SS specific hub and chainline

JamesM · Feb 26, 2012

I have a SS screw-on freewheel type hub (DMR revolver) which gives me no chainline adjustment, so I need to make sure I get the correct length BB to give me a straight chainline. The cranks I have are ISIS (Raceface Prodigy) and I don't have any old BB's to try. The chainring will go in the outer position on the crankarm. So is there a simple way to ensure I buy the right length BB?

cyfa2809 · Feb 26, 2012

Lewis1641 recently had similar trouble i think and was told you can space the freewheel somewhat.

Like you say though you will put it in the outer position so that means you could also use the inside.
Im tempted to stay start with a 113 but it can be hit and miss and if you did want to run the ring on outer you may need just a bit shorter than what the 'normal' one would be.

Do you have a previous bb from the frame as a starting reference?

What is the frame?

JamesM · Feb 26, 2012

The chainring i have only fits in the outer position. I was hoping someone would say that all screw-on freewheel type hubs line up with the outer ring if you run a chainline of say 50mm or something. That way all I'd have to do is find out what length BB gave that chainline for my crank. :?

JamesM · Feb 26, 2012

cyfa2809":2yy6wfca said:
Do you have a previous bb from the frame as a starting reference?

What is the frame?

No old BB and it's a GT Peace (26).

mike_eb · Feb 27, 2012

what crank are you using? look at sheldon brown for recommended bb lengths and then calculate which bb you'll need to use to increase decrease the chainline.

http://sheldonbrown.com/chainline.html

http://sheldonbrown.com/bbsize.html

and yes you can redish the wheel

suburbanreuben · Feb 28, 2012

Bingo!

http://raceface.com/instructions/CRANKS ... _crank.pdf

"All RF cranks are designed to have a 48.5-49.5mm chainline when installed on a 113mm ISIS crank"
This will be the distance of the middle ring from the centre line of the bike.
Working backwards, you need to find the chainline of the rear sprocket.
By measuring between the axle faces (that butt up to the dropouts) find the midpoint of the hub.
Then measurehow far the sprocket teeth (centres) are from the centre line.
Adjust the length of the BB axle to suit. eg, if the rear chainline is 53mm, the front has to go out to 53 too, so the BB needs to be8mm longer: (53-49) X2 .
This will move the pedals out a bit but it's no big deal.

JamesM · Feb 28, 2012

Cool, cheers for that!!!

So if I want to run the chainring in the outer position I then subtract 2 x the distance between the middle and the outer ring. Don't supose anyone knows what that is do they???

hamster · Feb 29, 2012

I have successfully run chainrings the wrong side - the counterbored parts to get the bolts to sit flush are only necessary to prevent then catch on the chain on multi-ring setups.

JamesM · Feb 29, 2012

My chainring (an FSA DH ring) is suposed to go in the outer position. It doesn't even fit in the middle.

SS specific hub and chainline

JamesM

Senior Retro Guru

cyfa2809

JamesM

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JamesM

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mike_eb

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suburbanreuben

Old School Grand Master

JamesM

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hamster

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JamesM

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