New Seatpost Shim Size: 30.9 to 31.6mm
New and in-stock: our 30.9 to 31.6mm seatpost shim (ST0931). Now, we know not everyone gets all warm and fuzzy about shims and spacers like we do, but this one's particularly exciting. Why? First, it's a different post size than we've worked with before (all our other shims are for 27.2 or 25.4mm posts. Second, this is one of those times where we get to deliver on our promise to you: we recieved numerous requests via the website for this spec.
30.9 and 31.6mm posts are common with the mountain bike crowd. If you've go a 30.9mm adjustable seatpost that you dropped $350 on last season, do you really want to have to buy another one just 'cause your brand-spankin' new frame has a 31.6mm seat tube? Hell no. We tested the shim with a wide variety of posts, a few of which are shown here, with brand names obscured (for no real reason):
And then, the stinker:
This one was super-tight. All others we looked at installed with a breeze, this one, however, would've required multiple jars of elbow grease. When you take the calipers to a seatpost, you'll find plenty of variance—common, because all manufacturing operates within a certain tolerance to the specs. What manufacturers call "30.9mm" actually ranges between 30.85–31.05mm in the posts we tested. Some were even slightly ovalized, measuring differently depending on where on the circumference of the post the calipers were placed. When you're talking about a shim that's only 0.35mm thick, with its own tolerances, sometimes things just won't work together. And that's before we even consider the tolerance of the frame.
For the best results, here's how you want to install the post:
1. Make certain the seat tube is clean and clear of debris. Wouldn't hurt to take the flex hone to it, if'n you've got one:
2. Install your seatpost clamp loosely
3. Install the shim, make sure it's flush around the top of the seatpost clamp
4. Grease, grease, grease
5. Install the post per the manufacturers' specs.