I decided not to go with a staggered set up so I can extend the life of my tires. I'm either going with the Falken 452s or the ST 110s with 19X8.5wheels all around.

Stock tires on the G35 are 215s. I wouldn't mind going bigger but I'm not sure what size I should get. I will be buying some winter tiers so I only want these tires for the summer. I see sizes ranging from 235-275, which should I get and what are the positives and negatives?

 

On 19x8.5 you can safely go 245

 

There was a tire calculator that I was checking out comparing your current tires to your new tires and what size you'd need to maintain your speedometer rating.

Current Tires: 215 55 17
Tires needed to achieve 0% speedometer change in 19" 265 35 19
Tires you recomended: 2.1% too fast.

Is 265s all around too wide?

Here's the link to that calculator.

http://www.miata.net/garage/tirecalc.html

 

For a 8.5 wide wheel 245s will fit just nicely all around. depending on the offset of your wheels, you can swing 255s.

 

I had 245 45 18s and now have have 245 35 19's and I wish I had gone with 245 40 19. My speedo is 2.5 mph fast.

Chose your offset carfully so you don't have rubbing problems. I had to add 5 mm spacers up front. Tirerack.com can show you the proper wheels in 19" for your car.

 

My wheel is 19.8 x 8.5 with a 35mm offset. I don't want any issues of rubbing whatsoever, nor do I want to roll my fenders. It's just too much work and I don't want to do it.

Will the 245 or 255 work with that rim?

 

you should be fine with 245... 255 may rub in the front...

 

alright I think I'm going with 245/40/19s. Do the 40s work well with 8.5'' rims

 

I thought you had a coupe. Since it is a sedan, the +35 offset will look great on the front, but not so much in the rear. Ideal offset for the rear is about +43-45. I had a previous set in 8.5 all around with +42 offset. look good for the most part. Just not sure about the rear look. if you care about the wheel looking flush then try to get an offset in 40-43 range.

 

yup... thats what i have on my stock 19's front and rear

 

the width of your tire won't change the speedometer ratings, if you have 245-40-19 and 315-40-19 don't make a difference because the height of the tire is the same. My stock wheels are 19's and there 225-40-19 front and 245-40-19 so if your going to get 19's and if you get 40's it won't affect the ratings

 

That's very untrue. The numbers on a tire sidewall represent the width, the sidewall height(% ratio), and of course rim size. The sidewall height is NOT a measurement but rather a percentage of the width. So having 2 tires with different widths and equal sidewall ratings will yield 2 different rolling diameters thus affecting the speedometer reading.

For evidence try using the miata speed calculator posted above (#3) and see that your example of 245's vs 315's is 8.3% different or 5 mph off when the speedo reads 65.

 

I thought the speedo wasn't based on the wheel but off the gearing...