Originally Posted by
Sixty Fiver
An mtb crank with a 24/34/44 mated to a cassette with an 11-30 makes for a wonderful touring set up as you can run a closer spaced rear block and still have decent low gearing and more than enough up top.
Road cranks often use larger bolt circles and will have a big ring of 52 or 53 and newer compact doubles run a lower small chainring to compliment 9 and 10 speed cassettes and offer sufficient climbing gears.
Biopace rings can be mixed with round rings... I prefer to use one or the other although a mismatched ring can be used in a pinch.
The square taper bottom bracket was invented by Stronglight and used for many decades and is still a viable system... newer bottom brackets have tried to reduce weight and improve on the bearing quality of the old 3 piece that used cups, 1/4 inch loose balls and races and improve on the interface by making them splined.
Problem with cartridge bottom brackets (most of them) is that they are not as smooth as the old style cup and cone assemblies and despite being virtually maintainence free their performance was lacking... an external bottom bracket addresses this by offering much better bearing support and materials that make for a very stiff and light bottom bracket.
This is going on a hybrid with a 3 x 6 setup. It has a 28/38/48 front crank with a 14-28 freewheel; this has so much overlap I could skip the middle chainring entirely. The current crank has had the drive-side pedal threading stripped out of it, so this is as good of time as any to switch cranks. I'm aiming to eventually turn this into a touring rig. My aim is to have relatively even gearing with a range between 25-30 and 80-90 gear inches.
From what I understand, the major benefit knee-wise with Biopace and the like is with low gearing. Small rings are relatively cheap, and if I like it I may opt for a full set of NOS chainrings. If I do this, is it going to be disconcerting to switch between oval and round while riding?
It has an early Tourney SIS derailleur on it now, and the only likely replacement would be a Tourney Megarange if I found a gear combination that would make the 34t low worthwhile. Both are triple RDs. The highest gear I can get on the back is 14t, or 13t if I squeeze a 7 speed freewheel onto the rear.
It has a cup and cone BB right now, and it's in good shape. Is there any reason I should opt for a cartridge BB? Can I simply replace the shaft to match whatever crank I get, provided it's square taper?