So I have a Thomson Elite stem whose clamp is 25.4 and I wanted to switch to some Nitto bullhorns, but they're all 26.0 clamp. I've read that people have successfully been able to run 26.0 bars in their 25.4 quill stems, but what about an open face stem? Is it possible or am I looking at buying a new stem?

Then today I got the idea to see if I could buy a 26.0 replacement clamp from Thomson instead of buying a whole new stem. I e-mailed them to see if this would work and the guy wrote back recommending I buy a new stem. He said the bars might fit but would fatigue faster.

So is anybody successfully running 26.0 bars in their 25.4 open face stem without catastrophic failure? Or should I just stop being a cheap ass and buy a new stem?

edit: updated

use a Thomson shim, or just get a shim put in there, super small but it'll do... .6mm is super thin, but I agree with Thomson and say get a new stem if you are worried bout the stress or catastrophic failure rate.

you can't shim a larger bar to fit a smaller diameter clamp. i'm sure you just misread that. obviously the preferred method would be to trade somebody for an equivalent thomson in 26.0, but right now that might be a bit harder. i filed out an old nitto quill to fit a 26.0, but i wouldn't do that to a thomson.

and you wouldn't have to file the stem to fit a larger bar.

do it, it's fine. i've done it. it's not ideal, but if you tighten it just right, nothing gets damaged.

I've done it with a standard stem where the clamp can somewhat reshape itself to comform to the larger diameter bar when clamped down. But I'm not so sure with an open faced stem as the solid face place is not giving and can actually 'crush' the bar. May be fine if you're using steel bars though....

hmmm...good point, i was thinking about negative effects on the stem, not the bars. i only ever did this quite some time ago with a mtb stem that had track drops on it, then a pair of bullhorns, but both seemed fine. since then, i've only used flats and risers...but iirc, i put both the track drops and horns in a 26.0 stem with no problem after running them on a 25.4 stem.

I've done it many times. Don't crank down on it.

100% right I misread. I saw it the other way around...

fine

Just make sure you clamp it evenly by alternately tightening the bolts in small increments.

I've clamped 26.0 bars in a 25.4 stem. I didn't have a problem. The bars aren't THAT much bigger.

I dont even know what size bars or stem I have, and I switch bars all the time, just do its fine

I have a 25.4 stem with 26.0 bars on my cyclocross bike. Nothing has slipped or dented, and I race it pretty hard. I say go for it.

I've got a thomson stem 25.4 with an EA50 road bars 26.0, no problems.

Thought I'd update this for the records since I noticed stress cracks in the stem's faceplate over the weekend. If anybody is considering doing this, I wouldn't recommend it.

not too bad for a year and a half, but a bit distressing nonetheless. maybe it only lasted this long because it was a thompson?

I've had stems break before because of stuff like that.....So I would not do it.

Yeah, the bullhorns were mounted for about half that time. Switched off between the horns and risers. I don't know exactly when the cracks started, but they're there none the less. Probably going to order a new faceplate from Thomson so I don't end up toothless in the near future.

It's 0.6mm difference in total diameter right? I wouldn't worry about it.

you should re-read the thread.

yes, you should worry about it.

with any other stem you might try it though i refuse to compromise safety in the least @ the bars/stem.
but really, i wouldn't mess w/ thomson stem: https://www.bikeforums.net/road-cycling/458531-cracked-thomson-faceplate.html

Once was enough. Is it ideal, well no. Does it matter? I wouldn't worry at all. The stress cracks that have shown up over time on the OP's stem are most likely from overtorqued and/or unevenly torqued bolts, which the majority of people end up with. We're not talking about piston sleeves and valve seals in a motor, we're talking about a stem that clamps onto a round metal bar with 2-4 bolts and 0.6mm difference in diameter.

holy smokes, I never knew. this is actually kinds frightening. I thought I'd read about 1 or 2 instances, but the more I dug into it, the more X2 horror stories surfaced! It's what I ride with right now. All the stories seem to center around the X2 though, and not the Eilte. Guess you can't take away that much material from the contact points and not have something like this happen. Still kinda shocking, considering it's Thomson.

I doubt it's something to worry too much about, as long as it's properly maintained.

unsure if it's relevant.. i have a nitto jaguar stem.. which i grinded the inside out to fit some 26.0mm bars... to my surprise the stem had a sufficient gap between the two clamping areas allowing me to still run 25.4 bars. so i ran 25.4 bars on the grinded out stem for a good 3+ months w/o any slipping or signs of stress/cracks.