Seeking recommendations for MTB gearing overhaul.

[Stu99]

I have an ancient 21-speed MTB and would like to replace the original Shimano STX-rc gearing and associated components.

Problem is that I am limited by the 7-speed rear sprocket (and chain stay specs).

What recommandations for a new cassette, derailers and shifters (and possibly front chain ring/cranks)?

Despite the age of the bike, I'd like reasonable quality components.

 

[Renard]

If you are changing all that you can go 8 or 9 speed.

 

[mickle]

When they moved from 7 to 8 speeds they added a sprocket whilst keeping the spacing and sprocket thickness the same. So the cassette and therefore the hubs (and frames) got wider by the width of one sprocket plus one spacer. When they moved from eight to nine they squished nine sprockets into the same space as used by eight speeds by reducing the width of individual sprockets and the spacers. So there are lots of compatibilities, ie an eight speed shifter will drive an otherwise seven speed system with no probs (you just have a redundant 'click'). A 9 spd cassette will slide straight on to an 8 spd cassette. Nine speed chains work well with 7 and 8 speed trannies. And so on.

Don't discount the option of widening your rear end to accept a larger OLND. (so to speak) I would be tempted to make the whole damn thing nine speed and be done with it.

 

[jpembroke]

Hmm, not sure. I know that 8 and 9 speed (and 10 speed on road bikes) cassettes all use the same freehub width but I thought that 7 speed was narrower i.e. if you put a 7 speed cassette on a modern freehub, don't you have to use a 7 speed spacer? As far as I recall, yes, you can fit a 7 speed cassette on an 8/9 speed freehub, by using a spacer, but not vice versa.

 

[Stu99]

Thanks for input so far.

I was led to believe (like jpembroke) that you can't replace a 7 speed sprocket set with 8 or 9 speed without widening the chain stays (which I an reluctant to do if it can be avoided).

 

[jpembroke]

Thanks for input so far.

I was led to believe (like jpembroke) that you can't replace a 7 speed sprocket set with 8 or 9 speed without widening the chain stays (which I an reluctant to do if it can be avoided).

and there is still the issue over the width of the freehub. If I'm right and you can't put an 8/9 speed cassette on a 7 speed hub then you'll need a new back wheel too. I think it may be a) stick with 7 speed, or get a new bike.