RBA Q&A: Frame Sizes

March 11, 2011
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(Then American champion) George Hincapie rides with teammate (then World Champion) Cadel Evans at the 2010 Tirreno-Adriatico race. Notice Big George’s body size relative to his bike.
(Photos: Yuzuru Sunada)

Dear RBA,

The Alpha rider on my Tuesday/Thursday club ride says I should be riding the smallest frame size I can comfortably fit. I noticed his saddle is pushed back almost all the way on the seat post, and he uses a very long stem. Are there any good reasons for this?
RBA: The correct frame size is always best. The legend of the small-size frame took root when everyone raced lugged steel frames that weighed between three and four pounds. Back then, weight weenies opted for the smallest frame they could ride, because removing three inches of steel tubing saved about three ounces-and the smaller frame was stiffer in a sprint. The downside of riding a tiny frame is that the longer stem makes the bike steer poorly on rough descents, and the setback saddle (while it can assist low-rpm climbing while seated) puts a strain on the lower back and reduces the efficiency and smoothness of your pedaling cadence.

Here’s a close-up of George Hincapie – the dramatic camera work helps illustrate Big George’s bike frame size relative to his tall body frame.

The funny thing is that the seatpost and stem extension are among the heaviest tubes on the bike, so replacing thin sections of frame tubes with a heavy, longer seatpost and stem to reduce weight is a foolish move. Besides, the whole small-frame theory is blown apart now that frames are made from carbon fiber. The length of a larger frame is added to the center of the tubes where the carbon is so thin that the weight saved by switching to a smaller frame amounts to less than 10 grams. Carbon also eclipses the stiffness- to-weight figures of any other frame material, which conclusively drops the hammer on the smaller-is-better theory.

This is long-legged, Italian Mirko Selvaggi’s Ridley Helium. The Vacansoleil rider fits this frame size, but his long legs require a tall seatmast.
Competitive cycling is populated by enough freaks who ride convincingly fast using odd setups and funky body positioning to substantiate almost any deviant theory on proper bike fit. Science says otherwise. Wind tunnel testing shows that a reasonably flat back is nearly as good as a perfectly flat one when it comes to low drag numbers. Power meter devices, now standard equipment on most ProTour racers’ machines, support what top bike fitters have been saying for decades: that a proper fitting bike and a comfortable body position are the key ingredients to maximizing a rider’s physical performance and the handling and efficiency of his or her bicycle.

Here’s Mirko Selvaggi during the 2010 Tour Down Under. Notice his long legs and their relation to his saddle height.

Professional racers are among the earliest adapters when it comes to evolving towards science-based improvements in bike and body positioning, so the recent shift in the pro peloton’s bike setups to facilitate a smoother, more efficient cadence carries a lot of weight. Bottom line: the correct frame size is best. If you are satisfied with your bike’s size and fit, ignore Mister Mini and stick with your present setup. If not, invest in a professional bike fit session and ride into the future with confidence.


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