Bicycle Mechanics - Why torque lockrings?

My Shimano cassette lockrings have a torque value of 40 N*m stamped on them. That's pretty damn tight, and I can't figure out why it would need to be that tight -- the lockring doesn't carry any drive torque, and it's got serrations to prevent it from backing off.

With such a tight lockring you'd need to carry a chainwhip and a wrench big enough to undo the ring in case you need to replace a right side spoke in the field. That's a lot of extra stuff to be taking on tour.

What can go wrong with a looser lockring?

I tend to keep mine a little loose on the tandem for the very reason you mention. The lockring did come loose once on the cassette of a tandem that friends of ours were riding with us. Other than jingling around on the axle and making the shifting sloppy as the cogs started to slide off, nothing much bad happened. Even if a cog had come completely unshipped with the chain on it, the worst that would happen is that the transmission would jam, but the wheel wouldn't lock up and skid or anything dangerous.

I've found that with our newer Shimano cassette, there is detectable play in the cogs if the lockring is not cinched down quite tight. It's as if the serrations bite early, before there's much load on the threads. On our older Campy tandem hub the cogs would hold still with even light torque on the lockring and yes, it was much easier to get it loose when we used to break spokes on that wheel.

Edit: and no, it never came loose on the road, either.

I've seen a poorly torqued lockring come loose. The results were a nuisance, not catastrophic but you'd rather it didn't happen.

There is (was?) a portable tool available called a "Hypercracker" that lets you remove a lockring by using your chainstay to retain the tool handle and you apply the torque with your crank. That said, I haven't broken a spoke is 20+ years and 120,000+ miles so my Hypercracker stays home.

The HyperCrank is no longer in production. However, you can now get a Stein Mini Lock Ring Tool (http://www.sheldonbrown.com/harris/stein-mini-lock/index.html).

Man, when it comes to stuff like that listen to the manufacturer. Unless you're a highly experience and qualified mechanical engineer you don't have the skills to judge them wrong. Manufacturers don't just come up with that arbitrarily. They have teams of mechanical enigineers who figure all that stuff out.

Improperly torqued fasteners tend to lead to mechanical breakdowns and things falling off. You don't want a cassette to come loose and shift around, dropping a chain, when climbing.

Man, when it comes to stuff like that listen to the manufacturer. Unless you're a highly experience and qualified mechanical engineer you don't have the skills to judge them wrong. Manufacturers don't just come up with that arbitrarily. They have teams of mechanical enigineers who figure all that stuff out.

Yep, then it goes through legal and marketing and gets all screwed up.

I mean, there's things you definitely don't want under-torqued. Generally things that result in you meeting asphalt on failure. But that's not one of them.

I'll admit, I just installed a cassette without a torque wrench, and have lost no sleep over it.

I tend to keep mine a little loose on the tandem for the very reason you mention. The lockring did come loose once on the cassette of a tandem that friends of ours were riding with us. Other than jingling around on the axle and making the shifting sloppy as the cogs started to slide off, nothing much bad happened. Even if a cog had come completely unshipped with the chain on it, the worst that would happen is that the transmission would jam, but the wheel wouldn't lock up and skid or anything dangerous.

I've found that with our newer Shimano cassette, there is detectable play in the cogs if the lockring is not cinched down quite tight. It's as if the serrations bite early, before there's much load on the threads. On our older Campy tandem hub the cogs would hold still with even light torque on the lockring and yes, it was much easier to get it loose when we used to break spokes on that wheel.

Edit: and no, it never came loose on the road, either.

X2 - mine is loose as well. I'm 215lbs, and have never had issues with the lockring. Then again, I'm anal about my maintenance, and tear just about everything down each season or when I get bored.

Threaded fasteners can loosen from very slight repeated movements over time. Unless your chain line is always straight down the center of the cassette, there will be a twisting motion that compresses and loosens the cog stack. A preload on a a fastener is always supposed to be greater than the maximum force that will be exerted on the fastener by outside factors. That's what keeps stuff from loosening on its own.

40 N*m isn’t that much, Campy calls for 50. When I’ve left mind a little loose I get ticking noises out of the cassette. Also, leaving them loose can cause them to shift ever so slightly while you’re riding, as mentioned above, and cause wear on the free hub. As they wear the free hub it causes them to get looser and more wear, get the picture. I think to get the lockring off without a chain whip in the field you would have to have the lockring pretty loose. You make it sound like you break spokes all the time, that’s why you want to change them in the field. If you’re breaking spokes all the time something is wrong with your maintenance program, LBS or the wheels you’re using. The last time I broke a spoke I nursed it home by loosening the brakes and taking it easy.

Also the torque is to generate sufficient friction between the cogs & spacers to lock the entire stack into one unit. This then spreads the pedaling loads across all the cogs' splines instead of just one. This is especially important on alloy freehub-bodies that easily get gouged. Having the lockring tightened to spec on these extends the lifespan tremendously.

On tour in Montana last year my lockring came off as I was tooling along in high gear. I had installed my cassette myself so I guess I didn't torque it down enough. Luckily I had the Stein tool. I reinstalled the lockring, but didn't quite get how to use the Stein properly, because I didn't torque the lockring down enough this time either, and a couple days later it came loose again. This time I was more careful and used the bike frame to apply torque. It hasn't come loose since.

Yep, then it goes through legal and marketing and gets all screwed up.

I mean, there's things you definitely don't want under-torqued. Generally things that result in you meeting asphalt on failure. But that's not one of them.

I'll admit, I just installed a cassette without a torque wrench, and have lost no sleep over it.

Hmm...I'll admit that's something I've never seen in all my years of wrenching on bikes, cars, motorcycles, trucks, etc. - marketing and legal setting torque specs. In most cases the important thing about torque specs is not over-tightening things. I've seen cases where it doesn't really matter but have never seen a case where setting it to the correct spec is a bad idea.

Never mind everyone, torque specs are just marketing BS. Just ignore them.

Also the torque is to generate sufficient friction between the cogs & spacers to lock the entire stack into one unit. This then spreads the pedaling loads across all the cogs' splines instead of just one. This is especially important on alloy freehub-bodies that easily get gouged. Having the lockring tightened to spec on these extends the lifespan tremendously.

+1
Loose cogs can damage the freehub splines, especially the expensive aluminum alloy freehubs. Keep your lockring tight.

I hadn't heard the argument before about locking the cogs into a single stack functionally. Makes sense.

Happily, with accumulation of experience in wheel-building, (and spreading the rear end of the old tandem out to 140 mm -- new ones are 145 or even 160) we stopped breaking spokes on that much-loved Campy hub. This gave me the confidence to give the lockring that extra cinch, knowing we wouldn't be breaking spokes, and we don't. The reliability has given the whole bike a new lease on life: it got a new paint job and an 8-speed Ergo refit this past winter. And when it goes on the road, the cassette will have a nice tight lockring.

The things I've learned from this forum!

Hmm...I'll admit that's something I've never seen in all my years of wrenching on bikes, cars, motorcycles, trucks, etc. - marketing and legal setting torque specs.

I was kidding, but I'd bet they do go through legal for anything where failure is likely to lead to injury. For what it's worth though - how do you know who's writing those specs you're using?

Take recommended tire pressures for instance - not too many cyclists seem to pay much attention to those. Sheldon always blamed the always-cautious legal departments of the manufacturers who would recommend overly cautious max pressures.

Then of course there's the all-time favorite, lawyer lips.