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650c/26" fixed gear rear for a single speed MTB question

ok,  so i have a khs solo one single speed mtb, and i am looking to swich it to a fixed gear.  it is my nasty weather, nasty funk on the ground commuter.  i am CONSTANTLY having issues with the brakes because of what it goes through.  i wish i could say that i take it to a happy shiny cleaning facility after every ride, and completely clean everything, but i cant.  and due to soft-tail frame design, i cant use typical fenders to protect the brakes.

 

the bike is intended as a single speed, with horizontal dropouts.

 

the question is, will any ol'e 650c fixed rear fit to the width of the dropouts, is the axle of the 650c compatible.   the reason for the swap is so i dont have to keep replacing the brakes.

 

and if the answer is 'yes', anyone got a 650c rear fixed they are trying to get rid of?

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Permalink Reply by Green Machine Cycles on January 26, 2010 at 6:55pm
First, you should determine whether the issue with the brakes is excess friction at the brake arm pivot, or friction within the cable housing. Those are the two most common problems with brakes that aren't as responsive as they should be. In the first case, it's unlikely that fenders would help the situation, since fenders won't keep road grime off the brake pivots.

Second, a wheel's rim and tire size don't necessarily have anything to do with the over-locknut dimension of the hub. Your hub is likely spaced at 130mm, but I can't tell from the photograph. Regardless, you shouldn't have too much trouble fitting standard fenders, since there's no chainstay pivot for the suspension. You should have a threaded hole on the underside of the monostay by the rear brake. If you don't, it should be relatively easy to have a hole drilled and tapped to accept a fender brace.

From the photo it looks like there's already room for a fender. I would give that a shot before looking around for 650c wheels. If it really won't work, try getting a slightly narrower tire. I realize that's not an ideal situation since it makes the rear wheel more vulnerable to potholes, etc., but it's cheaper than a new wheel. A 650c wheel will only give you 6mm more fender clearance, so it's probably not worth it.

Good luck!
Permalink Reply by Doug Haynes on January 26, 2010 at 9:16pm
I don't see why you could not fit fenders to that frame, or at the very least something like race-blades...
Permalink Reply by igz on January 26, 2010 at 10:21pm
i got the clip-on style...and it keeps some slop off my back, but not the immediate components, particularly the brakes. it is not drilled, and the design will not allow for such an accommodation.

now, mind you, the existing wheels are 26's, im not trying to drop down to try to accommodate the fenders...yes, there is space, just nothing to attach to.

so since 26" fixed gear wheels are not an item readily available at the LBS, i was figuring for a 650 fixed set.

im not so concerned about fender clearance, as much as width of the axle to the space between the dropouts. follow? or am i describing incorrectly?
Permalink Reply by Tony Adams on January 26, 2010 at 10:30pm
iggi said:
i got the clip-on style...and it keeps some slop off my back, but not the immediate components, particularly the brakes. it is not drilled, and the design will not allow for such an accommodation.
now, mind you, the existing wheels are 26's, im not trying to drop down to try to accommodate the fenders...yes, there is space, just nothing to attach to. so since 26" fixed gear wheels are not an item readily available at the LBS, i was figuring for a 650 fixed set.

im not so concerned about fender clearance, as much as width of the axle to the space between the dropouts. follow? or am i describing incorrectly?

And you want to remove the current rear brake and make up for the loss by switching to a fixed gear? Did you have a similar problem with the front brake?
Permalink Reply by igz on January 26, 2010 at 10:45pm
Tony, yes that is my philosophy on this. No brake, no problem. The front brake got fucked also, but took longer. I only relaced the rear tho. I was going to throw on a disc for the front, just have not got around to it yet. And yes, already has the adapter and mounts for it.

Mark, is it that simple...throw on a fixed cog? I thought that stuff was threaded differently, no?
Permalink Reply by Tony Adams on January 26, 2010 at 10:54pm
iggi said:
Tony, yes that is my philosophy on this. No brake, no problem. The front brake got fucked also, but took longer. I only relaced the rear tho. I was going to throw on a disc for the front, just have not got around to it yet. And yes, already has the adapter and mounts for it.
Mark, is it that simple...throw on a fixed cog? I thought that stuff was threaded differently, no?

Well, if I recall correctly, the threads for a cog are the same as for your freewheel BUT a fixed hub has a section which is smaller and reverse threaded for a lockring. If you intend to do any braking with your legs or trackstands or anything which puts reverse pressure on the cog you should get a lockring.

I'll try not to covet your disk brake when you get around to installing it.
Permalink Reply by igz on January 27, 2010 at 6:41am
Tony, correct, but the existing hub is not threaded to take a lockring, it doesnt have the smaller section.
Permalink Reply by Primitive Don on January 27, 2010 at 2:28pm
I would measure the width of the dropouts in millimeters to make sure the wheel hub is compatible (enough). A single speed would likely be narrower than 130, but the only way to find out is to measure. If the dropouts are ~120, you should be in business with that 650B fixed wheel.
Permalink Reply by igz on January 27, 2010 at 2:42pm
thats 120mm, ya? it appears to be 135mm (inside dimension) if my euro-measuring serves me correctly...

Primitive Don said:
I would measure the width of the dropouts in millimeters to make sure the wheel hub is compatible (enough). A single speed would likely be narrower than 130, but the only way to find out is to measure. If the dropouts are ~120, you should be in business with that 650B fixed wheel.
Permalink Reply by Primitive Don on January 27, 2010 at 3:21pm
Sounds like like the rear wheel you have has is MTB-specific and probably has 130 or 135 mm spacing. From what I'm reading on bikeforums.net, sounds like the best way to go is to lace a 135 mm SS MTB hub (like the Surly) vs. using a track-type hub which is most likely what you're asking about with the 650. Sounds like you can get spacers to take up the 15mm difference, but that the shorter axle may not be long enough work in your 135 mm drops. In that case, you'd need a longer axle as well.

I'm not an expert here, perhaps someone more experienced with fixed MTBs will chime in.
Permalink Reply by Nate W on January 27, 2010 at 3:29pm
Keep in mind you won't be able to see the reverse threaded lockring section of a hub while a freewheel is on it (I think) since a freewheel is much wider than a fixed cog.

But assuming you're right that it doesn't have it, your simplest and cheapest solution is going to be to thread a fixed cog on there nice and tight, and simply keep your rear brake on there just in case (even if in its cruddified state it's not working perfectly). Loctite and a bottom bracket lockring would add a little extra security for the cog.

650c (which =/= 650b) means a new tire, slight change in the geometry, strangeness all around. Plus I think a 135mm spaced 650c track wheel seems far harder to come by than a 26" single speed wheel at 135mm. Any shop with a QBP account should be able to order you a 26" fixed gear wheel with a surly hub spaced at 135mm - it will arrive in 1 day usually. Cheaper to get a prebuilt wheel than to get the hub and have it built up, but that's definitely an option too.
Permalink Reply by Green Machine Cycles on January 27, 2010 at 3:40pm
You should use a hub like the Surly, spaced at 135mm to match your frame's spacing. You might as well use a 26" rim, like the one you are using already (perhaps just unlace that wheel to reuse the rim, unnless it's in bad shape), since there are far more tire choices in that size. As for brakes, if you pull the brakes off the frame and pull the pivots apart and clean and grease them, you can usually rejuvenate them to useful condition.

Comments about use of fixed cogs on non-fixed compatible hubs are exactly right. Do not use a fixed cog without a proper lockring affixed.

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