Bicycle Mechanics - Very Easy Question

Hey guys, I'm fairly new to cycling and just got a new (used) GT ZR 3.0 road bike from someone on my campus. Overall the bike is in good shape, and has around a thousand miles on it.

I know for a fact that I need to replace the sprockets, their pretty worn. After changing gears, I usually hear a grinding sound as I crank, and when I'm sprinting, it sometimes feels as if it may slip a gear.

Do you think replacing the sprockets would fix this? Or what could it be?

Thanks :D

hey man yeah honestly if you know that your casette needs replacing, than you probably will have to replace you chain and sometimes your rings aswell. if you change your chain more ofter than you can get a much longer lifespan out of your rings and casette though
and yes, it would help

It's likely to be both the chain and cassette/freewheel need to be replaced. Depending on many factors, the chain can "stretch", and cause the sprokets to wear oddly. The odd wear interferes with the chain/cog interface and could cause the problems you describe.

As a quick check, measure the distance between the corresponding pins 12 links apart. Ideally, it should measure 12 inches. If it measures 12.125 (12 1/8) inches, then it's likely you'll need to replace both items. Some say a stretch beyond 12.0625 ( 12 1/16) inches is too much.

Start with this measurement and post the results.

Also, does this problem occur in all gears, or just certain combinations?

I just changed both the chain and the cassette. The chain was the third one. I found that when hammering, my chain would jump. Discovered that the middle ring was also worn and replaced it. All in all, not that bad considering the machine had 4800 miles on it.

How much do you think it would cost to replace both?


Thanks guys :)

For a pretty good description of chain stretch and wear, see: http://sheldonbrown.com/chains.html

Hey guys, I'm fairly new to cycling and just got a new (used) GT ZR 3.0 road bike from someone on my campus. Overall the bike is in good shape, and has around a thousand miles on it.

I know for a fact that I need to replace the sprockets, their pretty worn. After changing gears, I usually hear a grinding sound as I crank, and when I'm sprinting, it sometimes feels as if it may slip a gear.

Do you think replacing the sprockets would fix this? Or what could it be?

Thanks :D

How do you know you need to replace the sprockets? What you are thinking is wear could be an intentional profiling of the teeth, easily mistaken by the untrained eye.
If the bike really only has 1000 or so miles you may only need an adjustment. 1000 miles out of a drive train is low. If you are motivated & have time check out Park Tools web site for detailed instruction about how to do this. If not, take it to a shop.

How do you know you need to replace the sprockets? What you are thinking is wear could be an intentional profiling of the teeth, easily mistaken by the untrained eye.
If the bike really only has 1000 or so miles you may only need an adjustment. 1000 miles out of a drive train is low. If you are motivated & have time check out Park Tools web site for detailed instruction about how to do this. If not, take it to a shop.

+1. Your problem is probably gear shift adjustment. Bad adjustment causes more noise than worn chain and sprockets. You can do this for free with the help of http://www.parktool.com/repair/byregion.asp?catid=53