I’ve recently bought a new bike with a 30.9mm seat tube, but have a gravity dropper 27.2mm seatpost from before. I have used it in the new frame once or twice with a USE shim and had no problems, but I am worried about potential damage to the new frame.

Should I be worried, or not?

I have been trying to sell the seatpost so I can buy a 30.9mm one, but with no luck as yet.

Thanks!

normal ‘rule’ is that as long as the shim drops below the seat tube/top tube/seat stay junction by a bit you should be ok.

Scott, for instance seem to say that using a shim invalidates frame warranty, though, so may be worth checking.

Anyone damaged a frame by shimming?

One of my bikes came with a shim from new and bitd the only way to fit a USE post was to use a shim so I’m sure it’ll be ok.

What bike is it fitted to? I would make sure on any bikes I had the shim extended below where the first tube intersected with the seat tube to give it the strength the designed expected maybe?

I have thought that if you wanted to make a longer shim just to make sure you could file the lip off a second shim and lightly glue it lower down the seatpost to provide the extra support. Never needed to do it so far though.

I use my 27.2 dropper in my ragly marly with a shim.
And swap it between that and the voodoo hoodoo I bought it for as I use the under seat lever option as I hardly ever drop it.

I use a cane creek shim, and had some concern the same as you when first doing this.
But read of people deliberately buying undersized posts and using with a shim as said post had the desired flex they wanted rather than a harsher more ridged bigger post.

Cheers guys, probably just worrying without any need to.