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The great stem length debate - any good resources on the subject?

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#21 ·
Muse MTB said:
VERY OVERSIMPLIFIED...but making small changes one at a time with that very basic approach can yield great results. One thing that gets a lot of people hung up is forgetting that unless they are starting the quest for a new bike or willing to spend big money, some key geo variables are fixed for their current bike. Focusing on only what you can change makes the process easier, versus thinking you can make a current bike into the ideal bike.
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also, with air suspension and tires, getting them right can do so much to improve ride quality and is completely free!
 
#23 ·
snow snakes said:
I’m notorious among my friend group for constantly changing my bike setup just to try and understand the effects - my experience with a fitter in the past was extremely illuminating as far as the difference between “optimal” and personal comfort. I‘m just always looking to understand the “principles” as well to continue to help improve my knowledge base.
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it is eye opening! I learned that what I thought was "right" was only right based on comfort/familiarity, while my performance improved with a less comfortable position. But within a few weeks of adapting to it, I was more comfortable then ever. I could put in 30-50 miles on that rigid SS more comfortably than any other bike I'd owned over decades.
 
#24 ·
I tried a 45mm stem on a whim, but I just keep coming back to that length even across bikes. I can't say if it's due to being close to the offset on most 29" forks (44mm) or I just like how it handles. Like others, I've collected a drawer of stems and did back to back testing of 35mm, 40mm, 45mm, and 50mm. I used to swear by shorter stems, but now run the 45mm after testing.

Muse MTB said:
Body too upright= butt discomfort. ..too bent over= low back... discomfort
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Are we sure we're still talking about bikes.....? (It was a good summary, just couldn't resist the punchline. :ROFLMAO: )

One thing I will add is that pedaling forces & core strength make a BIG difference. If you aren't pedaling, your weight will naturally be forced onto the handlebar. Or someone with more core strength would be able to run a lower handlebar for handling/preference/fit reasons.

Sorry, two things: the fix to an issue might not be the obvious choice. I've solved back issues for customers by lowering handlebars when they came in swearing up and down they needed to raise them. Typically in this case the handlebars were too close for their natural body lean forcing more wight through the hands/back. Don't be afraid to experiment with adjusting something in both directions to see which is better.

Damnit, sorry, third thing: a proper fit starts with correct pedaling position. Dial in your seat height & fore/aft position before working on anything else. You'll need to go back and tweak it slightly as you change other things, but the last thing you want to do is spend all the time on your cockpit, then realize you need to change where you saddle is - which completely changes what you need for the cockpit.
 
#25 ·
It's so complicated, but I will share the things I've noticed in general:

1) I really like a 40mm stem with wide handlebars on like an enduro build. I currently run shorter because my bike is too large for me. I try to buy bike sizes that put me in this range.
2) 50mm stem works really nice on more narrow bars. It essentially steers the same as the 40mm stem, but the narrower bars help through the trees.
3) longer stems feel like steering an old motorboat with that stick in the rear, and it results in these big exaggerated sweeping motions. But as your bars get really narrow, it negates the really long stems. (i.e. old XC race bikes)
4) shorter stems notably hurt front wheel traction, but I don't mind the directness, just the loss of traction.
5) Lowering your bars just 5-10mm, notably improves front wheel traction, where-as raising it can be good for comfort, but bad for front wheel traction. A higher stack can be offset by long chainstays relative to the front center however (i.e. E-Druid).
6) there are actually several different set ups that can result in the same feel. Like a more swept back bar, can offset a longer stem for example. Even small variances in bar roll, stem height, spacer location, etc. all interplays. I don't have a formula but I wish I did!
 
#26 ·
I'm gonna go out on a limb and say stem length for me should almost be a fixed part of the geo like head angles (I know these are adjustable). I feel like the manufacturers design the bike around a certain head angle and stem length in order to have the bike handle a certain way. If you are going too far one way or another then I think the fundamental characteristic of the bike is changing. Bit like lowering or raising a car maybe. We'd all scoff at someone putting a 75mm stem on a trail bike, by the same token is 0mm stem changing things towards the other extreme? I know which one I'd prefer.
My current bike has such a strong weight bias to the rear (about 61% in the attack position) that I have to actively weight the front more than any bike I've owned outside a DH bike so I'm reluctant to go any shorter than the stock 50mm anyway.
 
#27 ·
jester6578 said:
I tried a 45mm stem on a whim, but I just keep coming back to that length even across bikes. I can't say if it's due to being close to the offset on most 29" forks (44mm) or I just like how it handles. Like others, I've collected a drawer of stems and did back to back testing of 35mm, 40mm, 45mm, and 50mm. I used to swear by shorter stems, but now run the 45mm after testing.


Are we sure we're still talking about bikes.....? (It was a good summary, just couldn't resist the punchline. :ROFLMAO: )

One thing I will add is that pedaling forces & core strength make a BIG difference. If you aren't pedaling, your weight will naturally be forced onto the handlebar. Or someone with more core strength would be able to run a lower handlebar for handling/preference/fit reasons.

Sorry, two things: the fix to an issue might not be the obvious choice. I've solved back issues for customers by lowering handlebars when they came in swearing up and down they needed to raise them. Typically in this case the handlebars were too close for their natural body lean forcing more wight through the hands/back. Don't be afraid to experiment with adjusting something in both directions to see which is better.

Damnit, sorry, third thing: a proper fit starts with correct pedaling position. Dial in your seat height & fore/aft position before working on anything else. You'll need to go back and tweak it slightly as you change other things, but the last thing you want to do is spend all the time on your cockpit, then realize you need to change where you saddle is - which completely changes what you need for the cockpit.
Click to expand...
mine was a very basic take...and you are spot on with all your points. Solid arguement can be made for proper saddle position being the absolute most important aspect of fit...but even there...trail/terrain dependant on what is right. The science of bike fit is VOODOO at best...and that was coming from my fitter who was educated on numerous fit systems.
 
#28 ·
On my old bike (26" NukeProof Mega 2012) I ran a 50mm Easton stem with 780mm Chromag carbon bars and it felt perfect.

My current bike (29" Trek Roscoe 9 2024) came with a 45mm stem and 780mm bars but steering felt sluggish so I swapped the stem out for a 35mm UniteCo and it feels much more responsive. I also changed to 810mm Deity carbon bars but do need to chop those down a little as after a few rides they do feel too wide.

HT and ST angles aren't too different between the two bikes (R9 is 1° HT and 0.3° ST slacker) but the R9 has 35mm longer reach and 46mm higher stack. I can't lie and say I fully understand the stack and reach numbers though.
 
#30 ·
I'll be honest, I didn't notice any difference in steering feel going from a 32mm stem to a 42mm. But the increased reach was noticeable and appreciated. Some people (and probably bikes) are more sensitive to small changes.

I say don't overthink it, just try stuff. Whatever you figure out "on paper" may not translate to the real world anyway. Plus, everyone needs a box full of old stems!
 
#31 ·
Could be in my head...but the closer the stem gets to the fork offset...the more responsive my bikes feel. I currently have 42 and 45mm stems on my bikes. Both with 44 offset forks. My V1 Following has a 51mm offset fork, and I used a 50mm stem.
 
Discussion starter · #33 ·
Suns_PSD said:
Also, I think it's harder to manual/ pull up the front end on a longer stem.
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I think that's true, all things being equal, but on bikes like the SST with a short chainstay (435, as short as I'd ever go again), it's pretty darn easy to get the front to come up if you want even with a 50mm stem.
 
#36 ·
DGUSMC said:
I think this because when I started this whole silly adventure of MTB I bought a bunch of cheap stems and bars and continue to play with and experiment with each bike I build.
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This is the answer. For any bike purchase. You get close with geo charts and test rides and then you dial it in with direct experimenting on your favorite trails or road circuits.
 
#38 ·
Part of the issue with stem discussions is that stem length isn't an intrinsic geometry characteristic in the way that trail and wheelbase are. What really matters is where your hands are in relation to the steering axis. Handlebar rise, backsweep and stem length all contribute to where your hands are relative to the steering axis. Running your bar rise vertical or inline with the bar will have a similar effect to changing stem length. You don't feel stem length directly, it's just a contributing factor to your cockpit setup.
 
#39 ·
Just from a purely logical perspective, I always wonder why 0 mm stems (top mount) aren't more popular. 100% direct steering input. Of course it would necessitate a slightly longer reach though. Always wanted to try one like the Aerozine XNC 10
 
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#40 ·
RS VR6 said:
Could be in my head...but the closer the stem gets to the fork offset...the more responsive my bikes feel. I currently have 42 and 45mm stems on my bikes. Both with 44 offset forks. My V1 Following has a 51mm offset fork, and I used a 50mm stem.
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Comes down to where your hands are in relation to the front axis. Hands in front = more stability, behind = responsive / twitchy.

The bar plays a huge role too.

A 70mm stem less bar back sweep gives me ~40mm at the bar CTR, which translates to middle of grips being at the same distance as fork axle (44mm offset):

Image
 
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