Which bottom bracket

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astrocan

Veteran
Location
Abingdon, Oxon
My Marin hybrid has not had anything new on the driveline for ages and now the bottom bracket is starting to creak so I am thinking its about time I got some new shiny cogs and chain.
The bike is a standard urban/hybrid set up and I mostly commute but also prefer to ride rather than drive and I do some longish rides a few times a year (70 to 100miles). I also like to keep the option of riding paths, lanes, and tracks open so have tended to prefer strength and reliability above lightness.

Last time I replaced pretty much like for like but this time I would like to consider some alternatives and was wondering what others think.

First up the BB, the current one is a square taper cartridge but I wondered about changing to one of the splined formats. What is the difference and what preferences do you have and why? I am not sure that external BBs are quite suitable for my purposes as I feel they are a bit exposed and consequently need more maintainance than they would get.

Moving on to the sprockets, my son has just got a new hybrid with a double front sprocket matched to a 9 speed cassette which I think would suit me very well. The option to use a larger big ring with a moderate small ring appeals to me, I can't remember the last time I was absolutely obliged to use my granny ring but I sometimes use it just so that I can keep that option open. What am I going to have to take into consideration if I go the double route. Will my current front derailleur work with it if the mech is correctly set up?

My only firm decision so far is that I intend to stick with a 9 speed cassette, partly because this still gives me enough gears and a reasonable range even with a double. I also have the budget to consider and with a fairly new changer and mech I would prefer not to spend it on stuff that is still performing well.

Your thoughts please folks?
 

henshaw11

Well-Known Member
Location
Walton-On-Thames
With the external BBs you're supposed to have the BB shell faced to ensure the bearings sit against the frame properly and are aligned to each other (or at least, as best as possible)..tho' I daresay there'll be someone along in a mo' that'll say that's a load of hogwash ;)

You may be able to get ISIS stuff discounted, but there's a reason for it - the bearings don't last well 'cos they're too small to fit between the BB shell and the thicker axle (hence the external stuff).
There's also the similar octalink stuff if it's still available, that may be marginally better but suffers from the same problem. (I've actually got both on a pair of bike's - one's a relatively expensive ISIS after the first croaked prematurely, the one with octalink hasn't had all that much use..)

I don't *think* external BBs are worse than anything else seal-wise - I think on some it may be possible to drop in new bearings, but I've not looked at them in too much detail.

There's something to be said for sticking with square taper - unfortunately there's not such a good range available now.
 

fossyant

Ride It Like You Stole It!
Location
South Manchester
Square Taper Cartridge BB's are fairly cheap.

I've had the UN54 etc fail, but what the hell. Cheap. Got one on the fixed and it's been fine for 2 years all weathers every day = smooth. Same can't be said for the MTB which get's light use, and comes out for snow and ice? New one every couple of years (10th of mileage of the fixed).

I also have a Dura Ace and Ultegra Cartridge BB's in two other bikes that haven't ever been touched in 10 years or more...... won't be able to get a new one though... :tongue:
 
Frankly I'd stick with square taper for now. If you go down the more 'esoteric' routes of splined you pay more for spares and options are limited. Nothing against external bearings however. I have these on the road bike (Shimano105)and the MTB (Shimano SLX-good value for money).
If you change your triple to a double you'll need to work out your chain line and it's unlikely the front mech will work, unlikely, not impossible. So budget for a new one.
 
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