Rear derailer adjust problem

[Stereo]

Have been adjusting my rear derailer on my new bike, but (using any front gear) the 3rd largest cog makes a noise. If I adjust the tension a little, it's fine but then the 6th cog makes a noise. Is this normal, or is there a way to make all rear gears work without rattle?

 

[Mr Pig]

Depends what the rattle is. Often the chain rubs off the front mech/dérailleur in some gears, typically when the chain is crossed, that is running outside to inside across the gears. When you change gear you should try to avoid doing this. Move a few gears across the rear cassette, then onto the middle gear at the front, then a few more on the rear to avoid running the chain at a harsh angle.

If the chain still rubs on the front dérailleur it probably needs adjustment. Set it about 2mm above the big ring when it's in top gear, set it straight/in line with the gear then move it in and out until it shifts the gears ok and doesn't rub on the chain.

 

[accountantpete]

Check that the cassette lock ring is sufficiently tightened.

 

[Stereo]

Thanks for the help, I'll have another bash tomorrow.

What does a more expensive derailer improve? Faster shifting, durability?

 

[Mr Pig]

What does a more expensive derailleur improve? Faster shifting, durability?

Mostly durability. They'll work a bit better but mostly they'll stay working ok for longer. Cheap ones shift fine but tend to get loose quite quickly. I use Deore ones, they seem a reasonable compromise between cost and durability.

 

[Stereo]

Thanks Mr Pig, good to know.

I recently got a Subway Carrera LTD, and having got the bike I noticed a mistake on the specification, which clearly states the bike has "SRAM X4 Shifters" but comes with X3 shifters and front derailer and an x4 rear derailer. Halfords are eager to fix this and have put the X4 shifters on order, but X4 are 8 speed whereas the current X3 are 7 speed. Is it OK to use an 8 speed shifter on a bike which has only 7 rear gears?

 

[Mr Pig]

Is it OK to use an 8 speed shifter on a bike which has only 7 rear gears?

I'm not sure. I wouldn't have thought so but some of the tech-guys on here should be able to tell you. 8-speed chains are thinner than 7-speed so I would have thought the shifters would move different amounts. Try a search to see what the SRAM shifters are compatible with. The front will be fine, if you do have an issue it'll be with the back.

However, You could just fit an 8-speed cassette? If it'll fit, not sure about that either! ;0)

It's not unusual to see bikes advertised using the highest spec gear part as the selling point, you'll often see a better rear mech than the front or shifters. It is actually the most critical part.