Stronglight Impact Triple and bb size

[beanzontoast]

Continuing my Galaxy do-up... have started (window) shopping based on previous suggestions (thanks all! ), and the questions are coming thick and fast.

Looking at the Stronglight Impact Triple, I see they reccommend a Stronglight JP400 110mm bb. (The bb does come in other lengths, but the page advertising the triple specifies 110mm bb). The bb on my Galaxy currently is 118mm. Does this mean I need to change it for a 110mm, or can I stick with the 118mm bb? Which am I better off doing?

I'm fitting a new front mech, and am hoping that I can just change the jockeys in the rear one. Will getting the bb size wrong throw the alignment with the front and rear mechs out or should they adjust to accommodate it?

 

[PpPete]

Sheldon says that 110 mm is right for Stronglight Impact Triple on a Tandem

Otherwise it's 115 mm.

And it looks like scanned that chart is scanned straight from a Stronglight document.

I'd chuck the chainset on the existing BB and see how straight the chain is when you are running middle chain ring to middle of the cassette.

Adjusting the mechs isn't going to make any difference to the basic alignment of the cogs themselves - but it is something you will likely have to do after you've got everything installed and lined up.

 

[PpPete]

Saddo that I am - I had to check on Stronglight site:

http://www.stronglight.com/stronglight/page.php?nom=produit&keyProd=impacttriple

115 mm is def the "right" one for you. Spa do seem to have it wrong.

I'd still try it out on the existing 118mm though (which is the usual recomendation for Shimano triples IIRC)

 

[andrew_s]

I've always used 110mm on my Impact triple.

There's no absolute "right" answer. So long as the mech will shift onto both the outer and the granny, and there's adequate frame clearance, "best" will depend on how you use your gears. I tend to use the outer (48) for general riding and only drop a ring when I get to a proper hill. I thus get a better average chainline with a short BB. If you spend most time in the middle ring, you'd want a little longer.

 

[beanzontoast]

Thanks for this info. I'll get the triple ordered and see what the alignment looks like on the 118mm first off. I'm happy to take my time getting it right, and it's not a huge expense to swap to something smaller, but didn't want to get it totally wrong just by not knowing what to look for.

 

[NickM]

I use a 113mm Shimano UN54 b/b (3mm longer on the drive side than the 110mm). As Andrew S says, there is no definitively correct length - I'm a middle-ring sort of chap! Your suck-it-and-see plan is a good one.

The Stronglight Impact is a differently badged Sugino XD (hence the far better finish than most Stronglight cranks), and requires a JIS-taper (rather than ISO) bottom bracket. It is 100% compatible with a Shimano cartridge b/b. This is an excellent combination for a touring bike - I see no reason to spend more.