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I had my carbon road bike at service and the BB bearings (again) needed replacing, according to the mechanic, the drive-side one was hardly spinning and the other one also pretty much done with. Can't say I didn't see it coming since I had some noise before, so I accepted it.

However, I own that bike for 4 1/2 years and as far as I can remember, this was the second (or even third) time that the bearings needed replacement, plus one or two stops at the LBS during season where they just took the BB out tackling some noise, regreasing it and handing the bike back. I don't have the bills but even assuming 2 replacements means I'd get less than 10k out of one set, the bike has done about 25k in total, it is a Ridley carbon frame, FSA BB386Evo BB, FSA BB86 cranks.

Talking to the mechanic, I asked if that kind of bearing turnover is feasible and he said pretty much yes, it is normal that bearings wear out every couple of thousand kilometers, I could have it even worse on some Rotor parts lasting about 3000k.

I ride about 4000-5000 km per year, pretty much exclusively in dry conditions, no winter riding and on good, clean roads, so no particularly bad conditions for a bike to operate in. No jet wash or dirt riding that the usual seals shouldn't be able to deal with, in my opinion.

Is the mechanic's statement feasible or are they just trying to sell their part of the story so that they have a programmed BB service every 1 or 2 years? Shouldn't bearings last a bit longer? I looked around in some related posts here and think this shouldn't happen under normal conditions on a well-serviced bike...

I know that some of the renowned Bicycles SE users will soon reply with "Welcome to the wonderful world of Pressfit" but can I take their statement for granted or should I rather look for somebody else to look after my bike? Primarily another specialist bike shop willing to diagnose deeper issues such as uneven BB holes, causing a bad fit and eating away bearings for breakfast?

(I'm watching quite a few YouTube channels which are pretty invested in fixing BB issues for good but I'm afraid such experts are harder to get hold of here in Austria than in the UK or the US. My LBS wasn't like "yeah, sure let's try that next" and more like telling me that is the normal and I can expect such repairs regularly, it's part of the deal... not sure if I should buy that.)

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    The recurrent theme in said Youtube channels are the frame manufacturing tolerances. You cannot just take a tap and make perfectly aligned threads. The opposite cups are often slightly off. I would not be surprised if it led to premature wear and not just creaking - which is what most people complain about. Nov 10, 2023 at 15:29
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    I have not had any good experience with FSA bottom brackets. In my experience, the bearings wear out extremely fast. If your cranks have a standard spindle diameter, I'd recommend trying something like a Wheels Mfg bottom bracket - I doubt it'd be more expensive in the long run than replacing the FSA one over and over. If your crankset is one of the FSA "special" ones with a non-standard spindle diameter such as 24.07 mm, I'd recommend pitching the entire crankset and bottom bracket into the rubbish pile and getting something reliable and standard like a Shimano 105 crankset. Nov 10, 2023 at 17:24
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    @AndrewHenle I think it is still the original FSA BB with various iterations of bearings, the invoice line says "Bearings FSA BB86 to 386 Evo crank 30mm", I assume this is a 30 mm spindle then, so I guess I could stick with that (but throw the money on a quality BB next time around) or get an adapter for 24mm hollowtech + 105 cranks. I yet can't tell if shifting really sucks but I soon get a new bike with GRX and Shimano cranks for comparison. :)
    – DoNuT
    Nov 10, 2023 at 17:37
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    @DoNuT If this is what's installed on your bike, there's really no way for the bearings to be kept in alignment - that plastic tube in the middle doesn't have the strength to maintain alignment in any way. Something like this is going to do a much better job in assuring the bearings are actually aligned. Nov 10, 2023 at 17:44
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    My Kona Honzo (stew hardtail) goes through external bottom brackets (Shimano only) about every 6 to 9 months. Granted, it’s a hard tail in the Pacific Northwest of the US. So that’s probably roaching the BB every 25 - 50 rides :/ (and that’s being generous)
    – Paul H
    Nov 10, 2023 at 21:25

1 Answer 1

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Bearings should last for longer. Shimano's basic BB bearings should last for some time. Some press-fit shell configurations are more problematic than others. For example, PF30 has pretty narrow spacing. This increases the load on the bearings, which leads to worse average lifespan - but not every 4-5 thousand km. Alternatively, 30mm spindles in some press fit configurations don't have enough space for large enough balls, which reduces the load capacity and life (e.g. Trek's old BB92 and 30mm spindles, PF86 and 30mm spindles). I don't believe that BB386 EVO is a problematic configuration, however.

Speaking of tolerances, this condenses some of the comments that Vladimir and Andrew made. If the bearing seats are not round, then your bearings are getting squeezed at some point in the rotation. If the centers of both seats are out of alignment, the same thing will happen. That will accelerate failure. I suspect that this is the problem, although obviously we aren't there in person. If the bearing seats are aligned and round but are undersized, same thing. Remember we are talking about fractions of a mm undersized or out of round, or maybe 1 degree or less out of angular alignment. In theory, undersize issues can be corrected by carefully sanding the bearing seat.

I think that best practice would be to check the frame before installing. I don't know how many shops have the tooling to do this. You can use digital calipers on the bearing seats, but those will only detect problems related to out of round and undersize. After you install the cups, they should both turn smoothly by hand. I don't know if the store checked these things. I am not trying to throw them under the bus. They might have done so, but there was some other problem that cropped up. You can check out Mapdec Cycles YouTube channel if you're generally interested. The problem is that those guys acquired high-precision tools to check BB tolerance issues, and I suspect many stores don't have these.

I can't offer a satisfactory solution other than to try to find a store with experience diagnosing press fit BB problems related to tolerances.

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  • Thank you for the detailed answer! I guess it also makes sense that doing lots of climbing (and thus, out of the saddle efforts) worsens the problem because of the forces and often uneven pedal strokes. BTW: No worries, I was watching and referring to Mapdec. I guess a fresh set of bearings at least buys me some time to figure the next steps out, i.e. a shop that can deal with such issue. Do you think, just aluminium cups without sanding could be beneficial in worst case I struggle to find somebody competent? Will definitely approach the next caretaker with these inputs...
    – DoNuT
    Nov 11, 2023 at 0:24
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    I actually contacted Mapdec via their social media and asked for some quick advice: Check for "witness marks" on the crank. Unfortunately, I don't have the tools to take the crank out but that calls for checkup next year before putting hard rides and big miles on next year.
    – DoNuT
    Nov 11, 2023 at 8:11
  • Another interesting take from Mapdec: Throwing in aluminum without fixing the frame would make the problem even worse because it takes away the compliance/wiggle room, so my options are to keep spending on bearings or find a specialist to get to the bottom of it (no pun intended). Leaves me with the question what is the most cost-effective approach, it's not a expensive bike...
    – DoNuT
    Nov 11, 2023 at 18:08

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