Bicycle Mechanics - Another BB question
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10-15-01, 09:47 AM
I've had this bike since last May, only have about 1200 miles on it, and the LBS says it needs a new bottom bracket. It was making a popping noise when I pedalled hard, and the mechanic says that I've simply worn it out. He says that big riders like me (6'3, 235 lbs) put quite a bit more strain on a BB, and that this is actually pretty high mileage for a comfort hybrid bike.
Even taking into account the fact that it's a pretty low end bike (Giant's cheapest model of Cypress), 6 months and 1200 miles seems like an awfully short lifespan for a bottom bracket. He's replacing it under warranty, so it won't cost me anything, but now I'm worried that 6 months from now I'll have to replace it again - and then I'll have to pay for it myself.
An interesting side note - the mechanic said that this BB is the longest he'd ever seen. He's having to special order it from Giant because he doesn't keep anything that big in stock. He says the frame is wider than usual, then with the triple chain ring on the bike it must have led Giant to use an extra long bb. I'm not sure how it could be relevant, but is it possible that this extra length has contributed to the shorter life?
Yes, it could. Most likely, since it is an unusual size, it's also from an off-brand supplier. ask at the shop if you are getting the BB from a recognised manufacturer. If it is such a strange size that you can't, this may be a part which will become unavailable in a few years.
Hard for me to believe. Only 1200 miles? Maybe the BB was very low quality thus it happened. I have never seen a BB give out in this short time. Maybe better to upgrade.
As far as the lenght - That is right being a triple crankset without much offset.
10-15-01, 11:22 AM
The mech at the LBS said that he would replace it with a better quality BB, but I assume he's going to order the replacement part from Giant, since it's their warranty that's paying for it. In that case, we probably won't get much choice as to manufacturer.
I'm actually hoping to use this as an argument in favor of just buying another bike. I think I under estimated the amount of riding that I would be doing, and I find I'm pretty annoyed by the low-end quality of other parts on the bike.
Surely my wife/financial adviser will see that I'd do better to get a new bike instead of replacing bottom brackets every 6 months. Of course, I hope she doesn't suspect that I'm replacing my bike every 6 months instead...
10-15-01, 01:35 PM
First of all, I, like you, am a bigger rider. I'm 6'0" and just this morning I'm down to 215 lbs. Yes, you will go through bbs more often, but 1200 miles is too soon. I suggest buying the tools and learning how to do this yourself will save you tons of money in the long run! BB tool maybe $15.00, crank puller maybe another $15.00, new BB another $30.00 (for a good one, less for a lower model) Initial cost $60.00, compared to the $50 - $55 the LBS will charge to do it for a cheap one! You can break even on the first one!
Secondly, the bb that was on your bike was probably below the bottom of the line. Manufacturers save money on places most people won't recognize. The bb is the first place to hide inferior parts. An upgraded bb should last significantly longer. For you I suggest staying with a LX or XT level. The XT is close to bomb proof!
Thirdly, (and I'm suprised D Alex didn't touch on this) that the longer lenght will increase the lateral forces on the bearings. The longer the lever arm (spindle length) the greater the lateral forces on the bearings. Once again, an upgrade should minimize these forces.
If you're looking for reasons to get a new bike, I think 1200 miles in 6 months on a hybrid is reason enough!
A logical person might think that a bottom bracket with longer spindles would use better/stronger bearings, but maybe this is not the case here. Yeah, an overlength spindle could hurt the bearing life, but there is really nothing you can do about the spindle length. If Shimano doesn't make the size you need, your choices may be very limited.
As far as cheaping out on components goes, the BB and the front hub seem to be the places where even "better" companies, such as Giant, do most of their cost-cutting.
10-15-01, 02:50 PM
Oddly enough, the LBS owner seemed surprised at the mileage - he said that people who normally buy the cheap hybrids may not ride 1200 miles in a lifetime (never mind that it equates to only about a 10 mile per day commute for 6 months). If that belief is shared by Giant, I guess they would try to save a little money in a place that ordinarily wouldn't show. While I don't expect pro quality components on a $300 bike, it does make me reluctant to buy another Giant. I also don't want another hybrid, but that's a topic for another thread.
What mileage could I reasonably expect from a decent quality Bb? Some of our more avid cycling friends are reporting up to 6000 miles or more this season. How often have they had to replace a bb?
10-16-01, 01:50 AM
Hmm, this sounds suspicious. Is the Bottom Bracket original equipment?
I have one original Sugino BB on my touring bike, which is 12 years old, and likely has 10,000 miles on it (original bearings). With regular maintenance, they will last nearly forever.
For a sealed BB, I have gotten as little as under 1000 miles on a super-fragile Dura Ace BB, to as much as (I'm guessing, here) 5000 miles on an Ultegra. Even my last "el-cheapo" BB, on a $300 hybrid, probably lasted 3000 miles, over 6 or 7 years.
10-16-01, 08:23 AM
Carl, I have a Shimano bb on my Cypress. I believe it is a 105. I didn't specify the bb at the time, but they were putting on a 105 crankset, requiring a new bb so I assume they used a 105. My LBS didn't have to special order it. As far as I can see, the bb shell is a standard 70mm wide. I haven't measured the axle length, but I am sure it is one of the standard standard triple lengths.
D*Alex, I hope I can get the kind of mileage you have on your old Sugino on the old 105 on my Bianchi. I really like being able to pull it apart, clean it and repack it to keep it going. I just did it recently strictly because the bike had been sitting idle for many years. The bb actually had almost no mileage on it. Next time I will replace the bearings with the high grade ones just so I know for sure what it has. It may have good ones now, but I guess there is now way of knowing.
10-16-01, 09:41 AM
Hey Hogwild, I wouldn't let your experience with a cheap BB prevent you from buying (or at least consider) another Giant. They're a good company and probably the best deal for the money right now. I imagine their choice of components is barely different (most likely better) than other companies at each respective price point.
10-16-01, 05:11 PM
Yeah, you're right - I just got carried away with my own rhetoric. I've heard too many good things about other bikes from Giant, and the Cypress gets pretty good reviews.
While I don't see myself riding a hybrid for much longer, there was no reason to slam the manufacturer. They're replacing the BB for free, after all.
Is a cartridge type BB replaceable with one that can be repaired/repacked? or does the frame have to be built for one or the other?
Modern BB shells are threaded to either English (35mm=1.375" diameter, 24TPI, self-tightening LH thread on the drive side) or Italian (36mm diameter, 24TPI, RH thread on both sides) standard, for which both conventional and sealed/cartridge BBs are readily available. To replace anything in the bottom bracket, you need to know your thread type (English for almost all non-Italian bikes), your spindle length, your BB shell width (68mm with most standard frame tubes, 73mm for many aluminum and other oversize frames, 70mm for Italian steel frames), and, for conventional BBs, your bearing cup thickness ("thick" or "thin") and spacing between bearing surfaces on the spindle. I have successfully (and extremely easily) converted two mountain bikes to cartridge BB bearings. The Specialized HardRock has a 68mm wide, English-threaded BB shell, whereas the aluminum-framed Ross Rock Machine has a 73mm-wide, English-threaded BB shell. Both took standard Shimano UN-72 cartridges, but with different spindle lengths.
The additional trick is to match the size of the spindle taper to that of the cranks, to ensure that the cranks seat properly. Although the taper angle is standardized, Shimano and Campy tapers end at slightly different widths, such that cranks often sit too far outward or inward on "foreign" spindles.
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