Handle bars and stem!

[Specialeyes]

Sensitivity isn't about torque, it's about the responsiveness in terms of change of steering angle to a given input through the hands. If the hands are on a pair of bars of a given width with only the stem length changing, then by very definition for a given movement of the hands with a longer stem the wheel will turn through a lesser angle. For a stem of 89mm length vs one of 100mm and 400mm bars, then the hypoteneus of the horizontal triangle that goes through the bars to the centre of the stem clamp is about 8mm shorter with the shorter stem, so around "4% more sensitive". That is an actual, non-zero difference and to argue otherwise is just rude or dogmatic imho.

I'd say that twitchiness is more about the unintended input that happens when you take one hand off the bars or, as mentioned above, hit a pothole, than it is about how the bike responds to intended steering input from the rider.

 

[Yellow Saddle]

If the hands are on a pair of bars of a given width with only the stem length changing, then by very definition with a longer stem the wheel will turn through a lesser angle.

No. That's not helpful.

 

[Specialeyes]

Edited my post above to reiterate the notion from the previous sentence 'for a given movement of the hands'. Maybe that'll make it more helpful. The rest of it is just geometry and, I would have thought, hard to argue with - but then, this is the internet

 

[12boy]

I believe twitchiness is related to:
Wheel size..Brompton twitchier than Holdsworth 700 c for example
Trail....low trail bikes are less twitchy than high trail
Wheel base... my mini velo at 934 mm wheelbase and 20 inch wheels is much twitchier than the Brompton with 1028 mm wheelbase.
Handlebar width...Brompton with 48 cm velo Orange Porteur bars much twitchier than with 505 mm Somafab moustache bars.. For a while hipsters were riding fixies with very narrow bars, say 12 inches. Seemed very dangerous to me.

 

[Yellow Saddle]

Edited my post above to reiterate the notion from the previous sentence 'for a given movement of the hands'. Maybe that'll make it more helpful. The rest of it is just geometry and, I would have thought, hard to argue with - but then, this is the internet

OK, so you've changed your mind and changed "angle" to "given movement of the hands." That's not helpful either. What do you mean by movement, perhaps then we can take this further.
It is hard to argue with a moving target and vague definitions.

 

[Specialeyes]

No, I've neither changed my mind, moved the target, nor changed the word 'angle'. I added 'for a given movement of the hands' to the sentence you quoted, as when quoted without the rest of the point I was trying to make, it made less sense than I hoped it would. To have a third and final attempt at making the point(s), a shorter stem will, ceteris paribus, make the effective lever from the rider's hand position to the centre of rotation of the steering, shorter. Maybe imperceptibly so for some, but still shorter. To argue otherwise is just wrong and to repeatedly call it nonsense without a reasoned counterargument just comes across as rude.

So, leaving aside any arguments about how one actually steers a bicycle, there must be some rotation of the bars in the horizontal plane, or the bike would continue straight irrespective of the angle it leaned to..

That shorter lever created by the shorter stem will make the front wheel deviate more from the straight direction of travel for a given movement of the hands around the bar/stem's centre of rotation (or 'steering input', if you will), than would be the case if the effective lever were longer thanks to a longer stem. That is the point that others upthread were making and that you were repeatedy dismissing as nonsense: that longer stems, provided they're within the rider's comfortable range of movement, will all other things being equal, make the bike marginally less responsive to steering input - i.e. marginally less twitchy.

I won't attempt to re-explain the other piont about 'twitchiness' being the opposite of directional stability and the way the bike behaves when unintended inputs such as potholes and lorry-induced crosswind gusts are encountered.

Really hope this clarifies! I'm even boring myself now

 

[MontyVeda]

Maybe all this discussion regarding presumed twitchyness needs to be in a thread of its own?

 

[iluvmybike]

i feel sorry for the poor OP after all of this!!

 

[vickster]

I have some (little) used bars of that size - ITM Elle - I think they are a standard clamp - but will check - if interested pls message me

@LibraRider ..these could go with the stem in classifieds

 

[LibraRider]

I have some (little) used bars of that size - ITM Elle - I think they are a standard clamp - but will check - if interested pls message me

hi

I tried the message you about these but I’m not allowed to

do you still have them? If so can you tell me a bit more about them? Pics?

 

[rivers]

I have a bike with a 90mm stem and one with a 100mm stem. My old bike had an 80mm stem, that I then swapped to a 100mm stem. The geometry makes more of a difference in handling than the stem length. My aero bike is the twitchiest of the lot, and it's the one with the longest stem.
@LibraRider, smaller, compact bars will also shorten the effective reach and bring your hoods closer to you as well. Best of luck

 

[iluvmybike]

hi

I tried the message you about these but I’m not allowed to

do you still have them? If so can you tell me a bit more about them? Pics?

Yes I do still have them - will get a photo later

 

[Racing roadkill]

Sensitivity isn't about torque, it's about the responsiveness in terms of change of steering angle to a given input through the hands. If the hands are on a pair of bars of a given width with only the stem length changing, then by very definition for a given movement of the hands with a longer stem the wheel will turn through a lesser angle. For a stem of 89mm length vs one of 100mm and 400mm bars, then the hypoteneus of the horizontal triangle that goes through the bars to the centre of the stem clamp is about 8mm shorter with the shorter stem, so around "4% more sensitive". That is an actual, non-zero difference and to argue otherwise is just rude or dogmatic imho.

I'd say that twitchiness is more about the unintended input that happens when you take one hand off the bars or, as mentioned above, hit a pothole, than it is about how the bike responds to intended steering input from the rider.

Nope, your theory and the practical are at odds. For reasons that I haven’t got time to explain ( it’s to do with the way your body position and weight distribution alter if you change stem length, without changing anything else, particularly angle ) the shortening of a stem significantly does make the handling of a given bike ( as long as you keep everything else constant ) relatively more ‘twitchy’ / lively. The argument isn’t “rude” or “Dogmatic” it’s physics, and the way it is. You’ve nearly come to the right conclusion in your second paragraph, but ‘swung and missed’. A lot of people change the stem lengths, and tell me they “didn’t feel a difference in handling, but it was more comfy” it then transpired that they had actually used a stem with a different angle ( usually more negative) as well, the angle change had mitigated the stem length change ( in terms of twitchiness ).

 

[Racing roadkill]

The geometry makes more of a difference in handling than the stem length.

Yes that’s correct, but if you keep everything else constant, changing the stem length will have an effect, however most people realise it, and whether consciously or sub consciously, adjust their position ( which is the key ) to account for it / mitigate it.

My aero bike is the twitchiest of the lot, and it's the one with the longest stem.

It’s an aero bike, they tend to be twitchy ( relative to a more conventional road bike, of similar size and general geometry) by design / because of the relative slight geometry differences, and tube shape and construction.

 

[iluvmybike]

I have a bike with a 90mm stem and one with a 100mm stem. My old bike had an 80mm stem, that I then swapped to a 100mm stem. The geometry makes more of a difference in handling than the stem length. My aero bike is the twitchiest of the lot, and it's the one with the longest stem.
@LibraRider, smaller, compact bars will also shorten the effective reach and bring your hoods closer to you as well. Best of luck

hi

I tried the message you about these but I’m not allowed to

do you still have them? If so can you tell me a bit more about them? Pics?

The bars are ITM Elle in size 38/40cm - little used as they were too narrow for me ( I also have the same in 40/42 for sale). The clamp size is 25.8. Ignore the 'stripey' bits in the photo as that is just where I took off the bar tape - I'll clean that off before sending. I also have a 90mm stem that I used with them - ITM carbon wrap - this will fit the std ahead type steerer (1 1/8th"). The stem can be flipped over if required. You can have both for £15 plus P&P