Stem 31.7 vs 31.8

bsplaw said:

Stupid question but can a 31.7 stem be used with a 31.8 handlebar?

You're talking about 0.1mm difference. It'll fit.

shannons dad said:

You're talking about 0.1mm difference. It'll fit.

I had an old Cinelli stem (26.4mm) and some new Cinelli bars (26.0mm) - I wasn't aware at the time that Cinelli had made the change. Even with this .4mm difference the fit was almost tight enough - but the bars rotated in the clamp and I wound up breaking the stem binder bolt trying to get it tight enough.

BSplaw has the opposite problem - the stem will be smaller than the bars. It may fit but it may also dig into the bars and damage them, creating a spot for fatigue to start. I don't think I'd risk it, but if they're old parts you could experiment before buying new stuff.

DiabloScott said:

I had an old Cinelli stem (26.4mm) and some new Cinelli bars (26.0mm) - I wasn't aware at the time that Cinelli had made the change. Even with this .4mm difference the fit was almost tight enough - but the bars rotated in the clamp and I wound up breaking the stem binder bolt trying to get it tight enough.

BSplaw has the opposite problem - the stem will be smaller than the bars. It may fit but it may also dig into the bars and damage them, creating a spot for fatigue to start. I don't think I'd risk it, but if they're old parts you could experiment before buying new stuff.

Agree with your analysis. As you said, the sides of the too-small stem and clamp will dig into the bars and create potential site for a crack to start. Crushing or gouging the handlebars .004 inches at the point where the bending loads are concentrated just doesn't seem like the thing to do. I'd want matching parts in this critical location.

IT'S 0.1 OF A MILLIMETRE!!!! 0.1!!! THAT IS NOT WORTH ARGUING OVER!! ARE YOU GUYS SERIOUS???????🙄

shannons dad said:

IT'S 0.1 OF A MILLIMETRE!!!! 0.1!!! THAT IS NOT WORTH ARGUING OVER!! ARE YOU GUYS SERIOUS???????🙄

I'm sure it would fit, in fact 0.2 mm would probably fit too. The question is why not buy to match? If Uncle Bob gave me a stem and Uncle Graham gave me handlebars and I didn't have enough money to buy a used part on eBay to match one or the other then maybe I'd risk losing some teeth or part of my skull. We don't know what the OP's motivation is but if he doesn't already have the stem and bars why would we advise him to get mismatched ones?

A quick eBay search finds a $6 stem with a 31.8mm clamp - BSplaw could sell his 31.7mm stem and come out ahead financially too.

DiabloScott said:

I'm sure it would fit, in fact 0.2 mm would probably fit too. The question is why not buy to match? If Uncle Bob gave me a stem and Uncle Graham gave me handlebars and I didn't have enough money to buy a used part on eBay to match one or the other then maybe I'd risk losing some teeth or part of my skull. We don't know what the OP's motivation is but if he doesn't already have the stem and bars why would we advise him to get mismatched ones?

A quick eBay search finds a $6 stem with a 31.8mm clamp - BSplaw could sell his 31.7mm stem and come out ahead financially too.

Take a reality check girls....!! They are considered interchangable. One story is the standard was 11/4" and some makers round up and some round down to get the mm equivalent. Same business with intechangability between 25.8 and 26.0 stuff...Now back to the regularly scheduled carpet smoking. 🙄

If you must loose 0.1mm, just use a hone. I bought a Brake Wheel Cylinder Hone for the power drill and took my 27.0 seat tube on the new frame out to 27.2 to take a suspension seatpost, nice job too. 😄

DiabloScott said:

I'm sure it would fit, in fact 0.2 mm would probably fit too. The question is why not buy to match? If Uncle Bob gave me a stem and Uncle Graham gave me handlebars and I didn't have enough money to buy a used part on eBay to match one or the other then maybe I'd risk losing some teeth or part of my skull. We don't know what the OP's motivation is but if he doesn't already have the stem and bars why would we advise him to get mismatched ones?

A quick eBay search finds a $6 stem with a 31.8mm clamp - BSplaw could sell his 31.7mm stem and come out ahead financially too.

I agree with you to a certain extent. If he doesn't already have the parts, then yes, buy a matching set for a dead-on-balls-accurate fit. But, if he already has them, they WILL fit without any problems whatsoever. There's a bit of 'spring' on the bar clamp of any stem, unless it's the 'open type', and that 'spring' is there for 2 reasons. 1) To allow easier fitting of the bar and 2) To take up any slack in a not quite perfect bar. Dhk was on about the sides of the clamp digging into the bar causing stress points. That would only be a problem if the sides of the clamp had burrs on'em which is easily fixed with a file and some wet'n'dry paper. For all the difference it would make, I'd stick with a bar/stem combo that out by 0.1mm, than fart around on e-bay, constantly bidding on a $6/£3 stem which may/may not have any history with it, then waiting a couple days/weeks! for it to be delivered. That's madness!!!