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  Latest update: 10/9/2023

Bicycle Sizing

Are you are investigating options to tweak your bike - new stem, seat adjustment - to make it more comfortable? Are you considering a new bike? Or maybe just planning on a bike trip and need to order a rental bike.

I. Sizing for a rental bike

The following 2 links should answer the question.

II. The science of bike fitting.

The Colorado Cyclist website has been around for years, and they specialize in fitting your new bike on-line.

As women often have unique sizing questions and problems, the Terry Bicycle webpage (a company that touts itself as specializing in women's frames) offers their ideas on frame geometry.

And finally, an online bike fitting calculator which will give you more detail than you may need. But it will help you come "close" to a best personal fit with an off the shelf frame or all the detail you need for an ideal customized fit.

Here are some additional of interest.

III. Saddle Adjustment.

This is probably my most frequent question from riders looking for a quick tweak in their setup. This article covers all the points to consider with specific recommendations. There are 3 elements in a correct saddle adjustment.
  1. saddle height
  2. saddle fore/aft
  3. saddle tilt

For height, a quick determination for saddle height is inseam x 1.06 to 1.09. Stand barefoot against a wall with a thick book between your legs. Pull it upwards, keeping it square to the wall, until it is snug, but not painful. Mark the top of the book on the wall. Measure the distance to the floor. This is your in-seam. Multiply x 1.06 and you will have a good approximation of your correct saddle height

To apply this measure (inseam x 1.06), first measure the length of your saddle (front to back) and determine the mid-point. Measure from this spot in a straight line to the center of the bottom bracket. Now you have a place to start as you play around to find your correct number while out on the road.

IV. Reprints from 2 interesting articles.

  1. An excerpt from an article on the web site of Malcolm Firth - Senior Coach, Association of British Cycling Coaches that may help to answer some of your questions about leg length and seat angles. His suggestions are based on analysis of data he gathered from various sources.

    ".......The two main measurements required for a correctly sized road frame are the seat tube and top tube lengths. These, together with the seat tube angle are the parts of the frame most influenced by your body size. Top tube length is generally taken to be the horizontal distance from the center line of the head tube to the center line of the seat tube, whilst seat tube length is the straight line distance from the center of the bottom bracket to the center of the junction between the seat tube and the top tube.

    To estimate the correct seat tube and top tube lengths for your road bike several measurements of your body and limbs will need to be taken. The first of these is your inside leg measurement. This is taken with you in a standing upright position, without shoes and with your feet about 25cm apart. The measure is then taken vertically from floor to crutch (the point on the crutch where the measurement is taken from is the bony protuberance known as the ischial tuberosity - the lowest part of the pelvic bone - that you sit on). The seat tube length is calculated as being 2/3rds of your inside leg measurement. Thus, if your inside leg measurement was 84cm, the seat tube length would be 56cm.

    The top tube length of your bike should be proportional to a combination of your trunk length and arm length. For these measurements you need to be seated with your back pressed firmly against an upright surface such as a wall. Trunk length is measured from the seat you are sat on to the top of your shoulder with you sitting fully upright. The forearm length is measured from the back of the elbow (with the back of the elbow pressed against the upright support and with the forearm horizontal) to the center of your clenched fist. Total arm length is obtained with your arm straight out in front and measuring from the upright support to the center of your clenched fist (keep your back firmly against the support). The measurements are used in the following equation: top tube length = 75.25% trunk length + 7.8% forearm length + 7% total arm length - 1cm. The answer should be rounded out to the nearest 1/2cm.

    For the seat tube angle you first of all need to measure your thigh and lower leg lengths. Thigh length is measured horizontally from the upright support to the front of your kneecap, whilst the lower leg length is measured from the top of your kneecap vertically to the ground. Then calculate the seat tube angle as: Cosine of 26.4% (thigh length / lower leg length). The answer should be taken to the nearest 0.5 degree.

    It is worth remembering that the calculations used to estimate frame size are generalizations based on average figures calculated from measurements on a wide range of riders. Within those averages there are variations typical amongst a group of people. Therefore, no formula can give the perfect frame size and riding position for every rider. The final, and most important check will be for you to try out the position you have arrived at during several rides of increasing distance and severity. Only then can your riding position be given the fine tuning that will be needed to make it the best one for you........"

    Weight distribution

    Why the emphasis on frame size? It has to do with both comfort of position and weight distribution. Weight Distribution. Bicycles handle best when 55% to 60% of bicycle and rider weight is on the rear wheel and 40% to 45% is on the front wheel. This will generally produce a comfortable ride and reduce the possibility of overuse injuries.

    When too much weight is forward, bicycle control, handling, and safety may be a problem, especially on descents. The chance of hand numbness, tired arms and shoulders, neck, shoulder, and upper-back pain is increased. When too much weight is on the rear wheel, control may be difficult in corners and front-end shimmy on descents is more common. Weight distribution results from almost all elements of bicycle fit, including pedal fore-aft, seat height, seat fore-aft, torso angle and reach. In addition to judging the fit by your level of comfort after a long ride, weight distribution can be checked by weighing the bike and rider and then seeing what percentage of that weight is on the front wheel while on a stationary trainer.

    And for TALL RIDERS.

    "A few other observations. Tall riders generally have longer legs in relation to their body length than do average height riders. For example, I am currently coaching a young rider who is 6ft 3ins tall, whereas I am 5ft 9ins. As you can imagine, when we stand his head is much nearer the clouds than mine. Not so when we sit, there is less than 2ins difference in sitting height. Of this extra leg length in tall people, the thigh is often a greater proportion of the total than with average height people. This means that to get the knee above the center of the pedal spindle when the cranks are horizontal, tall riders with very long legs usually have a shallow seat angle. In the case of your rider it sounds like the ratio of his thigh length to lower leg length is about 1.3 to 1, whereas the average height rider has a ratio of about 1.1 to 1 (see "Road Racing" by Hinault and Genzling). As a contrast, I once met a rider who was 6ft 4ins tall with a thigh to lower leg ratio of about 0.9 to 1. For him to get his knee over the pedal spindle he used a seat angle of 75 degrees.

    Tall riders with long legs and short bodies can sometimes encounter problems with backache. For example, a combination of long thigh, shallow seat angle, short body and the handlebar stem well down in the head tube can mean a more acute angle between thigh and body when the leg is at the top of the pedal stroke. For some riders this can put excessive strain on the muscles on the back of the thigh that help drive the thigh downwards, leading to backache. I seem to remember Alexi Grewal (the American rider who won the 1984 Olympic road race) saying that he encountered this problem and only solved it when he went to a steeper seat angle than had been previously suggested from his body measurements. This just goes to illustrate that you cannot go by formulas alone when dealing with individual riders. They just help you get into the right ball park, after that you need to find out whereabouts in the ball park suits you best."

  2. From Andy Pruitt(reprinted from This may help you understand why a good bike fit is so important.)

V. Frame building techniques.

This detailed critique on frame building will give those interested even deeper insight into how all those measurements come together and translate into bike performance.

Now for a few questions whose answers may help reinforce these ideas.

Q. I am a new rider and still in the Hybrid ranks with my 1989 Schwinn Crisscross. I recently did a two day 150 mile charity ride (second year on the same bike) and felt pretty good. I did ride extensively and did light weight training, spin classes during the week, weekend rides - anywhere from 20 - 40 miles on Saturday and Sunday. I maintained this regime for about 3.5 months prior to the ride. So I would consider myself in pretty good shape.

My question is the riders I rode with in the ride were in marginal shape - however they both had brand new road bikes. One had the Lemond -Alp Duez and the other had a FELT. Prior to the ride I found I was working doubly hard to keep the pace when we went out on training rides. In fact on one ride I hung with a group of 7 with road bikes for about 30 miles and I seemed to be the only one sweating. I weigh 210 and the other riders were about the same weight. However they finished a good 40 minutes ahead of me. My bike weighs approximately 25 lbs. - can the bike make that much difference in the ride? I am feeling a little blue today because I thought I was going to do much better. - TZ

A. Weight does make a difference, especially in the pedals and wheels as you are continuously accelerating and decelerating as you ride and the inertial resistance to acceleration is a big energy drain. And the geometry, rather than the weight, of the frame is a large factor as well. It is not the 5 pounds in the frame itself (which could easily be in two water bottles instead).

Q. I usually do road rides of 50 miles with 3M to 4M feet of elevation and I wear Sidi Bullet, (@ 650 grams), which are mountain bike shoes. Climbing is my weakness. Would I see any improved performance if I started wearing lighter and stiffer road bike shoes, such as the Sidi Genius 5.5 HT Carbon, (@ 540 grams)? NT

A. The weight in pedals, cranks, chain, and rims/tires (which has angular inertia when you are accelerating - something you are doing all the time even when on the flats) is much more important weight than in the frame, your water bottle, etc. The decrease in weight of these shoes might make some difference in climbing. But the stiffness or other design features would not. I once had a fellow at a local bike shop tell me that all he did was buy lighter rims - he biked a lot - and yet it allowed him to ride another 10 miles before he got to his usual level of fatigue.

All questions and suggestions are appreciated and will be answered.

Cycling Performance Tips
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