I just bought a Speed3, my first Mazda, my first turbo car, and my first front driver in many years. I have a Porsche 997S that I use as atrack/weekend car, but wanted something more fun and economical than my old4Runner as a daily driver. I've only put 200 miles on it sofar, but I believe it'sgoing to be alot offun, and reasonablypractical too.Managing the boost is a challenge when driving near the limit and trying to keep things smooth, but after some more break-in miles, I hope to get better at it. I digress, my question is regarding the rather odd tire size Mazda chose in the 215/45-18. I believe these are 7" wheels, so a 225/40-18 is larger than recommended for the wheel. I expect it would work fine, but I would appreciate hearing from anyone who has done it.

 

Actually thinking of putting same size tires on my MS3. As far as I know those will work fine. With that little extra width, they should fill out the fender wells nicely.

 

So are you saying you want to mount a slightly wider tire on te stock rims? Could be a good idea, not sure what it'd look like, and it might open up a wider selection fo rubbers than for mazda's funky size.

 

225/40R18 should work just fine...there are numerous regular 3's out there running that tire size on even wider rims. I currently run 225/45R17 on my 3 with no issues.

 

Don't really care about the look. Very few of the tires of my choice are offered in this oddball size, but most all are available in 225/40-18.

 

I'm thinking it'll be fine. It's a very small difference. A shop here got tires in for my PR5 and i did'nt realize till months later that one was a bit wider. And i'm picky! So it's prolly fine. Only thing is the stick rubbers are really nice. They just don't last long. I'm only gonna see one rotation before they are gone. Thats sick. Lemme know what tire and size you finally get, i'm interested in something as goof performance wise and less money. FYI my dealer quoted $244 each for the OEM. Not worth it for tires that last a year, unless it were a garage/track car.

 

Mazda6 with 17' stock tire size = 215/50/17
what many people replace with = 225/45/17

the same scenario is going on with u guys and the speed3. but my point is. WHY would u put on a lower profile tire to the same rim? (ur going from a 45 ratio tire to a 40). What u'll get is a 1-3% speedometer error, which means for every 1000 miles u travel, ur odometer would be 10-30 miles too much. and it adds up believe me.

 

Because a 45 series tire isn't necessarily a smaller sidewall than a 50...It depends on the with of the tire.

A 205/50 (50% of 205mm) has a sidewall height of 102.5mm a 225/45 (45% of 225mm) is 101.25 that's only 1.2% off. With the mileage I drive, I'm not worrying about 1%....The speedo can easily be off 1% from the factory (0.6 mph at 60 mph)...a negligible difference.

205/50 is the stock size on the Mazda3.

 

It's a compromise to gain a much better tire selection, and a slightly wider tire.The 225/40 will introduce a 2% speedo error due to its smaller diameter. But, to maintain the same OD, you would need a 245/40 tire, clearly too wide for the wheel. If I were buying extra wheels for the track, I would change to 17's, and go with 245/45-17(assuming adequate clearance), which would maintain the same OD, and offer an even greater selection of less expensive tires. But I'm not going to worry about a 2% error. The speedo is dead on now, and 2% is closer than many from the factory.