Tyre change

[Denis]

For the moment I've got Michelin Primacy 225/50R17 mounted on my 2012 Insignia. I've been looking on the net for some "thinner" tyres and I found some who are 225/35/R17 or 225/45R17 but is that doable/legal ? Cheers...

[Mo_miah]

with 17s your tyres should be 225/55R17
the 225/50R17 are thin compared to what it should be
its not illegal to have smaller diameter tyres but your speedo will show the incorrect speed but this can be re calibrated with opcom
would be better to get bigger alloys otherwise you will have tiny wheels in a huge wheel arch

[Denis]

So my speed isn't accurate neither at the moment ? On the Opel website they state that the tyre should be 55 ? Is a difference of more than 1 cm compared to the 50 I have.

[Mo_miah]

The difference is closer to an inch in diameter. So about 3 inchs around the circumference. So many rotations. It all adds up. Your speedo will be about 5% out. As its smaller then recommended you wont risk speeding.

[cmor]

Surely this will affect your insurance if you have an accident?

[Mo_miah]

Surely this will affect your insurance if you have an accident?

Still perfectly safe

[cmor]

It may be safe but it's a change from the specified tyres, most insurers don't like that.

[2000rpm]

Surely this will affect your insurance if you have an accident?

I would say that if the tyre size is mentioned in the owner's manual for the 1.4T then it's probably legal.
225/35 R17 and 225/45 R17 aren't listed next to the 1.4T in my 2012 owner's manual so I wouldn't chance it. Other countries may have different laws.
The currently-fitted tyres, 225/50 R17, are mentioned in the manual.

Then the rolling radius needs to be considered because it will affect speedo accuracy and may also impact on fuel economy.
The 35s will be 23.2" diameter, the 45s will be 25.0" diameter and the current 50s will be 25.9" diameter.
Where the speedo currently reads 70mph the 45s will read 67.6mph and the 35s will read 62.7mph.
If the engine currently revs at 1900rpm in 6th for 70mph according to a satnav/GPS, the 45s will rev at 1970rpm and the 35s will rev at 2120rpm.

[Mo_miah]

Manual says 225/50r17 are for winter tyres only, as they have thicker treads