I need to replace my 8spd shifter pod units.

I was going to avoid getting a whole new pod and buy shifters and levers separate because I prefer that set up.

There is no doubt that I will in the future get a 9spd cassette, and well being a tight arse figured use the 9spd shifter on an 8spd dérailleur just the action.

I've done this on old XT thumbies on a 7spd but not sure if it will seriously fuck up on sti shifters.

Its a really stupid question isn't it so i fully expect to be ridiculed for this most basic question, however, I figured I'd ask

Do not think it will work as 9sp pull slightly less cable than 8sp. You'd probably end up replacing the whole lot. 9sp chains are narrower than 8sp to fit into the narrower gaps on the 9sp cassette. Hence the different pull.

I've run 8sp cassette on 9sp shifters and had no end of problems with shifting between 4,5,6 gears. That said I thought I was using a 9sp cassette and used the full numnber of clicks.

Hope it helps.

I figured the cable pull would be different and the indexing would be out.

Good thing with thumbies was you could turn them to friction if you bent a mech or were bodging.

Ah well...wonder if the missus will let me buy some more parts for my dog of dying bike!