I have a 03 XK8 with 19" Apollo's that are in poor condition due to curb rash and chrome pealing.

Found a set of BBS Perseus 20" rims from a 06 XKR in mint condition with new tires for a great price.

Questions is will this rim/tire combo work without any issues or having to reset anything in the ECU?

Current tire/rim combo:
Front - 245/40/19
Dia. 26.7, width 9.65,sidewall 3.86, circumference 83.9, rev per mile 755.3
Rear - 255/40/19
Dia. 27, width 10.04, sidewall 4.02, circumference 84.9, rev per mile 746.5

New tire/rim combo
Front - 255/35/20
Dia. 27 width 10.04, sidewall 3.51, circumference 84.9, rev per mile 746.6
Rear-285/35/20
Dia. 27.9, width 11.22, sidewall 3.93, circumference 87.7, rev per mile 724.4

Edit:found a speed comparison for the tire sizes ---- MPH

Front-245/40/19 vs 255/35/20
19.8 vs 20
29.7 vs 30
39.6 vs 40
49.4 vs 50
59.3 vs 60
69.2 vs 70
79.1 vs 80
89. vs 90

Rear - 255/40/19 vs 284/35/20
19.4 vs 20
29. vs 30
38.7 vs 40
48.4 vs 50
58.1 vs 60
67.7 vs 70
77.4 vs 80
87.1 vs 90

Front difference is not to bad however the rear does differ a bit. Any input on the issues with the ECU or any other programming changes that may be required is appreciated. Not concerned with the speedo reading being off, I can deal/live with that.

 

I actually run 255/45/20 and 295/35/20, so in diameter size this is ok (and only small changes are needed in the rear for this isze of your car is lowered as well).

However the difference between the front and rear may not be too big or the traction control will think there is a an issue. At least that is if the rear is smaller, I don’t know what happens if the rear is bigger, but I wouldn’t take the risk.

Why not go for 255/45 in the front to keep the balance right?

 

Avos, thanks for the reply. Tire/rim combos are my weak point. I can wrench and handle electrician work with no problem but the black art of tires and rims are a mystery to me.

I checked the specs on the size you listed, see attached, and the size you are running both front and rear is quite a bit more of a different/larger than my stock and the size I'm asking about.

The new set I found already have new tires installed in the size I listed so would like to use them if possible.

 

The new wheel/tire combos are stock size for the front and only the aspect ratio of the rears are different. Stock rears are a 30 ratio versus a 35, only about a half inch taller. I doubt if you could tell the difference.

 

Typo, I use 255/40 in the fronts

What matters is the difference in diameter between front and rear. Iirc a 3 to 4% smaller rear will cause the traction control to step in, as said I don’t know what the will happen if the rears are bigger in your case.

 

Thanks Avos,

My question still remains concerning the reprogramming of the ECU or Transmission for the different tire size. I read in another post something about the tire/rim size has to be set in a program on the car.

 

No need, you are not changing the gear ratios,