gcl8a

I read somewhere that using a quick release was bad with single-speed bikes. This doesn't make sense to me, since the forces on the rear wheel should be the same regardless of whether or not you have a derailer.

But then the other day I totally mangled my derailer and had to do a quick conversion to single-speed to get home. The rear wheel slipped in the (horozontal) drop-outs two or three times, and I had to stop and realign it.

What gives? Someone enlighten me?

urodacus

? because more force is directed across a cog in single speed mode than in derailleur mode as there are more teeth wrapped (ie contacted) by the chain?

i have a SS conversion like you and have to make the QR very tight on the back wheel. next hub will be bolted.

gcl8a

But that shouldn't matter, should it? A proper free-body diagram shows that the net force is still the same. The only difference I can see is that a derailer takes a marginal amount of the force off the cogs due to the springs (if that -- my brain hurts).

But it's weird. I rode that bike thousands of km's: sprints, hills, everything, and never had the wheel slip. Switch to single speed and it's sliding around like a drunk on an ice rink.

Then again, perhaps the original derailer fiasco was caused by a wheel slip and and not through derailer adjustment incompetence. Hmmm...

Sammyboy

The danger is in power-start situations. On an SS or FG bike, you are sprinting away from standstill in a somewhat higher gear than you would on a geared bike (or if not, you're going to be spinning like mad). Also, on an FG, the reversal of forces, when you go from pedalling hard to resisting hard is something you don't get on a freewheel bike. I've got an SS with quick release, and I've never had a problem, but I don't think I'd run skewers on a fix. The only real problem I've had with slippage was riding a road bike with originally had 126 mm spacing, but somebody had fit a 9 speed rig, which meant that whilst it could be sprung into the frame easily enough, the dropouts were no longer parallel with each other. Had to tighten that thing down all to hell to get me across London.

radical_edward

You can tighten a 10mm bolt on axle much more than the 4mm or so nut end of a quick release. If you have ever messed around with hex or security bolt on skewers, you will know how easy they are to strip.

If you just have to run quick release, the classic chrome Shimano cam quick release has the highest clamping force you can get, and are all steel, so are much stronger than any bling aftermarket QR. Most shops have them in abundance in the junk bins of the workshop.

gcl8a

That's not the question. Of course a nut can be made tighter.

But why does a wheel that doesn't slip with a derailer all of a sudden start slipping when made single-speed, all else being equal?

dutret

1. The size of the cog is what matters, smaller means more force to put the same torque on the wheel. With a 16-18 you are likely to put a bit more force on the wheel when climbing and skidding but probably not starts.

2. there is no reversal of forces. There is a few degree change in the direction of them but not much.

dutret

because all else in not equal. What cog did you set it too? Did you stand and mash more then when geared?

radical_edward

Because, faced with a choice, the girlyman side of your brain takes over and clicks the shifter.

Without a choice, your riding is much more agressive and you use a lot more body english, pedal kicks, yomping to keep the bike moving.

You also tend to run a lower gear with single speeds, as acceleration is more important than top speed. The smaller your front ring, and the larger your cog, the greater the leverage. Sprinting out of the saddle in the big ring puts much less force on your axle than grinding up a hill in granny gear.

Combine these factors and the quick release clamping force is overcome.

radical_edward

Snap!

gcl8a

53-21 or so. Not sure on the 21, it was the third largest of an 8-speed Campy cassette. I'm sure I mashed some to get going, but I probably did when it was geared, too -- though I can't really say to what extent.

The more I think about it, though, the more I wonder if the wheel didn't slip to cause the derailer self-destruction (even though I was in low gear, I was mashing to get started up a hill from a dead stop). If it matters, the drop-outs are forged Campy, with Campy skewers.

I think tonight I'll go home and do the following test: Stand on my bike with the brakes locked and mash the bejeezus out of the pedals to see if I can get the wheel to slip. I'll report back. Or not.

Sammyboy

Quite. I run a 42/15 setup, where I might more normally be starting in 42/17 away from lights or somewhere where hard acceleration is neccesary. This means that I'm torqueing the chain more, which is what would slide the axle forward in the dropouts. If anything, I'd guess this is what happened to the OP


In terms of pulling the wheel forward, you're right. I was thinking of the twisting effect on an axle which won't be as strong as a solid, but that's not relevant to the post here.

dutret

There is more force on the chain not torque. The torque on the wheel is not higher.



If there is a significant twisting effect on the axle your bearings are ****ed.... really really ****ed.

gcl8a

Ouch. Tough love.

I was in 53-21, which shouldn't produce all that much chain tension.

But I hear what you're all saying -- mashing, yomping(?) -- I'm just surprised that the force would be that much higher. Time for some experiments.

dutret

yeah that shouldn't at all. Maybe you just didn't tighten the qr enough. They will slip with horizontal dropouts and gears too.

Sammyboy

Yeah, 53-21 doesn't sound like it'd be a problem.

radical_edward

Yomping is pulling up on the bars at the same time as pedalling when you are out of the saddle. Old, old track term.

spdrcr5

no matter what gear anyone here has on their bike they are never going to be able to generate the same amount of torque against that axle as a Pro rider can and they don't slip their QR so nobody here should be able to slip theirs.

I've been wondering the same thing. Why a bolt on an SS/FG and not a QR? What's the reasoning behind it? A bolt is much harder to loosen if you flat, so why is it being used? The OP could have had a problem other than a QR issue, so what about everyone else? What's the reasoning behind using a solid axle with bolts over a QR?

dutret

pro riders use vertical dropouts these days and the amount of force on the chain at 80rpms is enough less that at 0 that a strong ss rider with a small cog will in practice put high force loads on the wheel more frequently even if it is associated with less torque and power.

Hirohsima

I second the shimano QR's. Been riding singlespeeds for over 10 years and never had anything slip. EVER.

I clamp it down tight and am currently running 45/16 & 42/19 and have climbed some steep inclines where I was *crawling* up the hill, such that it probably would have been just as fast to walk my bike up the hill.... and it still did not slip. Have mashed off the line and nada.... no slippy.

I have used salsa QR's on my singlespeeds and they do slip a little. The holding ability of a knurled aluminum QR just does not seem to work as well as a steel QR.

Another thing that helps are good lock nuts on the axle that have decent knurling. The shimano ones like in this pic:

are OK but the knurling is shallow and the edges not sharp. I use old Campy locknuts that flare at the ends which has a larger diameter at the interface between the hub and the dropout.... it has more holding power. I also have had GREAT luck with old superbe pro locknuts that are REALLY grippy.

Cannot comment of FG, but for SS, there should be no reason you cannot use a QR

CenturionII

Per Sheldon Brown:

"As a result, it is widely believed that quick-release axles are not suitable for fixed-gear use. This is false! "

https://www.sheldonbrown.com/fixed-conversion.html

Sheldon Brown

Actually, that's not correct.

First of all, there's no "torque" against the axle other than the little that comes from bearing friction.

It's not the torque that's an issue, it's the linear pull on the chain.

The magnitude of this pull is directly proportional to how hard you push on the pedal, and the length of the crank. It is inversely proportional to the chainring size.

"Pro riders" don't need to push as hard on the pedals as clydesdales do, and in fact they can't do so, because their weight limits how much force they can apply to the pedals. (Lighter riders don't NEED to push as hard on the pedals, it's about power/weight ratio.) "Pro riders" can push hard for a longer period of time without getting all tuckered out, but the maximum chain pull they create is quite a bit less than an overweight tourist or mountain biker.

"Pro riders" rarely use a chainring smaller than 39 teeth, or occasionally 34 teeth if they run compact. Track riders rarely use a chainring smaller than the upper 40s.

Touring cyclists commonly have 24/26 tooth granny rings, which apply proportionally more pull to the chain for the same amount of push on the pedal.

For example, comparing a 24 tooth chainring with a 39 tooth, the 24 tooth ring will pull the chain 60% harder for the same amount of pedal force.

Sheldon "It's About Tension, Not Torque" Brown

blickblocks

I'm kind of confused by what you're saying Sheldon.

As I've understood it, since you're geared too high when starting from a standstill, the force of your pedalling is more than it should, so your chain is pulling harder. When you can spin on a geared bike instead of mash, you're trading an amount of force for an amount of chain pull. The chain isn't pulling as hard since it's moving faster.

Is this correct?

dutret

In practice:
A smaller chainring will ALLOW the rider to put more force on the chain.
A smaller cog will REQUIRE the rider to put more force on the chain in order to put the same torque on the rear wheel.

radical_edward

Think of it in terms of leverage. You have your fulcrum at the BB axle, the load at the chainring and your force at the pedal axle. The closer the load is to the fulcrum (ie a small chainring), the easier it is to move for a given amount of force.

So with a big chainring, YOU need to push a lot harder on the pedal to get things rolling. Those with smaller chainrings may be putting less energy into pushing the bicycle along (from a standstill at least), but they are doing more work