Low End Bicycle Shifting Question
 

I have a inexpensive (Trek 700) bike that I ride around town on occasion for errands, it is my rain bike, etc. It has a single chainring and 7sp cassette where the big cassette is this huge 34t thing. And 'behind that' (between the biggest cassette and the spokes) is this plastic thing that looks like a small plate.

This 'plastic plate' has come loose and bangs around (looks like it was held by plastic tabs which broke, I think). What is the purpose of this? Is it strictly to keep the chain from 'overshifting' into the spokes? Can I just take this thing off?

Thanks.

dave

The plastic pie plate is "spoke protector" aka dork disk, which just goes to show what many more experienced riders think of it. It's purpose is to protect the spokes if the chain is overshifted beyond the largest sprocket, and on many bikes, is also to keep the RD cage from snagging in the spokes. Putting the RD into the spokes is an expensive proposition, so this added measure of protection is worth the added weight or name calling.

Better bikes usually lack spoke protectors because their owners can be relied on to keep their bikes properly adjusted, and to an extent, better derailleurs hold adjustment better.

Keep in mind, that it's not only a matter of the derailleur adjustments. If the bike falls on it's right side, the hanger on which the RD can get bent inward, throwing all adjustments off in that direction, and causing an overshift next time you shift to low.

So that's why it's there, and it's your call whether you want one or not -- I'm 100% neutral, and don't use one, and don't advise against them either.

Since it's broken there are two ways to remove it. If the metal part where the plastic was affixed isn't also bent and causing problems, you can simply cut the plastic and discard it. Or you can remove it properly by removing the cassette and slipping the entire disc off, then remounting the cassette. In some cases you may need a spacer to replace the thickness of the disc, but not always.

Yes, you can remove it. It is a spoke protector, often derisively referred to here as a dork disk or, in the old days, pie plate.

Just make sure your derailleur's limit screw is set to prevent the derailleur cage from overshooting the large inboard cog and you're good to go. If the bike ever falls on the derailleur side or the derailleur or its hanger suffers some other trauma, be sure to check that you still cannot shift it into the spokes before you resume riding it.

FB/Jim, thanks for the responses. But you do realize that I had to wait 8 MINUTES for two high quality answers. Hopefully folks will do better next time :)

dave

There goes their pay raises for 2015!

Jerry, those were the old days. Now they are fired :-)

dave (born at Barnes Hospital in St. Louis, BTW)

You're very lucky. Just as often you'll get two fast, quality answers that are in 100% disagreement in every detail.

I use spoke protectors. I always keep my bikes well adjusted but they can save a lot of grief when some knucklehead knocks into your derailleur (like in a bike rack) and bends it inwards without you knowing it or you pick up a stick on the trail.

I use chain catchers in front, too. Digging a greasy chain out of the works can spoil a pleasant ride.

OK - the blowtorch goes back into the cabinet :-)

dave

The rule Ive heard is you can take it off if you can remove it without having to break it. Basically this gets down to being able to remove a cassette, which requires two tools used only for removing and installing cassettes. The assumption is, if you own those tools you're probably trustworthy with setting your own limit screws as well.

As usual, FBinNY hit it on the head though.

If you're willing to wait 16 minutes, I can give you an answer that's half as good.

My gawd, that made my entire week. Maybe even my month.