Bicycle Mechanics - 31.7 bar 31.8 stem will it fit?

Deda Newton 31.7 diameter bar and a new Thomson X-2 31.8 diameter stem.... is this so close it doesn't matter? Please nobody write "It should work" without previous experience, I'll be haulin' on this thing in field sprints... need to know for sure from somebody that's done the same....

todd richards (NEW Merlin Agilis with Campy ! )

Anything will work if you bend, squeeze, twist, or distort two pieces together with enough force.

Why you would want to do this is beyond me however. You clearly know that the two sizes do not match, and yet you want to use them anyway? And not only use them, but RACE with them??!!!

^^^^.....Actually, the two are close enough to be considered interchangable.

"Close enough" is for hand grenades. I prefer my components to match exactly, especially if I'm racing with them.

^^^^....Sure :rolleyes:

"Close enough" is for hand grenades. I prefer my components to match exactly, especially if I'm racing with them.

So you're one of those types that only uses a bar and stem from the same manufacturer, then? Your fears are ungrounded.

From Inside Traiathalon, full article link (http://www.insidetri.com/train/bike/articles/1304.0.html)

Making it work: Have a brew, fix your bike
By Lennard Zinn
Inside Triathlon technical writer
This report filed December 10, 2002
A can of beer always helps to make problems seem less important, but sometimes, it can actually fix bike problems! Aluminum beverage cans are 0.1mm thick and are easy to cut with a knife or a pair of scissors, rendering them quite useful for making minor spacing adjustments on a bike.

A beer can shim will give .2 mm increase in diameter which is twice the amount needed. Stem are supposed to be tightened down onto the bars. The .1 mm reduction will be within the elastic limit of the stem deformation so go ahead and do it.

.1 millimeters = 0.00393700787 inches
I doubt anyone's tolerences are that close anyway.

So you're one of those types that only uses a bar and stem from the same manufacturer, then?

No - I'm one of those types that makes sure my handlebar diameter matches the nominal stem size.

This question comes up every so often and I get a laugh out of the worry worts ;)

The REAL size of the bars is 1-1/4 INCH. When converted to metric units this works out to 31.75 mm. Some companies round off this number to 31.7 and others round to 31.8. Key thing is that both are the SAME.

Keep it real please.

Ed

No - I'm one of those types that makes sure my handlebar diameter matches the nominal stem size.

As Gomez308 points out, most manufacturers (possibly Thompson excepted) don't hold that tight a tolerance on the clamp diameter, so even if you match nominal specs from different manufacturers it's entirely possible to end up with more than a 0.1mm mismatch. This really isn't an issue at all, unless you're neurotic. I'd bet that having 4 bolts instead of 2 makes much more of a practical/functional difference.

This question comes up every so often and I get a laugh out of the worry worts ;)

The REAL size of the bars is 1-1/4 INCH. When converted to metric units this works out to 31.75 mm. Some companies round off this number to 31.7 and others round to 31.8. Key thing is that both are the SAME.

Keep it real please.

EdYou are kidding.... right? What would the muppets do to entertain themselves? Actual measurement of some TTTs advertized as 31.8, showed mesurements of 31.8,31.85 and almost 31.9.

It's true. The manufacuring tolerances are such that very often 31.7 thru 31.9 are all the same specification. You're lucky if the bar and especially the stem is perfectly rounded :)

The REAL size of the bars is 1-1/4 INCH. When converted to metric units this works out to 31.75 mm. Some companies round off this number to 31.7 and others round to 31.8. Key thing is that both are the SAME.

I've heard that story.Makes one wonder why a manufacturer not in the US woud pick 11/4" as a 'standard'? Another story is that 31.7 was introduced by deda,but most othwers go with 31.8.

It's not unusal for the bike industry to pick standards around BSA units; a couple of big ones that come to mind are steerer tube sizes and frame tubing sizes: 22.2mm = 7/8", 25.4mm = 1", 28.6mm = 1-1/8", 31.75mm = 1-1/4", 35mm = 1-3/8"

It's not unusal for the bike industry to pick standards around BSA units; a couple of big ones that comes to mind are steerer tube sizes and frame tubing sizes: 22.2mm = 7/8", 25.4mm = 1", 28.6mm = 1-1/8", 31.75mm = 1-1/4", 35mm = 1-3/8"And that all happened long ago too.

Ah... manufacture tolerances....mmmmmm.....elastic deformation......ohhhhh.... metric SAE conversions...... 5.56.....7.62....yummy

Not sure if this is how the bike people do it, but if my guys don't do this....watch out!

The internal diameter of the clamp should alway be slightly bigger than the ouside diameter than the bar. there is a gap between the face plate and the stem or a gap in the ID on the stem. Cranking down on the screws closes the gap is reduced . But wait, the clamp does not grip the bar completely all around. This is esp true with open face plates. What ends up happening is that the front and back of the bar is in contact with the front of the face plate and the back of the stem, and that is it! There is hardly contact all around. This is enough to hold every thing together. So if the tolerance of the 31.7 bar can go as high as 31.9, the stem would be 31.95 (or such). And the lower end tolerence of the bar may be 37.6! Stacking tolerences, there can be .35mm delta ! (just throwing out numbers, not stating that they are the case) . A bar and clamp is good as long as the contact between the bar and clamp occurs at the front and back. (ok, the face plate and stem deforms a bit and wraps itself around the bar some) If the bar is bigger than the ID of the clamp, the contact is not fore and aft, but at the top and bottom (near the split line) and will hold up the clamp. Eventually, as the metal deforms, it'll loosen up again. If the difference is larger than some number, the joint will never clamp right.

I ride Dade Pista handlebars which is listed as 31.7 on an FSA OS-115 stem which is listed as 31.8. I race this and with properm torque haven't had any movement at all.

I ride Dade Pista handlebars which is listed as 31.7 on an FSA OS-115 stem which is listed as 31.8. I race this and with properm torque haven't had any movement at all.Hallelujah! Just what the OP asked for.

That would have been too easy!