Ok this may seem stupid but:
I'm looking at a new stem, Deda Murex.
Deda lists it as 26,00mm clamp diameter.
Deda also lists 215 handlebars as 26mm (standard).
I've seen a few listings at online retailers for
215 handlebars as 25.8mm. Is this just a misprint?
bad measurement? rounding?

thanks
Marty

Measurements are not Standard.

I've use 26.0mm aluminum bars in 25.8mm stems and it works fine. I'm not sure about the reverse, tho.

Vice-versa works as well (under most circumstances). We're talking about 0.008" difference here.








Maybe I'm paranoid, but is the Ad-Bot following me

I wouldn't do it... I was going to try the same thing once, but it was apparent that the fit was wrong before I even bothered to tighten anything.

26mm is the more common "standard", but 25.8mm isn't exactly uncommon, either. (And then there's the new "Over Size" standard.)

Mismatching the sizes will result in high point-loading of the handlebar, which significantly reduces the handlebar's strength where it meets the stem. Since it's so easy to get matching parts, why bother with making perfectly good parts weak?

-Erik

between the same handlebars they usually are standard.

I think you'd be ok using the deda handlebar w/ the deda stem. it would be stupid for the manufacturer to make two different clamp sizes that are so similar...

good luck.

Between the same brands yes, but the measurements are exactly like mountain bike tire sizes. No standard between different companies. There are some tires that measure out to be the exact size, and there are other others that are over but are called that size and there are some that are called that size, but ar smaller.

For example a 2.5 highroller is more like 2.35 and a 2.5 michelin is more like a 2.7

The bars are 25.8mm OD. The stem clamp is 26mm ID.

If they were both the same, how would the bars be able to fit inside the clamp, or the clamp tighten?

Because part of the circle of the clamp is missing... If you were to snug-down the face plate without the bars in place, you could see and feel this without measuring. By the same token, when the bars are installed there is visible clearance between the faceplate and the rest of the stem.

While a non-removeable faceplate stem would be more forgiving of a size mismatch (it's designed to flex some), it's still not the best idea... The flexible side would accomidate the mismatch, the rear side will not flex (since it's held rigid by the rest of the stem) and thereby lead to point loading.