Hey guys. Quick questions as usual. My stock tires (225/45/18) are gonna be wearing out soon, and will be replaced with winter tires, and then I am going to use my new set of rims/tires for spring/summer time.

Heres where the question comes in. The tires that came with my deal were 235/40/18. Obviously the speedometer will be a tad off. So my question is, should I get winter tires in the 235/40/18 size as well? Can Mazda recalibrate my speedometer and whatnot to be more accurate with the different tire size? Is this safe to do? Am I better off selling the tires that came with the new rims and getting the stock size?

Thanks again as usual.

 

I woud keep the tires that came with the rims for now. Sure the speedo will be off but not by alot. They will also help a little with acceleration since the effective gearing will be a little lower. For snow tires just get the stock size 225/45/18. You will want the extra height compared to 235/40 and the wider the tire the worse snow traction will be.

Only problem with 235/40 tires is that you will be putting extra miles on your car. So for every 100 miles you actually travel, it will say you've driven 102.2. If you are OK with that then no worries.

Unless you can get enough money from selling the 235/40/18s to buy another set of tires I wouldn't worry about it.

Also as far as I know, the speedo uses the transmission to detect speed. I don't think there is a way to calibrate it to different sized tires.

 

Awesome. Thanks for the info. Guess I'll just burn these tires out and stick to 225/45 as soon as I can.

 

17" steel wheels and 215x55x17 tires are best for dedicated snow tires.

Less expensive rims for sand/salt/snow abuse and thinner/taller tires for less 'snowplow' and greater ground clearance.

https://www.rx8club.com/canada-forum-35/2009-r3-winter-tire-rim-suggestions-157560/

Summer alternatives are 245x40x18. Fit aok and nice wider look. Minor speedometer affect.

 

If you ever want to calculate the speedo affect use this:

http://www.wheelsmaster.com/rt_specs.jsp

Put in the stock setup on the left and your new setup on the right. In the table below it will tell you how much it will effect your speedo.