I have a 2020 Trek Farley 5, the seatpost is 31.6mm diameter. This clamp/collar is meant to replace the stock clamp, which means the inside diameter of this clamp needs to be large enough to fit around your FRAME at the seatpost, which in most cases, for a seatpost with a 31.6mm diameter, should be 34.9mm. My stock clamp IS 34.9mm inside-diameter, the clamp I ordered was a 34.9, but it is really more like 33.5mm.After reading a few other reviews where it was mentioned this being too small, I bought it anyways, because there aren’t exactly a wide selection of seatpost clamps for those wishing to install a cargo/trunk rack on our bikes… uh, anyways… I removed the stock clamps, pulled out the seatpost, and when I attempted to put this clamp over the frame… yeah no. I had to “put some back into it!” Then, the bolt that came with the clamp was roughly 5mm too short to thread through the clamp & wouldn’t even start threading, so I had to rummage through my parts to find a bolt. I finally got a bolt threaded, only to realize that I couldn’t get my seatpost back into the frame, even though the bolt wasn’t causing the clamp to tighten down…. I even removed the bolt completely and STILL couldn’t get my seatpost back into the frame.After fiddling around with it for a few minutes, I decided that I didn’t care about returning it, so I took my dremmel to it! I sanded the inside of the clamp, removing the paint… which was considerably thick, and then removed appx. 0.5mm of aluminum all around the inside, together I would say I easily removed 1mm. I then took some fine sand paper to it and smoothed it out, polished the inside a tiny bit, and all this allowed me to finally get my seatpost back into the frame. No, I’m not worried about my shaving off some thickness having caused any long-term damage or making the clamp weak. It’s thick enough that I’m not even remotely concerned, and the stock clamp is about half as thick as this one is anyways.*Oh yeah, this clamp only came with 1 bolt, the bolt that clamps down onto the frame. The two bolts for the rack mounts were nonexistent… not sure if it’s supposed to come with them or not, but the description does say, “Eyelets for rear rack, Allen screws included” as in, PLURAL… but there were none. Not a big deal, because I had extras with the rack I bought anyways.To anyone not wanting to dremmel their new parts, in this size (34.9mm) anyways, I suggest a different brand.

I love this product! It has allowed me to lower the seat on my ebike by about six inches. This is great! Now I can sit on my ebike without feeling like I’m going to fall over, all while retaining my rear basket and removing it’s ridiculous mounting point to my seat post.If I love this product then why only four stars? The mounting holes for the rear basket are far too close. They should be spaced about and inch or two further apart.Yes, they may require a bit more material to build them this way, but in doing so they can alleviate the stress that is placed on the hardware of your rear bracket/basket.Otherwise, it works as intended, and is a good alternate choose to seat post mounting.

I bought the 28.6mm version, fits O.D. of my seat tube ok. It has a wide internal ridge at the top (rests on the seat tube top) with resulting diameter ~26.4mm which will not accept my 26.8mm seatpost. This is on a thin wall bike titanium frame. I might return it, or might file out the ridge for clearance, haven’t decided.

Tight fit but worked fine with seat post and rack.