Asking a question of the experts here –

I'm doing the next door neighbour a favour and servicing the wife's commuter bike and the drivechain has had it.

Everything bar the shifters and mech are fubared. Unfortunately it's a 5 arm chainset and they're in short supply, or so it seems. It appears the cheapest option (this is just a keep it running type thing we're doing) is to buy another chainset

Something like THIS but it does seem to be a 9 speed according to the FSA website.

The question is then; how will it work if I keep everything else 8 speed?

Your experiences would be appreciated

Cheers

Gaz

It will be fine, first bit I changed on my old orange clockwork when I started upgrading from 8 to 9 speed was the chainset and had no issues. Similarly I'm running a 10 speed chainset on my commuter, and the rest of the drivetrain is 9 speed.

Cheers Boatman that's encouraging.

Anyone else?

Yes, it'll be absolutely fine. I've done the same many times.

I have mixed and matched from 7- 9 with drive train and shifters occasional indexing issues (which you can adjust out)
Currently Hack bike = 9 speed crank, 7 speed chain and cassette and 8 speed shifters

Road Bike = 6 speed crank + chain 8 speed sti's and 9 speed (mtb)cassette or 7 speed on the proper roadie tyres /wheel combo

It works iirc there is about .2 mm difference between rear sprocket thickness or about 1 – 2 mm across the entire casette.

Yes it'll work fine…just don't be tempted to try and save a few quid by keeping the old chain!

Don't listen to junkyard if you want things to work nicely, it may work after a fashion, but won't be great!

The chainrings work because the spacing doesn't change, just the thickness of the actual sprocket. If you tried to put a 10 speed chain on 7 speed rings (for example), the sprockets would be too thick, but there's no problem with a chain being wider than the sprockets.

As long as your chain, cassette and shifters match in number of speeds you'll be absolutely fine.

yes dont listen to me about my bikes njee20 knows best about them sorry

9 speed chainset will work with 8 speed everything else because the wider gap in the 8 speed chain will fit over the thinner teeth of the 9 speed chainset. Might not work the other way around though as the narrower chain might jam on the thicker rings.

As said above, spacing is the same.

I'm not saying your bikes don't work Junkyard, although there's a vast degree of subjectivity involved with 'works', but to recommend people mix and match chains cassettes and shifters is pretty daft. It will just not yield satisfactory results in the vast majority of cases.

There are some exceptions, you can use a 10 speed chain on a 9 speed drivetrain, it will wear quicker, but the weight weenies like doing it.

A 7 speed chain/cassette will more or less work with an 8 speed shifter as the gaps are identical, the chain is the same 7-8 speed, but the 8 speed cassette is wider. 8/9 will not work, as the cassettes are the same overall width, with the 9 speed sprockets closer, an 8 speed shifter will constantly overshift. Whatever you say.

My road bike works perfectly, and is fairly ecclectic mix (and that is 'works' as in well enough to win club time-trials on)

10 speed Ultgra cassette (with a nice red SRAM lock-ring)
10 speed chain (SRAM something-or-other)
10 speed rear shifter (105)
9 speed rear mech (XTR Shadow)
3 speed front shifter (Tiagra)
3 speed front mech (Sora)
Double chainset (Tune Bigfoot)
XTR UN91 Bottom Bracket
9 speed big ring (Stronglight something)
8 speed little ring (Sora)
Aligator I-link cables

Just make sure rear shifter/cassette/chain are all for the same number of speeds, everything else should be fine. If running a double-ring with a three speed shifter like I do you will just have a dead shift, where you pull the lever and nothing happens, not really an issue.

drivechain?

9 speed chainset will work with 8 speed everything else because the wider gap in the 8 speed chain will fit over the thinner teeth of the 9 speed chainset. Might not work the other way around though as the narrower chain might jam on the thicker rings.

a 9 speed chain will work on 7 8 or 9 speed Hyperglide cassettes but is not wide enough to fit onto a 7 speed Interglide cassette sprocket.

An 8 speed chain will jam in a 9 speed cassette and work absolutely fine on 8 or 7 speed hyperglide cassetes sprockets.

7 & 8 speed chains come in 2 flavours; HG for 1.8-1.85mm sprockets and IG for 2.35mm wide sprockets.

http://www.sheldonbrown.com/speeds.html