# Chainline Question



## davgus (Oct 29, 2006)

I'm getting ready to build a Soma Wolverine with a Shimano Alfine 11 and a Gates Carbon belt drive. I want to gear it like a mountain bike which means I will need to use a crankset with 104 BCD. I'm thinking of getting a SRAM road or cyclocross crankset with a removable spider and using a Northshore Billets spider. I can't find any information on the chainline measurement I'll get with that setup. Can anybody help me?


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## Pinchphlat (Feb 27, 2009)

Hi Davgus,

Well I have never put a road crankset on my A11 mountain bike, but I do understand the chainline of this hub.

First thing, are you talking about the Di2 version of the A11 hub? If so, be aware that the standard Gates sprockets/chainrings do not fit the hub (specifically the motor unit gets in the way). Gates have made a special set of sprockets for Di2, but they only come in one ratio flavor - 1:1.9.

As for the chainline, I know that a road crankset on a 68mm English threaded bottom bracket shell is compatible with the hub (provided you are using external bottom bracket cups). You need to have the rear sprocket dished inwards, and the front chainring place on the inner position of the crankset (a chainline of 41.8mm to 41mm, rear to front). 

If you are keen on running with a road crankset to get a narrow Q-factor, then you could always go with a compact crankset (no need to swap the spider) and just get some compact road chainrings. They come in low tooth counts (down to 33T) which should allow you to get a gear ratio like that of a mountain bike. 

Of course if you do not care about the Q-factor, then you could just install a mtb crankset and dish the rear sprocket outwards.


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## davgus (Oct 29, 2006)

I'm not planning to use the Di2 hub. I want to be geared like a mountain bike. The largest sprocket that will fit the Alfine hub is 26 tooth. The smallest chainring that will fit a 5 bolt 130 mm bcd crankset is 46 tooth. I don't think Gates makes a chainring for a compact 110 mm bcd crankset. So I need a 4 bolt 104 mm bcd crankset. The chainline on a mountain bike crankset is about 50 mm. So I'm looking at a road crankset with a Northshore Billets 104 mm bcd spider.


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## Pinchphlat (Feb 27, 2009)

Normally a triple spider on a road crankset means that the chainline on the middle position is 45mm, and the outer position is 50mm. If you instead used a double mountain bike spider, then the chainline would presumably be the same as a road crankset i.e. 41mm on the inner position, and 46mm on the outer position.

Either way you will have trouble with the Gates belt system on a Shimano Alfine hub, as the Gates rear sprocket for the hub runs a chainline of 43.6mm. 

The way most alfine-belt riders sort the chainline out is to run a mountain bike crankset on a 68mm bottom bracket, and to move drive side bottom bracket spacers over to the non-drive side (or get thinner spacers to dial in the chainline). If you use a road crankset, you will be stuck with a fixed chainline - they have no capacity to use spacers.

The other option is to get your hands on a Gate crankset - they make one that suits the alfine chainline.


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## davgus (Oct 29, 2006)

I put a mountain bike crankset on the frame with no spacers on the drive side and the chainline is 51 mm. Gates doesn't offer a four arm crankset for the Alfine and I don't think that the one they have would clear the chainstays. I'm giving up on belt drive.


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## Pinchphlat (Feb 27, 2009)

That is strange - a mtb crankset should have a chainline about 51mm with spacers, not without. Unless the bottom bracket shell is 73mm and not 68mm? However I understand that the Soma Wolverine has a 68mm shell, so I have no idea why you ended up with 51mm when moving the spacers. Sorry I couldn't be of more help.

I can't blame you on giving up on the belt drive though - I only use chains with my A11 hubs for a reason.


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## stevelim (Jul 23, 2008)

Just checking to see if anyone might have found a solution to this? I'm also building a Wolverine with an Alfine 11 (not DI2). I'm kind of tied to a square taper BB and would prefer to run a lower ratio than 46/26 (using a 130bcd). That is, has anyone found a 104 bcd crank solution?


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