Singlespeed & Fixed Gear - 120mm hub on 130mm

just to get this straight. i've read some threads stating that spacing a 120mm hub to fit 130mm spacing will prevent using both sides of a flip flop hub because the hub will be off center. this makes sense, but when searching for 130mm hubs, i find 120s that say "will fit 130 with longer axles and spacers". they don't mention redishing the wheel or making the free side obsolete. is it true that using spacers on the 120mm hub to straighten the chainline will leave me with only a fixed/no free?

I think it depends on how your cranks and bottom bracket are set up. Since the bottom bracket is centered and the hub will be centered in the dropouts, I don't see any reason why you shouldn't be able to get a good chainline on both sides of the hub.

Of course, I'm not a professional bike mechanic.

do you mean that if, for instance, my cranks are too far out and i got a shorter bb axle, i may be able to line it up? depending on the geometry of the frame of course.

As long as your BB is the right length for standard road (double) cranks, you just need two 5mm spacers for the axle, and make sure your chainring is on the inside of the spider.

just to get this straight. i've read some threads stating that spacing a 120mm hub to fit 130mm spacing will prevent using both sides of a flip flop hub because the hub will be off center. this makes sense, but when searching for 130mm hubs, i find 120s that say "will fit 130 with longer axles and spacers". they don't mention redishing the wheel or making the free side obsolete. is it true that using spacers on the 120mm hub to straighten the chainline will leave me with only a fixed/no free?

Firstly, you should NOT use spacers on the hub to straighten chainline. Your hubs (especially on a fixed gear) should be centered in the dropouts. Your dishing is what changes chainline.

If you have problems with chainline, you need to either get an appropriately sized BB axle, or maybe chainring spacers/cog spacers. The former is preferrable to the latter. Look here (http://www.sheldonbrown.com/chainline/) for more information.

Hope this helps!

You can space a 120 and keep the flip-flop ability but you might need to play with your BB length. You might want to look into IRO hubs. They come in a 130 spacing. Personally I like a 120 on a 130 bike. Gives you chainline options. Matt...drop me a PM, we should get a Sacto ride started. Nice to know there are more of us in town.

Firstly, you should NOT use spacers on the hub to straighten chainline. Your hubs (especially on a fixed gear) should be centered in the dropouts. Your dishing is what changes chainline.

If you have problems with chainline, you need to either get an appropriately sized BB axle, or maybe chainring spacers/cog spacers. The former is preferrable to the latter. Look here (http://www.sheldonbrown.com/chainline/) for more information.

Hope this helps!

Que?
how does dishing affect chainline? doesn't changing dish just re-center the wheel in the frame after you've added different width spacers on either side?
Sometimes you need to unevenly space a flip-flop hub. fixed cogs and freewheels often have vastly different shoulder to cog widths so in order to maintain proper chainline on both sides of the wheel, you need to space each side unevenly. Then you re-dish to center the wheel?

or am i dumb?

no baxtefer, you're not dumb. That sounds perfectly right to me.

Que?
how does dishing affect chainline? doesn't changing dish just re-center the wheel in the frame after you've added different width spacers on either side?
Sometimes you need to unevenly space a flip-flop hub. fixed cogs and freewheels often have vastly different shoulder to cog widths so in order to maintain proper chainline on both sides of the wheel, you need to space each side unevenly. Then you re-dish to center the wheel?

or am i dumb?

you are certainly correct, vomitron needs to lay off the pipe whilst posting.

Yeah, I don't know what rocks I was smoking when I posted that, but cleary it was some rough ones.

What I meant was, chainline can be effected by non-zero dished wheels (like when you take a multi-speed freewheel and thread on a cog without redishing the wheel), but clearly that didn't come out the way I wanted it to. I had never heard of uneven spacing on axles (I was always told by mechanics that it would mess up your trail), but I guess it makes sense for flip-flop hubs.

I meant well, I swear.

I was always told by mechanics that it would mess up your trail

you know some dumb mechanics then.
Trail has nothing to do with either rear wheels, axle spacing and chainline and everything to do with head angle, fork rake and wheel diameter.

PS. those non-zero dished freewheel hubs are dished because of uneven axle spacing. You usually have to respace then redish for it to work properly.

As long as your BB is the right length for standard road (double) cranks, you just need two 5mm spacers for the axle, and make sure your chainring is on the inside of the spider.

This just clarified a whole mess of things for me, thanks!

thanks guys, i think that a part of the problem is that on the cheap dotek cranks, the chainring is pretty far out and is one piece with the cranks. i'm looking for some different cranks before i replace the bottom bracket.