Fitting a road bike to the rider has become more of a science than ever, yet there is still plenty of art in a good fit. It may take some time, but once a rider has a good fit, maintaining the same fit on a new bike is critical. How do you tell what size new bike can achieve the desired fit? For example, what size stem and how many spacers are needed?
One way to think of the task is to divide the dimensions into two categories: frame dimensions, and rider dimensions. The frame dimensions describe how long the seat tube and top tube are, etc. and the rider dimensions describe where the rider contacts the bike such as seat height and setback, reach and drop to the bars, etc. The rider’s fit is correctly maintained on any frame if other components such as seat post, stem, etc. properly bridge from the frame dimensions to correctly meet the rider dimensions.
If you know your rider dimensions and have frame dimensions to compare, then you can choose between different frame sizes and predict what size components are needed (seat post, stem and spacers, etc.). If the component sizes are reasonable then the rider’s position can be duplicated on the new frame. Unfortunately, making the comparison isn’t trivial, since some of the dimensions aren’t purely vertical or horizontal, and it also seems more difficult these days now that head tubes are extended sometimes, top tubes sometimes slope and different brands measure their frames in different ways. However, if you have a CAD package and enough dimensions you can draw in the frame and rider dimensions and find out the component sizes that might complete the fit.
Below is an example from Franck, who had his fit professionally determined to establish his rider dimensions. I used these dimensions to find out what size Madone might work well for Franck.
Based first on his desired seat height (845 mm), and by refering to the Madone’s seat height table, Franck could consider either a 62 or 64 cm Madone. He’ll need the optional tall seat cap. (The green line is for a different rider, not Franck.)
For the handlebar position, I used SolidWorks to make a sketch of Franck’s bike and rider dimensions.As you can see from the drawings, I’ve used the bottom bracket as “home base” and positioned Franck’s saddle and handlebar clamp according to the rider dimensions from his fitter. I also used the Madone’s geometry table to sketch in a few frame dimensions.
Looks like Franck could comfortably ride a 64 cm Madone in a Performance fit. He could try a 130 or 140 mm stem angled down, using about 25 mm of spacers (including the head set top cap).
I also tried the frame dimensions of a 62 cm Madone, which could fit Franck with 44 mm of spacers (including headset top cap) if the stem also became longer: 145 mm – not a commonly available length! So in a Madone at least, a 64 looks best for Franck.
As always, questions and comments are welcome!
Damon Rinard
Jeff Juneau
Any updates on Project One timing for 08' Madones?
January 03, 2008 at 04:37 PM
Matt Haughey
Is it true the 64cm and 62cm Madones use different types of carbon? I was asking on another cycling site (I'm 6'4" and have a high seat height, but I don't like a long top tube) and someone said the 5.5 Madone in 64cm actually uses the cheaper white carbon frame instead of the black one the 62cm is using. Is that true? If so, was it due to size/stiffness issues?
January 04, 2008 at 12:09 AM
Rafi maman
Hello Damon
I have the original Madone 5.2 58 cm
and the ride on them feel very comfortable(seem to be the dealer in Israel did a very good work on fitting them to my dimensions).
These days I thinking to buy the new Madone 6.5 pro fit.
My question is should the dimension of the farme need to change?
Or do I stick on the same frame size and might be need to change the length of the stem, position of the saddle and spacers?
January 04, 2008 at 05:54 AM
Damon Rinard
Hi Matt,
The 64 cm Madone 5.5 will be OCLV Black, 5.1 will be OCLV White, the same as the other sizes. These are the only two Madones available in the 64cm size.
Damon
January 04, 2008 at 10:46 AM
Damon Rinard
Hi Rafi,
Glad you like your original Madone! The new Madone Pro fit is practically identical, so if you are happy with your position on your bike now, I recommend the same frame size in the new Madone. There should be only a few millimeters difference in spacers or stem length, or maybe even no difference!
Thanks,
Damon Rinard
January 04, 2008 at 11:05 AM
Ryan
You design the best bikes in existence. Keep up the good work!
January 24, 2008 at 09:36 PM
FRANCK
Hi guys,
I am proud to see that you used my personal postural study to help Trek consumers to determine which size is the best for them.
Since the moment i sent you that study i had to consider my position again because i had a back surgery so i used one of the best guy in france who actually works for professional teams renowned in the peloton (Tour de france)to determine what would be the best position for me ( I have a draw but i can't sent it via that web site) on my future bike (That guy also offered me to built a titanium frame but hey! it is very pricy!).
According to his study the saddle height is still 84,5 cm, the lenght of the frame should be 603cm, the seat angle 71,3°, the head tube angle 72,5°, the head tube lenght 215 cm, the chain stay 417. That is for the frame!
Concerning my postion as i told you my saddle height must be 84,5, the difference beteween my saddle and the top of my handdle bar 5,92 cm, my saddle set back 11 cm from the bottom bracket and THAT is the main point because with a 72,3° inclined seat tube on a size 64 or 62 i really don't know if my saddle will allow me to reach 11 cm because as you know, even if all the saddles have the same lenght (about 27,5cm)the mettallic rail is short so i don't know if the rail will be long enough to set my saddle back! And this is vey important because of stability, safety, frame resistance.
About the lenght of my stem the distance between the nose of my saddle and the handle bar must be 55,73 cm (if you draw a straight line)SO i don't know what stem lenght i should use on a Trek because the head tube angle is 74° compare to the 72,5° of my study AND having a shorter stem is maybe dangerous for the bike stability.
OK, that is it for today, i don't know if Trek people could help me with that to determine the best size for me BUT i want to say something about that company anyway:
I would like to thank Scott Daubert and Damon Rinard for their professionalism and courtesy because they always take the time to answer you and help you ! It is something rare and they desserve a great respect for that!
Sorry Damon and Scott if i harassed you with all my questions during those past months, trust me, i didn't mean to embarass you in any way! I hope you could answer that message and let me know if i can still think about fitting a trek (62 or 64 ) according to the datas i sent you on that message!
If not, it is not a big deal, sometimes you have to face reality and if a bike doesn't fit you, there is nothing you can't do about it!
Thanks again for your great help and i wish you a great day.
FRANCK
May 24, 2008 at 03:23 AM