# 31.7 and 31.8 mm OS handlebars and stems diameters



## clm2206 (Sep 12, 2006)

Hello

As you probably know, the most popular OS diameter for stems and road handlebars is 31.8mm. However, Deda has its own 31.7mm diameter standard, only shared by their stems and handlebars.

It would be safe to set a Deda (31.7mm) handlebar on a -let's say- Ritchey 31.8 clamp diameter stem? How to fill that little gap? It is unsafe? Any ideas?

Best regards,

Carlos


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## DIRT BOY (Aug 22, 2002)

clm2206 said:


> Hello
> 
> As you probably know, the most popular OS diameter for stems and road handlebars is 31.8mm. However, Deda has its own 31.7mm diameter standard, only shared by their stems and handlebars.
> 
> ...


Yes you are fine. The standard is in between. Euro rounds down and US rounds up.

It's the same thing.


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## clm2206 (Sep 12, 2006)

Thanks Dirt Boy!!


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## B05 (Jul 31, 2011)

I'm having a difficult time installing my new Deda stem with my old 31.8 handlebar. It doesn't secure the handlbar well. I got it to clamp properly once but since I wanted to adjust my reach I took the bolts out again and now I can't do it any longer.

This is frustrating.


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## Kontact (Apr 1, 2011)

B05 said:


> I'm having a difficult time installing my new Deda stem with my old 31.8 handlebar. It's doesn't secure the handlbar well. I got it to clamp properly once but since I wanted to adjust my reach I took the bolts out again and now I can't do it any longer.
> 
> This is frustrating.


I don't understand what's happening: The bolts won't go in, or they won't hold the bar when tightened, or they won't tighten?


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## acg (Feb 13, 2011)

Is it a carbon handlebar? I had a similiar thing happen to a carbon seatpost. It kept on slipping no matter how hard I camped it. The LBS says the carbon seatpost went "out of round" from a few years of hard use (it was on my mountain bike). I replaced it with a non-aluminum one.


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## B05 (Jul 31, 2011)

Kontact said:


> I don't understand what's happening: The bolts won't go in, or they won't hold the bar when tightened, or they won't tighten?


I got it to tighten once, but since I wanted to adjust my reach I took the stem out. 

Now, I've been trying to tighten the bolts again onto the stem but it just fails. I checked the threads and they're still good. I can get the bolts into the stem but it's not tight enough and the handlbars slide forward.

It's an Aluminum handlebar.


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## Kontact (Apr 1, 2011)

B05 said:


> I got it to tighten once, but since I wanted to adjust my reach I took the stem out.
> 
> Now, I've been trying to tighten the bolts again onto the stem but it just fails. I checked the threads and they're still good. I can get the bolts into the stem but it's not tight enough and the handlbars slide forward.
> 
> It's an Aluminum handlebar.


At a guess, if the bolts aren't stripped, you crushed the handlebar when you (over)tightened it the first time, and now it does not have the right shape to be clamped any more.

Time to go to a bike shop.


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## looigi (Nov 24, 2010)

I bought Deda Zero100 bars and measured their diameter with calipers in a number of directions and places. Within the .02mm (0.001") resolution of the calipers they were basically indistinguishable from a number of nominally 31.8mm bars I have.


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## bdaghisallo1 (Sep 25, 2007)

The O/S standard is actually 1 1/4 inches, which is 31.75mm exactly. Deda rounds down to 31.7 and everyone else, it seems, goes up to 31.8. That's all there is to it. All standard O/S bars and stems are compatible with each other. Deda's new 35mm diameter bars are a different story of course.


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