hears one for 30psi

[Magnum]

In my car it doesn't feel like I am running to slow or fast. But if the speedo was right on stock tires then the calculation above is correct.

[30psi]

I've got a GPS sat nav, and a GPS radar detector, and in all 3 S12's Ive had they've shown that.

Even my Nissan Micra, that would show 80mph but was actually 70mph. The only car that was close was my Dads Honda.

The manufactures do it because the last thing they want is a case against them where someone can prove the speedo under reads, so they purposely make it do the opposite.

[s13eater]

i've got a graph which was done on the RR, it shows mine at about 6mph out.