Singlespeed & Fixed Gear - Stripped Nashbar Hub

I got my fixed gear on Monday. I bought it off ebay and the guy said he only rode it once. The wheelset is in immaculate condition, except it feels like my hub might be stripped already. Tonight when I was riding it if I put too much pressure on it either way it would skip a little. The hub is threaded for fixed/fixed so I could always use the other side, but if it's going to strip that side too then I'd rather try to get it replaced either by nashbar or the seller. I'm going to take it into the bike shop tomorrow, but I was wondering what you guys think?

i have a nashbar hub and haven't had any problems. i do lots of skidding/skipping. are you sure the lockring is tightened all the way? mine was doing the same thing and it turned out I didn't have the lockring tightened all the way.

How would I go about tightening the lockring? I'm a fg newbie.

with a lockring wrench.
after tightening the cog with a chainwhip.

Of course, if you don't have the aforementioned tools, ride the bike up a hill really standing on the pedals, and get off without using backpressure. Now, your cog is on real good. Now use a screwdriver and hammer to rotate the lockring tighter. Note: it's reverse-threaded. Or... just take it to your LBS

Just JB weld the busted side and save the undamaged side for later. The jb weld will hold.

If you aren't sure what you're doing, take it to the LBS pronto. Sounds possible it may not be stripped yet, in which case you shouldn't be riding it until you tighten the cog and locknut.

That's the plan as of now. Will update this thread with the results tomorrow evening.

Of course, if you don't have the aforementioned tools, ride the bike up a hill really standing on the pedals, and get off without using backpressure. Now, your cog is on real good. Now use a screwdriver and hammer to rotate the lockring tighter. Note: it's reverse-threaded. Or... just take it to your LBS


Do NOT do this! This doesn't apply all that much torque to the cog. The theoretical torque application would be the input torque DIVIDED BY the gain ratio. you'd be using the same method to backpedal, which could conceivably unscrew the cog/lockring.

It's best to do this with a 12" chainwhip and a GOOD lockring wrench. As I pointed out in another thread where someone used this method (and it resulted in hub-tragedy), the equivalent of 140 lbs on a 170 mm crank with a 40x16 gearing can be accomplished with only 32 lbs (approx., I'll find my calculations later) on a 12" chainwhip.

140 lbs is probably a good estimate of loading, at least for me, since that's my weight. But at any rate, it hi-lights the point that you can accomplish much greater torque with a chainwhip and lockring than you can just using that guy's method.

Take it to the shop if you don't have the tools.

Don't forget the rotafixa method:

http://204.73.203.34/fisso/eng/schpignone.htm

Do NOT do this! This doesn't apply all that much torque to the cog. The theoretical torque application would be the input torque DIVIDED BY the gain ratio. you'd be using the same method to backpedal, which could conceivably unscrew the cog/lockring.

It's best to do this with a 12" chainwhip and a GOOD lockring wrench. As I pointed out in another thread where someone used this method (and it resulted in hub-tragedy), the equivalent of 140 lbs on a 170 mm crank with a 40x16 gearing can be accomplished with only 32 lbs (approx., I'll find my calculations later) on a 12" chainwhip.

140 lbs is probably a good estimate of loading, at least for me, since that's my weight. But at any rate, it hi-lights the point that you can accomplish much greater torque with a chainwhip and lockring than you can just using that guy's method.

Take it to the shop if you don't have the tools.

whatever... nerd

Looks like it's stripped. Took it into the shop and the guy tightened it with all his might and it still slips. I'm going to take it into a different shop tomorrow to get it looked at. If it is stripped is it possible to get it replaced by nashbar or do I have to try and get a refund from the seller? If they do replace it will I only get a hub? What can I expect?

you can expect........ nothing

It's not a manufacturing defect, it stripped due to improper installation/maintenance.
suck it up and either JB weld it on, or use the other side.

i had this prob with the original hub that came on my langster. i'm assuming that the hubs are of comparable quality. I had the wheel replaced by specialized (after assuring them that i had been riding with a brake and wasn't skidding), and it happened again, at that point i built a wheel up around a dura-ace hub. my advice is to scrap it and get a better hub.

JB Weld is good stuff. That's what I would do.

I doubt there's anything wrong with the hub yet. Threads don't really strip "just a little". That's like being a little pregnant.

What cog is on there? It's entirely possible that the cog isn't wide enough to properly seat against the lockring. Surly's were notorious for this back in the day. A Dura Ace or EAI cog aren't that much and are fine quality. Go DA if you can stay at 16t or smaller, EAI if you must go over. Know that there have been a few reports of EAI cogs cracking, but that seems to be relatively rare.

This guy doesent knowwhat he's talking about. Given the guy only weighs a 140, and the length to the point loading on the crank is probably about the same as the length to the equivalent point loading (your hand is about 3 inches wide) on a chainwhip-- you can just look at the gain ratio as your force reduction.

Simply put: You'd be putting at least 500 inch pounds of torque on that cog.

Plenty if you as me.

I'll leave the proof as an exercise to the reader, however, the calculation goes as follows:

(140 lbs * 170 mm * 1/25.4 in/mm) * (16/40 teeth/teeth) / 12 in = 31.233595800524934383202099737533 lbs.

your logic, simply enough, would lower the location of the force by 3.0 in/2 = 1.5 in, so the effective lever would be 12 - 1.5, or 10.5.

31.2336 lbs * 12/10.5 in/in = 35.695538057742782152230971128609 lbs.

capiche? I'll typeset my work and all the steps of my logic and post them when I get a chance. I may be only 140 lbs, and I may be a dork, but I'm secure in my understanding of the mechanics at work here (despite probably poor assumptions about the magnitude of the loading at the cranks, but they illustrate my point pretty well.). I'll be sure to use a bunch of diagrams.

And to correct an errata in my original post, the gain ratio was not what I had intended to use in the calculation. it should be input torque divided by GEAR RATIO equals output torque. Neither you nor I are free from mistakes...

I agree with the frog

/physicist

I just have to hope that my calculation informs someone's decision. People, even engineers that I deal with, aren't always capable of thinking without seeing a worked example in front of them. The mechanics of the system really aren't all that advanced.

As an aside, does anyone have any idea of the length of a typical chainwhip? I "built" my 12"er out of a funky bar that I had in the garage and an old chain. I looked around, but couldn't find any specs on them...

I'll leave the proof as an exercise to the reader, however, the calculation goes as follows

Are you standing on the handle of the chainwhip?

No, I guessed that the maximum loading that I would possibly apply at the crank was probably about the equivalent of my weight (this might be kind of low, but it illustrates my point).

I calculated that, on my bicycle as an example (geared sort of low, a higher gearing would only increase the validity of my hypothesis...), an equivalent torque delivered via 12" chainwhip would require only about 32 lbs. I may only weigh 140 lbs, but I KNOW I can push 32 lbs with my puny nerdy body.

My point: It's MUCH easier to tighten the cog and lockring appropriately with a chainwhip. Besides, It's possible for you to reverse the forces on the pedals and produce an equivalent torque in the opposite direction, loosening the cog/lockring assembly.

I'd just rather not see someone get hurt because someone on the internet hypothesized without logic or calculation that something was safe, when in fact I feel that I've just proved that it is not.

But, a person can instantaneously produce more torque than their weight alone. Simply jumping down onto the crank will give you more torque. Likewise in an all out sprint the upper body can deliver additional downforce allowing you to generate more than the 140 lbs you weigh. Sufficiently more? Beats me, I don't feel like doing the math.

Of course I recommend "the Italian method" which is going to deliver more torque than any standard chainwhip without a cheater bar. Of course you have to be careful not to completely strip the hub or cut new threads.

Chainwhips work well too, I just don't have one in 1/8".

Italian method = Rotafixa + pretentious accent

Actually, Rotafixa is Italian. "plus: the cog is fixed following a method learned by an old italian champion, sprint gold medal at Tokyo '64 olympic games: there is no lock ring on the rear hub..." -- Paolo from chaingang rotafixa s.p.a.

I admit that it is significantly difficult to calculate an estimate for the instantaneous input torque, but the relationship between the force required to create the input torque and the equivalent force required to do the same on an appropriately long chainwhip makes the decision a no-brainer. I'll possibly examine the mechanics at work in the rotafixa method and derive certain relationships with generalized variables. I've actually already done that for the other generalized case, but it was months ago and I had no intention of sharing that work, so it wasn't in a ready to be published form.

Also, I'm sort of busy at work... and didn't want to go through the entirety of my work again, but I wanted to show that the OP really should find some other method of fastening the cog to the hub, for his/her own safety.

I just thought the insinuation that the OP should just torque up a steep hill and that would generate significant moment on the cog so as to not allow the opposite motion to happen on the corresponding downhill was totally without merit. I therefore actually did some work to show that the poster was wrong.

the rotafixa method provides the same torque as the same force applied to a ~330 mm (12") chainwhip.
That is, Whithout the associated potential for knuckle-busting slippage.
Think about it, you're just using the wheel's radius as your lever arm.

It will give you a little more torque unless you're working with a 24" wheel. On top of that, I find it easier to work with and can more readily deliver full force with both arms or possibly even my legs (in practice that's not really necessary).

Your hub is probably not stripped. If it were, the cog would spin freely, not move forward and back a little. What it sounds like is that your cog is narrow enough that your lockring isn't making contact w/ it, so you need a spacer between the cog and hub to push the cog outward (in the direction of the lockring).

um, yeah... pretentious American accent. I thought Rotafixa was some Americanized marketing style word that Ron Popeil hocks. You know...

"These new Rotafixa cranks are recommended to sell for $160. But I'm selling them for not 140, not 120, but $100, AND I'm giving you a free vegetable slicer! Now, can you beat that folks?"

I just have to hope that my calculation informs someone's decision. People, even engineers that I deal with, aren't always capable of thinking without seeing a worked example in front of them. The mechanics of the system really aren't all that advanced.

As an aside, does anyone have any idea of the length of a typical chainwhip? I "built" my 12"er out of a funky bar that I had in the garage and an old chain. I looked around, but couldn't find any specs on them...



I just whipped out my whip...

Study that whip and tell me that the distance between your center of rotation is 12 inches. Obviously yours could be larger than mine (not bloody likely), but of that 12 incher I'm looking at, the effective length, that is the distance between that center of rotation and the point at which your loading is centered, is considerably less than a foot. I'm looking at approximately 8 inches.

The point that I think you are missing is that if a person chooses to go this route (I agree that it should be done properly with a whip) they shouldn't be able to back that cog out. Think about this. If you do as the initial poster advised and put great bit of force on those cranks (either up hill or accelerating) then secure the lockring, there's no reason for the thing to slip causing strippage. Theoretically you have tightened it at your personal maximum, and nothing YOU can do will back that sucker off. If your 200 pound buddy wants to ride it just tell him no.

I commend you on your calculations and persistance on this matter. I am surprised that my initial guess of 50+ pounds was quite high. Excellent work. You have definitely proven that you know your sh*t and I regret and retract that former statement. Appologies for assuming there are rampant misinformed know-it-alls.