Do you trust your handlebar stem?

drfabulous0 wrote:Two bolts

drfabulous0 wrote:

Two bolts is a poor design as you now realise, if they are not tightened evenly then one can be taking excessive force, four bolts or one are better.

I’ve been a bike mechanic for many years and I have to warn you guys not to put to much faith in reccommended torque settings, it is not uncommon to do up stem bolts to the manufacturer’s specification and find that the bars will slip under a slight load. An experienced mechanic can not only make a fair estimate of torque without the torque wrench but can also feel when the bolts are under sufficient but not excess tension.

Two bolts no worse than 4: http://www.eastoncycling.com/bike/wp-content/uploads/2010/04/RD-06-2Bolts.pdf (Although now Easton have followed the fashion to 4 bolts, suspect you can’t find this paper so easily on their website anymore.)

The bigger problem is not a faceplate that is too loose at recommended torque settings but one that is overtightened by someone who doesn’t have the benefit of a torque wrench.

And the bit about “experienced” mechanics being magical – leaving aside the fact that this is a fairy tale, a mechanic who doesn’t own/use a torque wrench doesn’t deserve the sobriquet “experienced”.

SideBurn wrote:Flying Scot

SideBurn wrote:

Flying Scot wrote:

I remember these ITM 2 bolt stems failing about 10 years ago, the bolts were gash and there was the torque vs thread friction issues.

I have been lucky for 10 years? :|

Possibly, I just remember reading about it before, though they werent the only ones, I’ve no experience of it myself.

I’m using a 20 year old titanium quill stem on my road bike.

gmac101 wrote:When you design

gmac101 wrote:

When you design a bolted connection like stem / bar joint you calculate the tension in the bolt that gives you a strong enough joint. The problem is that measuring the tension in the bolt is pretty tricky without special equipment so the most practical thing to do is measure the torque you impose on the nut or the bolt head as a “proxy” for the actual bolt tension. The problem is that it’s not very accurate! It’s a classic first year engineering degree lab to torque up a series of bolts in different conditions and then measure the actual tension in the bolt. If I remember correctly it’s about +/- 25% accurate. The problem is that friction in the bolt/nut system eats up the torque and very little is used to actually tension the bolt but the friction in the system is also very dependent on condition. Some factors include, bolt & nut material, type of grease used (if any) location of the grease on the bolt, foreign bodies & corrosion. If you don’t replicate the conditions the manufacturer assumed when they worked out the recommended torque you could be a long way out from the bolt tension intended. And of course we are all using calibrated torque wrenches aren’t we? So Dr Fabulous0 when you torqued up to the manufacturers recommendation you may well have prepared the bolt better the manufacturer expected and so didn’t reach the required tension.

I love this kind of stuff. Genuinely. I wish I knew about engineering.

MKultra wrote:
I await the

MKultra wrote:

I await the storm of pedantic rage but be honest chaps, buying a torque wrench is not a cure for being cack handed.

That’s exactly what it is a cure for, do bolt up to specified torque, then stop.
Not, tighten, tighten, tighten, and then a bit more till you think you got 11.8Nm

The thing is most people don’t realise just how little 15Nm and less is, especially when they’re swinging off the end of an XL length Allen key.

You can even get the ones that stop going beyond the set torque if you’re really stupid/hamfisted.

I have never had a stem fail
I have never had a stem fail on me or a bolt snap (for now touch wood), I also have never used a torque wrench on ally or steel stems.

With the exception of carbon where it is critical to get it right with a torque wrench I would be of the opinion that if you don’t have the feel for getting it right yourself with just an alan key then perhaps you should be taking it to the LBS rather than doing it yourself.

I await the storm of pedantic rage but be honest chaps, buying a torque wrench is not a cure for being cack handed.

When you design a bolted
When you design a bolted connection like stem / bar joint you calculate the tension in the bolt that gives you a strong enough joint. The problem is that measuring the tension in the bolt is pretty tricky without special equipment so the most practical thing to do is measure the torque you impose on the nut or the bolt head as a “proxy” for the actual bolt tension. The problem is that it’s not very accurate! It’s a classic first year engineering degree lab to torque up a series of bolts in different conditions and then measure the actual tension in the bolt. If I remember correctly it’s about +/- 25% accurate. The problem is that friction in the bolt/nut system eats up the torque and very little is used to actually tension the bolt but the friction in the system is also very dependent on condition. Some factors include, bolt & nut material, type of grease used (if any) location of the grease on the bolt, foreign bodies & corrosion. If you don’t replicate the conditions the manufacturer assumed when they worked out the recommended torque you could be a long way out from the bolt tension intended. And of course we are all using calibrated torque wrenches aren’t we? So Dr Fabulous0 when you torqued up to the manufacturers recommendation you may well have prepared the bolt better the manufacturer expected and so didn’t reach the required tension.

Quote:I am writing this just

I am writing this just to warn others to look very critically at their stem and ask yourself is it fit for purpose?

Maybe *that* is what Chris Froome is doing?

http://chrisfroomelookingatstems.tumblr.com/