Hello all,

Just looking for a sanity check here. A few summers ago, I bought some 18" wheels for my summer tires, and put on 225/50R18s, which according to my calculations were a close match on diameter and speedometer to the stock 225/55/R17 2008 G35x sedan setup.

I recently had to change repair shops, and the new shop is telling me the 225/50R18s are almost an inch too large on diameter and I shouldn't be using them. According to my calculations they are wrong, but as part of my research I did notice a couple things:

1. 245/45R18 is probably a better match on size than the 225/50R18 I went with.

2. The stock tires Infiniti puts on the "sport" version of the G35x sedan are 225/50R18 fronts and 245/45R18 rears.

Since I'm about ready for a new set of tires anyway, should I switch to 245/45R18 on all 4 corners and be OK, or should I be doing 225/50R18 fronts and 245/45R18 rears like Infiniti puts on the "sport" model? I know you need to be careful about changing tire sizes on the G35x because of the AWD and the ABS systems. My preference would be the same size on all corners if that's OK, to give me more options on tire rotation.

Thanks for any input,

nbhms

 

I have an '05 X. I run 235 35 r18 and have run 235 45 r18 and 235 40 r1 all without issues. The only thing to look out for is the outer diameter of the tires. Match that all around and you will be fine. If you want to go wider in back than front, you can do that also but you will have to research the OD of the tires and most likely change the tire series (distance from ground to wheel) in the rear. If you care about your speedo being accurate, well tough. I believe you can have it re-programmed. All I do is use my GPS to figure out what the difference is and use my speedo accordingly. I prefer going down in size because I feel like I'm going fast but get way less tickets....

 

245/45R18 should be just about bang on for speedometer, according to online calculators. But I do the same, I have a GPS which I use for speed comparison. I like the look of wider rear tires, but unlikely to do it since I prefer the easier tire rotation of same tires all corners.

 

If your 18" wheels are from 8 to 9" wide you'll be fine running the 245/45/18s. That tire shop is full of crap though, you were gold w/ the 225/50/18s too