shav wrote: Those tyre sizes are fine as
No they are not as they have different rolling diameters. Would be fine on a 2WD or one of the many 'part time' 4WD cars.
steveP wrote:The myth of the same rolling diameter on all 4 corners doesn't hold water.
It does with a Subaru.
It's obvious that the only difference in the OPs selected tyres is the tread width, applying this to the same aspect ratio gives varying diameters of 1.33%. While this sounds insignificant, and it is to most cars, it will cause heat build up in Subaru's fitted with manual transmissions as they use a viscous (limited slip) center differential to allow for variations in the average speed of the front and rear axles due to cornering, same as a RWD diff does for the rear axles. The automatic transmissions use a system similar to most other brands where the drive to the rear axle is controlled by a 'wet clutch' which can be applied (or not at all) to increase or decrease the drive to the rear axle. The front axle is always driven. At with any clutch, there is slip involved so this will counter the speed variance between the front and rear axles. Having said that, it's still a bad idea to run different rolling diameters between front and rear.
I have seen a Jeep do some nasty stuff just after new tyres (identical to the rear) were fitted to the front and the difference in tread depth was enough to upset it. Similar situation with a Falcon where it freaked out the ESP.
Take a look at some of the cars that run staggered rims and tyres from factory and you may notice that, due to the different tread widths, the aspect ratio is different to give almost identical rolling diameters.
Don't run different rolling diameters on Subarus kiddies...