In this installment of our ongoing series on upgrading components, I provide tips, tricks and even one big consideration related to the job of installing a new bottom bracket and crankset. Because this is a lot of information to digest at once, I’m breaking it into 2 articles, the second of which will follow in Part 4 of the series next week’s issue.
I like to think of the crankset and the bottom bracket, as the heart of the bicycle. Your frame and wheels are important, but without a crankset and bottom bracket you wouldn’t be able to pedal your bicycle down the road. And, there’s a connection with how fast and hard your heart is working to power and turn the crankset.
So that you know what things are called as you’re reading directions – and can also talk to your bike shop using the right names – let’s start with a glossary of basic terms you might run into.
Brief Bottom Bracket and Crankset Glossary
- Bottom Bracket (“BB” for short): this term is used to refer to both the bearing mechanism and the part of the bicycle frame that it fits into
- Bearings (sometimes called Cartridge and/or Sealed Bearings): what the crankset spins on
- Axle or Spindle: the shaft the crankset attaches to, often integrated into the right crankarm – or both crankarms
- Bottom Bracket Cups: these hold the bearings and fit into the frame, though some new BB designs don’t use actual cups (see Press Fit Bearings)
- Press Fit Bearings: bearing that are a friction fit inside the bottom bracket of the frame versus the cup-type
- Crankset: the entire assembly – crankarms, chainrings and bottom bracket
- Crankarm: every crankset is composed of two crankarms
- Right/Left Crankarm: the one with the chainrings/the one without
- Chainrings: the sprockets attached to the right crankarm
- Spider: the part of the right crankarm that the chainrings bolt onto
- Chainring Bolts and Spacers: the chainring attaching hardware
This week’s resource
Perhaps the most challenging thing about crankset and bottom bracket upgrades is figuring out what kind you have on your bike. But, that’s all-important in order to purchase the right one for easy installation. To help, here’s a nice reference by Park Tool. Be sure to get the correct type for your bicycle. If you can’t figure it out, bring your bicycle into your favorite shop so that they can sell you the right parts.
Considerations for Crankset/Bottom Bracket Upgrades
Consider this before purchasing a new crankset
Because cranksets are among the most expensive components, you can save a big chunk of money (the cost of upgrading to the latest components group) if you can keep using your current crankset. Note that it won’t match the look and style of new parts because the makers typically redesign them and add features with each upgrade.
But, if you’re frugal and your crankset and bottom bracket are still in fine shape, you might want to keep it. It depends on what you have and what components you’re upgrading to, but in manycases you can get away with it. For example, I run a nice old 9-speed crankset on my newer 10-speed components.
You might hear that that’s not possible because the more speeds the drivetrain has, the narrower the chain is. Which suggests that the new 10-speed chain is too narrow to work on my 9-speed crankset.
While this used to be a problem with some cranksets (the chain could tend to drop between the chainrings and even get jammed), most modern drivetrains can be adjusted to work fine with the narrower chains. So, if you’re on a budget and want to try to avoid the cost of a new crankset, you should try it and see if it works and only buy the new crankset if it’s required.
Reasons to go for the upgrade
Usually if both chainrings and the bottom bracket are worn out, you might as well upgrade to the new setup rather than buy all the parts for your old unit. Besides getting something that matches the rest of the parts, you’ll know you’re hammering on brand-new crankarms, too. On an old crankset you never really know how much strength is left. And yes, riders do break crankarms, once in a blue moon (I have).
Tip: When you’re walking next to your bike and lifting it over things like curbs and steps, pay attention to your crankarms! If you don’t, you can strike the ends of the arms on things, which can create a weak spot right at the pedal axle and could cause a crack or break eventually.
Once you decide to upgrade your crankset you get to change some cool things if you want to, too. You might want to try different gearing, like the new popular 52-36 sub-compact (or “semi-compact”) gearing. Or maybe your bike fitter recommended different length crankarms to smooth your pedaling or add power. Now’s the time to try it out.
Don’t forget to come back next week for the 2nd half of this article, when I’ll walk you through the process of the upgrade.
Jim Langley is RBR’s Technical Editor. He has been a pro mechanic and cycling writer for more than 40 years. He’s the author of Your Home Bicycle Workshop in the RBR eBookstore. Check out his “cycling aficionado” website at http://www.jimlangley.net, his Q&A blog and updates at Twitter. Jim’s streak of consecutive cycling days has reached more than 8,000. Click to read Jim’s full bio.