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TA Cyclotourist/Stronglight 49d

Posted: 5 Jul 2019, 10:09pm
by mercianman
Does anybody know of a good quality sealed BB which is compatible for this type of chainset. I know I can buy a TA one from Spa cycles, but you are looking at £100 plus

Re: TA Cyclotourist/Stronglight 49d

Posted: 5 Jul 2019, 10:56pm
by Brucey
the two chainsets you mention use different bottom brackets from one another. Unless you mean TA cranks with 49D chainrings?

cheers

Re: TA Cyclotourist/Stronglight 49d

Posted: 5 Jul 2019, 10:59pm
by mercianman
I know the rings are interchangeable and assumed the BBS are. In that case I will need to decide which set of cranks to use

Re: TA Cyclotourist/Stronglight 49d

Posted: 6 Jul 2019, 10:56am
by LollyKat
On my old hack bike I still have TA Cyclotourist cranks on an old FAG sealed BB. I had a bit of trouble with the alignment - the 26 inner (of a triple) barely clears the undimpled chainstay although the BB is an assymetric one with the longest RH spindle the shop had. Probably an ISO / JIS incompatibility - I'm sure Brucey can be more specific. It does work, though.

Re: TA Cyclotourist/Stronglight 49d

Posted: 6 Jul 2019, 12:06pm
by slowster
According to Sheldon Brown the difference between ISO and JIS is not the angle of the taper, but rather that the cranks are manufactured such that an ISO crank will sit further out on a JIS axle than it would on an ISO axle, and vice versa. So there are several potential issues with using the crank of one type on the axle of another:

A. Altered chainline.
B. Increased or decreased tread/Q factor
C. The taper on an ISO axle may not be long enough for a JIS crank to fit properly, and instead the crank may bottom out on the shoulder of the taper
D. An ISO crank on a JIS axle will not be as well engaged, i.e. a bit less of the crank will be on the axle.

I've just compared the fit of my Cyclotouriste LH crank on the following axles:

1. The original supplied and still used TA axle.
2. A Shimano UN55 cartridge, i.e. JIS taper
3. A Campag cartridge, i.e. IS0 taper

The distances between the inside of the crank (the surface against which a washer goes) and the end of the axle were as follows:

1. TA axle - 4mm
2. UN55 JIS - 5mm
3. Campag ISO - 4mm

It looks to me therefore like the TA Cyclotouriste uses an ISO taper, which is also the taper of that expensive modern TA Axix bottom bracket sold by Spa. There are various other cheaper brands of cartridge bottom brackets available in ISO taper, e.g. Token, Tifosi etc.

Note that this is completely at odds with the information in this 2008 thread, when a forum member contacted the TA importer and was told TA cranks are JIS. However, TA's website currently states that the Axix bottom bracket is ISO taper, and it seems unlikely that TA would make its current premium BB in ISO taper and its cranks in JIS taper.

I don't know what length axle you would need, but FWIW my TA axle measures 116.5mm and was sold as a double axle. I've never bothered to measure the chainline with that axle installed, and any variations in the symmetry/asymmetry between brands might mean that the same axle length for different brands could give a different chainline.

Re: TA Cyclotourist/Stronglight 49d

Posted: 6 Jul 2019, 12:58pm
by Brucey
current/recent TA cranks are indeed ISO. However much older TA cranks weren't either ISO or JIS but something slightly different again.

Differences in BB spindles extend far beyond the taper angle and length; this doesn't make much difference to anything when you are fitting a new crank to a BB but in used cranks it can make all the difference; the cranks deform to match the spindle in such a way as the best BB you can use is one that is *identical* to the one that was in there previously.

Specifically the flats on the taper can be a different length and a different width (even if they might be ISO or JIS nominally) and this can make for problems with used cranks; they might not settle immediately, they might not give a good alignment, the cranks might persistently work loose. There are much larger variations in this aspect of crank/BB fit than most sources acknowledge.

cheers