What's the tallest tire that would work well , stock is 245/50

 

Without screwing up the speedometer, ecu or brake issues?
When changing tire sizes, we recommend staying within 3% of the diameter/height of the original tire. Any more than this and you face the risk of brake failure. FROM: Tire Size Calculator - tire & wheel plus sizing

Read: https://www.mazdaforum.com/forum/whe...ensions-30376/

and: Tire Size Calculator - Tire & Wheel Plus Sizing

 

so what size ( tallest ) would be the max that's safe ?? Thanks

 

I may be good at math, but really! Do the calculation yourself, you have your tire size (or go outside and read it), add 3 %, use link given.
Explore tire sites for sizes.

 

In other words, nothing bigger than a 255/45 width. I am assuming you are running 19's now?
Looking again, and still assuming the 19" OE wheel size, a 265/45 would work also, but will be 2.6% TALLER than OE. In other words your speedometer reading will be low by approx 2mph @ 65 mph indicated, but by more the faster you drive.
275/40-20" is the closest match I can find in a plus 1 sizing. They're about as perfect in diameter and circumference as you will find.
The question is, do you have the wheels (width,) backspacing/offset and fender lip clearance for such a monster? Also when approaching the subject of offset, remember too that moving the center of the wheel too far one way or the other (out, or in) will increase the steering scrub angle and affect the entire steering geometry, as well as putting additional weight on components like wheel bearings, causing them to wear faster, and potentially more dangerous handling.
Also remember please that the bigger the wheel/tire combo, the heavier it will be (unsprung weight.) This has negative affects on braking and handling as well as with fuel mileage and wear items. Wider tires with a shorter sidewall will also reduce the ride quality.