[ECha3]

P255/45R18 fit on the front of my 2006 just fine. Your 255/50R18's would be 3.57% too big. Your speedometer would be 3.706% low. Many people would consider this varience from stock to be dangerous and/or potentially damaging.

265/40R18 would be 2.56% too small. 275/35R18 would be 5.41% too big and I'm pretty sure they would rub.

Play around with this:
http://www.1010tires.com/TireSizeCalculator.asp

Good Luck!

 

[ECha3]

^^^^^ Yep!

Thank you Echas. To be clear about the 255/45-18s fitting your 06 STS, I assume you mean you have them on and have have driven around on them for some miles? Any problems at all? Do you drive in city? rural? potholes etc?Let me know when you get a chance. Thanks in advance.

The DPO & his dealer had rotated the P235/50R18 - P255/45R18 every 15,000 miles. When I got it, the tires were on the wrong ends with no adverse effects (other than the blushes from the selling dealer).

I do wonder how big one could go with the ZF Steering. It seems to have a quicker steering ratio but I don't know if the turning radius changes. :hmm: