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Technical FAQ: Analyzing bike fits of the professionals

  • By Lennard Zinn
  • Published Aug. 6, 2013
  • Updated 18 hours ago
Chris Froome's position on the bike has sparked a number of reader questions regarding bike fits for the pros. Photo: Caley Fretz | VeloNews.com

This week, we’ll take a look at a question on bike fit that I’ve received for years, but have never answered in a column. Afterward, we’ll take a look at reader feedback on a claim one reader made last week regarding tubeless tires on motorcycles.

Dear Lennard,
While watching the Tour de France, I noticed some riders had a relatively short down stroke while pedaling. I’ve always thought that seat height should be such that the leg(s) are just shy of being fully extended. It seems important enough to have a dozen or so “scientific formulas” for figuring this out. Has something changed in regards to how to estimate seat height?
—John

Dear John,
For many years, a lot of people have asked me about this, and I never used this forum to go into it. So here you go! I consulted some of the best professional bike fitters I know and got some very interesting answers, one of them in the form of a video critique of Chris Froome’s position.

Two of these top bike fitters, Andy Pruitt (Boulder Center for Sports Medicine) and Todd Carver (Retül), position riders on over a half dozen Tour de France teams between them, frequently flying to Europe to do so, so they know intimately the positions used in the Tour. Pruitt fits the Specialized-sponsored riders of Saxo-Tinkoff, Omega Pharma-Quick Step, and Astana, while Carver fits riders from Sky, Garmin-Sharp, and Europcar.

I should also point out that the TV coverage of the Tour tends to focus in closely on riders at moments when they are going their hardest. I’m sure you’ve experienced pulling yourself forward on the saddle to get the most power you can for a short while. This effectively lowers your saddle position (your knees are more bent), but it is not the position you do the vast majority of your riding in, and the same is true with Tour de France riders.
―Lennard

From Andy Pruitt (Boulder Center for Sports Medicine):

The theories concerning saddle height or knee flexion at dead bottom center have not changed as for formulated bike fitting. Formulas are a starting place for positioning. The LeMond formula is 88.6 percent of crotch-to-ground inseam measurement, while the Italian method says with a level pelvis, place your heel on the pedal and you should have a straight leg at dead bottom center, then as you move your foot to the cycling position you will have a slight bend while pedaling. I have professed for years a measured knee bend at dead bottom center of 30-35 degrees. Truth is, they all end up in approximately the same place.

So if these are all starting places, what are the factors that affect the final neutral saddle position? There are many to list. Active ankling, hamstring flexibility, quadriceps flexibility, cleat fore/aft position, patella thickness and depth of the patella groove and specific event (pursuit versus long road race). Crank-arm length effects saddle height, but not end result functional knee flexion at DBC.

Myself and the Body Geometry Fit Team from Specialized are responsible for three ProTeams’ positions (75 riders), so I can assure you that those saddle heights are traditionally set. Retül’s saddle position philosophy is in line with mine, and they ‘re responsible for several more ProTeams. So what did you see? Camera angle? One moment in time where the rider(s) were under pressure and they had moved forward (on the rivet), producing more knee flexion? The best way to determine your personal saddle position is with the help of a professional trained bike fitter.

Thanks for asking!
Andrew Pruitt, EdD
Founder, Boulder Center for Sports Medicine
Medical consultant, Specialized Bicycles
Author, Body Geometry Fit

From Todd Carver (Retül):

We have been getting a lot of questions on that as well, so we actually did a five-minute video about it, and here it is.
Thanks for thinking of us!
Todd Carver
Founder, Retül

From Chris Soden (Pro Peloton):

Great question and one that we get all the time in the shop around Tour de France time. There is no doubt that you are watching some of the best athletes in the world and the finest cyclists in the sport in their prime. Yes, you would think that there would be some perfect formula that all follow, but the reality is each and every rider at that level (and all levels, for that matter) are unique and therefore require slightly different saddle heights and pedaling styles/motions based on flexibility, physiology, injury history etc.

There is no doubt that a slightly lower saddle height does produce more power for the short term, thus you see riders on the nose of the saddle when it gets going hard, or the stage finish is approaching. They are thinking about one thing — winning — certainly not about knee health or stress on the body.

Whilst there are some standard and repeatable ranges that all good cyclists share in terms of position, the reality is they might all be slightly different within those parameters and highly successful and powerful within that range. One of the first things I learned as a professional fitter is that there is no cookie cutter, perfect template that all must adhere to. You have to meet each athlete and client you work with, where they are as a person, as an athlete. Getting the right saddle height, and pedaling motion, for you is one of the most important things you can do to enhance your health and enjoyment in the sport. What you are seeing on TV during the Tour is a roughly 200-rider sample of that very notion. Thanks for the question.
Christopher Soden
Pro Peloton Cyclery

From Charles Van Atta (Boulder Center for Sports Medicine):

It is true that there have been a number of formulas and methods for estimating saddle height over the last few decades. The LeMond formula estimates saddle height based on a rider’s pressured inseam. A “heel drag” can be used where the rider is seated while the bike is held upright to verify if the heel touches the pedal top. More typically during a bike fit, the knee (flexion) angle is measured using a goniometer (statically) or via a movement capture system (dynamically). With those methods, we expect a degree of flexion when the leg is reaching the furthest point in the pedal stroke between the higher twenties and the low forties. That is a big range that allows us to account for pedaling styles (lower and higher heel), hamstring flexibility, joint limitations, and other concerns.

We do all this while the rider is pedaling on an indoor trainer and seated. On the other hand, images coming from the Tour de France are real-time versions that involve riders adjusting their style and body position to achieve what they need at that moment in the race.
Charles Van Atta
Cycling Biomechanist, Boulder Center for Sports Medicine

From Kevin Bailey of 3D Bikefit:

Seat height is determined several ways now and has developed over the years. Saddle fore/aft has a major effect on saddle height. New motion capture methods are very helpful for determining correct saddle height. The angle of the knees depends on methods applied. If you use center of the knee, it averages about 30 degrees, but if you are using the Lateral femoral condyle center using a goniometer from the Trocantor to Femoral Condyle to malleolus/lateral ankle bone for road fitting metrics, it’s best at around 38 to 40 degrees.

While professional riders have great equipment to ride, they may not always have the perfect position.
Kevin Bailey
Founder, 3D Bikefit

Feedback on moto tubeless

Last week, I ran Dave’s question without either commenting on or editing out his comment about motorcycles not using tubeless tires. This may have been ill advised, as I was flooded with emails about the use of tubeless tires on motorcycles. Here are two that explain it clearly, one of which comments on our long-running road gear range thread as well.

Dear Lennard,
I’m sure you’ve already received a zillion notes about this, but your correspondent, Dave, in today’s Tech FAQ is incorrect when he says that motorcycles do not use tubeless tires. In fact, nearly every road motorcycle, and many off-road motorcycles, run tubeless and have done so for years. Furthermore, most high-end road motorcycles use tubeless radials. If you ever rode the old Panasonic radial bicycle tires in the early 1980s, you will doubt that this can be true, since the Panasonics had super-flexible casings that made the bike wobble all over. The difference is that the casings on moto tires are very stiff, and the sidewalls are relatively short, so that the tires have the radial advantage of spreading the contact patch widely without the disadvantage (on a motorcycle, anyway; cars are another story) of a flexible sidewall that would inhibit good cornering stability. As a bonus, the moto radials run cooler than bias-ply tires, extending casing life.
—Ted

Dear Lennard,
I believe Dave, when replying that motorcycles do not use tubeless tires, was referring to dirt bikes. [Ed. note: some off-road motorcycles also use tubeless tires.] Street bikes have been primarily tubeless for 30 years or more. Ever since cast rims became popular.

For those looking for the ultimate in climbing gears, SRAM mountain derailleurs use the same 1:1 actuation as the company’s road derailleurs. This makes their road shifters compatible with their mountain derailleurs. Currently on my Madone I’m running an XO derailleur with an 11-36 cassette on the rear, paired with 52/34 chainrings in the front. Pickup in the front isn’t instantaneous, but it works quite well. In back I think the XO actually shifts better than the Red I originally had on it. The spread in the rear leaves some big gaps, which at times can be annoying, but now I can go up anything. I just have to spin like crazy to do it.
—Mark

FILED UNDER: Bikes and Tech / Technical FAQ TAGS: / /

Lennard Zinn

Lennard Zinn

Our longtime technical writer joined VeloNews in 1987. He is also a framebuilder, a former U.S. National Team rider, and author of many bicycle books, including Zinn and the Art of Mountain Bike Maintenance and Zinn and the Art of Road Bike Maintenance, as well as Zinn and the Art of Triathlon Bikes and Zinn's Cycling Primer: Maintenance Tips and Skill Building for Cyclists. He holds a Bachelor’s degree in physics from Colorado College. Readers can send brief technical questions to Ask LZ.

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