MKS BMX Chain Tensioner 10mm w/Allen Key. for 8mm Thick dropouts

These work extremely well, but read the specs and follow the directions. This is for an 8mm (or slightly narrower) rear-facing drop out (aka track fork end). There is a different 5mm version suitable for some frames. I used this to setup a folding fixed gear bike on a Dahon Speed Uno frame. Note the directions call for the washer to go INSIDE the fork ends, although it is possible to use it on the outside with slightly reduced holding power (slightly reduced because the serrations on the axle nut tend to be broader and more aggressive than those on the cone locknut against which this is supposed to sit. That said, people seem to love to argue about this, and other designs, e.g. the Surly Tuggnut, are designed to sit on the outside under the axle nut, so both approaches are viable). Mounted on the inside will add a bit to your O.L.D (over locknut dimension)., though steel frames can be bent open a bit without a problem to accommodate this, and can be resized with more aggressive bending to hold the larger spacing neutrally, though this may be best left to your local bike shop. Mounting on the inside also allows compatibility with a quick release system, though the Surly Tuggnut design has its own solution for this with outside mounting, and does have the advantage of being faster to install/remove (by not wrapping around the whole fork end), so you might consider that as well.

This is a very well made little gadget and the chain adjustment is quite fine. For example, a 1/8 turn of the allen wrench makes a big difference in chain tension. Be sure to rotate the crank several times and check the tension along the entire length of the chain. Chainrings are rarely perfectly centered so the tension will change as it rotates.The description says that these are "10mm.... For 8mm thick dropouts". The 10mm refers to the slot where the axel fits. If you use a 15mm wrench to tighten your axle nuts, then this is the size you need. The 8mm refers to the actual thickness of the frame at the end of the dropout. 8mm is probably a nice fit on most aluminum frames, but best to check your bike before ordering.As you can see from the official photo, the base slips over the ends of the frame.

I have used several chain tensioners on my single speed santa cruz chameleon and have had very limited success. I usually lose tension within half an hour of hard riding ( single speed is a 42 x 12 so I really have to crank on the pedals to get the bike going).Luckily this clever MKS tensioner has solved my problem! Highly recommended for anyone that wants an effective, neat and clean looking set up for their single speed. Worth the money!

I like the design on this, but I tried to use it on my Black Market Edit One, and the drop outs are too short, like they likely would be on most BMX bikes, so buyer beware, if you have the currently trendy (stupid) ultra short dropouts, this wont work!

Doesn't look like much. But is rock solid, easy to fine tune. Fits beautifully in my Surly Steamroller.

While you can get some chain tensioners for much cheaper ($3-10), this MKS tensioner is worth it. The allen key bolt keeps everything nice and flush, and the telescoping design gives you a pretty good range. It does only come with one per package, but two is optional, not required. If you decide to just use one (drive side), once you work out the optimal chain tension, slightly tighten the axle nut on the drive side, make sure the wheel is centered, then tighten up both sides.

Perfect!One of my dropouts was oddly wider than 8mm, so I used a dremmel to widen the chain tensioner to fit. Having two is the way to go. Once the second was in place, tightening and straightening my wheel was a breeze.

This is the best you can get

The most amazingly well made and precise chain tensioner ever made.