All along, single speeding and 29 inch wheeled bikes have seemed to be like “pie and ice cream”, like they just belonged together. Certainly there are reasons for that, but since a preponderance of single speed mountain bikes are 29″ers these days, it has come to my attention that the method of chain tensioning is not at all agreed upon, nor does one method go hand in hand with 29″ers.

Let’s take a quick look at the contenders for the tensioning job and point out some pros and cons.

raleighcxss 011
A stainless steel faced track end.

Track Ends: Track ends, or horizontal drop outs, are the oldest method of tensioning a chain for a single speed drive train on a bicycle. It is extremely effective and extremely simple. Most commonly used on bicycles built to be ridden in velodromes, or “tracks”, the track end got its name from this use, but now you see this type of drop out in wide use today on fixed gear bikes and some mountain bikes. Track ends require the use of bolt on axles for the most part.

Pros: As stated, these are simple. There really isn’t much you can do wrong here, unless you get the wheel bolted in crooked. The track end is mechanically sound, and speaking of sound, it is silent in use. They are durable too, and with no moving parts to get lost or futz with, these seem to be the perfect solution to tensioning a single speed bike, unless………..

Cons: Well, unless you are running disc brakes, have trouble with slipping the axle forward, and if you want to have the versatility of running gears. Disc brakes are really the biggest problem here. (Karate Monkey owners all say “Amen!”) When you change gearing on a disc braked single speed with track ends, you also have to adjust the rear brake caliper. This also may or may not come into play while removing a wheel, where some issues may arise with getting your rotor to clear the caliper. Sometimes loosening the rear caliper is necessary. Another con is having to use a chain tug, which is necessary if you are getting axle slip. This adds complexity to what is supposed to be dead simple. Not a deal breaker, but also not great. Finally, running geared will require some sort of additional piece on your drop out to accommodate a derailluer, or if the frame is like a Karate Monkey, and has a integral derailluer hangar on the drop out, you may need to use a special “plug” to keep the axle from moving from the ideal position in the track end. More futzing! Not to mention the fact that you probably will need to carry a wrench to remove the wheel anyway.

osblackbuckg-teds 008
Eccentric bottom brackets come in many variations. Here is a split shell type.

Eccentric Bottom Brackets: No, we’re not discussing bottom brackets with odd behaviors, this refers to an insert in an oversize shell with an offset threaded aluminum hole that you thread a traditional bottom bracket into. This then can be rotated, and effectively “swings” the bottom bracket in an arc that can be used to tension a chain. The method of securing the aluminum insert into the over sized shell that is part of the frame varies. Some use an internal expanding wedge, like a Bushnell eccentric bottom bracket. Some use a “grub screw”, or pinch bolt that essentially pushes the eccentric into the frame from one side. Then there are split shell eccentrics which, as the name implies, have a split outer shell that is fitted with threaded bolts that pinch down upon the aluminum insert, preventing unwanted eccentric rotation. All use a traditional vertical drop out in the back that allows for easy wheel removal and the use of quick releases.

Pros: Eccentric bottom brackets allow for the use of a traditional drop out in the rear of the bike which means you can use a traditional quick release instead of a bolt on axle. No chain tensioners, no messing with disc brakes, and if the drop out has a derailluer hanger, conversion to a geared set up is a breeze. So, why isn’t this the best method?

Cons: Eccentric…creak…bottom brackets can….creak!…be noisey, which can be rectified, but usually requires a tear down of the bottom bracket assembly. Not easy. Sometimes they are prone to seizing up, which can be really annoying, and the opposite, slipping, is also an issue. Some eccentrics, especially the pinch bolt type, can cause a frames EBB shell to ovalize, thus ruining the frame. Not to mention that in general, frames are heavier with an eccentric bottom bracket.

Siren+Song+Dropout
Sliding drop outs, like the one shown here, have been widely used as a chain tensioning solution for single speeders.

Sliding Drop Outs: As the name implies, these drop outs move, or “slide” in a slot to achieve tension on a chain. Like the eccentric bottom bracket, sliders allow for the use of a quick release. There are several versions of sliding drop outs in use, but in principle, they are all basically the same.

Pros: Sliding drop outs can be set up to have the brake mount be part of the slider. This makes for trouble free wheel removal. Of course, a quick release can be used, and adding a slider with a derailluer hangar is usually an option. So why aren’t sliders the way to go?

Cons: Sliding drop outs can slip, making your chain tension go slack, and can cause you to throw a chain. Not only that, but on bikes with tight tire clearances, a slipping drop out can cause contact with the tire and frames chain stay. Getting a slider to stay tight requires extra washers sometimes, and getting enough tension on the slider bolts without stripping out threads or rounding out bolt heads can be tricky with some designs. Sliders look clunky to some, with the bolts and modular pieces breaking up the lines of a traditional seat stay/drop out/ chain stay look. Some designs are cantilevered out from the junction of the seat and chain stay to the point that breakage of the frame is a concern.

Conclusions: While each style of single speed chain tensioning mentioned here is popular, not one can be agreed upon, and each has its detractors and fans. All are in use on 29″ers. I have used all three extensively and in several variations. I have experienced problems with all three, and have had great success with all three on separate bikes. In my opinion, I like the EBB or slider best because I can use a quick release. Of those two, I like the way an EBB system looks the best, but I have ridden creaky EBB’s that drive me nuts, so that isn’t always a great way to go. That said, in my opinion, my choice for the best chain tensioning device is the split shell eccentric bottom bracket. I do like several sliding systems, and the new style that will be coming on the 2010 Superfly SS is very intriguing. That said, I’ll be happily single speeding on about any of these styles of chain tensioning devises on any given day! They are all great when they work, and besides, I like bicycles!