Dojj,
As an objective opinion, that is pretty much spot on . Obviously if I had said that, I would have been shot down in flames being accused of belittling Rod's pet tuner's figures .

Stu,
I think that you're being a little harsh, as although the rolling radius "should" be kept identical (for speedo accuracy etc), it is very rare that this happens.

The standard size tyre on the Sierras is 205/50x15 and the common upgrade is 215/40x17, which is an increase of almost an inch in diameter (and on the 2wds, lots of people fit 235/40x17s on the rear, which is nearly 2" bigger).

On the Escort, the standard tyre size was 225/45x16 and the common upgrade is 225/40x18, which is also an increase of almost an inch in diamter.

I think all he was trying to say is that these tthings can all have an effect.