Bicycle Mechanics - 26.4mm bar in a 26.0 clamp?

To add to my inquiry regarding quill to thrdless stem adapters, I plan to use a drop bar with a 26.4mm center in a threadless stem that has an open face 26.0 clamp it seems sturdy enough (not tested on the bike, just bolted the bar into the stem to try it). There is a little space between the two plates of the stem, they do not meet together completely as with a 26.0 bar.

Would anyone think this was a bad idea? Anybody do it with good results? Just thinking of safety, sturdiness, etc. Not concerened with it not 'looking right" , etc . this is a beater bike, but I still ride it hard. Just did 30 miles on it this weekend and have a few more metric centuries coming up in the next few weeks.

I weigh over 200 lbs and like to stand and hammer a lot. The bar is a fairly light Control Tech 6061 AL, 46mm c-c.

What kind of handlebar? I wouldn't try this with a carbon fiber handlebar or even a super lightweight aluminum bar. Hmmm - 200 lbs and like to stand and hammer. How's your dental coverage? New stems and handlebars, even the good stuff, are cheaper than bridgework.

The issue is that, as you tighten the stem, all of the force is concentrated in four lines along your handlebar where the corners of the stem and face plate meet. You could try to minimize this by filing a little relief in the stem and face plate at those four corners.

The issue is that, as you tighten the stem, all of the force is concentrated in four lines along your handlebar where the corners of the stem and face plate meet.

wouldn't this also happen if the stem was a perfect fit (26.0 stem and 26.0 bar)?

Find a shim to put in there, soda or beer cans. If you have calipers they might be handy here

If the bar is 26.4 there is no way you can shim it to 26.0. You cant buy negative shims.

^^^... put down the carpet pipe. He doesn't need a shim the bar is too big for the clamp!

To add to my inquiry regarding quill to thrdless stem adapters, I plan to use a drop bar with a 26.4mm center in a threadless stem that has an open face 26.0 clamp it seems sturdy enough (not tested on the bike, just bolted the bar into the stem to try it). There is a little space between the two plates of the stem, they do not meet together completely as with a 26.0 bar.

Would anyone think this was a bad idea? Anybody do it with good results? Just thinking of safety, sturdiness, etc. Not concerened with it not 'looking right" , etc . this is a beater bike, but I still ride it hard. Just did 30 miles on it this weekend and have a few more metric centuries coming up in the next few weeks.

I weigh over 200 lbs and like to stand and hammer a lot. The bar is a fairly light Control Tech 6061 AL, 46mm c-c.Simply put...Don't do it,unless you want to prove Darwin right. It's too big a misfit.

oh, yea. My lack of paying attention to posts probably tells me i need to go to bed :p

FWIW, I rode for a month with a mtb stem on my road bike (26.0 aluminum bar in a 25.4 stem). It seemed sturdy enough - no slippage or flex, and I managed to keep all my teeth.

Having said that, I realized that it was just a temporary measure until I could get the proper stem ordered. Actually, I got a new bar as well. Mostly because I wanted a different bend, but also just in case the smaller clamp had done any damage to the old bar (doesn't appear to have done so, though.).

My 2 cents: it can be done, but I wouldn't consider it a long-term solution.

I wouldn't do it. The contact surface area would be reduced greatly in the bar-clamp interface. This concentrates the load in the smaller areas that are touching, making those spots prone to failure. Also, when you pry open the clamp, it doesn't spread out evenly. The edge & corner next the split remains the same curvature and radius. When putting the larger bar in, the edge & corner of the clamp will end up biting into the bar with immense pressure. You'll have intense stress-risers at that point and the bar will snap prematurely.

Try it and see, get your eyeball close to the bar and look across it through the stem. You'll see plenty of air-gaps all the way through.

Ok, thanks Guys. I'll avoid my miserly quick-fix idiocy!


Thanks for the voices of reason, that's why this forum is so great!! :)

I've been riding a fixed gear with bullhorns (ie bigger lever than drop bars) 26.4 bar on a 26 quill clamp and in almost a year of riding hard 5 days a week I've never had it slip. Aluminum bars and I weight over 200#. As long as it's just a small gap between the screw holes and not a bad fit, there is really no issue. I don't know why everyone is making such a big deal about it.

Many ride without helmets and get away with it for various lengths of time. Why temp Darwin over a few bucks?

I've been riding a fixed gear with bullhorns (ie bigger lever than drop bars) 26.4 bar on a 26 quill clamp and in almost a year of riding hard 5 days a week I've never had it slip.....I don't know why everyone is making such a big deal about it.

"Getting away with it" isn't the same as doing it right and having the bar slip isn't the potential problem. What the mismatch can cause are stress raisers in the bar resulting in sudden and catastrophic breakage. You get no warning until you kiss the pavement. Your call.

sold - I'd rather play it safe.

I'm gonna keep looking for a 26.4 clamp stem cause I really wanna use these nice drop bars - They are new, 46 cm wide; the old ones on the bike now are only 38cm! I'm about a 45" chest so I need the wider bars.

Next time I buy stuff on closeout I'll pay more attention......

^^^....Why don't you just ditch that threadless adapter and troll ebay for an old cinelli stem that had a 26.4 clamp?

Just this afternoon I started messing with this same situation. I bought a 2004 LeMond Buenos Aires recently and am missing my old Cinelli 66 bars. I took the front clamp off the 3ttt stem on the LeMond and put it up to the Cinelli bars - by feel it fits the same, though the rating of the stem is 25.8mm and the bars are 26.4mm. In digging on the net I found one comment that 26.4mm stems/bars actually measured closer to 26mm in reality. So we're talking ~.2mm difference here.

It's cold and rainy today, so maybe I'll give it a try.

In digging on the net I found one comment that 26.4mm stems/bars actually measured closer to 26mm in reality. So we're talking ~.2mm difference here.

It's cold and rainy today, so maybe I'll give it a try.The cinelli bars I just measured were right on 26.4.Would rather rely on a caliper than internet rot.

I've been riding a fixed gear with bullhorns (ie bigger lever than drop bars) 26.4 bar on a 26 quill clamp and in almost a year of riding hard 5 days a week I've never had it slip. Aluminum bars and I weight over 200#. As long as it's just a small gap between the screw holes and not a bad fit, there is really no issue. I don't know why everyone is making such a big deal about it.

Amen to that! Bunch of pantywaist crybabies around here. We are talking about at most, a .4mm difference- and a CLAMP- which is designed to be tightened.

^^^...words of wisdom fom a muppet who has done too many endos without a helmet?

^^^....Why don't you just ditch that threadless adapter and troll ebay for an old cinelli stem that had a 26.4 clamp?

That's exactly what I'm going to shoot for - I do hope to find my needed extension (100mm is ideal, though 90-110 is okay....I have a 70 and a 130 with 26.0 clamp currently....so getting a 26.4 in 100 or so length will let me get the proper upper body extension and bar width)

just a matter of waiting for the right one to pop up. But the prices seem fair enough on these nowadays.

I understand what the other dudes are saying - it's probably OKAY to mismatch in some cases. But I do ride hard, so why risk it if the proper fit is readily available? I just wasn't sure whether it was risky , hence my thread.

Thanks again.

^^^....I'll check my stash.If I have a 100 in a 26.4 it's yours for the shipping.

^^^....I'll check my stash.If I have a 100 in a 26.4 it's yours for the shipping.


Thanks!!!! :) I really appreciate that. pls feel free to pm with any details.

I have found a few on ebay in the last few weeks but they always seem to be super longs....
as I said, a 110 would be cool as well. The 130 I tried on that bike locks my elbows out a bit and I gather a 120 wouldn't be much different.

Just this afternoon I started messing with this same situation. I bought a 2004 LeMond Buenos Aires recently and am missing my old Cinelli 66 bars. I took the front clamp off the 3ttt stem on the LeMond and put it up to the Cinelli bars - by feel it fits the same, though the rating of the stem is 25.8mm and the bars are 26.4mm. In digging on the net I found one comment that 26.4mm stems/bars actually measured closer to 26mm in reality. So we're talking ~.2mm difference here.

It's cold and rainy today, so maybe I'll give it a try.


i should have warned you b4 you tried it.

I once bought a bianchi track bike, with 3T track drop bar and a very short stem (about a 70mm extension). I wanted a 110 or so with a set of bullhorns on there.

First thing I did was remove the track bars and try to throw them on a bike I was selling (I love the look of track drops but I don't ride on a track and I find them impractical for the street). I don't recall the brand of stem on the bike I was selling - it may have been a Cinelli, maybe just a cheap SR, but I essentially ruined the track drops by forcing them into that stem ("grunt grunt - but they're road bars - they HAVE to be the same size, right?" :rolleyes: )

As I watched the bars being destroyed by my own two hands I soon recalled removing a set of cinelli road bars from a cinelli stem on a bike given to me a few years earlier - someone had ruined the frame by jamming the seat post down into the frame with a mallet (a featherweight Columbus steel tubed Tommasini racing bike..... hurts me to even think about it....)....those bars got so scored in the clamp area (and I lost about 10 lbs in sweat) during removal they obviously were the wrong size....someone had clearly shoved a 26.4 bar into a 26.0 stem, though I didn't know that Cinelli had changed sizes back then. I assume the bar and stem were of a different vintage (there were Campy GS components mixed with Record on there as well) Being both parts were Cinelli maybe they didn't know any better, kinda like me with the track bar fiasco.....

Speaking of that bianchi track bike, Later I wound up using the original 70mm track stem with the new bullhorns (26.0) I bought - imagine my surprise when they started slipping on the first ride. I soon realized a shim was in order, and it worked okay after that, but I hasten to add I didn't ride that bike very much and never hard at all. One reason may have been my knowing the bars were mismatched, and I prefer to keep all my teeth.

In retrospect, even with the open face stem clamps making it more 'do-able', I'll be sticking to correct bar-stem sizing from now on.

Well, laziness set in as I looked at my project and I didn't do any bar-swapping yesterday. The thought of all that re-taping got to me. I'll leave the Cinelli 66 bars on my old DeRosa as an example of the way things used to be.

In that preliminary messing around, I was surprised to find that the 3ttt stem and bars on my LeMond are not knurled at all. All this talk about slipping and bars & stems are completely smooth now!

Wouldn't it be easier to get a new OS road stem and take a little bit out of a standard-road-to-oversized shim?
It is what I'm planning to do with my NOS Cinelli bars unless someone can point out any glaring errors I've made.