Yep fronts are wrong should be 245/30/20 I'm surprised you haven't had lsd probs
ideally you should have
FRONT 245/30/20 on 20" x 8.0" to 9.5" rims giving - 0.71% difference to standard 225/45/18
REAR 275/30/20 on 20" x 9.0" to 10.5" rims giving - 0.69% difference to standard 245/45/18
OR
FRONT 255/30/20 on 20 x 8.5" to 10" rims giving + 0.20% difference to standard 225/45/18
REAR 285/30/20 on 20 x 9.5" to 11" rims giving + 0.19% difference to standard 245/45/18
do you know what size your rims are ?