HOW TO REPLICATE YOUR IDEAL BIKE FIT ON ALL OF YOUR BIKES (WITH DOWNLOADABLE WORKSHEET)

3 bikes with same positional setup angles and distances
Three bikes, all with the same relationship between the bottom bracket, saddle tip, and bar center. Note that the saddle model and handlebar reach/drop are the same on all bikes. The shifters are different, which may require a bit of minor adjustment on each bike.

If you’re like many serious cyclists, you probably own more than one bike. Whether due to having different bikes for different conditions, having a backup on hand when our main ride is in the shop, or just the inability to keep from buying the latest and greatest toy on the market, most of us tend to find ourselves with a variety of horses in the stable.

From a performance and injury-prevention standpoint, we would to prefer to find an “ideal” bike fit on one bike that maximizes efficiency, performance and comfort, and then precisely replicate that fit on each of our other bikes. Many cyclists struggle to achieve this consistency of fit, however. What with different seat tube angles, top tube lengths, bottom bracket heights, and the rest of a seemingly innumerable list of variables, many riders find themselves constantly fiddling to try to eliminate the knee twinge they feel on the Trek, the neck strain they feel on the Specialized, or the numb hands they get on the Giant.

The solution is simple in theory: make the body’s position on each bike precisely the same. But measuring this – especially the angles, down to hundredths of a degree perhaps – is beyond the ability and tools of just about everybody. The solution that is  within reach of everybody, however, is to grab a tape measure and match some easy measurements of length on an X-Y axis – on a grid, essentially – and if we get these measurements right, the tiny gradations in body angles will naturally take care of themselves.

Everything revolves around the bottom bracket – no pun intended! When your sit bones are the correct angle and distance from the bottom bracket, and your hand position is the correct angle and distance from the bottom bracket, your fit is precisely the same on any bike.

hard vs easy to measure
It would be very difficult for the individual cyclist to accurately measure the angles in the two images on the left, but actually quite easy to measure their equivalents on the right.

Still, however, it is a challenge to find a way to be truly precise in our measurements. There are tools on the market that shops and pro mechanics use for this purpose, but they are pricey for the average rider who just wants to match up a couple of bikes. Fortunately, there is a simple and free solution that requires nothing more than a corner of your home, a tape measure, and a little basic math

The key to this method is the precision provided by the fixed positions of the floor and wall, and fixed positions on our bikes. By using them as the basis for our precise measurement, there is no confusion about things like bottom bracket height, stem angle, tire width, etc. We are able to compare apples to apples, so to speak, on each bike – saddle to bottom bracket, bottom bracket to stem, saddle to stem – with precision down to the millimeter.

Using the precise positions of the wall and the floor, we can make some simple measurements and do a little subtraction to find our bike fit to the millimeter.

CAVEAT: In order to a get truly precise measurement, we must use the same model of saddle, the same model of handlebars, and the same  model of shifters. No other component of the bike makes any difference whatsoever, but having these three items match exactly is required to be precise to the millimeter. If you are riding different components on different bikes, you might do best to set up with exact matches, and afterward change out the components one by one and make small adjustments to make things feel closer to perfect. Alternatively, just know that the measurements and adjustments should get things pretty close – probably close enough – but not exact.

NOTE: I have listed what seem to be a lot of steps below, but if you use the downloadable worksheet provided, you’ll find that the procedure is actually quite straightforward. And if you can’t view or download the worksheet for some reason, following the written steps is still fairly simple. And be precise!  84.3 mm is not “meh, 84 mm”.

FAQ’s:

1. Does it matter that my wheels are different or my tires are fatter or thinner? No, not at all. The calculations for 4, 6, 8, and 10 remove all distances except those between the bottom bracket, the saddle tip, and the handlebar center.

2. Do I have to the back tire against the wall? Can I use the front tire instead? Absolutely, although you will have to change where the measurements are made (for example the “3” measurement will now be fairly short to the handlebar rather than the longest measurement)

Step Zero: Place your bike with the “preferred” fit in a corner of your home, garage, wherever. Be sure the floor is a firm surface, not carpeted, and that the wall is flat  where you will set the bike’s tire and will measure from, without any interfering projections like moulding or an electrical outlet.

Step Zero Point One: Set the bike as vertical as you can, and use a tape measure, preferably one that has markings for millimeters, to set the two wheels an equal distance from side wall. Simply measure to the center of each tire and move the bike to make them equal.

two tape measures with both english and metric markings
I strongly recommend you use a tape measure that has metric markings, and you MUST measure precisely (i.e. 84.3mm is not “meh, 84mm”).

Step 1. Measure from the rear wall to the center of the bottom bracket and record as “Measurement 1A” .

Step 2. Measure from the floor to the center of the bottom bracket and record that as “Measurement 2A” .

Step 3 Measure from the back wall to the center of the handlebars (the center of the “tops” on a road bike). This is “Measurement 3A”.

Step 4 Subtract  measurement “1A” from the longer measurement “3A”. Record this measurement as “Measurement 4A”. This is your preferred horizontal distance from the bottom bracket to the handlebars. Notice that it would be difficult to just take a tape measure and precisely find this horizontal distance on the bike, since the handlebars are so much higher than the bottom bracket. But by taking two easily measured distances and subtracting one from the other, it is simple to calculate it to the millimeter!

Step 5. Measure from the floor to the center of the handlebars, this is “measurement 5A”.

Step 6. Subtract “measurement 2A” from  “measurement 5A”.  This is your preferred vertical distance between the center of the bottom bracket and the center of the handlebars..

Step 7. Measure from the floor to the tip of the saddle. Choose a point on the tip and use it exactly for all of your saddle measurements. This is “measurement 7A”.

Step 8. Subtract “measurement 2A” from “measurement 7A” This is your preferred vertical distance between the saddle tip for this model saddle and the center of the bottom bracket. Call it “measurement 8A”.

Step 9. Measure from the wall to the tip of the saddle. This is “measurement 9A”.

Step 10. Subtract “measurement 9A” from “measurement 1A” (yes, one minus nine). This is your preferred horizontal distance between the saddle tip for this model saddle and the center of the bottom bracket. Call it “measurement 10A”.

You now have four precise measurements – #4a, #6a, #8a, and #10a that you can apply to any bike frame and produce an equivalent, precise fit.

We can’t apply those measurements directly to another bike with precision, however. Instead, we make the same measurements on the second bike using the same procedure, then compare those different #4’s, #6’s, #8’s, and #10’s, then change them the appropriate amount to make them match on the second bike.

So the next step is to set up your second bike, “bike B” in the corner just as before, and make the same ten measurements and calculations for that bike. You can call these measurements 1B, 2B, 3B, etc.

Once you have the second set of ten measurements, we do some simple math to determine our CHANGES.

Calculate “CHANGE4 (Stem Length)”: Subtract 4B from 4A. This may be a positive or negative number. This is “CHANGE4 (Stem length)”, the amount you must change the horizontal stem length to match your preferred “Measurement4”.

You can use that number to make your change vs. your current stem, or you can add “CHANGE4” + “3B” to get a new “3C” measurement from the wall (REMEMBER that the CHANGE number may be positive or negative, so you may end up with a shorter “C” number!)

Calculate “Change6 (Bar height)”: Subtract 6B from 6A. This may be a positive or negative number. This is the amount you must change the vertical stem height – by changing the stem angle and/or changing out the spacers on the steering tube – to match your preferred center-of-handlebars fit. You can also add CHANGE6 to 5B, giving you a new measurement “5C” that you can make and/or to verify your stem/spacer changes from the floor.

Calculate CHANGE8 (Saddle height): Subract 8B from 8A. This may be a positive or negative number. This is the amount you must change the vertical saddle tip height to match your preferred fit. This is more easily done than the stem since you simply move the saddle. you simply add this number to 7B, giving you a new measurement 7C from the floor that you can use to set the saddle higher or lower .

Calculate CHANGE10 (Saddle fore/aft): Subtract 10B from 10A. This may be a positive or negative number. This is the amount you must change the horizontal saddle tip distance to match your preferred fit. Again simply add this number to 9B, giving you a new measurement 9C from the wall that you can use to set the saddle forward or back.

If you have made all your measurements correctly, and all your adjustments properly, both of your bikes should now have the exact same measurements for 4, 6, 8, and 10, and your body’s position in space should be the same on both bikes, regardless of the geometry of each bike’s frame!

Once you have made your position changes, you can verify that both bikes match simply by measuring for and calculating 4, 6, 8, and 10 for each bike. They should be perfect matches!

Congratulations and enjoy all your bikes!

(NOTE: My husband and I first found this method in a weekly VeloNews Q&A column by Lennard Zinn, and we used it to match up the first new bikes I’d bought in ten years to my old faithful Fuji Supreme SL. We also found that it was great for matching a fit to a rental bike when cycling overseas. The post by Mr. Zinn was smart and logical, but it still took some mental gymnastics to get the process right each time, and since it was the only resource we found online about this method, we decided to really break it down step-by-step and put together a downloadable worksheet that anybody should be able to use to punch in the numbers with great results. We’re indebted to Mr. Zinn for putting us on the right track with this great at-home method!)

3 Comments

  1. Please comment and let Fundamental Velo know how this worked for YOUR bikes!

  2. Bryan

    Can someone confirm that Step 4 is written incorrectly? Shouldn’t 1A be subtracted from the longer 3A?

    • Corrected. Good catch, thanks! I had it right on the printable pdf but muddled it in the writeup.

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