nawi

I've only been cycling for a few months, but I keep having an issue with my bike.

The problem is as follows: When I am riding my bike my chain seems to 'jump/slip' forward suddenly, which causes my the pedal that I'm pushing forward to jerk forward.

I took my bike to the shop where I brought it from and they had a fiddle, but the issue is still there.

This problem occurs when I am standing while cycling (i.e. going up a hill) and when I am putting some force onto my pedals, because of this I was wondering if my problem is a result of my riding style, rather than being a result of my bike.

The mountain bike that I am having a problem with is a GT Aggressor XC3, the gears changers are Acera Shimano's and I have 24 gears and the crankset is by SR Santour (if that information is of any use).

I hope you lot can help me as I am really getting in to mountain biking, but this issues is worrying me. Thank you for any help!!!!

rankin116

Where did you buy it? They need to adjust your rear deraileur.

Look here for a little help.

ed 

Normally, I'd say it's a worn out drivetrain, but your bike is only a couple months old? It's fine until you put the power down and then it "jumps" a tooth?

nawi

I brought my bike from Halfords in England, how hard is it to adjust the rear derailer. Should I attempt to do it myself, or should I take it back to the shop for them to do it. I want to become good at maintaining my bike, but I obviously don't want to damage it by doing maintenance that is to complex for me.

nawi

I got my bike last summer, but I have hardly used it. So I don't think that it can be anything that has worn out. I think that the chain is jumping the teeth on my gear cassettes, possibly on the forward one.

jcook1989

Derailer adjustment isn't to hard. It just takes practice and a little trial and error. The website above has is a great place to start. I would try it your self and if your problem isn't fixed then I would take it to the shop and have them do it but ask if you could watch them to learn how to do.

Cobwebb67

Riding style could be the problem. Shift to a lower (easier) gear earlier before you start up hill. Learning the gears and adjusting them to fit the situation will be very helpful.

rankin116

wut

nawi

I assume you don't agree with that remark.

ed 

Apparently if you lack style...your chain will skip a tooth to teach you a lesson.

cyclezen

in order of issue importance/cost - assuming wheel alignment is not an issue

check RD adjustment (rear Derail)...EDIT - not FD, my dyslexic senior-osity... (but gimme my discount!)
check chain condition/lube, check for tight links
check cable and cable run for problems - replace worn cables
check that chain is proper spec for cogset - 7&8 spd use one type, 9 spd uses another
check that you're not using incompatible RD and shifter (as in SRAM and Shimano together)
check chain for stretch, if more than .75%, replace chain
if chain is stretched beyond 1% limit - then needs new chain AND cassette
check cogs which skip for wear - replace worn cogs or entire cassette

if the chain is OK and not stretched, the easiest way to check the cogs (if you don;t really know what you're looking for when inspecting cogs) is to get a 'good' cassette and put it on. If the skipping stops, you have an answer...
ALWAYS replace the chain when replacing a cassette - a partially worn chain will prematurely wear out new cogs - a new chain is cheaper than again replacing the cassette in the not far future.

ALWAYS check your chains for stretch in about 300 mile intervals or so; in order to 'catch' worn chains BEFORE they get to 1% stretch... shorter intervals if you do rides which require a lot of sudden hard crankin, intervals or accels...

EDIT - one other thing, since bike is relatively new - if the chain is a bit too long, dependin on the ring and cog set you're in, it may skip also. If you're crosschaining heavily, that can also allow the chain to skip.
often its a combo of small issues, none of which alone will cause a skip - dirty, rusty, sticky chain with a tight link, crosschained, and standing to hump over some unexpected obstacle or body (like the rider who biff'd directly in front of you ...)