The Steering System -- Guide to Bicycle Technology

The components that make up the bicycle’s steering system are illustrated in Fig. 6.1. It comprises the front fork, the head set bearings that hold it in the frame’s head tube, the handlebars and the handlebar stem. Before proceeding to the technical details of these components, the steering principle will be described. Guide to Bicycle Technology (article index) This greatly aids in an understanding of the way frame geometry and the steering components act together to influence the bicycle’s handling characteristics.

6.1. The parts of the steering system

The Steering Principle

The steering system not only serves to control the bicycle in curves, it is equally essential for going straight and for balancing the bicycle under all circumstances. Anybody whose front wheel has ever been caught in a parallel groove, such as a streetcar track, can confirm that even going straight is an impossibility with locked steering. Guide to Bicycle Technology (article index) Actually, the bicycle never goes in a completely straight line. Instead, it always follows a more or less curving path, always deviating a little to one side or the other, corresponding to similar deviations in the vertical position of bike and rider.

When the center of gravity is to the right of the point of contact between wheels and road, the bike leaning in that same direction, the rider regains his balance by pointing the steering further to the right. This causes the bottom of the bike to move back under the center of gravity, restoring equilibrium — but only temporarily, because the bike now starts to lean in the opposite direction. In turn, this lean is countered by steering slightly in that same direction, causing it to move back under the center of gravity and beyond, ad infinitum.

Fig. 6.3 illustrates the relationship between speed, lean and deviation. At low speeds, this serpentine-action is quite distinct, with considerable steering deviations. At elevated speeds, the deviations are smaller, although the lean relative to the vertical plane tends to be greater at any steering angle than it is at lower speeds. To get a feel for this movement, low speed riding, consciously trying to follow a straight line, is educational.

6.3. The cyclist leans into the curve. At higher speeds, more lean is required. At lower speeds, the steering deflection is greater. A sharper curve requires both more steering deflection and more lean.

Natural and Forced Curves

To ride a curve, the simplest way is to use the natural lean. To follow a curve to the right, wait until the bike is naturally leaning in that same direction, and then don’t do anything for a while. Thus, the bike is not brought back upright, but continues to lean further and further, until quite a distinct lean angle is reached. Now it is time to steer noticeably in the same direction, avoiding the crash that would have followed the excessive lean, while forcing the bike in the desired direction.

This method of steering is referred to as the natural turn arid is illustrated in the LH detail of Fig. 6.2. It has one drawback: it requires a lot of time and room to maneuver. If there is not enough of either to follow this method, use the technique referred to as the forced turn. This method is illustrated in the RH detail of Fig. 6.2.

6.2. Turning techniques compared: Left: Natural curve. Right: Forced curve.

To carry out the forced turn, the cyclist first steers in the direction opposite to his intended path. This causes the bike to lean in the opposite direction. Rather than correcting this right away, the bike is first allowed to drift further with increasing lean in the direction of the intended curve. When a significant lean is reached, the rider finally steers in that same direction, resulting in a tight and sudden curve.

Most of this is usually done subconsciously, although this is the very thing that makes learning to ride a bike confidently so difficult at first. It also explains why beginning cyclists, or riders who use a bike with drastically different steering geometry for the first time, feel and act so insecure and often ride so unpredictably.

Steering Geometry

How well a bike steers and handles, how accurate and predictable, and how comfortable it is to ride, is largely affected by its steering geometry. This is the relation ship between angles and dimensions of the parts of the steering system as they relate to the total bike.

Although the manufacturer of a ready-made bicycle has predetermined the steering geometry, it is quite useful for the technically competent rider to know how a certain characteristic is achieved. This is all the more important if one considers that a remarkable number of manufacturers and bicycle sales people haven’t the faintest idea how it is done correctly. The result is that they finish up producing or selling bikes that are less stable than they should be.

Fig. 6.4 illustrates the most important concepts that play a part in determining the bicycle’s steering geometry, and indirectly its handling characteristics. How predictably a bike handles and how much stability it has, is largely determined by the dimension called trail. This is the distance between the contact point wheel/road (point A) and the point at which the imaginarily extended steering axis crosses the road (point B).

6.4. The effect of steerer angle and fork rake on trail: The same trail can be achieved with any angle, providing the fork rake is reduced when the angle becomes steeper.

At any head tube, or steerer, angle of less than 90’ (and typical values are far below that, namely 66—741, combined with a straight fork, point A lies well behind point B. Thus the amount of trail, dimension X, would be quite big. This would result in a distinct tendency of the bike to follow a straight course, requiring relatively strong steering forces, or significant external effects, to deviate from this straight path.

6.5. Trail effect increases with shallower steerer angle.

6.6. The effect of trail decreases when the wheel is turned relative to the direction of travel.

As the illustration shows, the fork is usually bent for ward — the distance over which this is done is referred to as rake. This brings point A forward, closer to point B, decreasing the amount of trail. Thus, the more raked fork on any given head tube angle achieves less trail, decreasing the bike’s inherent stability and in creasing its agility. Obviously, the same amount of trail, and essentially the same stability, can be achieved with different head tube angles, providing the rake is selected correspondingly to provide the desired trail with each angle.

Even so, there is a difference between the way bikes with the same trail but different head tube angles handle. The bike with a shallow angle is somewhat more sluggish and only responds predictably up to a certain steering deviation, after which a phenomenon called wheel flop sets in. This means that the bike over-steers abruptly beyond this point. The advantage of the bike with the smaller head tube angle lies in the increased comfort due to the greater flexibility of the more inclined and more distinctly bent fork, making this solution more desirable for touring on rough surfaces. Trail values typically fall between 50mm for a quick-steering criterium racing bike to 65mm for a stable touring or mountain bike.

Of course, the head tube, or steerer, angle for any given frame is fixed. It can be determined on the built-up bike following the method illustrated in Fig. 5.13 in the preceding section. Racing bikes typically have a head angle from 73.5—74’. Touring bikes have an angle of around 72’, while mountain bikes may have one as small as 67—68’, although the trend is towards steeper head angles, 70—71’ being more typical these days for most mountain bikes.

Fig. 6.4 shows how the fork rake can be chosen to match any head angle while still arriving at the required trail. Fig. 6.7 simplifies the selection of the appropriate fork rake that gives a certain amount of trail once the head tube angle is known. These graphs are based on the following formulas:

X1 = R cos α Y x sin α

X2 = sin α (R x cos α Y x sin α)

where:

X1 = projected trail

X2 = effective trail

R = wheel radius in mm

Y = fork rake in mm

C = head tube, or steerer, angle.

The difference between the two values X1 and X2 bears some explanation. The value X1 is the one commonly used, but does not give as accurate an impression of actual stability as X2. The latter, which we refer to as effective trail, is what some authors call stability index, creating the impression that this is a dimensionless value. However, it can easily be determined, as we have done above, and should be used in preference to the conventional value X which we refer to as projected trail. The difference between the two values increases as the head tube angle decreases, making it critical to use the right one, especially on mountain bikes and touring or utility machines with a relaxed geometry.

The formula also makes it obvious that the wheel radius enters into the calculation. Small-wheeled bikes should consequently be built with less rake than the values indicated in the table for 650—700mm wheels (nominal sizes 26” and 27”). As the formula and Fig. 6.7 suggest, even a completely straight fork barely pro vides enough trail for adequate stability on a bike with 20” or smaller wheels — important on folding bikes and children’s bikes, as well as on recumbents and some other special designs. Essentially, such bikes with small wheels should have very little or no rake at all if they are to provide adequate directional stability.

6.9. With the same rake and steerer angle, small wheel bikes have less trail.

6.10. EDCO Competition headset with steel races and aluminum fittings.

The Headset

The headset bearings form the rotation support for the steering system in the frame. Fig. 6.11 shows how it is typically built up, consisting of a fixed bearing in the bottom and an adjustable one at the top. The lockring may either have the form shown or it may have projecting teeth that match similar teeth in the top of the upper bearing cup. Often on mountain bikes arid other machines with high handlebar positions, the locknut is built up with a high collar that stabilizes the handlebar stem. On some mountain bikes, an anchor for the brake cable may be installed between the locknut and the adjustable cup, replacing the lockring.

6.11. The headset assembly. Left: Cross section through the head tube. Right: Parts of the head set.

The ball bearings of the headset are loaded differently than those of most other bicycle applications. Whereas most other bearings rotate constantly and are loaded radially, i.e. perpendicular to the axle, the headset bearings hardly rotate and are loaded axially, i.e. in line with it. This is an unfavorable condition for ball bearings, since impacts from the road are transferred to the balls which remain in the same location, causing pitting of the bearing surfaces in those spots, referred to as brinelling. This is the reason mountain bikes are nowadays often equipped with so-called oversize head sets, requiring an oversize head tube and a fork with a matching steerer tube as well. To date, there is no standardization of oversize headsets, so they are not readily interchangeable.

Headset Maintenance

Since the headset is so unfavorably loaded, it is quite important to keep it well adjusted and lubricated and to overhaul it occasionally, especially when it is noticeably loose or tight. You can check whether it is too loose by lifting the wheel off the ground and checking whether the fork can be moved relative to the frame at the fork crown.

In order to establish whether the headset is too tight, again lift the front wheel off the ground and check whether the steering can be turned from the fork crown (where there is less leverage than at the handlebars) without noticeable or irregular resistance. Unfortunately, the problem of a rough or tight headset can rarely be solved by means of adjustment, although that is the first step. Only too often, it is the result of damage that can only be eliminated by completely overhauling, and perhaps replacing, the headset.

Adjusting Headset

Usually, this can be done without removing anything from the bike. On mountain bikes it may be helpful to remove the straddle cable of the front brake if it is of the cantilever type — just make sure it is replaced again afterwards. It is preferable to use special matching headset wrenches, although it can usually be done with the aid of a large crescent wrench.

Procedure:

1. Unscrew the locknut on top of the upper headset by about two turns (models with toothed lockring: far enough to disengage the teeth).

2. Lift the lockring up enough to free the adjustable cup.

3 Screw the adjustable cup in or out a little, as required to tighten or loosen the bearing, respectively.

4. Push the lockring down on the adjustable cup again.

5. Tighten the locknut, making sure the lockring and the adjustable cup do not turn with it.

6. Check operation of the headset and repeat adjustment if necessary.

Headset Overhauling

This procedure must also be followed to remove or replace the fork. Before starting, the handlebars must be removed, possibly also the front wheel and the front brake, although it usually suffices to undo its cable attachment. You’ll need special headset wrenches (or large crescent wrench), a rag, and bearing grease.

6.12 and 6.13. Oversize headset (left) and the tools for its installation and maintenance (This is the Garry Fisher unit, while many other manufacturers use different sizes, requiring different tools.

If the bearing races must be replaced as well, special removal and installation tools should preferably be used. In a pinch, it can be done with provisional aids, which will be described in the procedure. As with so many parts on the bicycle, care must be taken to re place items with matching ones, since there are several different types of screw thread standards for headsets. The recent introduction of oversize models has added even more confusion. There are other differences as well: for example, the (excellent and reasonably priced) Shimano 600 headset requires that the fork’s steerer tube must be cut off shorter than it is for other models.

Disassembly procedure:

1. Unscrew and remove locknut.

2. Remove lock washer and/or brake cable anchor.

3. Unscrew and remove adjustable cup, while holding frame and fork crown together.

4. Pull the fork out of the head tube, catching the bearing balls from upper and lower headset bearings (usually held in bearing ball retainer).

5. If the inspection that follows indicates the bearing cups and the fork race are damaged, remove these as well. This should preferably be done with special tools, but can also be accomplished by following the illustrations 6.14 and 6.15.

6.14. Fixed race removal without special tools.

6.15. Fork race removal without special tools.

6.16. Fixed cup installation without special tools.

6.14, 6.15 and 6.16. Headset overhauling work can be done following the provisional methods shown here. However, it is preferable to use special tools.

Maintenance and Installation:

1. Clean and inspect all bearing components. Replace any parts that are damaged or corroded. Damage usually takes the form of pits in the bearing surfaces of the bearing races. Ideally, the bearing balls should always be replaced, using either loose bails or a matching retainer. Different manufacturers sometimes use different sizes, although 5/32” is the most common.

Note: If the bearing races show brinelling (pits) and you don’t want to replace them, try replacing the bearing ball retainers with loose balls.

2. Clean and slightly grease the screw-thread surfaces.

3. If necessary, install the new bearing races, preferably with special tools, although it can be done with out, following Fig. 6.16.

4. Fill the scrupulously cleaned bearing cups with bearing grease.

5. Hold the frame upside-down and install the bearing balls in the lower bearing cup, taking care to orient it so that only the balls, not the metal of the retainer (if used), contact the bearing cup and the fork race.

6. Install the fork, alter checking that the fork race is also perfectly clean and slightly lubricated.

7. Firmly holding the frame and the fork crown together, turn the whole thing upside-down, so the upper headset is on top again, with the fork’s steerer tube protruding.

8. Install the bearing balls in the fixed upper cup, again taking care to orient the retainer (if used) so that only the balls, not the metal of the retainer touch the bearing cups.

9. After checking whether the adjustable cup is clean and slightly lubricated, screw it onto the steerer tube until the bearing seems correctly adjusted.

10. Install the lock washer, any brake cable anchor that may be used, and the locknut, tightening the latter relative to the adjustable cup.

11. Check the adjustment of the bearing as outlined above and correct if necessary, following the procedure Adjust Headset above.

The Front Fork

Fig. 6.18 shows the construction of a typical front fork. It comprises the steerer tube, or fork shaft, two fork blades, a fork crown that connects them together, and fork-ends, also called front drop-outs. Slightly different are two recent variants, called unicrown and switchblade fork, respectively, and illustrated in Fig. 6.17. The two latter versions are popular on mountain bikes, although not better in an engineering sense. The unicrown design is cheaper to make. The (heavy) aluminum switchblade crown design has no virtues at all. It is meant to allow exchanging fork blades, but as we’ve seen, the steering characteristics are too sacred to fool around with and this fork is quite a bit heavier than other models.

6.17. Unicrown and switchblades mountain bike forks.

Material selection and construction of the fork are analogous to what was said in Sections 4 and 5, respectively. Generally, steel and aluminum frames are each equipped with forks of the corresponding material. Composite and magnesium frames usually come with aluminum forks. These tend to be softer than steel forks, providing more shock absorption. The fork-ends should be as thick and accurate as possible, and what was said about the (rear) drop-outs in Section 5 applies here too.

6.18. The front fork

The steerer tube of a replacement fork is usually provided long enough to fit even the largest frame, so it may have to be shortened to provide the right length to match a smaller frame. The screw thread may then have to be re-cut, a job for which any bike shop should be equipped. Table 4 summarizes the different common thread types. When cutting a steerer tube down to size, the stacking height of the headset must be considered, measured as shown in Fig. 6.19, add adding 2mm (3/32”) clearance. The fork race, which is part of the lower headset, should match the collar, or shoulder, on the fork crown, which may have to be machined for an accurate fit.

The front fork is a particularly heavily loaded part of the bike. Being cantilevered out, it is not loaded only in tension and compression as most other parts are, it is also the first one to be damaged upon collision impact. Even so, it should not be too heavy, to provide adequate shock absorption. Ideally, the fork blades should flex only parallel and remain linearly aligned, while lateral flexing should be minimized, all of which is best achieved with round fork blades. Just the same, most fork blades are made of oval cross section, probably justified only by questionable aesthetic and aerodynamic arguments.

6.19. Steerer tube length depends on headset stacking height and head tube length (adding 2mm spacing).

6.20. Typical high-quality fork with in vestment cast fork crown and drop-outs.

Internal reinforcement of the steerer tube and the fork blades is appropriate. Unfortunately, the shaping process with which the fork blade diameters are made less at the bottom, where the load is minimal, than at the top, where it is greatest, results in increased wall thickness in the area with the smaller outside diameter. To compensate for that, high-quality forks are made of taper gauge tubing, which starts out thicker at the top and finishes up having a nearly constant wall thickness all the way down alter forming.

The fork-ends are similar to the drop-outs described in Section 5 but do not have an adjusting feature. The slots in the fork-ends point down almost vertically. Recently, mountain bikes have been supplied with Koski forks or imitations made by others than this California mountain bike builder and designer. These forks are characterized by fork-ends with a ridge that traps the axle nuts or the quick-release in place in order to pre vent the wheel from coming loose accidentally — and defeat the main purpose of the quick-release.

6.21 and 6.22. Top: Reinforced mountain bike tandem fork — indestructible but rather heavy. Below: Cinelli investment cast fork crowns.

6.23. Simple fork alignment check

Fork Maintenance

The front fork tends to get damaged when the bicycle runs into an obstacle. Any of the distortions depicted in Fig. 6.25 may result, depending on the nature and direction of the impact. It should be inspected alter any collision, and whenever the steering characteristics seem to have deteriorated. Sometimes it is possible to bend a fork blade back into shape if the damage is not too severe and the material is relatively soft. Otherwise, the fork will have to be replaced, following the procedure outlined under Overhaul Headset. For the inspection procedure, a long metal straightedge is required.

Inspection Procedure:

1. With the fork still installed in the frame, sight along the fork blades from the side, to verify whether any damage as shown in Fig. 6.25 is apparent. If so, the fork should usually be replaced, although a straightening suggestion is given below, which sometimes works, depending on the strength of the fork.

6.24 and 6.25. Left: This is what happens in a frontal collision. Although shown on a cheap bike, the same happens to a fancy model.

Right: Three typical kinds of fork misalignment.

2. Leaving the fork in the bike, place the straightedge in line with the center of the head tube and check whether there is a less pronounced bend of the fork blades relative to the steerer tube. If the distortion is slight, you may be able to continue riding

the bike only if the steering does not have a rough spot — check carefully as described in the headset maintenance section above.

3. If necessary, remove the fork from the bike, following the procedure Overhauling Headset. Place the fork exactly perpendicular to the edge of a perfectly straight, level surface as shown in Fig. 6.23. Verify whether all four points actually make contact simultaneously: the fork-ends and one point each near the top of the fork blades. In case of deviation, measure the difference: if it is more than 2mm, measured at the fork-ends, the fork must either be replaced or straightened.

4. You may try to bend the fork straight by clamping in the steering tube and placing a 60cm (2ft) long metal tube over the fork blade that is bent, trying to force it back into shape. If it does not work, you will need a new fork.

6.26. A crude way of making a fork: The ends of the stays are simply flattened.

Handlebars and Stem

Virtually all modern bicycles use handlebars that are connected with the rest of the steering system by means of an adjustable stem, as shown in Fig. 6.27. The handlebars proper, often referred to as the handle bar bend on a racing bike, are clamped in the collar at the end of the stem. The stem is clamped inside the fork’s steerer tube by means of a wedge- or cone- shaped clamping device that is tightened with the ex pander bolt which is usually recessed in the top of the stem (see Fig. 6.30).

Of the two methods shown in Fig. 6.30, the one with the wedge is more popular these days, and is recommended for applications in which the handlebar height is frequently adjusted. The method with the cone, though harder to loosen, does not deform the steerer tube as easily, allowing a more accurate angular alignment of the handlebars.

Stems and handlebars are generally made of aluminum, although welded high-strength steel stems and handlebars of the same material are finding their way onto high-quality mountain bikes. This is one application where careful dimensioning of strong steel alloy can provide greater strength and less weight than can be achieved with aluminum. Mountain bike handlebars may also be made of the same material, as well as titanium and carbon fiber reinforced epoxy. On racing bikes, these materials are not practicable, since they can’t be easily made in such a complex shape — unless you want to pay as much for the handlebars as for the bike frame.

In order to avoid the possibility of breaking the stem, it should never be clamped in less than 65mm (2 1/2”). Many manufacturers mark this point of minimum insertion, and if this is not done, you can take care of it yourself with the aid of an indelible marker. Both the height and the reach (or length) may vary, as shown in Fig. 6.29, and should be selected to match the desired posture on the basis of the rider’s size. Most bikes are sold with stems that have too much reach to be comfortable for most women, arid should be replaced by one that fits at the time of purchase.

Handlebar Dimensions and Types

Handlebars are also available in different widths. On a racing bike, the correct dimension is such that the arms are parallel all the way from the shoulders to the wrists when holding the drops (the ends of the racing handlebars). On mountain bikes, the arms spread out slightly, but even here a width of 55cm (22”) is as wide as comfort and handling ease allow. Wider handlebars, popular on early mountain bikes, require too much upper body movement when maneuvering at low speeds. If necessary, a hacksaw can be used to cut the bars down to size from both ends, after first having made sure the brake levers and gear shifters can be in stalled far enough from the ends to allow room for the hands.

Triathletes and time trial cyclists, who typically ride considerable distances without need for difficult maneuvering and braking, like the aerodynamic ad vantage offered by special handlebars that point far for ward and support the arms on pads. These are often referred to as Scott bars. They allow a different, more stretched and forward-leaning body posture, which does reduce wind resistance. A special type of gear shifter is available that is installed at the ends of such bars.

The diameter of the handlebars is greater in the middle portion than over the remainder of their length, to pro vide a point where they are clamped, while still allowing insertion in the stem. This thickened section usually contains a reinforcing sleeve or insert. Unfortunately, the ends of the reinforcing sleeve cause a so-called stress raiser, which sometimes leads to fatigue cracking, causing the handlebars to suddenly break apart. This kind of damage is least likely if the reinforcement is put around the outside, even if this is aesthetically less pleasing. Whether inside or out, it should be at least 7.5cm (3”) long to distribute the stresses far enough away from the most sensitive location at the ends of the stem clamp.

Drop handlebars, i.e. the kind used on racing bikes, are usually finished off by winding handlebar tape around them. As an alternative, foam plastic sleeves can be used, requiring the brake levers to be removed first. Handlebar tape is available as adhesive cloth, as non-adhesive plastic and in fancy versions made of leather. The ends of the tape are tucked into the handlebar ends, after which the handlebar plugs are in stalled. Mountain bike bars have plastic handgrips at the ends. Clip-on bars, which have become popular in would-be racing circles should have comfortable grips.

6.27. Handlebars and stem.

6.28. Example of clip-on handlebars for a lower riding posture and reduced wind resistance. Not suitable for d handling situations.

Handlebar Maintenance

The following descriptions will deal with the height and angle adjustments of the handlebars, and replacement of the individual parts, as well as the installation of tape, sleeves and handgrips.

Adjusting Handlebar Position

This work usually only requires the use of a wrench that fits on the expander bolt, usually a 6mm Allen key. Only simple utility bikes still come with hexagonal, non-recessed bolts, for which an open-ended or box wrench is used, and sometimes you need a hammer or any other blunt, heavy object.

Procedure:

1. Facing the bike from the front, clamp the front wheel between the legs.

2. Loosen the expander bolt by 3 - 4 turns. If the stem does not immediately come loose, lift the front of the bike off the ground by the handlebars and hit the head of the bolt with a hammer to loosen the wedge or cone inside.

3. Place the stem at the desired height and angle, and tighten the expander bolt partway while holding it in place.

4. Check to make sure the handlebars are perfectly aligned perpendicular to the frame; then tighten the bolt firmly.

Handlebar Angle Adjustment

The angle under which the handlebars are oriented relative to the horizontal plane can be adjusted after loosening the binder bolt that clamps the collar of the stem around the handlebar bend. You need a matching wrench.

Procedure:

1. Facing the bike from the front, clamp the front wheel between the legs.

2. Loosen the binder bolt by 1 - 2 turns, until the bar is loose enough to be turned

3. Turn the handlebar bend into the desired orientation, and tighten the bolt partway while holding the handlebars in place.

4. Check to make sure the handlebars are perfectly aligned and then tighten the bolt firmly.

Remark:

If it turns out to be impossible to tighten the handlebar bend fully, first try lubricating the binder bolt, which makes it possible to tighten it more easily. If that doesn’t work, you may make a shim out of a thin piece of aluminum (e.g. an aluminum beverage can) to fill up the space between the exterior of the handlebars and the interior of the clamping collar — you may have to open up the clamp by wedging a large screwdriver in.

6.29. Stem dimensions

6.30. Expander bolt details

Replacing Handlebar Bend

To remove and install the handlebar bend, while retaining the stem, e.g. when the bars are damaged, the brake levers and anything else mounted on the handlebars must first be removed on one side. In addition to a wrench for the binder bolt on the collar around the bars, you may need a large screwdriver.

Removal Procedure:

1. Hold the bike in a work stand or, when not avail able, clamp the front wheel between the legs, facing the bike from the front.

2. Loosen the binder bolt fully and remove it.

3. If necessary, spread the collar apart as shown in Fig. 6.32, so the handlebar bend is free to move.

4. Twisting to find the most favorable orientation as you work around the bend, pull the handlebar bend out of the stem.

Installation Procedure:

1. Twisting the handlebars in the most favorable orientation as you work, push them through the collar as far as possible.

2. To get the thicker middle section in, spread the collar open with the large screwdriver.

3. Hold the bars in the desired orientation and tighten the bolt partway while holding the handle bars in place.

4. Check to make sure the handlebars are perfectly aligned and then tighten the bolt firmly.

6.31. SunTour mountain bike stem with double clamp (or binder) bolts.

Replacing Stem (with or without handlebar bend)

If the handlebar bend should remain attached to the stem, first remove the brake levers or cables and any thing else installed on it that is connected to the bike.

Removal Procedure:

1. Hold the bike in a work stand or, when not avail able, clamp the front wheel between the legs, facing the bike from the front.

2. Loosen the expander bolt by 3 - 4 turns. If the stem does not immediately come loose, lift the front of the bike off the ground from the handlebars and hit on top of the bolt with a hammer to loosen the wedge or cone inside.

3. Lilt the stem out of the front end of the bike.

Installation Procedure:

1. Clean and lightly lubricate the exterior of the stem and the interior of the steerer tube that is accessible through the headset locknut.

2. Place the stem in the desired height, and tighten the expander bolt partway while holding it.

3. If the handlebars are installed, check to make sure they are perfectly aligned perpendicular to the frame, and then tighten the bolt firmly.

Installing Handlebar Tape

Old handlebar tape is removed after loosening the handlebar end plugs, as shown in Fig. 6.33. Adhesive tape may have to be cut, after which it is advisable to clean the adhesive off with denatured alcohol (methylated spirit). Usually, one roll of tape is needed for each side. First lift the rubber brake hoods off the levers so they clear the handlebars.

Procedure:

1. Adhesive tape is wound starting from a point about 7.5cm (3”) from the center, working towards the ends. Overlap each layer generously with the preceding one and wrap in an X-pattern around the brake lever attachments.

2. Non-adhesive tape is wound starting from the ends, after tucking a piece inside. Work towards the center, and overlap as described above for adhesive tape. Fasten the ends by wrapping some adhesive tape around it.

3. Install the end plugs, referring to Fig. 6.33.

6.33. Typical handlebar end plug details

Replacing Handgrips or Sleeves

To remove old handgrips or foam plastic sleeves, you may either put some dishwashing liquid underneath after lifting the end with a screwdriver, or you may simply cut them lengthwise with a sharp knife, depending whether you want to reuse them or not.

Before installing the new items, remove all traces of detergent (or any traces of adhesive and old tape when replacing tape with sleeves). You may ease the process by softening and expanding the new items in hot water. To make sure the grips stay in place, you may squirt some hair spray inside before pushing them on.

Seat and Seat-post