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I’ve searched for mountain bike specific fit studies and found nothing. While mountain, road and tri “engines” are all the same the fit requirements are different. Road and tri have to factor in aerodynamics and tri have to factor in running and how muscles are affected by doing both riding and running. Plus road bikes are somewhat constrained by ridiculous UCI tech rules. For Mountain we have to compromise fit for muscle use and technical aspects like descending and uphill tech.
One thing road riders look for too is being balanced on the saddle. You don’t want to be leaning on the bars. So if you get on your drops or hoods and you can’t take your hands off without pedalling faster or engaging your core you need to change something. Often moving the seat rearward provides the fix.
Mountainbikers tend to ride more upright anyway for descending and there isn’t really much need to be aero. Plus most riders have their feet further forward on the pedals which affects the hip torso angle and balance. But when I see a mountain bike set up with a seat that tips down I think that’s a response to a too steep seat angle and too low of a bar. If the seat is horizontal and you’re leaning hard on the bars you slide backwards. The fix isn’t tipping the saddle forward but moving it back, the feet forward, raising the bar or a combination of the three.
I also think having the same rear centre length for all frame sizes is stupid and lazy. Some manufacturers are varying the rear centre but most don’t. Being short, I don’t have much issue with short chain stays but I sense the fix for tall riders looping out is the steep seat tubes. That affects how bikes fit me in a negative way.
I don’t think slack angles are good though because full suspension bikes sag and change that and more so when climbing. One thing that would be nice is for manufacturers to pride sagged angles and not static. Most bikes run more rear sag that front so static angles aren’t really relevant other than for comparison purposes.
This is an interesting topic for me. I think mountainbike geometry is still in a state of flux with respect to fit. Other geo aspects are settling out such as head angles, trail and offset. Good stuff.
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