Putting in a BB with a shorter axle

[KneesUp]

My bike was "pre loved" when I got it, and there is no way the bottom bracket can be the original, so I don't know for certain it's the correct width.

It has a triple, and the front derailleur - free of limit screws - can move a fair way further in than in needs to in order to get the chain on the small ring. However, even with the limit screw completely removed it only just makes it to the outer ring, and to do so you have to move the (friction, bar end) shifter a little further than it feels like it wants to go.

There seems to be plenty of clearance between the cranks and the chainstays, so it strikes me that if I got a slightly narrower BB it would move the rings in (meaning I could still get to the smaller one, and the bigger one would be more comfortable for the derailleur) without the cranks fouling the chainstays.

Is there anything else I need to consider that I've not thought of?

 

[mjr]

Whether moving the chainrings in will result in the chainline changing enough that it rubs on the inside of the outer ring in too many gears. That's all I can think of.

 

[Ajax Bay]

Bear in mind that course of action will also reduce by a few mm, your 'Q-factor' aka 'tread' (US?) The consideration above ( @mjray ) will be more likely to come into play if your triple is 50-39-30 as opposed to 52-42-30, but only marginally so.
If you haven't yet, Sheldon is worth reading (and supports the move you intend) - extract:
"With a road triple, you mostly use the two bigger rings, the granny is only occasionally used, and only with the larger rear sprockets. With a double where the small inner chainring is used only for "bail-out" gears, the outer chainwheel should line up with the middle of the cluster. For a road triple, having the cranks close-in is good, because it increases the usability of the big ring. Generally, the middle of the cluster should line up half-way between the two outer chainrings. You may need to move the right crank out farther if the inner chainwheel rubs on the right chainstay, or if the chain rubs on the next larger chainwheel in any combination that you use."

 

[accountantpete]

What's the make/model of the chainset? - you can usually google the correct BB width for well known makes.

 

[KneesUp]

Thanks all. What Sheldon says is correct as ever @Ajax Bay - I don't use the inner ring much, and when I do it's a desperate measure, so it's with the larger rear cogs.

The chainset is an old Campagnolo Exa 9 speed, although whereas once it was 52-42-32, it is now 52-42-22.

I think I will try a narrower BB - thanks again.

 

[Ajax Bay]

42-22 That's quite a step, up or down. Frantic double changing then. Have a look at the gear calculator for that:
http://www.gear-calculator.com/?GR=DERS&KB=22,42,52&RZ=12,13,14,15,16,17,19,21,23,25&UF=2125&TF=90&SL=2.4&UN=KMH

 

[Tim Hall]

Has the bb been swapped for a JIS taper instead of an ISO one? Even if the axle length is the same, the chainset will sit farther out. Campag use ISO taper as far as I know, while Shimano and lots/most others are JIS.

 

[KneesUp]

42-22 That's quite a step, up or down. Frantic double changing then. Have a look at the gear calculator for that:
http://www.gear-calculator.com/?GR=DERS&KB=22,42,52&RZ=12,13,14,15,16,17,19,21,23,25&UF=2125&TF=90&SL=2.4&UN=KMH

I generally don't use the 22 but I live in a hilly area, and sometimes have heavy panniers on. Plus I'm not very fit! Not much about my cycling is frantic

EDIT - writing my other reply below, it occurs to me that it's 28, not 22 at the bottom end. Still a bit of a jump though

 

[KneesUp]

Has the bb been swapped for a JIS taper instead of an ISO one? Even if the axle length is the same, the chainset will sit farther out. Campag use ISO taper as far as I know, while Shimano and lots/most others are JIS.

I didn't know that - it had a generic chainset on it when I bought it, but it was very worn, so I stuck a cheap decathlon one on. The Campag one was off a frame I bought from @vernon (who was as lovely as everyone says he was) - I put it on this bike because the decathlon one was a 42-32-22 which was a bit low. Because it went on, it didn't occur to me that it might not be going on 'properly' as it were. It's a Shimano BB so I assume it's JIS.

 

[accountantpete]

It should be ISO for Campagnolo. Something like 111mm for triples with traditional seat tube (28.6) or 115mm for bikes with 32/35mm seat tubes.

 

[Ajax Bay]

AASHTA
Sheldon
And this is presumably why your cranks are so far out. Need to get an ISO square taper BB for your Campagnolo triple.
ISO/J.I.S. Interchangeability
"If you install an ISO crank on a J.I.S. spindle, it will sit about 4.5 mm farther out than it would on an ISO spindle of the same length.
"Theoretically, ISO cranks should only be used on ISO spindles, and J.I.S. cranks only on J.I.S. spindles.
"In practice, you can very often get away with mixing these sizes, as long as you select a spindle length that gives the desired chainline."