Help - Seat height as function of inseam

Triathlon Forum
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I know that this discussion has occurred numerous times and on numerous forums so I apologize upfront for bringing this up yet again. However, I would like to understand once and for all what should be similar between riders and what can change based on preferences.

I know that there are several schools of thought when it comes to getting fit on both road and triathlon bikes. Some people like a steeper position, some like a bigger saddle-to-pad drop (play between Watts and Aero), some like bigger crank arms (cadence and knee-to-chest clearance), etc. I assume that there are ideal angle ranges for knee, hip and shoulder and that a proper fit has some to do with comfort, flexibility, and strength. The question that I have is this: should the seat height as a function of inseam be relatively constant? I assume that different pedal/cleat systems can change this measurement a little bit. That aside, I have seen the old road racer quote of seat height = 0.883 X inseam. Is this a good metric?

I’m a little under 6’ 3" and have a 35" inseam. According to the formula above, I should run my seat at 78.5 cm. My first bike fit was done with specific angles in mind and the fitter set me up at 86 cm! My glutes and hamstrings were definitely screaming for a while until they got stronger and/or more used to the fit. I felt okay for a while but always felt like I was teetering up on my seat! After a while I lowered it about 2 cm (which seems like a big change) and then had a race where my upper quads fatigued immediately (seat height or hip angle?). Then I had a recent bike fit where the fitter looked more at my biomechanics than using specific angles. He set me up at 83.2 cm. This is still a lot higher than the formula above suggests. I checked out data that was available for a few pros and it tended to suggest that they sit within 3 or so cm of the numbers predicted from the above formula. Is there something that I’m missing?

I just want to make sure that my glutes/hamstrings don’t fatigue during a race from being seated too high and that my quads/knees don’t fatigue from being seated too low. If I end up testing out a lower seat height should I more my seat back so avoid too small of a knee angle? What’s the science and what’s the art to fitting?

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You really need to go to a good fitter. Make sure you bring the pedals and shoes you plan to wear as the stack height on brands change quite a bit. No one on this site can properly answer that question for you…but only give you a guestomate that will put you in no better situation than you are in now.

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I understand but how do you determine who’s a good fitter? My first fit was done by a guy at pretty large establishment. He fit me by using ideal angles for the knee, hip and shoulder. The result was a really high seat. A lot of friends and riders thought that my seat height after the fit was way too high. Then I recently went to another guy who is a biomechanical specialist who has worked with several local pros. He doesn’t really use specific angles. He watches you ride on a trainer and adjusts you according to flexibility, back placement, etc. I haven’t really ridden my bikes too far with those measurements so I can’t speak to them. However, the seat height still seems really high relative to other people of my height and inseam. I would just like to know who to believe. Or do I just keep changing positions and training for awhile to see how my body reacts until I find an ideal position by feel?