wheels out of balance, mine does the same and has had new discs since and still does it.

i have same problem with my corsa c it doesnt vibrate the steering wheel, its just the pedal judder..is it the rear breaks instead of frontss

It will definatley 100% be warped drums! If its just the pedal juddering then it HAS to be rear brakes, if it were fronts the steering wheel/car would twitch around.

Im very hard on my brakes and have done this to quite a few sets now. Easiest thing is to whip the drums off give em a good clean (dont breathe in the dust!). see if theirs any life left in them or the shoes by inspection. If they are all ok then take the drums to any local engineering place and get them to see if they are out-of-round by using a micrometer on the inner faces, only takes two secs. if they are out by more then 0.1mm then renew drums and shoes.

i ruled out warped discs because i had the car serviced a few weeks ago and they said the discs and pads were fine, %50 worn. wasn't doing it with my standard 14's but it was a soon as i put the 16's on it did.
think 'ill give them a phone anyway and get them to check the balancing, it the bloody least they can do after scratching my speedline! thats why it had to get refurbished.

warped discs

could be a number of things, yeah could be balancing which is cheap to sort, could be warped disks, not so cheap, could be traking, and could even be worn control arm bushes,

another thing is the steering wheel does not shake at high speed which it should if the wheels need balanced.
the cars a 00X corsa B sxi if that has any relevance.

i have just put my 16's back on after having 2 refurbished and getting two new tyres.

problem is when i brake heavily the brake pedal vibrates and pulsates under my foot.

i think the wheels need balanced but i thought i would get a second opinion before i phone the garage.

any help would be appreciated, thanks very much, Kenny