Is anyone thinking of upgarding their tires to 245/45 or 40/18??
Also I've noticed that the 350Z has different tire sizes on the front and back. Is this a possiblity on the RX? It looks like there is lots of room for an increase in tire size according to the wheel wells.
Looking for your thoughts!

JayDee

 

245/40/18 should not be a problem but it will be about .9 inches shorter. There are a lot more tire choices in the 40 series vs the 45 series.

 

If you go with a different overall diameter you will have to account for the rpm/speedo/odometer differences.
I wouldn't put a staggered tire setup, ie rear tires wider/larger than the front on a car that doesn't come stock like that. Staggered tire setups are done for a reason and are designed to fit the suspension. If the 8 is non staggered, keep it that way.

 

Hmmm; accordion to my calculations, a 245-40/18 would only be about .25" smaller in O.D. than a 225-45/18. I would think this would have a pretty insignificant effect on meter readings.

I agree with Quick_lude about using two different sizes, especially if the car has 50-50 weight distribution and fairly neutral handling.

 

The specs I checked for S-03's says only a .3" difference between 245/40 and 225/45, does the RE040 have a different spec than the S-03's for the 225/45? They weren't shown on tirerack. The .3" shouldn't really be noticeable but .9" might be.

 

When I looked up the height of the 2 sizes they were on 2 different rim widths. On the same rim width the difference is only about .2 to .3. The difference between 7.5 and 8 inch wide rim made it the .9 difference.

 

This is a good error calculator: http://www.mindspring.com/~toy4two/tire.html

According to that, the 245/40/18 is only off by .99% from a 225/45/18 tire. So your speedometer will show a slower speed and your odometer will be off by 10km less over a 1000km distance.

 

If the tire is less than 100% wouldn't it read more mileage than you are really traveling.

 

I have found that the 255/40WR18 is only .2% slower than stock. Not enough to make a difference!

 

Side wall difference between the 225/45WR18 and the 245/40WR18 is only .1 inch and tire diameter is only .3 inches smaller so it should be practicaly nill.