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@Wheelsonfire
I wasn't being sarcastic at all. I genuinely want the guy to educate me.
I'm not looking for any kind of argument either. It's simply an interesting subject.
"If the hands are in line with the steerer, there is no leverage."
with bars with excessive sweep when loaded downwards with enough force you will literally be able to see the leverage in the form of flex. same with excessively long stems.
"Bicycle steering and handling is super complicated " You're certainly not wrong there. There is indeed a lot going on. But I wouldn't go so far as to say "no-one really understands what’s going on".
Relating the physics to real life (ie. actually riding the bicycle) is where it gets more difficult and somewhat subjective to understand exactly what is going on and why.
Ps. did you miss my previous question or was I simply so polite you also mistook it for sarcasm?
I’m cutting bits of wallpaper to the nearest mm but will reply when there’s a window of opportunity!
To the OP, if your bike has ‘modern’ MTB geometry (steepish seat angle, longish reach etc) and is the right size for you, then it’s likely you only need to nuance your bike fit and bike handling characteristics within the 35-50mm stem range.
What works for you is likely to be influenced by a combo of factors such as head angle, stack height, fork travel, handlebar length and handlebar backsweep. But I doubt there would be ‘wrong’ stem length for you, and I agree with your observation that bike manufacturers have decided to split the difference by shipping 42/45mm stems.
On my trail bike (Starling Murmur) I’ve tried 35, 40 and 50mm stems as I have all three in the shed. I’ve settled on 40mm as a happy middle ground - there were no odd steering characteristics and my shoulders /arms were nicely relaxed on longer rides in the saddle. I’ve coupled this 40mm stems with a SQLab 12 degree backsweep bar at 780mm, and this backsweep has had a much bigger effect on steering and comfort than stem length did.
Finally, I’d be careful not to use a longer stem to fix the feedback you’ve had about keeping your weight back….I’m not a longer stem is needed to bring your weight forward. Perhaps a higher rise bar would, in the first instance, help with downhill confidence and weight distribution. This is only a suggestion, as I don't know your set up of course. Good luck!
Isn't it? -
Moment about steerer = Hand Force X Hand Distance from steerer (stem length and bar sweep doesn't matter)
But if hands are forward or behind steering axis, your hands move in a variable arc relative to steerer, so there becomes a translational or x/y force component (stem length and bar sweep matters).
But yeah, matching stem length to offset is nonsense. As someone pointed, offset doesn't matter, its trail and wheel flop with reference to hand placement versus steerer that matters.
Weight on the front wheel too as a factor disregarded in the stem length versus offset nonsense.
In other news, I think all parties are partly correct, hands relative to steerer is part of the puzzle, as is bar sweep and stem length (whether hands are in line with the steerer).
Some more hands relative steerer stuff, if the stem is really long, so big hand to steerer offset, you're not really turning the bars as in pushing/pulling directly back with your hands in a "y direction", you're also pushing/pulling to the side in the "x direction", I think that's a good way to picture it.
Some more hands relative steerer stuff, if the stem is really long, so big hand to steerer offset, you’re not really turning the bars as in pushing/pulling directly back with your hands in a “y direction”, you’re also pushing/pulling to the side in the “x direction”, I think that’s a good way to picture it.
Pretty much how road bikes work.
The hoods / drops are ~200mm forward and ~200mm sideways from the steerer.
Roadie steering tip that I only learnt the other day, when coming up the inside line in a chaingang and need to look behind to see if you've got clearance to pull out to the right, drop your left elbow, you can then look behind / right as long as you want without inadvertently following where you're looking!
Road bikes give a pretty easy to understand example of @chiefgrooveguru's (correct) assumption that hand position alters weight placement and the forces going through the steering axis. But that doesn't mean stem length used to get that position has no affect on where and how those forces are applied or the leverage they'll produce.
Hand/grip position relative to steerer axis. Is a product of stem length and angle and bar length, shape, roll and grip position. But two identical hand positions achieved by different stem lengths and correspondingly different shape bars won't transfer forces in exactly the same way.
But two identical hand positions achieved by different stem lengths and correspondingly different shape bars won’t transfer forces in exactly the same way.
They will transfer the forces to the steerer exactly the same. The only thing that matters as far as the force on the steerer is concerned is the position of your hands relative to the steerer. There might be more or less flex with some bar and stem combinations but that's not what determines the force acting on the steerer.
Oh I agree that turning forces perpendicular to the steerer would be transferred more or less the same. What I'm disagreeing with is that all the forces loading the stem in other directions would also be transferred exactly the same.
What I’m disagreeing with is that all the forces loading the stem in other directions would also be transferred exactly the same.
If your hands are in the same position relative to the steerer, the forces on the steer will be the same. The path they take to get there is irrelevant, the only thing that matters as far as the steerer is concerned is where your hands are. Sure, if you had a two foot long stem and bars with crazy sweep, the stem and bars would be loaded differently than a short stem and straight bars, so they would flex like mad, but the forces at the steerer would be exactly the same under a static load. It's the same as those silly Z shaped cranks, all they do is weigh more and flex more, they make no difference to the forces acting on the BB axle. (If you put shock loadings through the system, the flex in the bars and stem will soften the shock loading at the stem, but that's not what we are talking about here.)
I still disagree. The forces exerted through steering and weighting a bike are far from static and you simply saying that the forces will be the same isn't exactly a convincing me to think any differently.
those cranks have no relevance to what we're discussing here.
I still disagree.
chiefgrooveguru knows what he's talking about. I understand the intuitive appeal that different bars and stem should make a difference, but it doesn't. Intuition is not a good guide on this one.
I guess the best way I can explain this is:
1. imagine the grips are on the end of a massive chunk of aluminium billet, that is glued or welded to the steerer tube. Those grips are in the same place vs the steerer tube as with your favourite bar and stem combo (for me that’s 50mm zero rise stem and 760mm 40mm rise Renthal bars).
2. Then machine away the rest of the billet so it looks like your fav bar stem combo.
3. Get another billet and machine away a total different shape, just leave enough material there for it to be stiff enough.
4. Do the same again but go wild - make some silly shapes in between steerer and grips.
5. Ditto
They’ll all handle the same. There will be differences in compliance but the handling won’t change unless they’re so bendy that their shape effectively changes.
I remember changing from the stock stem and bars on my Levo to the current ones on there. There was a change in feel there - the stock stem was a skinny little 45mm thing, totally unsuitable for a 150mm ebike. The front end felt so much more positive pushing it into turns with a much stiffer stem resisting flex around its axis.
I recall discussing this with Keith @ Banshee and he said he preferred getting the grip height from bar rise more than stem spacers because like for like a higher rise bar is more compliant.
But it all ends up a muddle if you get compliance/flex/damping mixed up with geometry effects.
Thanks for taking the time to explain your thoughts.
I get what you're saying. But we don't have super stiff steering components.
So I still think the leverage acting through the bar/stem clamp will make a slight difference to how those forces are shared when the front end is under various riding loads. Think weighting while cornering and preload as well as pulling up on the bars (bunny hops, manuals etc). I'd expect that slight difference to increase the longer the stem and more extreme the bar sweep. Nothing that's hugely significant while riding of course. Especially with sub 50mm stems and normal bar sweep. Numbers. But still.
Don't know what you do for a living or how well educated you are in physics etc. But I'm guessing neither of us have access to testing equipment to find a definitive answer for sure.
BMX flatland bars with zero sweep and a long stem on a long enough steerer to accept lots of spacers. Might be a workable DIY experiment. Far from ideal. Though. And still very subjective/difficult to judge what's actually going on without access to a lab with high tech stress measuring equipment.
So I still think the leverage acting through the bar/stem clamp will make a slight difference to how those forces are shared when the front end is under various riding loads.
It won't. I spent a year studying engineering before I realized that I hated it and changed to a philosophy major. I think chiefgrooveguru actually works as an engineer. The path the forces take won't change the force acting on the steerer, it's just a matter of geometry. Sure, the amount of flex in the system might change, that's a different question.
Flex can be quite substantial, You can get a 'feel' for it when bike packing if you have a rigidly mounted fork rack with a tall bag because the bars will move relative to it as the steerer / stem / bars all deflect.
Nowhere near enough to impact on handling though.
It's like watching a bike land in slow motion, yes the frame splays out slackening the head angle, but by nowhere near as much as the fork compressing steepens it.
I've also swapped the really rubbish OEM stem specialized use for a better one, it makes a huge difference to how the bike feels, but that's down to stiffness and the resulting feedback and confidence in the front wheel going where your brain tells it and it telling your brain there's grip. It's not the same as handling.
Road bikes are a great testbed for this as there's a huge variety of bar shapes and quality. But they all (flared bars aside) fundamentally position your hands inline with the bike when holding the drops. Swapping bars should make negligible difference, and it has no impact on the handling, but it can make a bike feel completely different swapping to some quality bars.
I have only just come to this thread and I am not an engineer or mathematician.
From my admittedly limited and amateur understanding - if you have a backwards swept bar with no rise (I ride one), with back sweep equal to stem length does it not remove the impact of stem length?
“…Don’t know what you do for a living or how well educated you are in physics etc.”
I did a mechanical engineering degree and after a diversion through some sales and financial services stuff accidentally started what’s become an audio equipment manufacturer (and can be found on YouTube waving my hands about whilst talking and playing bass, explaining/demoing physics and concepts and gear etc)
“I get what you’re saying. But we don’t have super stiff steering components…
When we’re looking at bike steering, we’re looking at a system where we’ve got force inputs at our hands and a reaction force from the front contact patch. Both of those generate a torque around the steering axis. Even at peak load (turning hard under a compression) there’s relatively limited shear force at the tyre to rotate the steering, not enough to change the geometry of the steering assembly.
There are a lot of other forces going through the front wheel and fork and bars but they generate minimal net torque around the steering axis so they won’t be able to distort the steering geometry to a significant degree.
What will happen in all these systems are higher frequency vibrations and resonances but they won’t change steering behaviour.
I suppose what I’m trying to say is that from the perspective of steering geometry and applied torques, we DO have super stiff steering components. In terms of flex in other directions the steering components do vary in stiffness and that affects the ride feel especially for lighter (too harsh) or heavier/stronger/faster (too flexy) riders.
“It’s like watching a bike land in slow motion, yes the frame splays out slackening the head angle, but by nowhere near as much as the fork compressing steepens it.”
I’ve been trying to figure that out from the huck to flat slo-mo videos on pinkbike. I think the frame isn’t bending much at all, it’s actually the fork itself bending, mostly at the steerer:crown:stanchions junction. So I think that the compressing fork is steepening the head angle (on a hardtail) whilst the bending fork is increasing the offset. (Despite that I enjoy using lots of the travel on my 160mm hardtail!)
From my admittedly limited and amateur understanding – if you have a backwards swept bar with no rise (I ride one), with back sweep equal to stem length does it not remove the impact of stem length?
Doesn't it introduce flex?
Anyway, I've been meaning to try to throw a spanner in the works by muttering something about seatless competition trials bikes - with their ridiculously long stems.
I’ve got my big bike back (Hope V4s went off for a factory refurb after 6 years of use), so I thought I’d compare the bar/stem set-ups on both.
So Moxie and my Levo have essentially the same geometry at sag, except the Levo has 20mm less reach and 20mm more chainstay, and the seat angle is slacker so the ETT is about the same.
Both have 50mm zero rise stems, and much the same stack and spacers. And 40mm rise 760mm wide FatBar Lites, which is one of the least swept bars you can buy (7 deg).
Running a straight edge between the centres of each grip, it passes 25mm in front of the centre of the steerer tube on the Levo and 35mm in front on the Moxie. That’s purely due to my preference in bar rotation on the two bikes, nothing else has changed. That’s the number I’d call Effective Stem Length.
Most bars have more backsweep than Renthals and obviously wider bars increase that setback more, so with 35mm stems you can end up near zero ESL.
Coming back to this at this page ... I'm glad someone mentioned L-shaped cranks.
The other point to mention is that a bike can ride really well wth your hands well behind the steerer rather than in front. When you think about how you steer a slack HTA MTB with a tendancy to opposite lock as a bike slides in a corner, or how pulling up/back is such a big part of MTB handling.. maybe +ve length stems on MTBs are just another roadie carry-over waiting to be killed off.
"The other point to mention is that a bike can ride really well wth your hands well behind the steerer rather than in front. When you think about how you steer a slack HTA MTB with a tendancy to opposite lock as a bike slides in a corner, or how pulling up/back is such a big part of MTB handling.. maybe +ve length stems on MTBs are just another roadie carry-over waiting to be killed off."
The thing I always notice as ESL approaches zero or goes negative is that weighting the bars, either consciously or accidentally, no longer has a stabilising effect. With some ESL then when you push on or load the bars, the force required to turn the steering increases. Personally I like how as I get my weight onto the bars in a corner, it gets harder to turn the bike, so you're adding stability. Likewise, if I hit a big bump, brake hard, or land front heavy, that weight transfer tends to straighten the bars rather than turn them.
Maybe that's why I have the bars rotated more forward on the hardtail and more backwards on the ebike - because the latter is inherent very stable (heavy and full-sus) so it doesn't need as much steering self-centering?
The thing I always notice as ESL approaches zero or goes negative is that weighting the bars, either consciously or accidentally, no longer has a stabilising effect.
Sounds right, as we push down we're also pushing forward and positive stem/ESL has some tiller effect - it should work the other way with a negative length, stability and centring when pulling back off a drop or jumps. More important that some feedback is there and you're used to it though.
“it should work the other way with a negative length, stability and centring when pulling back off a drop or jumps.”
I’m far from brilliant at jumps and drops but I don’t think I tend to pull back much, if at all - it’s much more of a preload, pop, push thing. But even if there were a pull that’s usually a far more controlled state, where you’re dictating what you want the bike to do, rather than reacting to what’s coming at you.
I know what you mean, it's more about a weight shift back - what I mean is when your input at the bar is in a rear upward direction, not forward. Perhaps not enough or not often enough to mean any stability from a negative stem/ESL is worth much.
Below is a link to Peter verdone’s starfighter it has a one piece bar and stem thst mounts the bar behind the steerer.
I’d post a picture, but I can’t remember how
https://www.peterverdone.com/starfighter/