Finding the right size frame
 

I currently ride a 56cm Trek and I am doing some planning on my next build. I was looking at the bikes of pro riders more or less my size and decided that Philippe Gilbert is my guy. While looking at his bikes I was a little surprised. As a 5'10" rider, he is using a 50cm frame!

It is somewhat acceptable for sprinters to go one or two sizes smaller but for a guy like Gilbert it looks weird. What's even weirder is that when racing for Omega Pharma Lotto he was using a 56cm frame.

Here are the two bikes:

http://cdn.mos.bikeradar.com/images/...h9q-670-80.jpg
http://cdn.mos.bikeradar.com/images/...nac-670-80.jpg

and their respective measurements:

Canyon:

Rider's height: 1.79m (5ft 10in)
Rider's weight: 72kg (159lb)
Saddle height, from BB (c-t): 780mm
Saddle setback: 75mm
Seat tube length, c-t: 552mm
Seat tube length, c-c: 520mm
Tip of saddle nose to C of bars (next to stem): 587mm
Saddle-to-bar drop (vertical): 115mm
Head tube length: 150mm
Top tube length: 560mm

BMC:

Rider's height: 1.79m (5ft10in)
Rider's weight: 69kg (152lb)
Saddle height, from BB (c-t): 751mm
Saddle setback: 59mm
Seat tube length, c-c: 480mm
Tip of saddle nose to c of bars: 581mm
Saddle to bar drop (vertical): 122mm
Head tube length: 133mm
Top tube length: 535mm

Without even looking at the measurements, you can see the saddle setback difference. Both bikes feature very long stems (12 and 14 cm) and the saddle heights are completely different.

If you look at his riding position, not much has been changed and I think both look comfortable:
http://cdn.media.cyclingnews.com/201...1_full_600.jpg
http://www.tourdownunder.com.au/imag...pe-gilbert.jpg

Does this mean that you can fit anyone to any bike? Is frame sizing a complete lie?

This guy is not some water carrier or peloton filler, he is the ex world champion and on multiple occasions the leader of his team. How can he have such different measurements on different teams?


Links for more photos and complete component list:
Pro bike: Philippe Gilbert's BMC TeamMachine SLR01 - BikeRadar
Pro bike: Philippe Gilbert's Omega Pharma-Lotto Canyon Aeroad CF - BikeRadar

I would disagree about the positions looking similar. In the top photo his back is essentially parallel to the ground and his arms stretched out quite a bit. In the lower photo his back is at a near 45 degree angle and his arms in quite a bit. Could b photo angle but they do look quite different to me.

Something isn't quite right about a 30mm saddle height difference between bikes. How could that be for a top rider?
What is similar is a saddle tip to handlebar distance of 580mm between bikes. This is a critical dimension for reach.

To answer your question....yes...a rider can ride multiple frames. For example when this rider turns 70, he maybe on a 58.
Same guy with same reach but lack of flexibility. On a 58 his saddle tip to handlebar distance will still be the same ~ 580mm with normal size stem
...but his entire cockpit will be rotated up and his handlebars will be level if not slightly above the saddle versus well below. And this is what an older rider of his dimensions would prefer without the flexibility or core strength of a top pro or amateur.


So yes, a rider can size down on a frame which will slightly reduce horizontal reach (top tube) but increase drop which allows the same reach from saddle tip to handlebar center on a smaller bike. This is what many pros do...they ride 1-2 frame sizes smaller than common riders because of their superior flexibility, core strength and reduced body mass.

FWIW, frame size is also largely a preference, even among top riders. For example, Lance who is virtually the same size as Gilbert rode a 58 cm Madone throughout his career with 580mm top tube and 130mm stem and only 75mm of drop...if that. This fact is what casts a dim shadow on the whole concept of a 'pro fit'. LA's preference to satisfy this reach which was the same as Gilbert...~575mm saddle tip to handlebar center...was achieved with more horizontal reach and less drop. Btw, this type of fit I believe is vastly better for the average rider than the trend of smaller frames with shorter top tube and more drop to achieve the same reach for a given rider size....because the reality is, more drop requires more flexibility and core strength which an average rider lacks.

Get a pro fit you wot regret it.

Well, 53.5cm is a pretty long top tube for a 50cm frame. Add a 140mm stem and total reach is 67.5cm. The other bike is 56cm plus a 12cm stem for a total of 68. Reach ends up being about the same.

That also caught my attention, why call it a 50 when it's 53.5?

Horizontal reach might be the same but the saddle to bb still doesn't make sense to me, the saddle set backs are different as well.

I agree with you on this one, he also rode 175mm cranks at 100rpm which doesn't really make sense on paper but he probably felt better like that.

You could say feel...I believe feel doesn't have much to do with it. Pros test against the clock. Lance was faster on 175mm cranks. Btw, if you listen to Leonard Zinn, Lance was correctly placed on 175mm cranks per his inseam.
Point to discussion here is physical size of a rider is only one metric. Riders exactly the same size in the pro peleton can ride completely different frames sizes as noted. One metric where there is relative close agreement as an example here...is the reach dimension of saddle tip to handlebar. It is perhaps surprisingly similar for pro riders relative to body size....even though that reach dimension can be constructed with very different drop and horizontal components of reach.

OK, first of all, deciding to pick a frame size based on what someone else rides is absurd.

Second of all to understand frame sizing, you need to look at just 2 numbers - Reach and Stack. this is about TT bike sizing, but the concepts apply. No two manufacturers describe their bike sizes the same way, so looking at the number they use to describe the size is pretty meaningless.

(edit, clicked send too soon)

Thirdly, there's very little reason to suspect you will sit on your bike the same way Gilbert does - he's a pro, has been riding for years, and is likely fit to his bike to maximze aerodynamics at the expense of comfort. Unlikely that you will want to ride the same position, even in the unlikely event that all your body dimensions and flexibility are identical.

Good luck with your search - getting professional fitting help is well worth whatever you spend on it.

BMC sizing is strange. What they call 52 is really about a 56. They measure their frame sizing on the seat tube (which is very short due to compact geometry). So if he's riding a 50, it's closer to a 54.