Right now I have 225/55-16 , and I was wondering if I put on 245/45-18 ... the overal diameter is about 1" bigger, what happens other than the speedo will be reading something wrong. Is that 1" a huge deal? I know I should get 245/40-18 but I might not be able to.

This might be a stupid question... sorry.

 

actually, that is perefect, depending on what wheels you are getting [width].

Factory overall diameter of 225/55/16 = 25.74 inches/654mm
Aftermarket overall diameter of 245/40/18 = 25.72 inches/653mm

Difference of .15% and -1mm

 

Hey, I was just wondering about 245/45-18 which is a little bit bigger. I know with 40% its good.

 

That would be a no-no. Overall tire diameter would increase to 26.68 inches, or 678mm.

That is a 3.67% or 24mm.

 

So does that mean avoid at all possible costs, or , I wouldn't do it, but it doesn't really matter if you do.

BTW. Nice wheels Legendary

 

One inch increase in overall diameter is huge when done at the same time with widening your tire wall cross section. An issue related to this include the ability/inability to do a full turn of the wheel without the tire touching the inner fender well.

 

What about the NAV system- is it affected?

 

With 19s, the ideal tire size is 245/35/19 and with 20s, the only tire size that fits is 245/35/20. So the overall diameter increases by an inch when you get 20s especially with the GS...I'm not sure about other Lexus models tire sizes and wheel diameters.
Does that mean that all GS cars with 20s would not be able to make full turns without the tire touching the fender well? I haven't heard of GS owners with 20s complaining about this

 

I remember reading in a post that deviating more than 3% in overall diameter could create suspension problems or put additional stress on parts of the suspension. Maybe someone could confirm this. Incidentally I'm moving from 225/55R16 to 245/40R18 on my GS when the weather finally gets better. I was told not to do 245/45R18 because of rubbing against the wheel well as well as because it was too much of a diameter difference.