Vauxhall Tigra brake judder through steering wheel

Make sure the caliper pistons are not siezed-did they push back easily?
Also check that the new discs are seated properly on the hub-remove any dirt or corrosion.
Unless they sit absolutly square to the hub, you will get a judder.
Are the wheel bearings ok?

the pistons went back easy and the bearing are ok and the disc seated ok

if the judder was there before you changed the discs/pads, and it`s still there now, you have to wander if the problem lies in the steering colum universal joints or the rack itself--but i am guessing now.
sorry i can`t help further

Track rod ends and tie rods are very prone to where out on these vehicles...

i,ve changed the off side track rod end the n/s is ok the problem there before i changed the disc,s and pad,s i get it when i brake hard not soft braking

Check for any excessive play in the tie rods...

how do i check the tie rod?

If this happens when you press brake pedal during the on position make sure the caliper pins are clean, oiled and slide through their rubber seats. Usually i would try anther set of discs and pads 1st to rule out this problem. Also try once you stop driving feal both front wheel incase of excessive heat this would suggest brake binding on. Do not try and touch discs as will be very warm

i have find the problem it was the road wheels they were not the proper one,s for the car i got the proper wheels now and the problem gone