Short Ahead Stem

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pioneer
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Re: Short Ahead Stem

Postby pioneer » 17 Feb 2012, 6:27pm

I like the look of the angled stem from Spa'. Might be having one of them in a couple of weeks. Still tweaking the new bike.

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531colin
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Re: Short Ahead Stem

Postby 531colin » 17 Feb 2012, 8:18pm

As somebody already said, a 60mm 40deg stem has a lot less "forward" than a 60mm 6deg stem.
(Spa have lots of stems that aren't on the website....but be kind to us....we're moving......currently the phones are in the old shop, and the stock is in the new shop :roll: )

As for the "short stem changes the handling", I think that depends on how much you change it, and how much you un-weight the front wheel.
Moving my hands from the hoods to the tops doesn't make a difference that I'm aware of.
But at one stage, due to an elbow injury, I fitted very swept riser bars to a bike that had straights on about 130mm stem, so my hands went from a good 100mm in front of the headset to behind the headset......that un-weighted the front wheel enough to make the steering decidedly light, and rather unpleasant.

Yael
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Re: Short Ahead Stem

Postby Yael » 17 Feb 2012, 10:26pm


series3safari
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Re: Short Ahead Stem

Postby series3safari » 18 Feb 2012, 9:24am

Thank you one and all. In the end I ordered this one
http://www.ebay.co.uk/itm/Planet-X-X-Fo ... 6b1bce4c00
that Tony pointed out to me (see thread in "Wanted" section.

Thanks to MockCyclist but I won't take his 70mm stem as I have an 80 and am looking something 60mm or less. It is all about trying to get comfortable on my Surly LHT. Bought a 60cm framed complete bike second hand, decided it was too long so bought a 58cm frame in a nice discontinued colour from Mosquito bikes (Truchachino I think) and sold the 60cm frame on this forum last week. But still not sure if I am that comfortable on the 58 tho have not been far on it yet, so looking to shorten the stem further. Might be moving down another frame size yet! Anyone got a spare 56cm Surly LHT frame kicking about?

On stems, I actually aslo quite like the look of the angled stems from Extra UK so might look at them in due course. And as I did not notice there was a second page on this thread until this morning then I overlooked Yael's very useful and totally appropriate suggestion, but there you go. Thanks again.

Clive

swansonj
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Re: Short Ahead Stem

Postby swansonj » 23 Feb 2012, 8:47am

CJ wrote:The stem length has negligible effect upon the steering characteristics of a bicycle, which is entirely a function of steering geometry, front tyre properties and the weight carried by it. And that's the one way in which stem length does have a small effect, by letting the rider sit a bit further back, there will be a bit less weight on the front tyre, which makes the bike insignificantly less stable and easier to steer. But if you need to sit futher back, you need to sit further back and needs must locate the handgrips accordingly.


I entirely agree that getting the posture right is the top priority (I have remarked before that the first thing I did on receiving a mega-expensive, supposedly custom-built tandem from Chas Roberts was to change the stems because he hadn't believed us when we said we wanted a more upright posture).

I also agree that in practice, the biggest effect on steering handling comes from any shift in weight from front to back, and this is likely to dominate all other effects of moving the bars while keeping the rest of the steering constant.

But surely, in principle even if not important in practice, bars in front of the steering axis is a stable equilibrium, bars through the steering axis is a neutral equilibrium, and bars behind the steering axis is an unstable equilibrium? That is, when there is a deflection from straight ahead for whatever reason, the tiller effect corrects it for bars in front but exacerbates it for bars behind.

You would not notice this in actual riding because the other effects of a slight deflection, set by the steering geometry, would probably dominate, e.g. whether a small deflection of the steering raises the bike's CoG or not, and how the castor effect works. We all know that bike steering is very complicated to describe mathematically. But you would notice it if you experiment with a bike on a bike stand. I wonder if this could be the origin of the assertion by some bike shops that bars in front of steering axis is more stable - they say it because it is actually true for a bike not touching the ground?!

Just speculation on my part. The real reason could just as easily be that bars in front is traditional for racers. My advice to anyone would be the same as other people have said: by far the most important thing is to be comfortable, never mind what it looks like.

james01
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Re: Short Ahead Stem

Postby james01 » 23 Feb 2012, 9:09am

swansonj wrote:[
But surely, in principle even if not important in practice, bars in front of the steering axis is a stable equilibrium, bars through the steering axis is a neutral equilibrium, and bars behind the steering axis is an unstable equilibrium? That is, when there is a deflection from straight ahead for whatever reason, the tiller effect corrects it for bars in front but exacerbates it for bars behind.

You would not notice this in actual riding because the other effects of a slight deflection, set by the steering geometry, would probably dominate, e.g. whether a small deflection of the steering raises the bike's CoG or not, and how the castor effect works. We all know that bike steering is very complicated to describe mathematically. But you would notice it if you experiment with a bike on a bike stand. I wonder if this could be the origin of the assertion by some bike shops that bars in front of steering axis is more stable - they say it because it is actually true for a bike not touching the ground?!

Just speculation on my part. The real reason could just as easily be that bars in front is traditional for racers. My advice to anyone would be the same as other people have said: by far the most important thing is to be comfortable, never mind what it looks like.


Yet some of the most stable bikes are those Dutch style ones with handlebars well behind the steering axis. And what about recumbents!

Brucey
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Re: Short Ahead Stem

Postby Brucey » 23 Feb 2012, 10:12am

an interesting observation is what happens when you go over a bump whilst riding one-handed. The bikes that kick worst IME are the ones where you are putting a fair amount of weight on the bars, regardless of the handlebar style.

The 'tiller' argument is questionable; if you are holding the bar with two hands (since you don't want to be twisted out of line either) there is an additional self-centring action anyway.

As has been stated before the primary stability comes from the trail designed into the steering geometry. This applies to all kinds of bikes. Other things can affect it slightly, (but only slightly) when seated. Out of the saddle is very different, and I for one don't clain to understand what is going on here very well at all.

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

mrjemm
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Re: Short Ahead Stem

Postby mrjemm » 23 Feb 2012, 4:08pm

I think the tiller effect would be most pronounced if there is no side element, i.e. distance from stem. If you just hold a long stem, like a tiller, it would be more effective than on a bar to one side with same length stem; in that one-handed over a bump situation. For my own example, I ride around town mostly on the tops, using the cross brakes there, but in town there's a right curving downward hill where I turn off to the left near the bottom, and always feel uncomfortable signalling and braking from the tops here, and prefer to go down to my hoods. Not sure if that relates or just shows the clutter of my thought processes though.

As for out of the saddle, I am not sure in this case, but from mobiking, know that standing increases your stability because your mass goes to the pegs instead of the saddle, so lowering the CoG. Unless you clamp your knees tightly of course... Hence dirt riders rarely sitting down, while GP riders always sit down and stay low on the bends, which improves flickability (I think).

Or am I confusing myself?

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531colin
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Re: Short Ahead Stem

Postby 531colin » 23 Feb 2012, 10:00pm

james01 wrote:........Yet some of the most stable bikes are those Dutch style ones with handlebars well behind the steering axis.......


Quite so....a bike with huge trail and very slack head angle is the exact bike that will handle properly with very little weight on the front wheel. Its the steering geometry that causes the stability, not the handlebars.

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531colin
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Re: Short Ahead Stem

Postby 531colin » 23 Feb 2012, 10:06pm

Brucey wrote:an interesting observation is what happens when you go over a bump whilst riding one-handed. The bikes that kick worst IME are the ones where you are putting a fair amount of weight on the bars, regardless of the handlebar style. ......................


mrjemm wrote:I think the tiller effect would be most pronounced if there is no side element, i.e. distance from stem. If you just hold a long stem, like a tiller, it would be more effective than on a bar to one side with same length stem; in that one-handed over a bump situation. ..........................


Doing a hand sling or a Madison sling, you always put the one hand you have on the bars right in the middle by the stem....not to do so is far too exciting!

JEJV
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Re: Short Ahead Stem

Postby JEJV » 24 Feb 2012, 12:21am

CJ: +1
series3safari wrote:Does anyone have any good ideas where I will get a short ahead stem in a silver finish - to fit 25/26mm bars. Looking for something around 60mm or perhaps less. Got a nice 80mm stem last year, a velo orange I think, from a small ebay retailer in Cambridge, but struggling to find a shorter one now.


Is this 25.4mm clamp (normal for flat bars) or is this for old drop bars (26.0mm? 26.4mm?). Getting this wrong could have unfortunate consequences.
DO NOT GET THIS WRONG.

Our 11YO used to have:

http://www.sjscycles.co.uk/thorn-cnc-al ... prod11799/

on big-wheel bike.

I think I have one used and one unused spare, if anyone is interested.

11YO now has 105mm -40 degree, with swept back bars.

Looking randomly on chainreaction:

http://www.chainreactioncycles.com/Mode ... elID=15838

So not sure why there is a problem finding a short stem.
Don't drive on the railroad track.

Brucey
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Re: Short Ahead Stem

Postby Brucey » 7 Mar 2012, 2:43pm

saw this;

http://www.chainreactioncycles.com/Models.aspx?ModelID=15838

is 45mm short enough?

Mind you, the looks are.... 'challenging'... :shock:

cheers
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Mick F
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Re: Short Ahead Stem

Postby Mick F » 7 Mar 2012, 2:53pm

swansonj wrote:But surely, in principle even if not important in practice, bars in front of the steering axis is a stable equilibrium, bars through the steering axis is a neutral equilibrium, and bars behind the steering axis is an unstable equilibrium? That is, when there is a deflection from straight ahead for whatever reason, the tiller effect corrects it for bars in front but exacerbates it for bars behind.

+1 on that!

If the stem is long, you lean forward, pushing the 'bars straight. This gives a stable ride even if the fork/frame rake is inherently unstable.

The stem has no effect on the bike's stability - I agree - until you sit on it, hold the 'bars, and ride.
Mick F. Cornwall