Maybe it's just because my last tyre had over 10k miles on it but I replaced my old RoadSmart II front tyre with another of the same model and it used to be rock steady up to 138mph now if I go over 115mph the front end starts to oscillate, lucky for me I had a long long straight road to ease off the throttle and let things settle down.

But it's definitely worrying since I used to be able to take sweepers at 100mph+ but I'm very nervous to even try that now.

The tyre pressure is exactly the same as it was before 32psi for canyons and 36psi for commuting. No changes to the fork tubes or preload/compression/rebound damping either.

Maybe I just haven't felt a truly round front tyre in a long time? The bike is definitely more willing to change direction at speed which is nice but I lost so much stability (I'm very very light on the bars).

Is the tyre well balanced?

I don't know the name of those in english (sorry), sometimes they fly and the tyre starts bumping at high speed.

Yeah I watched them balance it. I'll have to double check that all the weights are still glued to the wheel.

Loosen and tighten the axle cinch bolts. If you back away your caliper pads you may be able to check tyre balance to a degree. My guess would be balance first then go from there.

Did you only change the front or did you do front and back?
I never replace just one tyre I always change as a new set.

Comrade: Assuming you had it changed at the shop by an apprentice - spacers still in ?

have they fitted it on the rim the right way round? check the direction of travel arrow..

Good thinking but I always take my wheels off to have them changed. I just double checked and it looks like both spacers are on. Is there a way to check without me taking the wheel off? (side to side play or anything?)

Oh!! You would know

If your spacers weren't fitted correctly your brakes would drag shockingly as the alignment would be out. i would loosen pinch bolts, bounce then re tighten, some times it can take 3-400Ks for a tyre to bed in and scrub in, a few heat cycles help too. Hopefully the tyre isn't old stock, give it a thorougher check over.