I should have inquired about this in my original post.
Replacing the stock 18" wheels and tires for the Lexus 19"s from LA Wheel.
Am I right in assuming that the closest tire size I can get to maintain speedo and odometer accuracy would be the 245-45 series?
Thanks
Doug

 

245/45/19 translates into a side wall that is 4.338 in tall. Add that to 19in wheel and you have a combo that is 23.33 in tall.

The original tires are 235/50/18 which translates into a side wall that is 4.625 in tall. Add that to 18in wheel and you have the original combo being 22.62 in tall.

That is a 0.71 in difference that is going to cause a slight difference in reading, the speedo will read a little less than the actual speed. (You will need less wheel turns to cover the same distance you would with the original combo).

 

straight from the lexus site:

235/50R18 V-Rated all-season tires
245/45R19 Y-Rated summer tires

those are within the spec

luxo, your calculation is wrong. you forgot to x2 on the sidewall. for 19s, the overall diameter should be 27.68, and for 18s it's 27.25

with 0.4" difference overall, it's negligible

 

Why x2?...

I thought the /35 and /45 was in reference to the percentage of the width.

For example 245/45/19:

245 (this is how wide the tire is in milimiters) x 45 % (the ratio) = 110.25mm which is 11.02cm that equals to 4.38in. If the wheel alone is 19" in diameter, you add the 4.38in and you get the diameter of the wheel + tire.... Am I missing something?

 

haha yeah, you are missing the fact that 4.38" is the sidewall height, and you have two sidewall when you are trying to calculate the diameter (tire wrap around the wheel)

 

Thanks guys, that's the way I figured it, only comes to a 1.58% difference. So if speedo says 80MPH you are actually racing along at 81.26
Cheers
Doug

 

just the instrument error deviation alone can be that much already you are fine

 

Automated calculator
http://www.1010tires.com/TireSizeCalculator.asp

 

Ok, that makes sense.