Now the first tire lever will come loose, so you may use it in a fourth location, if necessary.

7. When enough of the tire sidewall is lifted over the rim, you can remove the rest by hand (Fig. 8.27).

8.27. Removing tire bead from rim

8. Remove the tube, saving the valve until last. Push the valve out through the valve hole in the rim,

while holding back the tire.

9. Try inflating the tube, and check where air escapes. If the hole is very small, so it can’t be easily detected, pass the tube slowly past your eye, which is quite sensitive. If you still have difficulty finding the hole, and if you have access to water, dip the tube under water, a section at a time: the hole is wherever bubbles escape. There may be more than just one hole.

10. Make sure the area around the hole is dry and clean, then roughen it with the sandpaper or the scraper from the patch kit, and remove the resulting dust. Treat an area slightly larger than the patch you want to use.

11. Quickly and evenly, spread a thin film of rubber solution on the treated area. Let dry about 3 minutes in hot, dry weather, up to twice as long in cold or humid weather.

12. Remove the foil backing from the patch, without touching the adhesive side. Place it with the adhesive side down on the treated area, centered on the hole. Apply pressure over the entire patch to improve adhesion.

13. Sprinkle talcum powder from the patch kit over the treated area, or you can leave the cellophane on the patch so it does not stick to the inside of the tire.

14. Inflate the tube and wait long enough to make sure the repair is carried out properly.

15. Meanwhile, check the inside of the tire casing, and remove any sharp objects that may have caused the puncture.

8.28 Rim suitable for both tubular arid wired-on tires — quite superfluous.

16. Let enough air out of the tube to make it limp but not completely empty.

17. Push the tire far enough on the rim to allow seating the tube completely in the rim bed under the tire, starting by putting the valve through the hole in the rim.

8.29. Pulling tire bead over rim edge

18. With your bare hands, pull the tire back over the edge of the rim (Fig. 8.29), starting opposite the valve, which is best to do last of all. If it seems too tight, work the part already installed deeper into the center of the rim bed, working around towards the valve from both sides.

19. Push the valve stem up and make sure the tire is fully seated.

20. Make sure the tube is not pinched between rim and tire bead anywhere, working and kneading the tire until it is free.

21. Install the valve locknut, if appropriate for the type of valve used, and inflate the tube to about a third its final pressure.

22. Center the tire relative to the rim, making sure it lies evenly all around on both sides, checking the distance between the rim and the moulded ridge on the side (Fig. 8.30).

8.30. Checking for tire concentricity

23. Inflate to its final pressure, then install the wheel.

Remarks:

1. If the tire is wider than the rim, you may have to release the brake, and tighten it again afterwards. On the rear wheel, refer to point 1 above for installation.

2. On a particularly narrow rim, points 18 - 20 are quite important. This same work, as well as the removal of tire and tube, are much easier on wide rims than on narrow ones.

3. Rubber solution and patches have a tendency to dry out if stored at high temperatures. It is a good idea to replace both once a year.

When a tire or tube is hopelessly damaged, it must be replaced. Like the puncture repair, this may have to be done away from home. Although I have rarely found it necessary, most people always carry a spare tube and replace it, rather than repairing the old tube. This must also be done if the valve leaks or if the tube is seriously damaged. To do this, follow only the relevant steps of the instructions for fixing a flat. Replacement of the tire casing is done similarly. Make sure the rim tape that covers the spoke ends is intact (join the ends with a patch if necessary).

The Rim

8.31. Some common rim cross sections

Quality bicycle rims are made of extruded aluminum, while cheap bikes may have rims made of bent steel sheet, either chrome-plated or stainless. Steel rims are not usually stronger than aluminum ones, even if the latter are significantly lighter. This is due to the box profile that can be used for extruded sections, while the cross section shape of the steel rim is much less structurally sound. Fig. 8.31 shows the various cross sections used. Steel rims should never be used on bikes with rim brakes, since the braking deteriorates sharply when steel rims are wet (much more so than for aluminum rims).

Most steel rim manufacturers try to fool the public into thinking that serrating the sides of the rim will improve braking. Actually, there is only one profile that does this trick, though at the price of noisy braking and high brake block wear. This is the patented Van Schothorst design with intermittent diagonal grooves. A new design by the same manufacturer that looks deceptively like an aluminum rim, on the other hand, does not seem to offer improved wet weather braking.

The spoke holes are installed alternatingly off-set to the left and the right of center, corresponding to the direction the spokes run in the assembled wheel. Campagnolo has a series of rims with spoke holes that are accurately aligned, guaranteeing a wheel that maintains its shape and tension. In order to prevent cracking of the rim at the spoke holes, these points should be rein forced by means of bushings, which should connect inner and outer sections on the box-section, or ‘double bottom’ design. At a minimum, a washer should be in- stalled between nipple head and inside of rim to distribute the spoke forces around the hole.

The size of a rim is determined in accordance with the ETRTO designation arid corresponds closely to the size designation for the matching tires. To give an example, a rim with designation 622 X 18 has an inside width of 18mm and a rim bed diameter of 622mm. Most tires with 622 in their designation will fit on this rim.

8.32 and 8.33. Above: Some Weinmann rim types. Below: Campagnolo racing rims.

8.34. Hard anodized rim from Sun. Al though these are excellent rims, the hard anodization is superfluous and only reduces braking efficiency.

The strength of the rim is only relevant within the total assembled structure of the wheel. In fact, most kinds of rim deformation are not really the result of a weak rim, but of insufficient spoke tension. Even so, the strength and rigidity of the rim itself do matter, since they help distribute the forces over more spokes. Very, very few rims are made of heat treated aluminum, which is stronger than regular aluminum. Although some of these models are dark gray, it is not generally true that all dark gray rims are heat treated, or particularly strong for that matter. The color is not due to heat treating, but to anodizing with a dye. Anodizing to significant depth increases the surface hardness of the rim, but has no significant effect on its strength. It should also be noted that anodized rims tend to pro vide poorer wet weather braking than plain aluminum ones.

The easiest way to test the lateral rigidity of a rim, is to place it halfway on a flat table, with the other half projecting. Holding it down firmly, while pushing the overhanging part down, will indicate how easily it is deformed (but don’t apply so much force that permanent deformation is caused, which may happen on a weak lightweight rim). The radial rigidity is verified by standing the rim on end and pushing it down from the top. By and large, heavier rims, assuming the same material, are stronger; higher profiles lead to more radial rigidity, and wider profiles to more lateral rigidity.

The Spokes

8.35. Details of spoke and nipple. The butted spoke shown below is referred to by the gauge numbers for each of the sections.

8.36. Comparison of wheels with compression and tension loaded spokes.

The spoked bicycle wheel is a unique construction, since the spokes are not loaded in compression, as is the case on a wagon wheel (or most other wheels), but in tension. This allows the total forces to be distributed over all but the two bottom spokes, whereas they must always be carried fully by one or two spokes on other wheel types (including in principle the disk wheel, even if that does not have spokes as such — this is one reason for its greater weight). The spokes of the convention al bike wheel can also be kept very thin because the tension loading does not transfer a bending moment on the spokes. Fig. 8.36 compares the loading cases for the wagon wheel and the bicycle wheel.

Despite the obvious technical advantage of the wire- spoked wheel, some manufacturers and would-be innovators never give up on reinventing the wheel. Consequently, we regularly see the introduction of such abominations as cast aluminum or cast plastic wheels built on the basis of the cart wheel. They are heavier all right, and they can’t be straightened when bent, but they are by no means technically satisfactory, as was verified by tests conducted at the Aachen Technical University some years ago.

Spoke length calculation (all dimensions in mm):

Fig. 8.35 shows two versions of the spoke with the nipple that connects it to the rim and by which it is tightened. In fact, the higher the tension, within reason, the stronger the wheel. When the tension is lower, the sequence of stress variations through which the material goes is more demanding as the spokes are intermittently loaded arid released during the rotation of the wheel. This tends to induce metal fatigue, leading to breaking, usually directly at the bend near the head.

The illustration also indicates how the spoke is measured. Its size is quoted as the length from the inside of the bend to the end, while the thickness is usually quoted as a gauge number. Recently, spoke thick nesses are, more logically, referenced in mm — see Table 7 for conversion of the gauge numbers into mm. When two gauge numbers are quoted, the spoke is butted, meaning the ends are thicker than the middle section. This leads to greater flexibility and consequently to greater strength than a spoke that has the same thickness over its entire length — despite the reduced section. Any associated weight savings is insignificant.

Nowadays, stainless steel is commonly used for spokes. Even though this is a fine material, it is not necessarily correct to assume them to be stronger than regular spokes made of galvanized steel. Their advantage is that they don’t corrode. Corrosion not only weakens the spokes over time, it also makes it harder to turn the nipple, often causing the spokes to break when an attempt is made to tighten or loosen them.

Spoking Patterns

The spokes are installed according to a certain spoking patterns, some of which are shown in Fig. 8.37. The simplest pattern is that of the radially spoked wheel, where the spokes do not cross each other. Because this pattern does not lend itself very well to the transfer of a torque (the application of a rotating force on the hub, tending to twist it relative to the rim), the various tangential patterns have been introduced. This makes sense on the rear wheel and on any wheel with a hub brake, but there is no reason at all to choose anything but radial spoking for the front wheel of a bike with rim brakes, providing the hub flanges are strong enough to withstand the resulting radially oriented spoke forces.

8.37. Various spoking patterns

8.38. The effect of an 800 N rotating force on the tension of individual spokes when these are pre-stressed at 350N.

The various tangential spoking patterns are identified by the number of spokes that each spoke crosses on its way from the hub to the rim: 1-cross, 2-cross, 3-cross and 4-cross. The latter has proven to lead to fewer spoke breakages and is universally used in European professional road racing circles these days. The whole pattern is actually simpler than it appears, since it is repeated every fourth spoke on the rim, every second spoke on either hub flange. The place to start looking is at the valve — it should lie between two nearly parallel spokes, leading to the LH and the RH hub flange, respectively.

Generally, bike wheels have 36 spokes each, although it was customary until the early sixties to use 40 spokes on the heavily loaded rear wheel, and 32 on the less loaded front wheel. Smaller wheels require fewer spokes, down to 20 for a 16-inch wheel. In recent years, the craze for lightness and reduced air resistance has brought back full-size wheels with fewer spokes, requiring matching rims and hubs. For the rear wheel they are only suitable for easy terrain and light riders. Similarly, oval and even more radically sectioned spokes have been introduced to further reduce the air resistance of lightweight racing bikes.

Whatever number of spokes and crosses, the spokes al ways run alternatingly to the LH and the RH hub flange. Depending whether a particular spokes lies on the inside or the outside of the flange, they are referred to as inside and outside spokes. In the case of the radial spoked wheel, all spokes are outside spokes. On all other wheels inside and outside spokes alternate on each hub flange. Since the outside spokes wrap furthest around the hub flange (and since they stand under a slightly less acute angle), they are generally less prone to breaking. Consequently, the spokes that take the driving forces should preferably be outside spokes — on a rear wheel these are the spokes on the RH side that radiate backward at the top of the hub. On a front wheel with a hub brake, these are the spokes that radiate forward from the top of the hub.

In cross section, the spoked wheel may take any of the shapes depicted in Fig. 8.46. Obviously, the front wheel is generally symmetric (an exception might be a front wheel with hub brake), while the rear wheel is generally off-set to accommodate the freewheel block with its sprockets, pushing the spokes on the RH side into a much steeper angle relative to the axle (or a more acute angle relative to the wheel centerline). This asymmetry is referred to as wheel dishing and leads to proportional differences in spoke tension with attendant breakage probability. Cassette hubs, which were previously praised for a favorable bearing configuration leading to fewer broken axles, also excel in this respect, since they require less dish, preventing broken spokes.

8.39 and 8.40. All major manufacturers use automated spoking machines these days. Despite their accuracy, some manual truing and final tensioning is often required.

Spoked Wheel Maintenance

The spoked wheel should be seen as an integral structure, so it is hard to distinguish between specific rim and spoke maintenance jobs. When a spoke breaks, the rim deforms. When the wheel wobbles, it is generally corrected by means of spoke manipulation. To re place a rim or a hub, you have to replace the spokes. All parts mutually affect each other.

Replacing Spoke

Sometimes it is tricky to replace a broken spoke. The most heavily tensioned arid loaded spokes on the RH side of the rear wheel are generally not accessible with out first removing the freewheel, or the series of sprockets on a cassette hub. This operation is described in Section 10. If the nipple also has to be replaced, the tire must be deflated, so tire, tube and rim tape can be pushed over to gain access to the nipple from the top of the rim. You will need a spoke wrench, or nipple spanner, and some Vaseline.

Procedure

1. If the hole in the hub that corresponds to the broken spoke lies inaccessibly under the freewheel, remove the freewheel, as described in Section 9.

2. Remove the old spoke. If possible, unscrew the remaining section from the nipple, holding the latter with a wrench. If not, deflate the tube and locally lift tire, tube and rim tape off the rim, after which the nipple can be replaced by a new one.

3. Locate a spoke that runs the same way as the broken one: every fourth spoke along the circumference of the rim runs similarly. Check how it crosses the various other spokes that run the other way, using it as an example.

4. Thread the nipple on the spoke until the latter has the same tension as the other spokes.

5. If the spokes do not seem to be under tension, tighten all of them half a turn at a time, until they all seem equally taut and the wheel is reasonably true. If necessary, follow the instructions for Wheel Truing below to correct the situation.

8.41 and 8.42. Very strong hub flanges and straight spokes (in Weco’s cheap version above, or Royal’s fancy one below) allow radial spoking even on the rear wheel -- providing extremely low gears are avoided.

8.43. Simplified symmetry check. There are special gauges to do this more accurately.

Wheel Truing

If the problem is a serious one, the wheel being bent quite far over a large area, first straighten it roughly. Do this with the wheel removed from the bike. Support it in its two ‘low’ points, e.g. against the pavement and the curb, while pushing against it in the ‘high’ points. Push and check and push again, until it begins to look like it is level, and none of the spokes are excessively loose. Then proceed to the truing operation outlined below. For tools, you’ll need a spoke wrench and preferably a truing stand — a tool into which the wheel is held, with gauges indicating how far it has to be corrected. In a pinch you can install the wheel in the bike and use fixed reference points, such as the brake blocks.

Procedure:

1. Check where it is offset to the left, where to the right, by turning it slowly while watching at a fixed reference point. Mark the relevant sections.

2. Loosen the RH spokes in the area where the rim is off-set to the RH side, while tightening the ones on the LH side — and vice versa, as shown in Fig. 8.45.

8.45. Wheel truing is done by tensioning and loosening spokes selectively, as shown here for lateral and radial deflections, respectively.

3. Repeat steps 1 and 2 several times, until the wheel is true enough not to rub on the brakes.

8.46. Three forms of wheel off-set

Wheel Symmetry

In the assembled bike, the two wheels must be perfectly aligned one behind the other with the centerline through the bike, so it stays on track without undue steering and balancing corrections. One factor that comes into play here is the wheel dish on the rear wheel: it must be just enough to place the rim on the centerline through the front wheel and the rest of the bike. If necessary, the wheels are centered correctly to achieve this.

If the wheels are not in line, you may notice balancing problems, especially when riding a straight line with the hands off the handlebars. The person riding behind you can usually confirm the problem when he tries to visually align the two wheels. To establish how much correction is required, it is best to use a wheel alignment gauge, which may be bought ready made. On the other hand, you may also use the technique illustrated in Fig. 8.43. The idea is to correct spoke tension so that the rim is centered between the lock-nuts over the en tire circumference (check in at least three locations equi-spaced around the circumference). When you have finished, you may have to follow the Wheel Truing procedure above. A bike mechanic can carry out this whole operation in little time, in case you despair.

Wheel Spoking

This must be done to replace hub, rim or spokes. It is rather a time consuming and fidgety operation, only worth doing yourself if you value its therapeutic value, since any bike mechanic can do it incomparably faster and usually more accurately. Even so, the operation is not half as difficult as might at first appear, once one brings to mind how the wheel is built up. In my Bicycle Repair Guide, you will find a step-by-step account of this work. However, it is also possible to figure it out yourself on the basis of the following description.

First check on a completed wheel, always looking at it from a certain side (e.g. from the RH side). First check the configuration at the valve, noticing how one spoke runs from the first hole to the right to the RH side of one hub flange, while the spoke from the first hole to the left runs virtually parallel to the LH side of the other hub flange. Then notice how the pattern repeats itself every fourth spoke. Make a sketch of the con figuration at the valve and of one set of four spokes. This will be your pattern for the entire wheel.

8.47. Orientation of spokes either side of the valve.

8.48 and 8.49. Left: Simple wheel truing stand from the Dutch manufacturer Tacx. Right: professional model from the U.S.manufacturer Park Tools, to do the same job faster and more accurately.

The correct spoke length may either be selected on the basis of the old wheel, or by asking at the bike shop, consulting a spoke sizing table such as those from Sutherland’s Handbook for Bicycle Mechanics. To establish the correct size with the aid of such a table, you have to know detailed dimensions of the hub and the rim as well as the desired spoking pattern. Also note that on the rear wheel, the spokes on the LH side may have to be about 3mm (1/8”) longer than on the RH side to accommodate the different angles relative to the wheel centerline. You will need a spoke wrench, some Vaseline, a rag, a screwdriver, and preferably a wheel truing stand.

Apply some Vaseline to the threaded nipple ends, so the nipples will be easy to install and subsequent adjustment remains assured. Work in groups of 9 spokes (assuming a total of 36 spokes): first all inside spokes on one hub flange, followed by all spokes on the inside of the other flange, then all outside spokes on that same flange, and finally all outside spokes on the remaining flange. Refer to Fig. 8.50 for a sequence in detailed steps, referring also to your own sketch representing the required configuration. Finally, squeeze all spokes together in groups of four to release tension, and then follow the procedures entitled Wheel Truing and Wheel Symmetry to bring the wheel into the desired shape.

8.50. Four stages of the wheel spoking process. 1. The first 9 outside spokes, 2. The first outside spoke, 3. All spokes on one side, 4. The first spokes on the opposite side.

Disk Wheels

Since the mid eighties, disk wheels have been all the craze in time trial events. They offer markedly reduced air resistance compared to the conventional tension spoked wheel, especially at higher speeds. Since the upper portion of the wheel actually moves against the air at twice the bicycle’s speed, it can be seen that this factor is more significant than may appear at first.

Interestingly, disk wheels had been on the market as early as 1893, and their benefit was established even at that time, although few people realized their potential. Only alter Shimano introduced all sorts of other supposedly aerodynamic components in 1980, and it was soon established that none of them did anything significant, did one begin to realize how much more could be gained with more aerodynamic wheels.

The international sanctioning organization for bicycle racing, the UCI, did not allow the use of aerodynamic fairings on the bike or its components, but did not object to wheels constructed as one piece — as the disk wheel is. Thus, the disk wheel was given an artificial boost, even though, from a technical standpoint, these wheels were inferior to spoked wheels with added lightweight covers (which remained illegal in sanctioned races). At ridiculously high prices and at first excessively heavy, disk wheels soon appeared on any bike used for time trials. Ironically enough, this also became customary in triathlon, where the UCI regulations did not apply and where wheel covers would have been more appropriate.

The technical disadvantage of the disk wheel is obvious: it’s essentially the same heavy construction as the wagon wheel, which was so elegantly overcome by the tension-wire spoked bicycle wheel. The result was both a very difficult construction if the wheel is to be perfectly trued, and a high weight. Oddly enough, this high weight has been used as an argument in their favor, since the increased momentum is supposed to even out the movement. Actually this is correct, but it is no advantage, because these heavier wheels first have to be accelerated to the desired speed, which re quires more energy than is needed to bring a lighter wheel to the same speed. For time trials, where the bike is only accelerated up to speed once or twice, while subsequent acceleration and deceleration is in significant, the disadvantage is minimized, but it would make no sense to use disks for other events, where weight is a more important factor.

The other disadvantage of the disk is its sensitivity to cross winds, or any kind of wind on a curved course. One way around this is the three-, four- or five-bladed wheel. This too is a design that was available as early as 1893, and at the time advertised with the same arguments as today. It is almost as heavy as a full disk of the same materials — and even more expensive.

Recently, more sophisticated materials and construction methods have produced disk wheels of remarkably light weight that begin to compete with tension-spoked wheels, although they are incredibly expensive — and less flexible and less durable. Finally, the interesting Tioga Tension-Disk wheel, which is marketed by several Japanese manufacturers, should be mentioned. In this design, the conventional spokes are replaced by a kind of spider’s web of tensioned aramid (Kevlar) fiber, em bedded in a lightweight plastic membrane. It is still sensitive to cross winds, but it is technically as sound as the conventional spoked wheel and even lighter.

8.52. Aerospoke wheel for roughly the same wind resistance and less side wind sensitivity compared to a full disk. And the weight is remarkably low too, thanks to aramid fiber reinforced epoxy resin.

8.51. Full disk in the rear; tension wire construction, using aramid fibers, in the front.

Bicycle Drivetrain