Stem Length

pandosdad

Following some recent back problems, I have been thinking about my riding set up. My bike is a Giant Defy 1 size ML which has a 100mm stem. If I change this to an 80mm, will the steering be too twitchy? I have already moved the saddle foward.

godders1

Should be fine.

Unless the current reach is far too long I'd try 90mm first. 20mm is quite a jump.

pandosdad

Thanks. I will try that.

markthebear

You might want to try flipping the origional stem first, turning it upsaide down will raise the bars and bring them back slightly which should help with your back, all for no cost.

centimani

As suggested, try flipping the stem, but i run a 70 (yes 70) mm stem on mine and yes it may be a tad twitchier than my old bike, but not noticeably so, i ride one handed, on the tops, drops, anywhere on the bars, i dont, wobble around, high speed or low, its fine.

Why 70 ?...it is very short, but i like city riding and instant response, i like to mix it up with traffic. my old raleigh is so unresponsive and sluggish, i love the bikes comfort, but its like steering a supertanker. Plus a 70 stem gave me exactly the same reach (saddle to bars) on a new bike as on my old one.

jejv

pandosdad wrote:

My bike is a Giant Defy 1 size ML which has a 100mm stem. If I change this to an 80mm, will the steering be too twitchy?

No.
Use a 35mm stem pointing backwards if that gives you the position that suits you.
Can also put an extender on the steering tube if the bars don't go high enough.

pandosdad wrote:

I have already moved the saddle foward.

Not sure why you would want to do that - not sure why your back problem would be helped by changing the position of your bum relative to the pedals. If it was right before, why would it not be right now ?
If your reach is fixed, it'll help problems with your reach, but reach problems should be addressed at the front, not by moving your bum - assuming your bum was in the right place to start with.

mpdouglas

I agree with the previous post. Move your saddle to where it belongs for your knee position to be correct relative to the pedal (front of kneecap directly above pedal spindle when pedal is at 3 o'clock, horizontal position).

You shouldn't be moving the saddle to overcome problems of reaching to the bars. So if you reinstate your saddle to where it belongs, coming down 20mm on the stem is probably right and you can always then play around with which way up it is and the spacer arrangement to refine the bar position. I run an 80mm stem flipped over and I wouldn't describe it as twitchy.

jejv

I wouldn't be too dogmatic about any particular way of deciding where your bum should be.

Changing the stem length won't affect the underlying stability much, but it might make it feel a bit different - as if you put a bigger/smaller steering wheel on your car. There'll be a small change in weight distribution, and a small change in the "rotational mass"/"moment of inertia" of the steering system.

But you probably want to talk to folk who understand your back problem better. Try searching these forums for "back pain". Talk to the folk at your local cycling club. Talk to your GP. If your work pays for private health insurance, they may pay for a physio who knows what they are doing.

We don't know what caused your back problem - is it as simple as a poor bike setup ? Or something completely different ?