So how do i calculate BB spindle length????

[Drewson]

This might be a dumb question as i'm slightly sleep deprived.....(anyone want to buy a pair of one year old twins by the way??? :roll: )

The bottom bracket width is obvious but what is the general rule of thumb for calculating bottom bracket spindle length? I suppose it must be determined by the chainset being used?

What sort of clearance is acceptable between the cranks and either chainstay? A recent fitting of a campag chainset to my Litespeed gave plenty of clearance on the driveside, but only a few mm on the non-drive side.... :roll: I'm worried that any flex in the cranks might allow the crank to bash off the chainstay and damage it.....should i just get a different BB with a longer spindle?? Shame though as this McMahon Ti BB is v nice......

Hey-ho.....what's the craic here folks? :?

 

[FluffyChicken]

It's the chainset first, second the frame.
You need to aim for 47.5 for your chainline assuming skinny tubes. Modern chainsets aim for 50mm chainline.

Exotic chainsets may use other chainlines, and I'm assuming triple MTB setups.

But post your chainset and someone will hopefully tell you what you need.

As a rule of thumb (not sure who else uses it) If you have skinny tube (26.8 band front mech) you aim for the 47.5 chainline length, if you have fat tube and take the widest mech, then aim for 50mm front mech as you'll more than likely need to clearance and the mech is placed further out so centres a bit further away.
Everything else is in between.

There are plenty of posts on it and sheldon brown and bikepro among other places have general lists.

 

[GT-Steve]

phew, I was toying with asking this very question for the last couple of days, so I'm glad I'm not the only one that doesn't know

Tho I would prefer a more 'janet-and-john' type answer if there is one :roll:

 

[kaiser]

this might come out as gibberish but..

fit a bottom bracket that fits the shell (though not essential does make calcs a wee bit easier*)

fit the chainset

measure from the middle ring to the middle of the seat tube

as fluffy said you should be aiming for 47.5 + if your fat tubed.

so say you have fitted a 120 mm bb and your size is 51mm. effectively you have to move the chainset inwards 3.5 mm. to do this you need a 7mm shorter axle. i.e a 113mm or so.

whilst you have the chainset fitted though check your clearance between the chainstay and crank arm.

* if you fit a wrong size sheel you have to deal with offsets, not that tricky and its easier when your doing it but I won't even try to explain it.

 

[FluffyChicken]

..'janet-and-john' ..

It's not that easy

But janet & john is
1) Tell us your frame, and front mech band size.
2) Tell us your chainset.
3) Let RetroBikes do the hard work for you.


DIY methods
http://www.sheldonbrown.com/bbsize.html
http://www.bikepro.com/products/bottom_ ... able.shtml
http://bike.shimano.com/publish/content ... le.html/05)%20Crankset%20and%20BB%20Combination%20Chart.pdf
etc...

 

[Drewson]

OK, so i just measured from middle chainring to centre of the seattube. This is about 50mm on my Litespeed, so clearance is fine and hopefully the chainline will be acceptable. However, the clearance on the non-drive side is only approx 3-4mm....pretty close to the chainstay..... :?

By the way it's a Campag Euclid Chainset 91/92' era and seattube is 31.8mm.

(By the way.....someone please sell me a Campag Euclid Front Mech from 91/92' to fit this seattube size!!!!)

 

[cchris2lou]

you are going to need a long axle . be careful as Campa need a special type of square taper ( sheldon site knows which one ) .

Nigel at campioldy has plenty of front mech but they are not cheap .

 

[sq_root_of_2]

You can always check with Sheldon.

http://www.sheldonbrown.com/bbsize.html#chainline

Check to see if it is a JIS versus ISO issue.

http://www.sheldonbrown.com/bbtaper.html

 

[FluffyChicken]

OK, so i just measured from middle chainring to centre of the seattube. This is about 50mm on my Litespeed, so clearance is fine and hopefully the chainline will be acceptable. However, the clearance on the non-drive side is only approx 3-4mm....pretty close to the chainstay..... :?

By the way it's a Campag Euclid Chainset 91/92' era and seattube is 31.8mm.

(By the way.....someone please sell me a Campag Euclid Front Mech from 91/92' to fit this seattube size!!!!)

3 to 4mm is loads, I ran my XTR M900 closer than that for many year and had no problems.

124 to 130 length ish for Campag Euclid, can't quite make it out.
http://mtb-kataloge.de/Bikekataloge/PDF ... o/1991.pdf

It'll probably tell me in the Sutherlands 6th ed. but not got it on this computer.

 

[Drewson]

OK, so know i know a bit more about chainline and types of spindle, etc. That Sheldon Brown knows his stuff....

When measuring the chainline again i realise it is actually approx 52.5mm. This is obviously too long when really for the skinny tubes on my Litespeed it should be 47.5mm.

So i removed the BB and measured the length of spindle protruding from each side of the shell. It appears to be 2.5mm on the drive side and 2mm on the non-drive side. So i think to myself....."just turn the BB round and the drive side will come down to 47.5mm (perfect) and i will attain an extra 5mm on the non-drive side....surely that's the answer"....

However, looking at the BB shell it indicates right and left side fitting, and the spindle won't detach from the drive side easily so i would be fitting the BB opposite to what it tells me. Either i do that or assume that someone has put the spindle in the opposite way and attempt to turn it round.....

By the way....does anyone know how to easily remove the bearings from a BB shell as my non-drive side bearings need replacing and won't come out easily....?

The frustration :? :x .....please help....