I bought some 19" G35 wheels.
G35 size (19" stock rims): 225-40-R19/245-40-R19
350Z size (17" stock rims): 225-50-R17/235-50-R17
350Z size (18" stock rims): 225-45-R18/245-45-R18

I am looking to buy tires for the G35 rims. I have been playing with tire sizes using the "Miata tire calculator" site and get different % values for how much I am deviating from the stock diameter. Should I use the stock 17's or stock 18's for the baseline comparison? The % difference between the two is considerable. Thanks in advance.

 

Use the 19" sizes recommended for the "G". They will work fine on a "Z".

Lou

 

+1. It would be more simple to use the recommended tire sizes for the 19 inhch OEM wheels wouldn’t it?

 

It would be more simple to stick to the G35 stock sizes, I agree. But there are two reasons I am more inclined on other sizes (mainly F: 235-35-R19, R: 255-35-R19). These sizes are less purchased, and therefore, the prices are a bit less. Also, it's an added bonus to have them slightly wider.

Also, the tires I want, Goodyear F1 GS-D3 or BF Goodrich TDW-2 do not come in the G35 stock size of 225-40/R19.

 

You could put 245/35/19 on the fronts, instead of the 225/40/19. They would lessen the understeer (make the car more neutral handling). They are around the same height as the 225/40, but wider. You could also put 255/40/19 in the back to add a little more meat. I believe both sizes come in the Goodyears. Or you could stay with the 245/40/19 in back along with the 245/35/19 in front.

Lou

 

245/35 & 255/35

or

245/35 & 265/35

 

On the calculator.... if you had the 17" wheels on your car before you switched to the 19s... then use the stock 17" tire sizes for the baseline and whatever size tire you're planning on useing for your comparison. There are some pretty good recomendations in this thread as to what tire size you should buy. Plug those in and look at the difference.

Hope that helps.