Originally Posted by Avalanche325
ruirui,
The shim makes up the differance between the size of the seatpost and the inside of the seat tube.
Pull your seat post out and look for the size stamped on it. I would trust that more than a measurement, unless you used calipers.
Avalanche325, i've checked my seat post. it has 30.4mm stamped on there and total length is 95mm, i think. but for sure it's 30.4mm. so should i just get a seat post suspension with 27mm or 29mm? would i still need a shim?