Choosing the Right Size Tire

[Tire Guy]

There are a lot of questions posted about which size to use, and how wide of a wheel to use, especially when plus-sizing on the US-spec 6. So, here is an easy guide to refer to when looking for replacement tires. First, let's breakdown what the size numbers/letters mean:

P215/50R17 93V

P = Passenger Tire (does not appear always)
215 = Section width (in millimeters)
50 = Section height or aspect ratio (ie. sidewall is 50% of section width)
R = Radial construction
17 = Rim diameter (in inches)
93 = Load Index
V = Speed symbol

All of the components of your tire size are important, but when choosing a replacement or plus size, many of those numbers will change. You may have a wider tire with lower aspect ratio and a larger wheel. However, the last two characters are the most important.

For the US-spec model, you MUST choose a tire with at least a 91 (or greater) load index and a speed symbol of H or greater (H, V, Z, W, Y) [NOTE: Winter tires are excepted from this stipulation]. These last two characters refer to the internal construction of the tire and it is important to maintain the same or greater load and speed capability of your tires as per Mazda's recommendation.

What follows is a guide, by rim diameter of the acceptable replacement sizes for your 6, which rim widths are acceptable for that size and the minimum inflation pressure for that size on your 6. Please refer to this guide before posting questions about what will work on your 6 (for simplicity, I am excluding the P designation and the load index/speed symbol, see above for requirements). This list has been thoroughly researched. If you don't see a size listed here (ie 215/45R17), then it is not recommended for the US-spec 6.

16" (original equipment wheel is 16x7)

205/60R16 5.5"-7.5" 32 psi *original equipment size*
215/55R16 6.0"-7.5" 33 psi
215/60R16 6.0"-7.5" 32 psi
225/55R16 6.0"-8.0" 32 psi
235/50R16 6.5"-8.5" 32 psi

17" (original equipment wheel is 17x7)

215/50R17 6.0"-7.5" 32 psi (93+ load index), 33 psi (91 load index) *original equipment size*
225/45R17 7.0"-8.5" 35 psi
225/50R17 6.0"-8.0" 32 psi
235/45R17 7.5"-9.0" 32 psi
245/45R17 7.5"-9.0" 32 psi

18" (original equipment wheel is 18x7)

215/45R18 7.0"-8.0" 35 psi (6s, 6i), 38 psi (Mazdaspeed6) *original equipment size*
225/40R18 7.5"-9.0" 38 psi
225/45R18 7.0"-8.5" 38 psi
235/40R18 8.0"-9.5" 38 psi
245/40R18 8.0"-9.5" 38 psi

19"

225/40R19 7.5"-9.0" 36 psi
235/35R19 8.0"-9.5" 39 psi
245/35R19 8.0"-9.5" 36 psi

20"

225/35R20 7.5"-9.0" 40 psi NOTE: This fitment is BORDERLINE, but acceptable. Make certain you are choosing a reinforced tire (LOAD RATING 90).

NOTE: Section widths of 235 and above will probably require fender rolling. Check the offset of your wheels carefully before purchasing replacement tires. I was going to also include the overall diameter for each tire, but this can vary from manufacturer to manufacturer by .1-.2". Suffice to say that these tires fall within the "-2%, +3%" rule, meaning they are not more than 2% smaller or 3% larger than the original equipment tires, which have an overall diameter of 25.5 inches.

TAKE NOTE: When selecting replacement wheels and tires, the relationship of the wheel width to tire section width is very important! For maximum handling benefit, mount the tire on the widest wheel that size will allow. Mounting a tire on the narrowest width allowed will give better ride comfort, but won't give the best handling. In many cases, handling may be worse than before by mounting a wider tire on a narrow rim (ie. 235/40R18 on an 8 inch wide wheel vs. 215/45R18 on an 8 inch). Installing wider tires on your 6 will likely yield a handling improvement only if you have a wheel wide enough to take advantage of the extra tire width.

[Axion]

Awesome man, this should be pinned asap!

[mazda6sedan]

Great write up toyoguy! Thank you.

Question (235/50R16 6.5-8.5" 32 psi). Does this mean that the stock 16x7 can run 235/50R16?

[Stretch]

Nice list.

Chop half of those sizes off the list because they won't fit regardless of whether the fenders are rolled. Anything even a little bit larger than (or in wider cases, equal to) the stock diameter will be a problem behind the rear door unless you run a very skinny tire. Just a very minor reduction in tire diameter solves this. Thankfully, ToyoGuy's general guideline of not reducing your tire diameter by more than 2% doesn't seem to affect the Mazda6 (or at least I haven't seen any evidence of it).

245's will fit if you have the right offset wheel and you get the proper diameter (limited essentially to 245/45/16 or 245/40/17), yet 235/45/17 has been confirmed to rub both in front and rear. 225/45/18 also seems to not fit in the rear (according to a recent thread), though 225/40/18 fits rather easily. Those examples are all on +48mm offset wheels, an otherwise very usable offset. I'm sure there are many other sizes on the 'omit' list too.

With your fenders rolled as much as possible, you MIGHT get the following combinations to work:
a 225 wide tire on a +40 wheel.
a 235 wide tire on a +45 wheel.
a 245 wide tire on a +50 wheel.

To be safe, I'd recommend you take that down a step, in other words don't exceed a 225 on a +45 wheel, a 235 on a +50 wheel, etc. Some tires are wider than others and there is no way to predict what you are getting. You probably wouldn't notice much of a difference with a tire width change of only 10mm, so concentrate instead on getting a nice, reputable make/model of tire. A slightly reduced tire diameter helps fitment slightly by providing more camber gain by the time the suspension compresses, but ToyoGuy advises not to reduce your diameter by more than 2%.

Lighter is better except for in strength- lightweight cast wheels should be coupled with taller profile tires unless you drive on smooth streets. Wider wheels make the most of your tires- try to get a wheel wider than your tread width. I'd recommend a minimum wheel width of 7.5" (though 7" wheels are technically "safe") for most sizes with 8" highly preferred.

If you're not going to roll your fenders, you can do no better than a 225mm wide tire on the stock wheels are a 215mm wide tire on a +50mm aftermarket wheel. Most aftermarket wheels have a lower offset than 50mm, thus rolling your fender is required for almost anything aftermarket.

Remember, higher tire pressures (per ToyoGuy's list) mean you are putting less rubber on the ground, getting a firmer ride, and possibly (though unlikely) setting yourself up for uneven tire wear. A firmer ride (be it from aggressive performance tires, low-profile tires, or high tire pressures) seems to drastically reduce shock life. Tires are THE MOST IMPORTANT PART OF THE CAR and you should carefully consider your choice to match it to your suspension and goals.

Finally, lowering springs do NOT cause (or even influence) whether a tire setup will rub. It only increases the frequency and/or severity of the occurance.

[Tire Guy]

While I appreciate your comments, stretch, this thread is going to get complicated and confusing very quickly (exactly OPPOSITE the point of this thread). This is meant to be a simple, easy to understand guide about what sizes are acceptable, what width wheels they require and minimum air pressures.

These are oft-asked questions and this is meant to be an easy reference before posting another thread about, "What air pressure do I need?" or "Will this work on an 8-inch wheel?" There's too many of those already. For the sake of simplicity, save the offsets, what combos might/might not work if the sun is pointing in the right direction, etc. conditions for another thread.

Also, note: there is no guarantee that the 245 widths will fit (again, serious modifications may be necessary) but the tires listed meet the criteria for acceptable replacement and plus sizing.

[Stretch]

It's not like anyone listens to me anyway. I hope I didn't complicate things too much, but I think that's the nature of the beast. A lot of the tire sizes in your list will not fit (though they're technically safe). I'm the over-complicated disclaimer.

In summary: when in doubt, panic.

Just in case it reads that way, I wasn't being sarcastic when I said, "Nice list."

[Tire Guy]

Originally posted by Stretch+May 3 2005, 06:44 AM-->

Okay, now you're being humble? I'm sure a lot of folks on this board respect what you post (myself included) due to the amount of trial and error you have employed on your own 6.

<!--QuoteBegin-Stretch@May 3 2005, 06:44 AM
Just in case it reads that way, I wasn't being sarcastic when I said, "Nice list."

[snapback]403541[/snapback]

I appreciate the clarification!

[rambo2300]

What is the width and offset of the stock 17" wheels?

[BangHatch]

Originally posted by rambo2300@May 12 2005, 08:27 PM
What is the width and offset of the stock 17" wheels?

[snapback]410417[/snapback]

7" width. +60 offset.

EDIT: its right there in the wheel and tire faq btw
http://forum.mazda6club.com/index.php?showtopic=21280

[armyguyinfl]

I HAVE AN IMPORTANT QUESTION IF ANYONE CAN ANSWER FOR ME!!
I WANT TO BUY THEM 19" BBS RIMS.THE HAVE A 2" CHROME LIP IN THE FRONT AND 3 " LIP ON THE BACK.THEY ARE BEAUTIFUL RIMS.THE GUY SAID HE CAN GET THE RIMS I WANT WITH A BOLT PATTERN OF 114X 5 FOR MY CAR.EVERYTHING FITS PERFECT EXCEPT IT HAS A 38MM OFFSET.WILL THOSE FIT MY CAR.THE MAZDA6 5- SEDAN V6???
WHAT SIZE TIRES WOULD I NEED FOR THOSE RIMS?