I have 3 bikes (2 mtb 1road) all with different seat post diameters. Has anyone used shims. I have 1 favorite saddle. I can buy 2 shims for the fraction of the cost of new saddles. Just switch seat and post in seconds. Quick angle adjust when needed. Am conscerned about post or frame damage. Will go from 27.2 to 31.6 and 30.9. Can only ride one bike at a time!!
The shim will not damage either your frame or seatpost if it is of decent quality in my experience. Look for shims with a small lip at the top to ensure that the shim does not slide down into the frame. Use a "safe" lube on both the inside and outside of shim to prevent seizing.
I'm not sure how much of this is in my head or reality, but I seem to have to pay more attention to keeping the seat post bolt fastener "tight" when I use a shim.