0.2mm is it a big difference?

[02gf74]

I've thought of the coke can shim, but think it will be too thick. The difference is literally the thickness of a sheet of paper, all the way round. I had the calipers on a sheet too

a coke can is 0.1 mm thick (I make IS brake shims out of them) and proably thinner than your sheet of paper.

i wouldn't use the incorrect sized post in the frame.

 

[wookiee]

...so how does this differ to any seatpost shim???

 

[02gf74]

It doesn't. I won't use shims for reasons that may or may not be logical.

 

[wookiee]

It doesn't. I won't use shims for reasons that may or may not be logical.

Hmm fair enough...but some manufacturers BITD sold there posts one size only, with the idea that it was shimmed to the right individual size. USE seat posts springs to mind, but also my Orange P7 came from the factory with a shimmed post. Are shims that bad? Perhaps its more to do with how much post is in the frame?

 

[mattr]

Perhaps its more to do with how much post is in the frame?

Three things with shims, they can be too short, it adds another link to the tolerance chain, they can be too soft.

All three of these can cause a frame to fail.
Hence some manufacturers excluding use of shims in their warranty terms.

 

[Woz]

If the frame was steel or aluminium, I wouldn't hesitate with a beer can shim. In my exhaustive
research, not all beer cans are the exact same thickness - so you need to try a few.

Heineken came out the thinnest if I recall correctly, which is interesting as their
marketing is "Refreshes the parts other beers cannot reach".

 

[wookiee]

Perhaps its more to do with how much post is in the frame?

Three things with shims, they can be too short, it adds another link to the tolerance chain, they can be too soft.

All three of these can cause a frame to fail.
Hence some manufacturers excluding use of shims in their warranty terms.

...I'm still learning about them, so thanks for the info...had them on modern and retro bikes with no problems over the years and I am a sturdy 17.5 stone! Even my LBS recommended the shim and beer can method just a week ago!

Perhaps the to shim or not to shim is a different thread!

 

[mattr]

Depends on the frame and use.

A steel Road frame, with level top tube and 4-6" of exposed pin and 3" in the frame, I'd have no concerns about a coke can shim.
An aluminium mtb frame with 10" of exposed post and 4" of post in the frame, I'd get the right size post!

 

[jimo746]

OP: just find the correct sized post for the frame, you said yourself you'd be lost if the frame broke, if it happened out on the trail then that's one thing, but if it broke because you'd took a bit of a risk on an ill-fitting seatpost then thats a different thing altogether.
Personally I've used pre-made shims and coke can shims in the past and had no problems, but then I have maybe 6" of seatpost sticking out of the frame and the frames were steel.