Bicycle Technology: Seat and Seat-post

Not a technically exciting subject, perhaps, but some sensible and necessary things should be said about the seat, or saddle, and its peripherals. Fig. 7.2 illustrates a typical seat and the seatpost, or seat pin, used to attach it to the frame, as well as the binder bolt used to clamp it in. Several different versions exist of all these parts, and they will be covered systematically in the following sections.

7.1. Lightweight Cinelli seats.

7.2. Details of seat and seat post.

The Seat

7.3. The ultimate leather saddle: the Brooks Colt.

Seats may be made of several different materials. Utility bikes and cruisers have models consisting of a metal frame with springs supporting a plastic cover. Racing, touring and mountain bikes typically have seats made with a stressed, self-supporting cover, usually of leather- or fabric-covered polyamide (nylon), sometimes of firm leather. The ones intended for mountain bikes and touring machines are generally padded and somewhat wider in the rear portion, while those commonly installed on utility bikes tend to have a shape that defies any ergonomic and anatomic principles.

Leather seats easily look the most impressive, and some old-fashioned riders like the author swear by their comfort — which is bought at the expense of many miles of breaking them in and scrupulous care. Most of the nylon-based seats are actually just as comfortable — right from the start — and a lot easier to maintain. If a leather saddle should get wet, you’re not supposed to sit on it until it has thoroughly dried. Be sides, it should be treated with a special leather treatment (e.g. neat foot’s oil or Brooks Proofide) to prevent it from drying out and becoming too absorbent.

The shape of the seat becomes quite critical when cycling over long distances, where the cyclist pedals rather fast and applies noticeable force to the pedals. To allow freedom of movement without chafing, a narrow front end is required, while the rear must conform to the rider’s pelvic width. Women generally need a de sign that is rather wide in the back, as shown in Fig. 7.4: it should be about 6 - 8cm (2 - 3”) wider than the distance between the two bony protrusions. Due to the typically rather upright position used on mountain and touring bikes, these probably need saddles that are modeled on the woman’s seat, but more padded, as shown in Fig. 7.5. Excessive springiness, however comfortable it may seem, is not recommended, since it makes for a tiring lateral instability and inefficient pedaling.

Recently, saddle padding made of a gel material that takes on the rider’s shape, very much like the filling of modern ski boots, has been introduced. This is still not the ultimate solution to the comfort dilemma, since even this material is eventually penetrated and then feels as hard as a rock. More promising is the special gel material used e.g. as the seating cushion in modern wheel chairs, since this remains flexible even under en during pressure.

Most seats with a stressed cover are based on a frame with two wires, or rails, usually made of steel. Lightweight solutions with aluminum or titanium wires don’t measure up, since the minuscule weight savings is paid for at the price of inadequate strength, often resulting in a broken wire — and a ruined expensive seat. The inadequate strength is easily explained by the fact that it is practically impossible to make the wires any thicker than they are when made of steel, resulting in less strength when these weaker materials are used.

A few expensive leather models for touring, utility and mountain bike use have a double set of wires and in- corporate a set of coil springs in the back. Although I am not in favor of excessive springiness in seats, this is probably the most acceptable solution for those who like to ride in a rather upright position, which puts more weight on the seat. These models do require special matching support hardware.

7.4. Determining optimum seat width.

7.5. Padded mountain bike seat.

The Seat-post

7.6 and 7.7. Two attempts to make a more comfort able seat. The two- part design to the right was first introduced in 1898 and offered as a brand new invention during the nineteen- eighties.

The conventional tubular seat-post shown in Fig. 7.2 is mounted by means of the rather crude clip supplied with most cheap seats. This type does not allow very accurate angular adjustment of the seat relative to the horizontal plane, since the serrated clamp has notches that lie too far apart to find the optimum angle for com fort.

More modern seatposts are illustrated in Fig. 7.8. Usually, these either have an integrated fine-adjusting mechanism of some kind, or they are made up of separate parts: a tubular aluminum post and a separate, precisely adjusting head with clamp to hold the saddle wires. Of all types available, the old Campagnolo model with two hard-to-reach bolts in the front and the rear, as shown in LH detail of Fig. 7.8, is still the most accurate. More recent versions sacrifice some accuracy for ease of access.

7.8. Details of various common seatpost types. Side adjusting; Top adjusting; Bottom adjusting

As in the case of the handlebar stem, seatposts are not necessarily lighter when made of aluminum than when made of steel. Most of the modern fine-adjusting aluminum models are actually heavier than even a simple steel tubular clamp with matching clip. Due to design and construction constraints, it is often easier to make a really light adjustable seatpost of steel alloy than it is to do so of aluminum. On the other hand, the manufacturing technique for the aluminum version allows mass production and thus a lower price.

7.9. Saddle testing in Raleigh’s product testing laboratory, where wear shape retention and comfort are evaluated.

The diameter of the seatpost must correspond to the inside diameter of the seat tube. Although many utility bikes and cruisers use 25.4mm (1.00”) diameter, the most common sizes for racing and mountain bikes are size inside seat tube diameters, and the variety gets bigger from year to year due to the introduction of non standardized oversize steel arid aluminum tubing.

At least 65mm (2½”) of the seatpost must at all times remain clamped in at the top of the seat tube, which requires a long model on mountain bikes. Ideally, the seatpost should be marked to indicate the minimum insertion depth — something you can do yourself using an indelible marking pen, if necessary. The longer seat- posts introduced for mountain bike use, which are 30cm long or more, also seem a nice solution for people with long legs, who previously could never find a frame big enough to achieve the desired seat height. Unfortunately, the likelihood of these long seatposts being available in a size to match the bike in question is rather meager.

7.10 and 7.11. Left: Campagnolo mountain bike seat- post, which must be longer than those for regular bikes. Right: Typical mountain bike seatpost clamping detail.

Binder Bolt

Nowadays, virtually all racing and high-quality touring bikes are equipped with an Allen key operated binder bolt. This has the advantage of allowing adjustment without chance of either chipping the bike’s paint or deforming the nut of the binder bolt. On the other hand, some of these require the simultaneous use of two identical size wrenches, which may not always be available. Ideally, one of the two parts of which these bolts consist should have a prong that fits in a matching locating recess to eliminate rotation of that part, thus obviating the need for a second wrench.

7.12. Mountain bike seat with coil springs.

Reserved for folding bikes up to the late seventies, quick-release binder bolts, shown in Fig. 7.15, are now readily available and are universal on all mountain bikes. They are quite handy if you want to adjust the seat height frequently, but allow easy saddle theft. Actually, the quick-release is more a fashion item for most people, since many mountain bike riders don’t really use the adjusting feature on their bikes very much — or not properly. Instead they randomly set the seat in any one of a wide variety of uncomfortable and inefficient positions. For the mountain bike, you can find appropriate seat height adjustment instructions in my Mountain Bike Guide, in any of my other guides for other bicycle types.

7.13 and 7.14. On mountain bikes, it is often helpful to adjust the seat height while riding. The Hite-Rite allows you to do that and return to the origin al position. Place one side around the seat post, the other around the binder bolt. Tighten when the height is properly adjusted.

An adjusting aid for mountain bikes is the Hite-Rite. This connects the binder bolt location with the seatpost under spring tension, as shown in Fig. 7.13, preventing theft and vandalism at the same time as easing adjustment while sitting on the bike. The saddle is adjusted by loosening the quick-release binder bolt while applying your body weight in the desired location to bring the seat to that height, and then fastening the binder bolt again.

Mountain bikes that are frequently adjusted sometimes suffer from fatigue-induced cracks. These form either at the end of the split portion at the back of the seat lug or at the eye, or lug, through which the binder bolt fits. The former problem is minimized by drilling a 3 - 4mm (1/8” – 5/32” diameter hole at the base of the slot. The second problem can only be eliminated by correct design. A relatively simple solution used on some bikes is to separate the clamping function in the form of an external clip that is more easily replaced than a cracked frame. If the clamping action does not work properly, the split end can sometimes be filed out just a little, as shown in Fig. 7.17. In that case, also drill a hole at the bottom if the manufacturer has not done so.

7.15. Quick-release binder bolt as used on most mountain bikes.

7.16. Twisting motion to adjust or re move seat with tight-fitting seatpost.

7.17. File out this slot if it is not wide enough to allow proper clamping in of the seat post although it is the right size.

Seat Adjustment

Except on bikes with a quick-release binder bolt, this operation requires the use of a matching wrench (two wrenches in some cases). Covered here are the adjustment of the height and the angle of the seat top with respect to the horizontal plane, as well as the forward position relative to the handlebars or the pedals. You will need wrenches to fit the binder bolt and the adjustment bolts on the seatpost or its clip.

Height Adjusting Procedure:

1. Loosen the binder bolt at the seat lug by about one revolution (or undo the quick-release if provided).

2. Move the seat with the seatpost attached up or down — if necessary in a twisting motion per Fig. 7.16.

3. Hold the seat firmly in the desired position, aligned perfectly with the longitudinal axis of the bike, then tighten the binder bolt or the quick-release again.

Angle Adjusting Procedure:

1. Find out which bolt or bolts govern the seat’s angular orientation.

2. Loosen the bolt or bolts and place the seat under the desired angle with respect to the horizontal plane.

3. Tighten the bolt or bolts, while holding the seat firmly in place, also keeping it aligned with respect to the longitudinal axis of the bike in case of a seat- post with a separate clip.

Forward Position Adjusting Procedure:

1. Find out which bolt or bolts must be used to loosen the clip from the wires.

2. Loosen the bolt or bolts and move the seat forward or backward to place it in the desired position relative to the handlebars and the pedals.

3. Tighten the bolt or bolts, while holding the seat firmly, it under the correct angle and keeping it aligned with respect to the longitudinal axis of the bike in case of a seatpost with separate clip.

Replacing Seat-post and Seat

Follow this same procedure when only the seat (without the seatpost) must be removed, since it is easier to separate seat and seatpost once they are removed from the frame. Fitting wrenches, a rag and some Vaseline are required.

Removal Procedure:

1. Loosen the binder bolt at the seat lug by about three revolutions. On a bike with a quick-release binder bolt, undo the lever and then unscrew the locknut on the other side by one or two turns.

2. Pull the seat with the seatpost attached out of the frame — if necessary in a twisting motion per Fig. 7.16.

Separating and Installation Procedure:

1. If the seat must be separated from the seatpost, loosen the clip from the seat wires. Usually, only one nut or bolt has to be loosened to achieve this.

2. Remove the seat if desired.

3. If appropriate, attach the replacement seat the same way as the old one was. Don’t bother adjusting the seat angle just yet.

Seatpost Installation Procedure:

1. Clean and lightly lubricate the interior of the seat tube and the exterior of the seatpost to prevent corrosion and to facilitate later adjustment.

2. Insert the seatpost in the seat tube to the desired depth.

3. Firmly hold the seat in the desired position, perfectly aligned with the longitudinal axis of the bike, then tighten the binder bolt or the quick-release again.

4. Check and, if necessary, correct the angle and the forward position, following the preceding descriptions.

Leather Seat Maintenance

For those incorrigible ones who use a stressed leather seat, here are a few suggestions for its maintenance.

First, make sure it never gets wet. To avoid this, it is not enough to keep it out of the rain, you also have to wrap a plastic bag around it when transporting the bike on a car or in a pickup. And if it does get wet, don’t sit on it until it is thoroughly dry again, since the application of the rider’s weight on the wet seat will deform it hopelessly.

At least twice a year, and anytime it has been wet (but not until it is dry again), apply special leather treatment, preferably from underneath, where the leather is most porous and does not rub off so easily. The leather seat manufacturers Brooks and Ideale each have their own treatment grease or oil for this purpose, although equestrian saddle soap works too.

If the leather seat cover sags, carefully tighten the bolt shown in Fig. 7.18 to tension the cover slightly. This should only be done when absolutely necessary and not too vigorously, since the seat will develop an un comfortable shape with sharp folds near the sides if it is overstressed.

7.18. Tension adjuster of leather seat.

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