Hi all, new guy here. I have an issue with my bike, I think I might have the answer but I'm looking for confirmation from some of the learned bike techs on here.

I have a Carrera Subway 2 bought in Halfords about 2 years ago, it's an alright bike, it gets me to work and home every day and that's all it has to do, I do the odd longer 40k cycle here and there but the primary purpose of the bike is commuting.

My issue is with the gear cassette, it's an 8 gear Shimano set I have on there now. The issue is this, about three months ago the chain broke, this was while slowed down to cross a road and then while starting again, it clunked and broke, the link was completely blown and had been on the receiving end of a lot of force. I had a guy here at work show me how to fix it and the chain went on one link shorter. A few weeks later, same place on the road, I heard a metallic grinding and then the second gear just fell out of the cassette in pieces and hit the ground. I went to Halfords and had them replace the cassette, I didn't have the tools to do it myself.

Now I'm here 7 weeks later and the cassette broke again yesterday, the first gear this time, teeth ripped out of it and the gears were done.
I went down to Halfords again, I had some vouchers, got the toolkit and a new cassette and replaced it myself.
So now I'm at the point of having had a broken chain, and two broken cassettes in a very short space of time.

My question is what is causing this? I have an idea that it's because I don't tend to change the gears much. I tend to stick in 15th/16th gear a lot and when coming to crossing the road etc I don't gear down. Now I think this might be the reason as any time I've had problems it's been from a standing start and I have a lot of torque on the chain due to the low speed vs high gear and this is when I'd get the crunching sound and something blows.
Is it simply a case of needing to change gears more? I tend to stay on the middle cog on the pedal side of things as I don't do any mountain biking and I want to stop the tendency of cross chaining and simply don't need the full range of gears. Now today while riding to work I changed the gears when slowing to a stop to decrease the torque when starting up again.
Is this the answer to my problems? What else could be causing this issue? If there's a root cause I'd like to know what it is cos the Shimano cassettes are starting to cost me money, that's 70 euros now on them in 2 months, that's enough.....

It might seem like an obvious answer to most of you, but I'm curious if just changing my gears more often would be enough to solve my issue?

I'd appreciate any help on this one as I don't want to be buying a new cassette every few weeks, Oh one other thing, after changing the cassette, the chain appears to be quite clunky and not so smooth on the cassette, is this normal or again is there any adjustment that might be necessary? Thanks for any help or tips that you might be able to offer.

(apologies for my lack of terminology, but I'm not really into bikes, I use it to get to work )

Eoin.

Ok no worries, I just phoned Halfords and got to speak to the bike tech there, he's confirmed my suspicions that it's starting off in too high a gear.

I didn't realise that it could cause this issue, you learn something new every day.

Did you replace the chain when you replaced the 2nd cassette? if not, there's your problem.

A cassette should last 2-3 chains, but you should change the chain when you change the cassette.

If you are an all weather commuter, 2 years of commuting will have probably killed your drive train, would suspect your jockey wheels and possibly the chainset could do with replacing as well.

For starting in too high a gear, not convinced, unless cross chaining.

You should of replaced your chain when you replaced your cassette; sounds like a big factor in compromising the gears. Starting off in a high gear is not the problem, if it were there would be on fixed bikes or track bikes. This has good info. https://sheldonbrown.com/k7.html

BTW, my riding style involves a lot of sprinting, so I also use a lot of torque, never had this problem, if I did I would have changed out the chain and cassette together. Read the link, sheldon Brown can expain it better than me.

Eoinmag:

Do you have a picture of these broken cogs? I'd be very interested to see the failure mode. I agree with John Gault about the torque issue. I'm a heavy guy and ride hard sometimes. Never broken a cog before like what you've said. But I'd like to avoid it if I can so I'm wondering what's the mystery here. Thanks in advance.