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Just installed the CS-HG70 cassette and while doing some tuning, noticed that my chainring is no longer true, especially around the crank so am thinking about replacing the chainring set but can not find a decent 8 speed set but see a lots of 9 speed chainring set, can I use that instead?

Thanks

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2 Answers

Ideally, you should stay with gearing designed for the number of gears on your bike. If you must use a different design, stay as close as possible to the original, and make sure you go to a larger number of gears, like the 9 speed you suggest.

If you do use a 9 speed chainring set, be prepared for your shifting to suffer to some degree. (How much depends on the exact brands and specifications of your original, and the new set you pick. No, I don't have any way to tell you what to pick.)

It's also possible that you may occasionally drop your chain unpredictably. If it happens even once, then you need to find a good 8 speed set again.

This is the 9 speed compatibility chart from Shimano.

9 speed chart

This is the 6/7/8 speed compatibility chart from Shimano.

678 speed chart

As you can see, there are no cranks listed as duplicated on both charts. /There is also a note indicating sub par shifting if even some closely interchangeable parts are used.

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Yes; as long as you get a 7/8/9 speed compatible chainring set.

If you mean a strictly 9 speed labeled chainring set; Maybe. The more I look it seems opinion is divided between whether 6/7/8 speed chainrings are interchangeable with 9 speeds or not. A 9 speed chain is slightly narrower than a 6/7/8 speed chain, and this is especially important for the cassette. The distance from tooth-tooth is the same, though.

I've also seen some chainrings advertised as 8/9 speed compatible such as BBB Roundabout chainrings (8/9 speed compatible printed on the ring) or this set on eBay (Mowa MTB Chainring Set).

There is a possiblity that they are mistaken about the compatibility as @zenbike suggests, but both of those sources have good return policies.

It is worth noting that Sheldon Brown describes this as a non-issue in either direction.

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The reason you find disagreement is that too many mechanics seem to think that if you can bolt it up, then it must work together. And that too many amateurs think that they are qualified to hold an opinion on matters like this because they googled it, or even worked in a bike shop one summer when they were in high school. –  zenbike May 6 '12 at 10:34
    
Adding to that confusion, it would seem, would be that 7/8/9 speed compatible chainrings DO exist (as demonstrated), while some are only 7/8 and some are only 9. Depending on your own experience, you would form different conclusions - sometimes it bolted up and DID work. –  Ehryk May 6 '12 at 10:52
    
Anyone can simply state something as fact, yes. Being right is another thing entirely. The document linked here is the compatibility chart which includes the FC-M442 you referenced, and which someone's inaccurate forum post led you to believe was 6/7/8/9 speed compatible. As you can read, it isn't listed compatible with anything other than 9 speed. Drivetrain Compatibility chart –  zenbike May 6 '12 at 12:10
    
You are correct that anyone can hold an opinion, of course. The trick is making yours the right one to hold. Also, please save your political references for somewhere appropriate. In case you are confused, that isn't on this site. We talk about bicycles here. I've flagged that comment as offensive. –  zenbike May 6 '12 at 12:47
    
Fair enough. Answer edited to remove the FC-M442 reference. Is it your position then, that all 6/7/8 speed rings are not compatible with 9 speed chains, and vice versa? Or just the incorrectly linked Shimano ones? –  Ehryk May 6 '12 at 13:05
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