Front Chain Wheel& Crank Taper Help??

[BADGER.BRAD]

Hello All,

One of my old MTB clunkers needs a new front 2 or 3 piece chain wheel (along with a new chain!!) as I wish to higher the gearing some what I tried to fit a 2 wheel chainwheel from a racing bike (52/42) but found this went onto the taper too far and caused the chain to rub the frame. Are all these tapers different or is there just a difference between mtb/racers or 2/3 piece chainwheels ? The bike is curently fitted with a cheap 48/38/28 chainwheel and I do not wish to spend too much.

Any ideas or info appreciated.

Brad Dudley West Midlands


All spelling mistakes are computer generated!

 

[Amanda P]

It's not the taper that's different, it's the length of the bottom bracket axle (the bit with the tapers on) and how deep the recess in the back of the chainset is.

If the bike is a clunker, your best bet might be to find a bike shop that's willing to try a few different chainsets in the hope of finding one that will work without too much messing.

Otherwise, you might need to buy a new, longer bottom bracket axle or cartridge bottom bracket. They're about £10 - 15. (The difficulty is knowing how much longer - sometimes trial and error is the only way to know)

The reason for the difference is that MTBs have wide tyres, and wide chainstays so that they don't clog up with mud. Consequently, the chainrings need to ride some way out from the bottom bracket to clear all this.

None of this is necessary on a road bike, so chainsets and bottom brackets intended for them tend to sit closer in to the frame; the rider can keep his feet closer together and the bike is narrower.

When you try to mix road bike parts with mountain bike parts, difficulties like this can tend to arise. They can mostly be overcome, but it won't always be straightforward.

Why do you need to replace the chainset?

 

[BADGER.BRAD]

Hello Uncle Phil,
Many thanks for the info much appreciated, What you said now makes a lot of sense. I need to replace the chain set as they took a good knock at some point (my fault !) and now have quite a good bend in them (it was worse!) Because of this I thought I would take the op to up the gearing at the same time, all of the rear 5 speed freewheels I have come across seem to have the same amount of teeth 14 to 28. I have been told there are different ones but I have never come across any. The bike is used on the road 90% of the time and I only ever use the top 2 chain wheels and 80% of the time the top 3 gears.

Many Thanks

Badger.Brad Dudley West Midlands

 

[hubgearfreak]

this link may help?

 

[Amanda P]

If your chainset has removable chainrings, you might be able to replace bent ones with new ones, and possibly larger ones while you're at it.

These chaps carry a huge range of chainrings and supply by mail order. You'll need to find the bolt circle diameter (also called BCD or pin circle diameter/PCD) and order rings with the same BCD as your old ones. This Sheldon Brown page contains useful info on measuring this.

If it's a cheap and nasty chainset, the rings won't be individually replaceable, so you're stuck with replacing the whole thing.

If it's a real clunker, you may do best to visit your local tip or bike rescue place and find a bike whose chainset you can cannibalise there.

(In fact, come to think of it, I have a nasty steel MTB triple that I have no use for that you're welcome to for the postage price. No left hand crank for it, but your left hand crank's probably OK?)