Am wanting to put a bash guard on the wife's Sport Raven tour and because the chain is mounted on the outside of the arms need to move to the inside arm.
I calculated that I need to move it 8mm, so that would mean I need a BB 16mm longer.
Unless you fit the BB axle asymmetrically, more sticking out on on side than on the other.
What you want to watch out for is the tread width, what the trendy cyclists call the Q factor. It is axiomatically assumed that cyclists, and lady cyclists more so, are narrow-treaded and pigeon-toed. It's nonsense (I for one like a good, solid, wide tread) but all the same you don't want to go too far.
The BB that's in there is a BB UN54 71, at 110mm long.
I don't really understand what the 71 refers too, even after reading Sheldon Brown. Mine is a 68 and I think it refers to body length.
Would I be correct in thinking that I need a 68x127mm would give me the extra length?
Would the 73X112.5mm be virtually the same? By 1/2 mm.
UN54 is the Shimano bottom bracket model number. 68mm or 73mm is the width of the BB; I have no idea what the 71 refers to. 110mm is the axle length, and that is what you want to change.
You need to move crank without altering the position of the chainring relative to the longitudinal centreline of the bike. This chainline must fall and remain at 54mm for a standard Rohloff installation.
However, to start with, what makes you think you need a new bottom bracket? Can't you just mount the bashguard over the chainring on longer studs with spacers. Rohloff sells a sets of spacers (indeed, gives them away with new Rohloff gear sets) to adapt various fastening positions on a compact crankset to use with and without a bash guard, and these might do if you could find the right studs.
If you can't fit the bashguard on standoffs, I think you can get away with a 118mm bottom bracket and a small amount of asymmetry.
She regularly gets grease on herself so am try o fix this, and have a guard that'll fit. I don't like the look of the Hebie.
I don't like bash guards much. I think one should be able to ride one's bicycle in street clothes, without any special prepaparion or pegging up your clothes. For this purpose the Chainglider is ideal. However, if you don't want it, a bash guard is simply dangerous unless your wife rides in skintight lycro. Recently, while I waited for a Chainglider-compatable ring and the suitable Chainglider to arrive for a new motor, I used a bash guard, and in two weeks got my trousers caught in it twice. If it weren't for my lightning reflexes (translation: I was going slowly enough to save myself a broken leg or serious bruises), I might have been hurt. If you don't like the Chainglider, I think an over-chain oil guard is safer than a bash guard, and works better than a bash guard which doesn't stop you getting bashed and doesn't stop you getting dirty either.
