Right length BB for TA cyclotouriste triple?

Hopefully this is an easy to answer question.

What is the right BB length (68mm shell) for a vintage TA cyclotouriste triple chainset - square taper?

I know it depends on whether ISO or JIS etc. but was hoping just to attach it to a standard UN55 Shimano BB to make life simpler.

Re:

as you are on the MTB section, I guess you are going to install the chainset on an MTB?

Will that look right, as they were designed for touring bikes?

Also, they are not strong. As they are attached via a small ring near the BB centre and not onto a spider, you catch the ring on a rock, it will bend, as there is no spider to support it. Had it happen taking a road bike roughstuffing.

hmmm, okay - that's worth considering. Had it existing and thought it might look cool on my rebuild Dawes Ranger.

You might have a good point. Although, do you know the BB length anyway?

See here for the Velo Orange copy: takes a 124mm in JIS.
https://velo-orange.com/collections/cra ... -24x34x48t

As far as I understand the taper is neither JIS nor ISO (same angle but different thickness). Probably I'd start with a 122.5 (as they are commonest) and work from there.

Re:

Your correct in saying (above) that the TA Cyclotouriste chainset was designed originally with 'road' riding in
mind , since MTB/ Off Road riding had not evolved at that time

However in the early MTB/Off Road years the chainset was widely used both here and in the US
It may well be that the fact that TA ' were the only company to supply a 26T chain ring '
( Making Tracks magazine 1986 ) was a factor here

It does not compare in strength/rigidity to later designs with forged spiders , but at the
time found favour with many manufacturers including Raleigh , who used a copy of the TA
design in both the Mustang and the Maverick models . Geoff Apps also used TA triples
on several of his bikes , with the teeth removed from the outer ring to serve as a bashguard

So as a possible upgrade for your Ranger it would be ideal and period correct

As for B/B length , you will need to have your rear wheel in place c/w sprockets before you can
establish the correct chain line . Generally speaking the middle ring of the chainset needs to
be in direct line with the middle rear sprocket . Ideally you need a 'spare' B/B to play with to
give you a starting point

Re:

An update on my previous post

The straight ( 90 degrees to B/B spindle ) crank arms of the TA chainset mean that
an unusually long B/B is required to give adequate clearance between the arm and the chainstay

I put a Shimano UN - 72 x 128 mm long B/B into a TA chainset and measured
an effective chainline dimension of 51.5 mm ( B/B centreline to middle ring
centreline )

I also checked the chainline dimension on the rear wheel of a 1986 Maverick
( 15 spd , broadly similar to your Ranger ) and got a measurement of around 50 mm

It would appear that you will need a B/B of around the same length if you are to
avoid clearance problems and/or the chain rubbing on the tyre sidewall in the
lowest gear, as previously mentioned

You will need to check these dimensions for your particular application , however
I don't think that the overall length is far out , and it remains to be seen if you can
actually obtain a B/B of anywhere near that length ? Good luck