Jim’s Tech Talk
By Jim Langley
This week’s topic comes from RBR subscriber Kevin Meyers, who asked:
“I have an 11-year-old Co-Motion Robusta tandem. I have used it for racing and training. Should the bottom brackets be replaced after so many miles? So many years?”
Because they’re such hard-working components, whether it’s time to replace bottom brackets in any road bike, be it a single or tandem, is a great question. So I’m sharing what I told Kevin.
Bottom Brackets Let the Pedals Go Round
If you’re unfamiliar with the term bottom bracket (commonly called the “BB”), it’s the bike part that the crankset is attached to. Because it’s mostly contained inside the frame it’s hard to see.
So, here’s a photo pointing out one of the bottom brackets on a 2020 Co-Motion Robusta so that you can get an idea what it looks like and does.
The cups of the BB hold the bearings. And the bearings are what allow the crankset to turn when you’re pedaling. On a tandem bicycle, there are two cranksets and two BBs. And because two cyclists are aboard, there’s twice the load cranking on the BBs.
Takes a Licking and Hopefully Won’t Start Ticking
But, all BBs have to withstand a lot of abuse. Which is why BB noises such as ticks, clicks, creaks and clunks are among the most common bicycle glitch.
They result from all kinds of things that go wrong from the massive force of cyclists stomping with all their power (and all their weight when standing) on first the right and then the left pedal.
Over time, and over countless revolutions (consider that in only an hour you’ll pass 5,000 revs) this force can loosen things, wear out and even break parts. So, it’s a good idea to listen for any noises and fix what causes them if they occur.
Check Your BB Regularly
Plus, even if your BB stays silent, it’s a good practice to do a couple of routine checks at least yearly. If you ride in the snow, rain and dirt, which all attack BBs, you should check it at least twice a year.
Checking BB Health
Test 1 – feel for play
The first test is easy to perform. It’s a check to determine if any side-to-side play has developed in the bottom bracket. If it has, it could mean that it’s wearing out, or in a newer BB, it might only mean something has loosened and needs tightening. In an old bottom bracket, play can mean that the lubrication inside the bottom bracket has dried up and is no longer working.
To check for play, stand beside the bike and rotate the crank so that the pedal nearest to you is at 6 o’clock, which will put the away pedal at 12. Now, hold the crankarm closest to you with one hand, reach through the frame and hold the other arm with your other hand.
Holding the crankarms (not the pedals) firmly, push and pull to try to rock the crank inside the BB. If there’s play, you will feel movement and possibly a little clunk. If you find it hard to hold both crankarms, you can alternatively try pushing and pulling the crankarm positioned at 12 o’clock toward and away from the bike frame while holding the frame with your other hand.
In a properly fastened BB, you won’t feel any play when you do this test.
Test 2 – Feel for lubrication
The other test is to check how the crank(s) spins. In a nice new BB, the crank will spin smoothly with a slight resistance from the lubrication (typically grease) inside the BB bearings.
The way to feel for this is to lift the chain off the chainring and move it away from the crank so that you can turn the crank freely (no drag or rubbing from the chain). When you turn the crank, hold it gently and turn slowly so that you can feel how much resistance there is in the bearings inside the BB. If there’s enough grease in the bearings, the grease will slightly resist turning.
When you do these two checks, you’re hoping to find no play in the BB and also a nice-turning crank without binding or roughness.
If you have play, binding, roughness or worse (like grinding from corroded bearings), you’ll want to remove the cranks and investigate further and repair problems. Because you don’t want to risk a failure out on the road. But, also because even if the failing BB allows you to keep riding, it’s slowing you down and making you less efficient whether or not you can feel it.
11 years on the same BBs?
Back to Kevin’s question. Since he said he’s been training and racing on his BBs for 11 years, I assumed he hasn’t had any noticeable trouble yet. Which is pretty amazing considering how tandems torture bike parts.
But, at the very least, even if there aren’t any telltale signs, I told Kevin he should try to determine if the lubrication inside the BBs is still doing its job. The crank spin test is how to feel for this. But, you can’t always feel it through the crank.
So, an even better test is to turn the bearings with your finger to feel it. To do this means accessing the BB bearings, which means removing both cranks.
When in doubt, go to the source
The fact that Kevin hasn’t had to think about his BBs for 11 years could mean that Co-Motion sourced some incredible BBs for their 2009 Robusta tandem.
But, I couldn’t find a mention of the BBs they’re using on their bikes today or when I searched for specs on their 2009 model that Kevin owns either. So, I told Kevin that he should contact Co-Motion and ask them his question.
There’s no one who knows more about his Robusta than Co-Motion. So if he needs special tools or instructions for checking his BB bearings, they’ll let him know. And, if indeed, I’m right and he should replace them, Co-Motion will surely know what he should buy and how to install them correctly, too.
Here’s Co-Motion’s Contact Us webpage: https://co-motion.com/pages/contact-us. And here’s their full line-up in case you’re in the market: https://co-motion.com/collections/tandem-bikes.
Feel free to weigh in with your tandem BB advice for Kevin by leaving a comment.
I’m not a professional mechanic so I could be wrong about this, but I have bike with over 200,000 miles on it, and most of those was mountain road riding, and the BB has never been replaced and it still functions fine to this day, even the bearings have never been replaced, but I kept those cleaned and lubed quite a bit, but the most you should ever have to do is replace the bearings, the rest of the BB should be fine for many years. While I don’t ride a tandem it shouldn’t matter because there is only one person per BB just like a road bike.
Mark Follmer says
in 10 years/40k miles I have replaced the bottom bracket on my titanium/Ultegra 6700 road bike at least 6 to 8 times.
Kerry Irons says
The question “when should I replace” comes up all the time, but there really aren’t useful guidelines because component quality, riding conditions, maintenance, etc. all factor heavily. So the advice her can be extended to just about any component: examine it to see if there is play, if there is excessive friction, if there is binding, if there is roughness. Just about any part on a bike can be evaluated in this way. Replace/repair things when they need it, not by some arbitrary check point.
And to Mark Follmer: you might want to examine things to figure out why your BBs fail so quickly. Something’s not right there.
Tim Potter says
FWIW, I’m pretty sure the longevity of a BB depends on the quality of it, how well it’s sealed, if it’s a loose-ball bearing old-school style or sealed cartridge or outboard bearing/ press-fit style. They all have different life spans not to mention are designed to be serviceable or simply replaced when they go bad. Our shop works on mostly low-end bikes that start life with loose-ball bearing old-school style BBs; they typically loosen up over time and the owners continue to ride them til they practically come to a grinding stop before they seek a repair. We then have to deal with the years of neglect, rusted in cups, etc. They’re some of the worst, most challenging repairs we have to deal with. I believe a well-maintained and occasionally overhauled loose-ball bearing BB can last the life of the owner of a bike, but the industry has moved towards sealed units which are mostly disposable after they get contaminated w/ water and mud, etc.
Mark Follmer says
Thanks for the fast reply!
My theories as to why my bb’s fail:
1. I’m big (210 lbs)
2. Long crank arms. For many of those miles I had 180mm crank arms. I decided that didn’t make much difference, so I went back to a 175mm crank. Still pretty long.
Long crank arms > more force on the bearing.
3. How are you supposed to lube a Shimano BB anyway? And when I’ve taken them out, they still had lube.
4.. They are basically a throw-away/disposable design.
5. I demand a silent bike.. When the bb starts to click/clunk I get a new one. I’m getting pretty good at changing them out..
6. Wet and gritty conditions for much of the year. (?)
David Kamp says
Tandems are hard on BB cartridges and other components. My 12 year old Calfee tandem (30,000 mi) has seen at least 3 BB cartridge replacements, as well as other components. We’re not unusually strong, and my single bike components last forever. BB is 68 mm BSA (did I spec that right?). First two or three sets: Shimano UN72. Changed cranks (DaVinci) to get shorter crankarms, 170 and 150 mm, and installed Phil Wood cartridges, which have held up well, with only one bearing replacement so far. Nice thing about Phil Woods is that cartridge bearings are replaceable. Chain: 1000 mi max. Cables: replace OFTEN (thousands of shifts fray cables). Disc brake (Avid BB7) pads: replace OFTEN (tandems weigh a lot). Tires: huh, often.
Jim Langley says
Thanks everyone for sharing your comments and expertise with Kevin!
Rick Schultz says
The quality of the BBs is the driving factor. Enduro BB bearings that manufacturers pay $0.25 each will be worn out riding your bike from the bike shop to your car.
SKF bearings, highest quality in the world, used on Ferarri F1, MotoGP bikes, etc, are $150 per bearing but will last many many years. You get what you pay for in bearings.
Paul Ahart says
You took, the words right out of my mouth about SKF bearings. 60,000 mile/100,000 kilometer warrantee. All stainless steel with very substantial seals. Grease stays in, dirt/water stays out. Fantastic bottom brackets.
I have found that good old Shimano UN55 bottom brackets, at least on single bikes, hold up remarkably well, far better than the new lightweight stuff. You sacrifice durability for weight savings. Being in the business, I could have whatever I want on my personal bikes. I’ve sacrificed a bit of weight savings and gone with bullet proof durability. No argument.