Car juddering at motorway speeds

Can't really be anything else other than wheel balancing I'd have thought - it can only really be the vibrations from the ill-balanced wheels up into the chassis of the car.

Maybe rear wheels if you can't feel it through the steering

i had a similar issue last year. bought the car after the alloys had just been refurbed and when i say just done i mean the guy drove the car into the place i bought it from after doing them when i was there. my first time i put some speed down i thought my teeth were going to fall out as he hadnt balanced the wheels after refurb,got them balanced and there was still a bit of vibration around the 60 mark from the fronts, so i put the fronts on the rear and could feel it through the car still, eventually i got a decent set of tyres all round and no probs at all now. point being if the tyres are not decent tyres like mine were not then you could quite literally be going round in circles trying to get rid of the vibration

Do you have spigot rings on? Not fitting / having them would mean the wheel isnt fitted perfectly and that'll cause a vibration over 60mph

I had the same thing on an old polo. Spigots sorted it out