Nobody bike body will match everybody, even with probably the most adaptable bikes. It’s notably true for efficiency bikes, the place six or extra sizes are typical.
However a bigger body would have very totally different dealing with and efficiency traits if it have been only a scaled-up model of a smaller body. Moreover, the interplay between the body, wheels and rider imposes constraints, notably for small bikes.
So what steps do bike designers take to ascertain constant trip really feel, consolation and dealing with between bike sizes, and are they sufficient to make sure that a smaller rider on a small-sized body is using the identical bike as a taller rider on a bigger body dimension?
Supplies science
Trek Madone SLR Gen 7 raced by Italian rider Jacopo Mosca of Crew Lidi-Trek. Mosca is 173cm tall, so observe the small body triangle and relatively thick body members.
(Picture credit score: David Ramos/Getty Photographs)
The principal cause why a big bike body can’t simply be a sized-up copy of a smaller one is grounded in physics. Hooke’s regulation works on the tubing of a motorbike body, simply because it does on a spring. The longer the ingredient to which a load is utilized, the extra it would deform.
So a bigger body can be considerably extra floppy than a smaller one if each have been in-built the identical method, with the identical tube thicknesses. Bigger riders are more likely to be heavier than smaller ones too, accentuating this impact.
Because of this bike designers must tailor their designs to totally different body sizes to make sure constant efficiency.
Claudio Salomini, Head of the Innovation Lab at Wilier explains: “Dealing with is totally different due to the totally different geometry, however bodily properties additionally depend upon the body dimension.”
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We’ll discuss geometry additional on, however for now let’s consider the supplies science.
Salomini explains that Wilier designs each single tube of each dimension to acquire the identical mechanical properties. Wilier calls this course of Balanced Design and says that it ensures constant rigidity, dealing with high quality and consolation throughout its dimension vary. All manufacturers promoting efficiency bikes may have their very own model, with its personal title.
Wilier is various each the carbon fiber lay-up and the sizing of its body tubes between body sizes.
“We work from either side. Sure, the carbon layup is totally different dimension by dimension, however we work additionally on the ‘geometry’ of the tubing, basically making ‘fatter’ tubing on greater sizes,” Salomini explains.
“Huge frames should be ‘strengthened’ as a result of the triangle of the body is admittedly massive. That is the world the place our ‘balanced design’ helps us to offer the frames the identical total dealing with,” Salomini continues.
Balanced Design does imply that body weights improve a bit greater than can be the case if bigger sizes simply had longer tubes, he says.
Trek Madone SLR Gen 8 raced by Daan Hoole of The Netherlands and Crew Lidi-Trek. At 198cm tall, Hoole is a big of a rider. With the Gen 8 Madone, Trek tweaked the tube profiles to higher swimsuit particular body sizes.
(Picture credit score: Luc Claessen/Getty Photographs)
Different manufacturers observe the identical design ideas. Specialised calls it Rider-First Engineering and Trek too moved to size-specific tube profiles for its newest Gen 8 Trek Madone. Earlier generations of the Madone maintained the profiles of the members whatever the body dimension.
One impact of that is that smaller sizes of the Gen 8 Madone are lighter than in earlier generations of the bike.
Christie Sorenson, mechanical design engineer on the Madone Gen 8 undertaking says: “Prior to now, we had only one form, a 56, then we might scale from there for all of our bikes. You would not get as gentle on the small frames as you would possibly anticipate.
“For the brand new Madone, we had a second tube form that we used for the decrease half of our dimension vary. We’re getting lighter bikes on the smaller sizes, as a result of we’re designing particularly for these smaller sizes.”
Trek wind tunnel examined each body tube profiles and noticed related aero advantages throughout its dimension vary.
Steel-framed bikes will also be engineered to supply related trip qualities throughout the dimensions vary, though this might not be the case for lower-priced bikes. The butting in steel tubing, which reduces its thickness within the center and expands it in direction of the ends, the place welding or brazing takes place, implies that merely reducing a single set of butted tubes right down to the size required for a smaller body might end in tube thicknesses that have been unsuitable for welding.
As a substitute, manufacturers reminiscent of Columbus promote tubing units which are butted for a particular body dimension.
Geometry distinction between sizes
A bevy of Wilier bikes lined up on the fortieth Classica Comunitat Valenciana 1969 – Gran premi València 2024. Be aware simply how a lot smaller the third bike from the left is. Wilier says that trip really feel needs to be fairly constant throughout sizes as a result of it fine-tunes the carbon lay-up and tube profiles.
(Picture credit score: Dario Belingheri/Getty Photographs)
Variations in trip high quality between sizes aren’t only a downside of body stiffness and aerodynamics although. Dealing with traits change as body dimension alters.
Take a look at a geometry chart for any bike and there are delicate variations between sizes. A few of that is right down to easy trigonometry; an extended seat tube will end in an extended attain in a entrance triangle with the identical angles, for instance.
It is common for bikes to have the identical size chainstays throughout the dimensions vary, as chainstay size impacts each tire clearance and trip really feel. It will get extra complicated with the gap between the underside bracket axle and the entrance wheel axle, the entrance heart.
If the smallest frames have been only a shrunken model of the bigger ones, because the wheel dimension doesn’t change, toe overlap with the entrance wheel would grow to be a major security difficulty. So small-size frames sometimes have a slacker head tube angle than bigger ones, to make sure an enough entrance heart. On the identical time, the fork rake will increase, which is able to improve the path and therefore the body stability.
Wilier’s Salomini explains: “The primary difficulty for smaller-sized frames is the size between the underside bracket and the entrance fork axle. You should handle toe overlap. In case you promote an entire bike you employ the precise crank size (165 mm for instance, as a way to cut back the issue). To be safer our smaller sizes enable the usage of cranks of 170 mm.”
Toe overlap and constant dealing with are the explanation why some manufacturers, together with Canyon, match a few of their smaller-sized frames with 650b wheels instead of 700c. Even Canyon doesn’t use smaller dimension wheels on all its small frames although, with the Aeroad CF SL 3XS and 2XS utilizing 650b wheels, whereas the CF SLX and CFR grade Aeroad frames are designed for 700c wheels on the smallest 2XS frames.
So are bigger and smaller cyclists truly using the identical bike? Though bicycle designers take a number of steps to attempt to present a constant trip really feel and dealing with throughout their dimension vary, finally there’s a major distinction in geometry, specifically, between bike sizes. This ends in a level of dimension specificity in dealing with, notably on the bigger and smaller ends of the body dimension spectrum.
