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Discussion Starter · #1 ·
I'm sick of my cranks coming loose and am thinking of making the switch to some profiles or something. I think I have everything figured out except the spindle length. The bike is a p2 with a 73mm euro bb. It runs a 56mm chain line because of the offset rear triangle. Will a 6" spindle be enough to space the chain out that far and still have good engagement with the cranks?

andy
 

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Discussion Starter · #4 ·
hmm.. The way I figure 6" is about 152mm. With the spindle centered that gives me 76mm on either side. Chain line is measured from the center of the bb shell so 76mm -56mm chain line should give me around 20mm past the sprocket to engage the cranks, probably a little less. If I'm thinking about it right that is. Is that enough engagement? They offer a 6 7/8" spindle which would give me around 30mm. The big question is, how far onto the spindle do the cranks need to go. I can't seem to dig that number up anywhere.

thanks,
andy
 

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6" should be fine.

But you need to consider the length of cranks and what size chainwheel you have. That will have a huge affect on the spindle placement and fitting.
 

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Discussion Starter · #7 ·
The cranks will be 170 or 175. I might give 170 a try to get a little more clearance, but I don't think it'll make much difference. The chain wheel is 34t but it's a geared bike and is going to stay that way. I want to keep the chain line where it is now, 56mm or so, to keep the chain lined up with the 18t cog in the back. It'll stay on when I try to ride fakie in that gear with that chain line.
 

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Don't go shorter then 6", if you order them from a BMX site and they don't tell you the lenght of the spindle then its probly less, like 5 and something.

ANd If you get profiles you can run a splined sproket which is good for spacing things out.
 

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Discussion Starter · #10 ·
Well, profile got back to me and suggested I go with 6 7/8", though it looked like a canned response. Does anybody know about how thick the cranks are at the base? I should be able to figure it out with that number.

andy
 

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My Profile race cranks are about 33mm thick at the base. Subtract about 4-5mm for the bolt spacer (non-splined section) and I figure ~ 27-28mm as usable amount of spindle interface on each side..

Just as a comparison I have a 6" spindle with a euro BB. I use one cone spacer, 2 thick spacers and 1 small spacer on the non-drive side. Tree splined and one spacer on the drive side (no cone spacer). The Tree is so thick that I can't use the cone on the drive side.

My chainring is a 24t and it is about 2mm from the chain stay. Crank arms are as close as they can get without hitting the chainstay at maximum flex.

Pic for reference:

 

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Discussion Starter · #12 ·
Thanks demo-9, thats the info I needed. I'm not going for chain ring as close to the stays as possible, other wise I could probably get away with a 6" spindle. (the 34t ring fit with room to spare using the 52mm howitzer that came with the bike). It's gotta be that far out to get a decent chain line. I was ss for a week, didn't like it, so the gears are staying. That also means that I've got to use an 8 speed chain wheel, so no sexy splined tree wheel. I'm going to use the spider that comes with the profile mtbs and keep my 34t ring for now. I was worried that the 6 7/8" would end up looking like frankenstein with the bolts sticking out past the cranks but it seems that won't be the case.

andy
 
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