The Humble Square Taper

I've been mountain biking since I was seven years old and was in shops bothering surly mechanics in my teens and twenties. This is purely my opinion after wrenching in shops off and on for 30-plus years.

I give you the humble square taper bottom bracket, probably one of the most underrated pieces of bike tech.

What are some of the pros and cons of this old technology for attaching your cranks to your frame and, hopefully, having them spin for a long, long while?

The Pros

Back when mountain bikes had front derailleurs and three chainrings, manufacturers were cramming ever-larger tires into frames with shorter chainstays, and lots of different chainline spacing was experimented with.

Chainline is the distance between the centerline of the chainring and the centerline of the bike. A byproduct of all that experimentation is that there are lots of choices in spindle size, everything from 107 mm to 127 mm, with plenty of sizes in between.

For single-speed riders, that can be really great. You can get that super-nice straight chainline with a BMX freewheel threaded onto a hub, or get the cranks nice and close together. Some people call this Q-factor, the distance of the pedals from the centerline of the bike.

Another benefit is that the bearings in modern square taper bottom brackets are larger than some of the other options for cranks and bottom brackets.

Typically, you can also use one tool to remove about 85 percent of the square taper bottom brackets available, unless you want a blingy Phil Wood.

Solid older Shimano cranks are also widely available on eBay or at your local bike cooperative for not a lot of money.

Some people would consider this next part a con. I do not.

Square taper gets criticized for being flexible and not stiff enough. I think having a little flexibility in the drivetrain helps take some of the stress off other parts of your bike and your body. I've easily put 10,000 miles on cheap Shimano square taper bottom brackets.

The Cons

Proper installation is key, because it can cause problems if the bottom bracket or cranks are not installed correctly.

The two biggest installation problems are the bottom bracket not being torqued into the frame tightly enough and the crank arms not being tight enough.

For the crank arms, we're talking around 45 to 50 Nm.

Or, technically speaking, pretty damn tight.

There's also some debate about whether you should grease the taper or not. I've done both. Currently I don't use grease, because that's what Paul Price recommends with his lovely crank arms at Paul Components.

The important thing is getting everything installed correctly and properly torqued. A square taper crank that has worked loose can damage the taper in the crank arm, and once that happens you may have created a problem that tightening the bolt again won't fix.

There's Still Plenty of Life Left

Square taper is old technology.

That does not automatically make it bad technology.

You can still get inexpensive bottom brackets. There are plenty of good older cranks floating around. You can choose different spindle lengths to dial in chainline and Q-factor, and the whole system is simple enough that you don't need a drawer full of proprietary tools to work on it.

For a single speed in particular, I think there's a lot to like.

I think there's plenty of life left in the humble square taper, especially if you aren't hucking off a cliff or riding in the pro peloton.

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• single-speed