Bottom bracket types

geoff_ss

I'm intending to build a lightweight day touring bike. Most of my riding will be in hilly/mountainous areas so I intend to fit a 44/32/22 ATB chainset. I'm a bit out of touch and I see that some chain sets have a splined bottom bracket rather than the once more common square taper. What are the advantages/disadvantages of the splined over square taper?

thanks

Geoff

Monty Dog

I'd base your BB on your choice of chainset - particularly as external BB's are pretty well becoming the norm i.e. instead of the bearings and axle being a seperate unit mounted inside the frame, the cranks and BB are designed as a 'system'. The crank spindle is permanently mounted to the crank spider and runs in sealed cartride bearings mounted in cups screwed into the BB shell. The non-drive crank is then secured to the other end of the spindle - which usually has a splined fitting. The advantages are a big reduction in weight and increased stiffness. The larger size of the external bearings should improve bearing life but is offset by increased exposure to muck and water - bearings are relatively cheap and easy to replace though. Probably the best design is the Campagnolo Ultradrive which is well engineered and a lot lighter than a traditional design.

geoff_ss

Thanks MD

Ah, so that's what 'external' BB means! Are they ball races or cup and cone types with separate balls? Sounds a good system. I've almost decided on a van Nicholas Yukon (Audax) frame set it's components I'm thinking about now.

I like Campag stuff but it doesn't meet my needs. I have no use for a 50/52 chainring and I also need to fit a flat handlebar and all Campag brake/shifters are for dropped bars. I think they abandoned ATB components some years ago, unless they've changed recently. My neck and shoulders have to be considered, unfortunately

Geoff

gundersen

and all Campag brake/shifters are for dropped bars.

not exactly true
Campagnolo do have flatbar shifters and triple chainsets in 2008

gundersen

and all Campag brake/shifters are for dropped bars.

not exactly true
Campagnolo do have flatbar shifters and triple chainsets in 2008

geoff_ss

Thanks gundersen.

That's interesting. I, perhaps irrationally, prefer to use Campag becaue it was always what seemed out of reach when I started out. I'll look and see what's available when I go to see the frame. The management has approved a reasonable spend level - probably because she wants to get me back on a bike and join her. I suspect she wants me back on the front of the tandem too

Geoff

jpembroke

With regards your original query about BB types, I have attempted to summarise the merits of the various systems below:

Square taper: high durability, low stiffness (large bearings, narrow spindle)
Splined: low durability, high stiffness (small bearings, wide spindle)
External: high durability, high stiffness (large bearings, wide spindle)

Well, that's the theory anyway. For what it's worth, I'd steer clear of splined BBs (octalink and ISIS). I have to change the one on my MTB every year whereas the square taper BBs in my race and cross bikes seem to just run and run. Personally, I'd stick with square taper: It's cheap, simple, durable, and dependable - perfect for touring. Plus, there are loads of cheap chainsets available if you go down the square taper route. Having said that, you can now get a Shimano Deore MTB chainset with external BB for £45, which is a bargain.

geoff_ss

Thanks for that jpembroke. That's just what I was looking for. I have had problems with square taper cranks but usually only if they come loose on a ride and then wear. I have also known them to crack round the crank bolt (TA 49D IIRC) I may well try the external bearing type.

Geoff

Monty Dog

External BBs generally use sealed cartridge bearings which sit into machined cups which screw into the frame BB shell - they are not usually serviceable, although prising the seal off and giving them a clean and regrease can sometimes bring them back to life. If starting afresh, I wouldn't bother with an internal BB - even for the sake and faff of having to buy the right tools. External BB chainsets and BBs are cheaper in comparison to the internal type. Although the bearings are probably less durable due to their position, spending £12 a year for a set of replacements isn't going to break the bank.

geoff_ss

Most of the bearings I buy are for model aero engines and I get them from a local bearing stockist which is a LOT cheaper than from model shops. I'm sure bearings used in bottom brackets will be readily available from the same source. I use Derby Bearings and even good quality bearings are very cheap.

I suspect that the few miles I do these days won't necessitate replacement every year in any case.

thanks

Geoff