Bicycle Mechanics - 1" to 1-1/8" soda can stem shim?
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03-09-11, 10:35 AM
I currently have a 1 inch steerer and a 1-1/8 inch stem. Instead of buying a shim, I was wondering if it was okay to make my own shim out of a soda can. To me, an 1/8 of an inch isn't a huge gap to fill. What are your thoughts?
03-09-11, 10:41 AM
Any LBS will have the correct shim, soda cans may be too soft, $2 is cheaper than a bent frame....
03-09-11, 10:45 AM
9/8-8/8=1/8 diameter, half that is a 1/16th, difference in radius,
shim has to be that thick , soda-pop cans are way thinner, so ..
So, .. +1. Just go Buy the right shim
03-09-11, 10:47 AM
Shims are cheap - hell I bought one only to find that my new stem came with one.
03-09-11, 10:57 AM
The number of layers you'll need to fill that gap will make the soda can shim idea a non starter. The resulting stack of layers will be far more flexible than you imagine since it'll be very difficult to insert the last layer or two that you actually need to fill the gap properley. It may not look like much of a gap to your eyes but that is your lack of metal working experience coming into play. On wood projects a '32nd or '16th here and there isn't a big deal as wood is flexible. But with metal fits you need to be worried about a thou or two. That's a whole different level of acceptable tolerances. This is why seat posts come in 0.2mm size steps.
So this is not the place to go cheap. Get yourself the proper shim.
Like the others I agree that given the stakes and the economics you should just go out and buy the right shim. It isn't that you couldn't build up 1/16" with soda cans, but that you need good uniformity of thickness along with flex so the stem clamp can compress the shim onto the stem.
Shims made for the job are nicely concentric, and split in the back to compress along with the stem. I simply can't imagine not buying one unless it's an emergency someplace in the outback.
In that case the best shim can be made by winding gummed carton tape (wet so the layers stick) onto an oiled steerer (so it doesn't stick) until it's built up to the right thickness. Let it dry and stabilize, then slide off and trim the length to fit within the stem, and carefully make a 1/16" slot along the length for compression.
03-09-11, 02:38 PM
Any decent LBS should have the actual shims floating around. Shimming with soda cans, for something as critical as the handlebars is NOT a good idea.
03-09-11, 10:55 PM
An unscrupulous LBS did this to me once. I didn't know they had done it until I disassembled the fork for cleaning. As was mentioned above, a soda can is too thin. The LBS dealt with this by folding the can over itself several times. What I found was a messy wad of folded and crumpled aluminum.
So the answer to your question is yes, you can do it, because it was done to me and I didn't know it for several years. But I don't recommend it, because you may not have the same luck I did, and a real shim doesn't cost much.
03-10-11, 03:11 AM
I'm assuming you have a threadless fork and headset, else the question doesn't make a lot of sense. What hasn't been mentioned, is that on a threadless headset, it's pretty essential that the bottom face of the stem be aligned square to the steerer. Don't see how you can achieve that while wrapping up tape or 19 layers of soda can (did you know soda cans these days are about 0.08mm thick? They're about right for putting 27.2 seat posts in frames reamed to 27.4.)
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