Compatibility of 31.7 handlebar with 31.8 stem

Tech Tech Help
1

Hello everyone,

I’ve found a handlebar which I liked a lot but it has 31.7 mm diameter(Deda) and my stem is for 31.8mm (stock BMC stem).

I’m worried about their compatibility, safety and if the handlebar will slip during rides. I’ve also read that the real diameter is likely to be 31.75 which some companies round to 31.8mm and some to 31.7 but I don’t know to what extent this statement is true.

If someone has an opinion on this topic or experience of using Deda handlebar with diameter of 31.7 with a non-Deda stem for the standard 31.8 mm handlebar please let me know how it works together.

Thank you!

2

I’ve used a few different Deda bars with a few different stems, no issues.

As long as your stem faceplate isnt already bottomed out, you should be fine.

3 Likes
3

Should work totally fine. Either deda is silly and everyone is sane or vice versa. But have ridden deda bars with innumerable stems and never had an issue.

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4

I believe the standard is 1 and a quarter inch which works out to 31.75mm. Some manufacturers round the name to 31.8 and some to 31.7 but it’s essentially the same dimension.

11 Likes
5

I would encourage you to get precise measurements (with calipers) of the diameter of your current bars, and find out/measurements the deda bars…

In college, I built a fixie with modern aluminum bars that didn’t fit the old stem perfectly, but close enough. No problems…

…for 10 years, at least, and then the stress concentration I’d created at the stem caused catastrophic failure of the handlebars, sending me to the ground immediately and slicing my thigh open with the handlebar stub.

To each their own, but please don’t ride around me (or others) with a bar/stem combo that is “close enough.”

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6

Never knew this and makes so much sense!!

7

Fun fact: before 1959 1.25 inch was 31.75006 mm, since 1959 it is 31.75mm exactly.

4 Likes
8

Back in the day, there were those who liked the shape of Cinelli handlebars (with their 26.4mm clamp diameter) and the aesthetics of 3T/TTT stems (which used a 26.0mm clamp diameter) and worked very hard to combine them, there being no face plates for easy assembly. Ironically, the only person I know who had to have his jaw wired up when his stem broke was using a full Cinelli ensemble.