By Jim Langley

This week’s Tech Talk is based on my response to another excellent reader question. It came from an RBR reader named Jay who asked about modern bottom brackets, which employ sealed cartridge bearings.

They’re a bit of a mystery to many roadies since there are no obvious adjustments to make. This week I’ll try to unravel the mystery so you know what you’re dealing with and how to care for them.

Jay wrote: “I had a 9-year-old Race Face square-taper sealed cartridge bottom bracket with at least 18,000 miles on it. I finally noticed that the cranks felt different when pedaling and that there was side-to-side play. I had also been experiencing front derailleur rub for at least two years but thought it was my "flexy" steel frame. I had my LBS confirm that the BB had lived a good life, and had them install a Velo-Orange Grand Cru model. Pedaling felt normal again, and there was a distinct absence of front derailleur rub. My question is, How can you tell a bottom bracket requires replacement before allowing it to get so worn that you can feel it while pedaling and suffer issues like rubbing and play?”

Bottom brackets 101

Before I answer Jay’s question, I should explain how bottom brackets became the somewhat mysterious black boxes they are today.

If you’ve been riding for awhile you may remember that the standard road BB used to be a 3-piece design composed of a bottom-bracket spindle that the crankarms attached to (also called an axle), held in place by 2 cups that threaded into the frame. In between the spindle and cups were 2 sets of ball bearings allowing the spindle and crankset to spin smoothly inside the cups.

With the right bottom bracket tools, you could adjust these 3-piece BBs, take them all apart to clean and inspect the parts and bearings, and replace individual parts if needed when things wore out. You usually had to do this once a year – if you were lucky.

A lot of mechanics and roadies liked the easy maintenance aspect; however, it also meant that when you were riding, the BBs could loosen and cause problems. Also, it meant that proper installation and adjustment required skill and could be done incorrectly, leading to breakdowns on the road or worse, halfway into that century you trained for for so long.

Tip:  Whether you have bikes with 3-piece BBs or modern sealed cartridge types (keep reading), I recommend buying the basic tools needed to work on them and learning how to use them. It’s not a complicated job, and the tools aren’t expensive. The easiest way to pick up the right tools is to ride by a bike shop on the bike with the bottom bracket you want to work on, and ask the mechanic to show you which tools you need to buy. Once you have them, you’ll be able to install a new BB by following the instructions that come with them.

Sealed Cartridge BBs

To fix the limitations of 3-piece BBs, the bicycle industry responded by replacing them with sealed cartridge bottom brackets, which come in many styles but are designed to all but eliminate maintenance and breakdowns. That is because they employ sealed and basically adjustment- and maintenance-free bearings.

It’s not exactly accurate, but you can think of these sealed bearings as the old-style cup and bearing made together, which is why they are called “cartridge” bearings and BBs.

The idea is that the bearings are permanently lubricated and adjusted for life when they’re made at the factory. And the cartridges are pressed into the bottom bracket or the BB cups, or into the frame itself, depending on what style of sealed BB you have on your bike.

Replace don’t fix

But the biggest difference with the sealed cartridge BBs is that they are designed to be replaced when they wear out rather than being fixed. In comparison, the 3-piece BBs were designed to be disassembled, inspected and repaired by replacing individual worn-out pieces.

When sealed cartridge BBs came out, a lot of us worried that we’d be replacing them all the time and they would prove much more costly than the tried-and-true 3-piecers. But time has shown that a quality cartridge unit will last for at least several years with zero maintenance (consider the 18,000 miles it took to wear out Jay’s). Plus, they’re easy to install, run smoothly without any fussy adjustment, usually require no maintenance and, best of all, aren’t overly expensive.

Tip: We tend to think of sealed cartridge BBs as something new; however, it’s a time-tested and proven design going back at least 70 years in cycling and much further in machine tools and motors, etc.

Back to Jay’s question

I replied, “Thanks for the question, Jay. I've seen the same thing happen to lots of cyclists. Our legs are so strong, and pedaling is so easy and fun, it's often only major problems that really get our attention. An extreme example I remember is when I fixed a top woman racer's bike on the eve of a huge race. She said it was running great.

I routinely checked it over and found a problem straight away. Her bottom bracket bearings were rusted so badly that you couldn’t even turn her crank by hand, but only by forcefully pedaling.

She had no idea at all because it had gradually worsened and she was so strong she didn't notice. Many cyclists would have felt this, but the fact that she didn’t is a good lesson to check your equipment by hand, don’t judge by how it feels riding it alone.

And, paying more attention like this is the only way to avoid BB issues. A good way to do it is by setting a schedule for checking the bottom bracket. For most riders, once every month or so would be a good interval, if you're riding every few days.

How to check your bottom bracket

To do it, you just lift the chain off the chainrings so that the crank can turn freely. Then you turn it by hand nice and slowly and see if it turns smoothly with a slight hydraulic resistance from nice grease inside the bearings.

Next, you grab one crankarm with one hand, reach through with the other hand and grab the other arm and push and pull sideways. You are feeling for looseness or play in the cartridge sealed bearing BB. There shouldn't be any.

If there is, you want to figure out why. Usually, it’s as simple as something coming loose, like a cup or bearing, and tightening the bottom bracket will fix it. Sometimes it means the grease is completely used up and the bearings are wearing. In that case you usually replace the bottom bracket, which on modern units is not that expensive and pretty easy to do with basic tools. Or a shop can do it for you for not much money, too.

Tip: I like to keep the correct replacement BB on hand in my toolbox just in case I need it in the days before a race and don’t have time to get down to the shop. This practice has also saved the day for teammates when they realized theirs was shot at the last minute and I was able to set them up with my new BB.

Other checks to make

While you’re checking your BB, Jay, there are other things to check since they can cause problems, too, and they’re easy to inspect with basic tools. Make sure that all the bolts, both the ones holding the crankarms on and the ones holding the chainrings on, are tight. If you have a triple crankset, there are chainring bolts on the inside to check, too.

While you're checking that things are tight, it’s good to make sure the pedals are tight, too, since they sometimes loosen or weren't on tight enough to begin with, and loose pedals can cause problems, too.

I hope these tips help you get even more than 18K out of your bottom bracket!


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.

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