Bore enlargement seast post clamp; Is this possible?

Wheelinthai

I just bought GT Grade Carbon, and would like to put a rear rack on it. The factory seat post clamp is 30.9 and the ACCOR come in two nearest sizes 27.2 and 31.8. Would it be practical to have machine shop bore out the 27.2 clamp to 30.9 ?

buckmulligan

You're talking about boring it out to nearly 4mm greater diameter, which is obviously 2mm out of the wall all the way around. Are you sure there would be enough material in the clamp to bore it out that much and have any kind of structural integrity afterwards?

If you need to have one of these clamps, would it not be easier to try to shim a 31.8mm clamp?

lapavoni10

I agree, use the larger and shim out.
Leave the original clamp in place to hold the seatpin, and use the new one just for the rack.

Wheelinthai

Thank you very much BuckMulligan. I did a quick check with size 31.8 and 34.9 that I have on hand, and both do indeed have different dimensions. Also, they have lips to prevent sliding down the seat tube. This would preclude any boring out the clamp.

Wheelinthai

lapavoni10 wrote:

I agree, use the larger and shim out.
Leave the original clamp in place to hold the seatpin, and use the new one just for the rack.