spoke guards - the ugly plastic things that turn yellow

[mechagouki]

spoke guards - the ugly plastic things that turn yellow

AKA "dork disks" (in North America anyway). Shimano made a metal one that looks kind of cool on the right bike (pre-1988 really). As for protecting your wheel, they don't, a properly adjusted derailleur will never dump the chain between cassette and spokes, and have a good look at where the bottom of where your derailleur cage sits, outside the radius of any disc. Take it from me as a mechanic, I've seen plenty of poorly set up bikes with dork disks where the derailleur still ended up tangled in the spokes, yet it has never happened to me once in 20 years of riding singletrack. Way back before I knew what a freewheel/cassette tool was, I used to remove them by setting light to the bottom and letting them burn/melt through to the hub, then yank the rest off with vise-grips!

 

[xerxes]

My bike came with one on and it had been cracked and rattling about on the back wheel for nearly 20 years. When I changed the cassette a year or two ago I decided to get rid of it and I noticed that it had worn a groove in the spokes. If I'd left it on for another 20 years it might have actually cut through them.

 

[stevetait]

They suck! I was very suprised to see one as std fit on the Crossmax wheel of a STS XCR with full M952... Madness :?

(and here begins the GT jokes )

 

[Steve Kish]

... and with a pair of scissors, you could have the world's first 40T rear sprocket!

 

[one-eyed_jim]

As for protecting your wheel, they don't, a properly adjusted derailleur will never dump the chain between cassette and spokes

... until the derailleur hanger takes a knock.

and have a good look at where the bottom of where your derailleur cage sits, outside the radius of any disc.

... but much further from the spokes (which take a diagonal path from hub-flange to rim) than the top of the cage.

Take it from me as a mechanic, I've seen plenty of poorly set up bikes with dork disks where the derailleur still ended up tangled in the spokes, yet it has never happened to me once in 20 years of riding singletrack.

It's happened to me precisely once: perfect adjustment at the start of the ride, a tweaked mech hanger en route, and a major repair headache. Now that doesn't mean it'll happen to everyone, and it doesn't mean I'll put one on all my bikes, but that's because they're dorky and naff, not because they don't serve a purpose.

Now what happened to those cool derailleur guards that bikes came with in the late eighties?

Way back before I knew what a freewheel/cassette tool was, I used to remove them by setting light to the bottom and letting them burn/melt through to the hub, then yank the rest off with vise-grips!

 

[one-eyed_jim]

... and with a pair of scissors, you could have the world's first 40T rear sprocket!

The world's first? It's been done.

Here's one from 1935:

http://www.reneherse.com/images/DSC_00404.JPG

http://www.reneherse.com/Schultz.html

 

[FluffyChicken]

Now I've not got one but isn't that why they have now invented the little nobbles that stick out the back of the cassette ? At least that's what I assume they are for ?
Like the top chainring nobble to stop it dropping between the ring and arm (they don't, they do still get past that :evil

CS-M770

 

[mechagouki]

... but much further from the spokes (which take a diagonal path from hub-flange to rim) than the top of the cage.

That's true until the derailleur is bent, because the cage is the weakest part of the derailleur an impact from the side will tend to bend either the cage or the derailleur hanger, in either case the lower end of the derailleur defines an arc with its pivot at either the derailleur hanger or the lower knuckle of the derailleur. A smaller bend at the hanger translates to a much larger movement inboard as illustrated in the hastily prepared image below, it's quite possible to put the derailleur cage in the spokes after an impact whilst the chain and upper jockey are still below the largest sprocket, rendering the disk useless.

They suck! I was very suprised to see one as std fit on the Crossmax wheel of a STS XCR with full M952... Madness Confused

(and here begins the GT jokes Laughing )

I've seen one on a 2008 Cannondale Scalpel team, no brand is immune.

 

[one-eyed_jim]

That's true until the derailleur is bent, because the cage is the weakest part of the derailleur an impact from the side will tend to bend either the cage or the derailleur hanger,

I don't think cages get bent by impacts, do they? They just spring out of the way. You're right, of course, that a big impact can bend the hanger enough that the lower end of the cage is nearer the spokes, but those big hits tend to get noticed and corrected before you ride off. It's the little ones that just cause an overshift at the top of the cassette that are more dangerous, because it's so tempting just to tweak the indexing or shift to friction and ride on.

it's quite possible to put the derailleur cage in the spokes after an impact whilst the chain and upper jockey are still below the largest sprocket, rendering the disk useless.

Clearly, there are circumstances where a disk may be useless. That doesn't mean there aren't other circumstances where it may be useful.

That they're never cool is something we all seem to agree on.

 

[mechagouki]

That doesn't mean there aren't other circumstances where it may be useful.

This is very true, I have learned to throw them with ninja-like accuracy at friends, colleagues, children etc.