Question about Swapping Alloy Wheels?

Question

I have just bought a car which has 17" alloy wheels and want to swap them. The tyre size on the car is 205/40R17 and the ones i want to replace them with are 215/40R17. Would they be ok to swap or will swapping them class the alloys (or much rather the tyres) illegal? Thanks

Answer 1

As stated elsewhere, a 10mm increase in section width is not likely to cause problems either with the law or with your wheel arches, unless you are also lowering the suspension.  

The miniscule 0.40mm increase in rolling radius will likewise be of little concern.  That's less than the difference between a new tire and one that's half worn.

The increase in contact patch will have a nearly undetectable effect on cornering power (assuming you find the correct balance in tire pressure between uneven wear and steering response.  Manufacturer's recommended pressure may be a bit too low for optimum stability with the taller sidewall, but a higher pressure to compensate may cause the tires to wear early in the center, since the tire load is the same.)

One benefit I have found to going up in section width is that your tires protect your rims from damage on curbs.  (Yeah, I know.  Just stay away from curbs.  I have a history of being unsuccessful at that.)

The correct "Plus One-Half" tire size is 235/35R17, which would change your rolling radius by a nearly infinitesimal 0.02mm, but that 30mm of extra sidewall width could be a problem.  Oh, and then there's the problem that the Tire Rack doesn't list any tires in that size.  If you replaced the wheels, the same goes for the ideal "Plus 1" size - 225/30R18.

Answer 2

Tyre sizes are designed to fit in the wheel arches of the car. If you go for the wider wheel size make sure that the tyre does not hit the inner or outer wheel arch when on full lock. Also they are a certain size to distribute the weight of the vehicle over the 4 contact points of the tyre to the tarmac. Changing this can affect the balance of the car as the weight is distributed over a larger contact point.

Answer 3

There's no question of legality, so don't worry.

The new tyres will be 10mm wider, so not a great deal of difference - they are also only 8mm larger in overall diameter, so you'd be unlucky to encounter any problems.