I'm just about to buy a bike with Hayes hfx9-xc disc brakes and wondered what the implications of upgrading the 6'' rota to 8'' are?
Is it something I can fit myself and do I need to change the caliper? (been running squeaky vees for last 5yrs so not clued up at all!)
cheers

You will need the 8in adaptor, the caliper remains the same

And the adaptors are about a tenner a piece.

cheers!

I run the EBC 8" conversion on my hayes HFX 9. Works really well and if you are buying a disc & adapter at the same time its good value.

Yeah, but then you'd be running an adaptor on an adaptor

Also, check the maximum recommended rotor size for your forks.

Another question - why do you want to change to 8" rotors ?

Maybe he wants more brakes? I run 8in rotors on my bike

It is an adaptor on an adaptor kato as you say. Its a perfect fit and tbh i dont have a problem with it. If any part of it is gonna break, it will be the original adapter, not the new one from EBC.

Here is a piccie of mine EBC 8" Conversion

EBC Adapter on a Adapter is fine, it's a visibly 10mm wide, or 20 if 203mm disks bit of metal, you won't see it and it allows for some caliper fine tuning adjustent that you don't get with a normal adapter.

I just want an 8'' rota because I'm , how shall we say..er..15 st. I've also had several pant-wetting incidents in the peak district riding down peaks (surprisingly) and finding that my squeaky XT vees quite simply don't stop me! (and they are set up as best I can get 'em).
I didn't think I'd ever need bigger brakes than Vees until I moved oop norf and started riding "gert big 'ills'.
So, to recap, is there an all in one kit I can buy, i.e. adapter and rota? cheers

oh yeah bike has Nixons if that helps at all (are they strong enough etc)

More than

Dont bother with the 8" rotor I am 17 stone and ride the smaller rotors with no problems at all, they did get a bit warm on the scary bits of the Marin Trail an are so much better than cantis in the first place.

go big, you've no reason not to :-)