On Alfa number 15
AO Platinum Member
Join Date: Dec 2005
Location: United Kingdom
As long as you have at least V rated tyres on a Twinny you will be fine.
Both Y and W exceed this rating...
The construction and use regs state that the tyres need to be fit for the purpose to which the vehicle is put, not what it is capable of being put.
So in theory you should be able to get away with tyres rated up to 70mph if you don't speed.
However your insurance company is likely to argue that the tyres are not up to the manufacturers specification and refuse to pay a claim if you crash.
Load ratings are also very important. You can go for a higher load rating than that fitted originally but if you go lower you are risking tyre failure.
You will never be cool driving a Vauxhall.