cpsqlrwn

I see a lot of nice bars on eBay that are clearly designated as 25.8 clamp size rather than 26.0. Sheldon Brown's website indicates that this was an "in between" size designed to address both 26.0 and 25.4 sizes. I have always used 26.0. Can I use a 25.8 handlebar and be confident that my 26 stem will tightly clamp to that handlebar without using any shims, etc.? I know it's only 2 mm which actually translates to 1 mm around the circumference, but I have no experience with this. Hence the question. Thanks for any info.

steppinthefunk 

I think you'll be fine. Especially if its a steel stem.

due ruote 

TenGrainBread 

I would be surprised if you could fit a 25.8mm handlebar into a 25.4mm stem clamp. Perhaps if the clamp was spread (NOT recommended), but probably not. 0.4mm is actually quite a lot with parts that fit with tight tolerance.

I personally would not try to clamp a 25.8mm bar with a 26mm stem. It might work but there is a chance you are putting stress on certain parts of the bar center and stem clamp by not having contact all the way around. In all likelihood it would be fine.

I just tried using a 30mm seat collar on a 29.6mm seat tube and it was too loose to the point where it moved during tightening and bottomed out before fully tightening.

cpsqlrwn

.2 cm but I said 2 mm which is the same thing

lostarchitect 

No, it's 0.2 mm.

TenGrainBread 

If you have a handlebar that has a 25.8 CM clamp diameter I'd say you're bringing "oversized" to the next level

cpsqlrwn

Sorry, my mistake. That would be quite oversized!

SurferRosa

I just measured some 3ttt bars that were supposed to be 26.0. They measure closer to 25.8. The 26.0 3ttt stem still clamped the bars just fine.

daoswald

The circumference of the 25.8mm diameter bar is 81.05mm. The circumference of the 26mm diameter bar is 81.68mm. So the difference in circumference is 0.63mm (almost two thirds of a millimeter).

cpsqlrwn

Thank you for the circumference caluculation (2 pi r) but I was referring to the diameter difference at any point in the circumference, which would be 0.1 mm (0.2 diameter difference spread across two sides). Thank you for the input.

USAZorro

If you have the parts already, stick the stem in the steerer, the bar in the stem, and tighten everything down before putting tape on. If it seems tight, put some levers on, position yourself like you're riding it, and push forward on the brake hoods. If the bar stays put, you're golden. If not, you need to use a shim, or change something out.

TugaDude

Sure, why don't you give practical advice?

dddd

I have to ask, WHAT "3ttt bars that were supposed to be 26.0"?

TTT's clamp diameter standard WAS 25.8, not 26.0, and I can't recall another brand that described their sizing as 25.8mm.

Back in the day (late 1990's), we gathered up a pile of new bars and measured their clamping diameter. We decided there was no consistent appreciable difference between bars/stems labeled as 25.8 and those labeled 26.0mm.
There were differences among them, though which did not really correlate to their stated size differences.
TTT bars labeled 25.8 measured no different from our ITM bars labeled 26.0mm.

So in effect, you are perhaps now somewhat correct to say that TTT bars are "supposed to be 26.0", though they were never labeled as such by TTT.

Feeling compelled to properly match brand (published) diameters has probably led road-biking consumers to shell out additional many thousands of dollars in cash over the years, so perhaps good for the industry(?).

I sure find it easy for some reason to mis-type 25.8 as 26.8(!!!), corrected several times in this one post.

Bad Lag

It is actually 0.2 mm not 2 mm. 0.2 mm is 0.008", about the width of a human hair, or two.

If you are worried about straining the stem, use the wall from an aluminum soda can as a shim. They are about the right thickness, maybe a tiny bit too thick. It's worth a try.

SurferRosa

Grand Prix (1st ver.)

dddd

The soda can wall is polymer-coated on both sides, which can be very slippery vs. bare aluminum.

the good news here is that after thoroughly sanding off the coatings, the thickness is much closer to what is theoretically "needed".

Note that 12oz and smaller-diameter cans will be much thinner-walled than larger-diameter cans, so are better in this application where literally a .1mm thickness (.004") increases the diameter of the bars (or reduces the diameter of the stem) by a full .2mm.

Also best to shim the entire clamping area including the "tips" of both sides of the clamps, as these do tend to cause sharp-looking creasing to very thin bars.

dddd

Keep in mind that is not TTT's literature you are quoting.

But just as when you and I measured the bars, 26mm was deemed quite close enough.

In the rare cases that TTT packaging turns up, even on Ebay or wherever, you'll see 25.8mm every time.

Note also that the Gene Portuesi catalog you referred to shows stem quill diameters as simply "22mm", instead of the more-likely 22.2mm of those Italian stems.

So again, what is "supposed to" be one size just depends on whether it's the factory (or those "downstream") who are being quoted.

But I still suspect that the proprietary published 25.8mm size was created simply to boost sales, so 25.8 = 26.0 in my book.

All this reminds me of the different methods of measuring handlebar stem extension length that typically alter the center-to-center dimension by 5mm.
It turns out in this case that whether a stem is measured in the field (across the top, looking down) or measured off of a drawing (center-to-center, on center), can cause the measurement to be different.

And then there are a select few Nitto stems out there which end up being longer than described because of their having a zero rise or 90-degree angle instead of -17-degrees.
So a "10cm" Italian stem could actually measure near a full 1cm shorter perpendicular offset (between handlebar and stem quill) than a certain quill model made by nitto.

In other handlebar-stem-measuring trivia, a Cinelli or Ambrosio 26.4mm handlebar slips easily into a Shimano (Nitto) AX stem.
...and Trek 720's came from the factory with 25.2mm Beleri Franco bars clamped by 26.4mm Cinelli 1A stems.
...and Schwinn's smallest-size Circuit model came with a 1A stem and came with a fork steerer a half-inch too short to keep the "safe insert" line below the headset nut.

RobbieTunes

Now that they've argued, dissected, and beaten the subject into a minutiae death....best bet is to get a match, size for size.

If you need to shim it, let me know. I have brass shim material.

If you need to spread it a bit, take a standard flat screwdriver, insert it in the clamp gap, and turn it sideways. It should spread the clamp enough to get your 25.8 into a 25.4 stem, but if it isn't, leave well enough alone. I've put 26.4 bars into 26.0 clamps, and that's the limit I'd try to "stretch out" a clamp.

You have good judgement, and you'll know if you think you're spreading a clamp too much. Same as you'll know if that shim just doesn't seem right.