Great Article on Bike Fit

[fourflys]

I debated on posting this here or the bike fit discussion, but figured it would get more eyes here and it's not a specific person question..

Anyway, MyVeloFit posted a pretty interesting blog post this afternoon.. enjoy!

https://www.myvelofit.com/fit-academ...bike-geometry/

[benb]

That is a great article.

If I was at Trek/Specialized or some similar company that was big enough and powerful enough I'd start a program that incentivized dealers to upload anonymized fit data when they fit a rider to a given bike.

The article talks about the BMC Roadmachine having a curved line as you graph the stack:reach ratio across sizes.

A curved line might be much smarter than a straight line, because people don't scale linearly with height, and as much as they seem to want to deny it women are not linearly scaled smaller versions of men. But how do you decide how to shape that line?

The thing is how much data is out there on how people end up fitting? If they collected a lot of data they could probably optimize the stock sizes of the bikes in a more intelligent way.

Maybe they use some well known DB of body dimension averages.. but if those are from a non-cycling source are they ideal? Because say measurements of army recruits is your sample DB... does it actually have data that shows what kind of joint angles they can handle riding a road bike?

Maybe MyVeloFit is trying to build this kind of data from users and then sell it to bike companies.

But none of these online things really seem to have an intelligent way to input one rider's flexibility level versus another. Fitting one of these bikes depends on both your dimensions and where you fall in with the angles based on your flexibility and functional level.

[Likes2ridefar]

Reconfirms while i enjoy looking at the finishes of the crux and aethos they’ll never fit me. Even when I was racing competitively, I’d steer clear. I was fortunate the cervelo r5 was a team bike for a few years. Before that it was usually massive drop to the bar, a short stem/less spacers on a too large frame, or proper frame size and very not-pro spacers and stem setup. The year I purchased a roubaix was when i finally found a great fit not requiring a silly high stack or stem pointed up. It is why I only rode gravel bikes now since they tend to have that similar geometry. The 3t I have now looks like a race bike, kinda behaves like one, but fits like a roubaix…maybe my new favorite.

[benb]

The bike(s) they mention that get more aggressive as the size goes up seem the weirdest of all.

That does not seem to make sense, but I don't have data. It has never seemed like taller people trend towards shorter legs & longer torsos... it seems like it's the opposite.

My gut feeling would be an ideal curve would be for the smaller sizes bikes for men to have more reach and less stack proportionally and for the larger sizes to have more stack and less reach proportionally.

And then women would probably be different.

[Dave]

I didn't read everything because I've been using stack and reach for years now. I look for a stack in the 505-525 range, reach of 365-380 and a seat tube angle in the 73.5-74.5 range. I didn't read enough to see if STA was mentioned in the article, but that's the third dimension I look at to be sure of my seat post set back. I recently bought a Cervelo Rouvida with 524 stack, 370 reach and 74 degree STA, with the only stem angle -8 degree. The bike comes with a zero setback post that won't work for me and a stubby 90mm stem that's too short. You get what's sold with the bike with no substitutions at Mike's Bikes, Denver. This is the first pre-built bike I've bought in 34 years.

I cut over 30mm off the steerer, got a 110mm stem and 25mm setback post to correct my fit. The original seatpost sold quickly on eBay. I need to put the stem on eBay too, but they only work with Cervelo's special D shaped steerers.

The only situation where STA doesn't work might be an odd ball design with a curved seat tube that's placed forward of the BB centerline, with a straight portion for the seat post, like the Cervelo S5. Normal STA is just a straight centerline through the center of the BB.

[edgerat]

personally think that we are dumbing down fit by softening stack and reach. I have no idear on the flexibility of the bike riding population at large but, I feel like people are more flexible than they are being sold. Am a big fan of Neil Stanbury his fit philosophy at Road Cycling Academy on YT.

[vespasianus]

Originally Posted by edgerat

personally think that we are dumbing down fit by softening stack and reach. I have no idear on the flexibility of the bike riding population at large but, I feel like people are more flexible than they are being sold. Am a big fan of Neil Stanbury his fit philosophy at Road Cycling Academy on YT.

I have what I consider an endurance bike and it has a 564 stack and 393 reach. This makes it look as (or even more) aggressive than a BMC roadmachine, which they call an aggressive road bike.

Classic racing bikes of old had stack/reach ratios of closer to 1.32 in smaller sizes and 1.4x for larger sizes.

[boomforeal]

IMO, this guy doesn’t know what he’s talking about.

“Unlike measurements such as top tube, seat tube, and head tube length, stack and reach are the true indicators of how a bike will fit because they focus on the relationship between the two most important fixed points on the bike: The bottom bracket, and the top of the head tube. These points provide reference for both your saddle and handlebar position (your primarey points of contact), whereas tube length measurements on their own don’t effectively indicate how a bike will fit.”

How does the relationship between bb and top of head tube provide reference for saddle? Even if you assume a straight ST that comes straight out of the bb, you’d need to think all bikes have the same STA for bb position to make this case.

Reach only applies to fit when you’re out of the saddle — i.e. your contact points with the bike are the pedals and handle bars. I don’t think that’s the relevant fit figure you want to base road bike sizing around. ETT — the horizontal distance between middle of saddle and top of head tube — is going to be much more telling.

A bike fitter who a) doesn’t understand that reach is a handling number, not a fit number, and b) posts about it on the internet is going to confuse a lot of people trying to find a proper fit.

[NHAero]

Originally Posted by boomforeal

IMO, this guy doesn’t know what he’s talking about.

“Unlike measurements such as top tube, seat tube, and head tube length, stack and reach are the true indicators of how a bike will fit because they focus on the relationship between the two most important fixed points on the bike: The bottom bracket, and the top of the head tube. These points provide reference for both your saddle and handlebar position (your primarey points of contact), whereas tube length measurements on their own don’t effectively indicate how a bike will fit.”

How does the relationship between bb and top of head tube provide reference for saddle? Even if you assume a straight ST that comes straight out of the bb, you’d need to think all bikes have the same STA for bb position to make this case.

Reach only applies to fit when you’re out of the saddle — i.e. your contact points with the bike are the pedals and handle bars. I don’t think that’s the relevant fit figure you want to base road bike sizing around. ETT — the horizontal distance between middle of saddle and top of head tube — is going to be much more telling.

A bike fitter who a) doesn’t understand that reach is a handling number, not a fit number, and b) posts about it on the internet is going to confuse a lot of people trying to find a proper fit.

I'm no expert but I don't see it this way (at least for me).

I start with my saddle setback from the bottom bracket on my bikes, so for me, that's a fixed number I'm trying to achieve. ST angle factors into this but it would have to be way out of normal for me to have me reject a frame. Then I look at stack and reach to see if the frame can work for me with the bars (and ultimately the shifter hoods) I intend to use. Not enough stack and I need too many spacers or too weird of a stem. Too much reach and I can only achieve my fit with a very short stem.

Two frames with the same ETT can have different reach values based on different ST angles, so I've found reach to be more useful for me when deciding if I can make a frame work with my contact points.

Having said this, I happily ride my old Bob Jackson with a 60mm stem because the ETT is 572mm, and I happily ride my Supersix with an upturned stem because the stack is only 551mm. My custom Bingham has the same ETT as the Supersix but something like 50mm more stack so the stem is a 90mm -7 stem that has the same slope as the top tube. But all three have the same saddle and the same saddle setback to begin with, and ultimately the same actual reach to the hoods.

[KonaSS]

Originally Posted by boomforeal

IMO, this guy doesn’t know what he’s talking about.

“Unlike measurements such as top tube, seat tube, and head tube length, stack and reach are the true indicators of how a bike will fit because they focus on the relationship between the two most important fixed points on the bike: The bottom bracket, and the top of the head tube. These points provide reference for both your saddle and handlebar position (your primarey points of contact), whereas tube length measurements on their own don’t effectively indicate how a bike will fit.”

How does the relationship between bb and top of head tube provide reference for saddle? Even if you assume a straight ST that comes straight out of the bb, you’d need to think all bikes have the same STA for bb position to make this case.

Reach only applies to fit when you’re out of the saddle — i.e. your contact points with the bike are the pedals and handle bars. I don’t think that’s the relevant fit figure you want to base road bike sizing around. ETT — the horizontal distance between middle of saddle and top of head tube — is going to be much more telling.

A bike fitter who a) doesn’t understand that reach is a handling number, not a fit number, and b) posts about it on the internet is going to confuse a lot of people trying to find a proper fit.

I don't ignore ETT - old habits die hard, but I disagree with most everything you say. Stack and reach are the basis of fitting, not handling.

[benb]

STA and TT length and such is meaningless in this discussion, the article writer is right.

You can always put the saddle where it is supposed to be and it is assumed it is in the right place. You can do it with any STA and any ST length and any TT length. The bike might look ridiculous with the required seatpost setback or whatever but the fit will still work.

From there it is really a question of stack and reach just determining where the bars are.

If you still have a hard time making this work in your head start thinking about bikes that don't have a traditional frame. Delete the TT completely. Delete the ST completely. Maybe this bizarro bike just has the saddle attached to the seat stays and the whole thing connects to the rear wheel. Or maybe you deleted the seat stays completely and the bike has a weird curved seatpost that makes STA and TT length totally meaningless compared to a traditional bike.

E.x. Aesthetically I am better on a 72.5 STA and a slightly longer TT than my current bike. With the 73.3 STA I end up with my saddle pushed back more than is aesthetically ideal even on a 2cm setback post. But the saddle is still in the same place, and the bars are still in the same place. So that theoretical bike would still need to have the same stack and reach to have the bars setup the same with the same stem/spacers.

If road bikes weren't somewhat dictated by UCI rules we might be riding carbon frames at this point that would look completely alien compared to traditional frames and in that atmosphere the traditional measurements might be meaningless but stack and reach would still be relevant.

[Likes2ridefar]

Originally Posted by KonaSS

I don't ignore ETT - old habits die hard, but I disagree with most everything you say. Stack and reach are the basis of fitting, not handling.

Likewise.

[rothwem]

Originally Posted by boomforeal

IMO, this guy doesn’t know what he’s talking about.

The idea behind reach and stack is that it assumes that your saddle height and setback will be the same in relation to the BB, so stack and reach use the BB as the datum to measure off of. So a bike with a 395 reach and a 580mm stack should in theory fit the same whether or not the seat tube angle is 72 or 74 degrees. You might need a setback post or a longer seatpost to achieve the position, but once your saddle is where its "ideal", you should have the same cockpit setup.

With regards to handling, I'd say that's where the other stuff comes into play. Front center, rear center, bb drop, all that stuff effects how the bike handles and where the wheels are positioned relative to the rider. I went through this recently with my Emonda--I had the seat/bars/cranks in the same spot as they were on my Cannondale, but the wheels were farther back and the whole bike just felt weird.

[rothwem]

Originally Posted by benb

It has never seemed like taller people trend towards shorter legs & longer torsos... it seems like it's the opposite.

I don't really think this is true. Having longer legs makes you look taller though, so I suspect that you just notice them more.

People with long legs typically have long arms though, and that makes their "effective torso" longer. The people that are extra f'ed are the "t-rex" types with long legs and short arms.

I also read something interesting in another fitting blog where it mentioned that if you look at two people that have identical torso lengths but different length legs, the person with the longer legs typically has smaller feet than the person with the shorter legs, so the saddle height and setback tend to even out somewhat.

People are crazy, right?

[shoota]

Originally Posted by boomforeal

IMO, this guy doesn’t know what he’s talking about.

“Unlike measurements such as top tube, seat tube, and head tube length, stack and reach are the true indicators of how a bike will fit because they focus on the relationship between the two most important fixed points on the bike: The bottom bracket, and the top of the head tube. These points provide reference for both your saddle and handlebar position (your primarey points of contact), whereas tube length measurements on their own don’t effectively indicate how a bike will fit.”

How does the relationship between bb and top of head tube provide reference for saddle? Even if you assume a straight ST that comes straight out of the bb, you’d need to think all bikes have the same STA for bb position to make this case.

Reach only applies to fit when you’re out of the saddle — i.e. your contact points with the bike are the pedals and handle bars. I don’t think that’s the relevant fit figure you want to base road bike sizing around. ETT — the horizontal distance between middle of saddle and top of head tube — is going to be much more telling.

A bike fitter who a) doesn’t understand that reach is a handling number, not a fit number, and b) posts about it on the internet is going to confuse a lot of people trying to find a proper fit.

Add me to the list that doesn't agree with you, respectfully.