Bicycle Mechanics - questions re: nexus 8spd internal hub

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surreal
03-24-04, 03:09 PM
ok, the spacing of the nexus 8spd hub is 130mm. if i was to use a standard road crankset with a single chainring on it in conjunction with the nexus hub, what size bb axle would i need to get a straight chainline? any help would be very much appreciated.

-rob

Jonny B
03-24-04, 04:59 PM
Well standard road doubles (with the correct length BB) generally have a chainline of around 43.5mm, which means the inner ring is about 41mm from the centre of the the bike, the outer is about 46mm. For a triple, it's 45mm to the middle ring, so about 40mm on the inner, 50mm on the outer (figures from Sheldon Brown's site). Shimano's website doesn't give the chianline, but according to Sheldon, most old hub-gears are 40.5-42mm, so I'd imagine Nexus-8s are about the same. So if you have double cranks, use whatever BB length is recommended (probably 113mm if it's new, 107mm if it's older), and the inner ring. If you have a triple, use the next size down and put the chainring in the middle. You can fiddle around with chainring spacers, axle respacing (maybe not with a Nexus), and even adjustable BBs (if your budget will stretch; Royce and TA still do them I think, but they're not cheap), but as long as the cogs are within 2mm of each other you should be ok. You will need to get some single chainring bolts though.
randya
03-24-04, 05:11 PM
You might also be able to flip the sprocket cog on the hub over, which gives you a choice of two chainlines, since the sprocket is dished, but this might not work with the smaller sprocket sizes...

Jonny B
03-25-04, 07:42 AM
And you can flip the chainring over too. I knew I forgot something :)
robertsdvd
03-25-04, 08:02 AM
ok, the spacing of the nexus 8spd hub is 130mm. if i was to use a standard road crankset with a single chainring on it in conjunction with the nexus hub, what size bb axle would i need to get a straight chainline? any help would be very much appreciated.

-rob

Have you been able to get your hands on one yet?
MichaelW
03-25-04, 11:08 AM
With a double chainring, you can use the ring in the outer or inner position.
With the inner position, you can fit a "bash guard" on the outside.
Using the Outer position, you can use a narrower BB, and so have your pedals closer together (ie a low Q factor), which is good for aerodynamics, and usually for comfort, but check for pedal clearance at the chain-stay.