Bicycle Mechanics - 25.4 bars, 26 inch stem, soda can?

I have a four bolt 26mm stem and 25.4mm bars. I put the bars on without a shim and it didn't appear that there was any sizing issue. But .6mms is pretty significant, so I want to get this right. I cut some shims out of an aluminum soda can. Two, one for each face of the stem that comes in contact with the bar. I don't have a micrometer, so I can't measure the actual thickness of the metal (and I'm far too cheap to pay $10+shipping for a shim). Anyone know what the thickness is? I googled aluminum can wall thickness and got a range of average thickness from .009 inches to .013 inches. If my can falls within that range I should be pretty close to the .6 mms I need. When do I just call it good enough?

Personally, I sprung for the Nitto shims. But I thought I read somewhere on BF that the Jumex juice cans are the perfect thickness.

usually the energy drink cans have thicker walls, but I don't know how thick.

If it's a pop-top stem (as opposed to a quill) I don't even worry about it.

If it's a pop-top stem (as opposed to a quill) I don't even worry about it.

you should, as they're not all made the same and may not clamp the wrong size enough.

read your post, grabbed a soda can,cut it, and measured it at .13 mm or .005 inches. Tomarrow I will experiment with some stuff, as I have the same issue. I used 100 grit sand paper as my shim, it sorta works ?

I got a couple of google hits that agree with .005. This would mean I'm half way there, no? I suppose I should double up the shims then.

A strip of Diet Coke can has been keeping my handlebars secure for about 3 years. And if it was good for Greg Lemond in the Tour De France time trial... I figure it's good enough for all us mere mortals.

DanO

Yea, I have the same issue. Want to try the soma noha's arc bar with a 26mm quill stem. Part of the charm of reviving a vintage bike is to make the most of what you've got and not spend spend spend. I love the idea of a coke can rather than a rivendell shim. gonna try it! :D

ive run 25.4 bars in 26 stems and vice versa (!) with no negative effects except scraped up bars. it just depends on your stem and bars since neither are generally 100% perfect. if it feels snug and you can't move it with all your strength, you shouldn't worry about it.

Try using some 2 liter soda bottle material. I put a Ritchey 26.0 stem on my mtn bike by doing this. It's the right thickness but was a bit of a pain to install.

ive run 25.4 bars in 26 stems and vice versa (!) with no negative effects except scraped up bars. it just depends on your stem and bars since neither are generally 100% perfect. if it feels snug and you can't move it with all your strength, you shouldn't worry about it.

This is the singlehandedly most dangerous piece of advice i've read all month.

This is the singlehandedly most dangerous piece of advice i've read all month.

Ditto. Even if it "feels snug" and you can't move it, the handlebar can still rotate under enough impact force. If you're on a drop bar or mountain handlebar with extensions, this can dump you on your face.

At very least, use the correct shim: http://www.velo-orange.com/nittoshim.html

The right parts are cheap. New teeth are not.

I've had great success with soda cans, but I've also had failures. There is nothing quite so frightening as jumping a pothole, only to have the handlebars rotate out from under you when you land. I very nearly almost lost some teeth, or at least some skin.

What I learned? Soda cans work ok, but for a good strong shim, you need beah

132418

the wider can allows you to make a longer one piece shim, that in my experience has been more durable.

This is the singlehandedly most dangerous piece of advice i've read all month.

Thanks. Care to share your evidence or experience why, instead of this canned response?


Ditto. Even if it "feels snug" and you can't move it, the handlebar can still rotate under enough impact force. If you're on a drop bar or mountain handlebar with extensions, this can dump you on your face.

At very least, use the correct shim: http://www.velo-orange.com/nittoshim.html

The right parts are cheap. New teeth are not.

I read these scare tactics all day long on here. Losing your teeth would have more to do with riding style than a .6mm piece of metal.


I've had great success with soda cans, but I've also had failures. There is nothing quite so frightening as jumping a pothole, only to have the handlebars rotate out from under you when you land. I very nearly almost lost some teeth, or at least some skin.

What I learned? Soda cans work ok, but for a good strong shim, you need beah

132418

the wider can allows you to make a longer one piece shim, that in my experience has been more durable.

Do you think a real shim would have prevented this? It is just a tiny piece of metal. Enough force can cause properly fitted bars to move or even break.

Thanks. Care to share your evidence or experience why, instead of this canned response?



I read these scare tactics all day long on here. Losing your teeth would have more to do with riding style than a .6mm piece of metal.



Do you think a real shim would have prevented this? It is just a tiny piece of metal. Enough force can cause properly fitted bars to move or even break.

Oh please.

I don't even need to defend my assertion. Any mechanic who's wrenched on more than 1 bike will know that clamp diameter is non negotiable for quill stems. Especially for something that is such a huge mismatch.

And P.S it wasn't a canned response, I wrote it just for your dangerously incorrect advice.

Do you think a real shim would have prevented this? It is just a tiny piece of metal. Enough force can cause properly fitted bars to move or even break.

Yes, a real shim (or even a better home-made shim) would have prevented this. I'm willing to say this quite confidently since my new improved beer can shim has never slipped on me once. I'm not saying spring for the nitto (although it is the best option, I still haven't bothered yet) but at least do it right, and be a little careful.

even in a threadless stem, I can make my bars rotate just by putting all my 130lbs of weight on it when the bars are 25.4mm and the clamp is 26.0mm.

and yes, the bolts were tightened down as hard as can be without stripping anything.

Thanks. Care to share your evidence or experience why, instead of this canned response?

Do you think a real shim would have prevented this? It is just a tiny piece of metal. Enough force can cause properly fitted bars to move or even break.

I'm with Opie- I've worked on enough bikes, personally and professionally, to know that even the "correct" handlebars can rotate without enough torque on the binder bolt/bolts or if the bolt/bolts are torqued improperly. Putting a "tiny" piece of metal into a friction interface doubles (at very least) the chance that it will move with enough force applied.

I've removed (and thrown away) "soda can" shims that have distorted over time, allowing the bars to move in the stem clamp. That experience made me very cautious about the handlebar/stem interface.

Whether or not the bars rotate is NOT a valid test of your stem-bar combination. Mixing parts with different clamp diameters means that the clamping force is being put into a small area where the two different diameters intersect instead of spreading evenly over the whole clamp area. On a nice thick piece of metal, that's probably fine. On a very thin aluminum bar, you are likely to distort the shape of the bar at the clamp area and create stress risers. Rotation will be the least of your worries. Watch out for the bar cracking in half at the clamp. Steel is one thing...don't screw around with light weight parts.

@jds108 - do you mean a plastic soda bottle? That is too soft a material for a shim.

Soda/beer can aluminum is very high quality material. It should be fine for shims as long as the thickness is close. But I agree with the posters recommending using one large piece instead of several small ones.

hardware store has .010" shim stock. .6 mm = .024", so .010" shim would be very close.

Whether or not the bars rotate is NOT a valid test of your stem-bar combination. Mixing parts with different clamp diameters means that the clamping force is being put into a small area where the two different diameters intersect instead of spreading evenly over the whole clamp area. On a nice thick piece of metal, that's probably fine. On a very thin aluminum bar, you are likely to distort the shape of the bar at the clamp area and create stress risers. Rotation will be the least of your worries. Watch out for the bar cracking in half at the clamp. Steel is one thing...don't screw around with light weight parts.

@jds108 - do you mean a plastic soda bottle? That is too soft a material for a shim.

Soda/beer can aluminum is very high quality material. It should be fine for shims as long as the thickness is close. But I agree with the posters recommending using one large piece instead of several small ones.

Regarding the plastic bottle shim - why do you think it's too soft? I've been using it on my mtb for about a year now with no issues. The material is just the right thickness for this application (25.4 into a 26.0). I took a look at it after my first ride and didn't see any permanent marks in the plastic (i.e. plastic deformation).

I'm all ears if you really think it's a problem.

Regarding the plastic bottle shim - why do you think it's too soft? I've been using it on my mtb for about a year now with no issues. The material is just the right thickness for this application (25.4 into a 26.0). I took a look at it after my first ride and didn't see any permanent marks in the plastic (i.e. plastic deformation).

Well, I'm no engineer, so maybe I'm off base here. And as plastics go, that type is pretty tuff. But I've just never seen plastic used as a shim material in any application with fairly high stresses except where the part was specifically designed using special materials. The bar stem joint is pretty critical because it has lots of leverage against it and because a failure could be so dangerous. Any shim can deform over time which is why they aren't the best idea in general. But you've got to think that plastic is less tough and more prone to deform over time than even aluminum. As has been stated in other comments, a lot of people have gotten away with using the 25.4 - 26.0 combo with no shim at all. I would guess that the plastic has mostly migrated to areas with less stress as if you had no shim at all.

There's also a big difference between riding with a sturdy cromo bar/stem and some of the really lightwieght stuff. Ironically, the more expensive the bike, usually the more fragile these parts are. Not knowing what the OP has, I just wouldn't recommend something that doesn't seem safe to me.

Again, may never give you a problem. But I just wouldn't ride with that much depending on a piece of soda bottle.

Regarding the plastic bottle shim - why do you think it's too soft? I've been using it on my mtb for about a year now with no issues. The material is just the right thickness for this application (25.4 into a 26.0). I took a look at it after my first ride and didn't see any permanent marks in the plastic (i.e. plastic deformation).

I'm all ears if you really think it's a problem.

you can't get as much leverage out of flat bars compared to riser bars or drop bars.
might be different if you added some long bar-ends to the flat bar.

ive run 25.4 bars in 26 stems and vice versa (!) with no negative effects except scraped up bars. it just depends on your stem and bars since neither are generally 100% perfect. if it feels snug and you can't move it with all your strength, you shouldn't worry about it.

I once bought a used road bike with 25.4 bars in a 26.0 stem. It was tight, the clamp didn't seem pinched, and the bars didn't move when I tried. I didn't think to take the bars off to measure the stem diameter because it seemed just fine.

And it WAS just fine for several months, until I hit a pothole when riding on the hoods and the bars rotated.

When I got off the bike there was a crack 2/3 of the way through the face of the stem. If I had missed that pothole, and later hit something harder and it broke, who knows what could have happened.

Be careful, especially with stems.

But I've just never seen plastic used as a shim material in any application with fairly high stresses except where the part was specifically designed using special materials. The bar stem joint is pretty critical because it has lots of leverage against it and because a failure could be so dangerous. Any shim can deform over time which is why they aren't the best idea in general. But you've got to think that plastic is less tough and more prone to deform over time than even aluminum. As has been stated in other comments, a lot of people have gotten away with using the 25.4 - 26.0 combo with no shim at all. I would guess that the plastic has mostly migrated to areas with less stress as if you had no shim at all.

There are two issues with plastic. First is the strength. Plastic simply is not as strong as metal (ignoring a few exceptions). Plastic used as a shim will tend to extrude (picture the material thinning out at the clamping interface) when overloaded in compression. Even if your shim survived the torque from the stem, keep in mind that even road riding will offer significant additional loads on the shim (pulling and pushing on the bars with your hands at least).

The other issue is creep. Overtime when subjected to stress, plastic will relax. Where you once had tension/compression, you no longer will. You do not need to exceed the yield stress of the material for this to happen (which is a big difference between plastics and metals). Heat tends to make creep much worse. I'd be curious for plastic shim users to test their handlebars after leaving the bike out in the summer sun all day.

There are two issues with plastic. First is the strength. Plastic simply is not as strong as metal (ignoring a few exceptions). Plastic used as a shim will tend to extrude (picture the material thinning out at the clamping interface) when overloaded in compression. Even if your shim survived the torque from the stem, keep in mind that even road riding will offer significant additional loads on the shim (pulling and pushing on the bars with your hands at least).


:/

My campy dropouts did this - they squished and deformed under overtorqued rear axle nuts.

:/

My campy dropouts did this - they squished and deformed under overtorqued rear axle nuts.

Metal can extrude under pressure too, but it's at a much higher pressure than plastic would do the same. Sealing washers (typically copper or aluminum) are one-time use items due to the deformation they see from being clamped.

OK, thanks for the feedback. I'll have to look for some .3mm thick metal to replace the plastic as the shim.

Or just pony up the $10 to buy an actual shim, but I'm feeling cheap at the moment.