Author Topic: New Chainset for Santana Tandem -BB length  (Read 2152 times)

New Chainset for Santana Tandem -BB length
« on: 09 March, 2014, 08:59:37 pm »
Can anyone make a  good  guess on BB length to fit a Stronglight impact http://www.spacycles.co.uk/products.php?plid=m2b0s109p15 to a Santana - I know the 160mm OLN rear requires a longer than usual BB giving high Q (or tread) factor but don't have the tandem to hand  so to speak - this  is  an  enquiry on behalf of a  blind friend.
I remember that  front  mech  set-up on these machines is  tricky  because of the distance the chain-ring  is away from the seat tube.
Existing  chainset  is  Octalink - has now stripped  both right and left  hand splines  on consecutive  rides


Re: New Chainset for Santana Tandem -BB length
« Reply #1 on: 10 March, 2014, 12:48:14 pm »
We have used these cranks on a previous tandem, with 145 mm OLN and a 113 mm BB length. It worked flawlessly. If you add up the OLN difference (160-145), you
should be fine with a 128 mm BB. The exact BB that we used is this:

https://www.bike-components.de/products/info/p30317_Innenlager-BB-UN55-Vierkant.html

Available in 127,5 mm, very cheap and does the job very well! 

As you may already know, these cranks are rebranded Sugino cranks. You may sometimes be able to find the Sugino version on Ebay for cheaper.

Biggsy

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Re: New Chainset for Santana Tandem -BB length
« Reply #2 on: 10 March, 2014, 02:03:08 pm »
Shouldn't you halve the OLN difference?

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Re: New Chainset for Santana Tandem -BB length
« Reply #3 on: 10 March, 2014, 04:00:27 pm »
Yep! I assumed that the axle was symmetrical. which is wrong. The extra length of the BB axle is not split equally between left and right, but is not 100% on the right side.
I tried to find out the exact specs of the UN55 BB, but I failed. Even Sheldon Brown is rather vague on this point.

The BB is available in 122.5 and 127.5 mm. Since they cost only £10 each, I think you can afford trying both sizes!

Biggsy

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    • My stuff on eBay
Re: New Chainset for Santana Tandem -BB length
« Reply #4 on: 10 March, 2014, 05:22:01 pm »
I confess that I wasn't thinking very clearly earlier.  Actually, I tend to assume modern BBs are symmetrical (or nearly) unless stated otherwise - so I'd try the 127.5 first.

A shimmed front mech designed for a larger seat tube should help if the current one can't reach the rings.
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Re: New Chainset for Santana Tandem -BB length
« Reply #5 on: 10 March, 2014, 08:12:27 pm »
Thanks  for  the  tips, will pass  them on