Proper tire size for 18" rims?

[WeatherB]

Hi,

Anyone know the proper size tire for 18" rims? I purchased a set of Mazdaspeed rims for my hatchback, but have been seeing conflicting information on the most appropriate tire size (yes, I searched!).

I'm pretty much settled on a tire width of 215. However, I am not sure whether I should get 215/45R18 (stock Mazdaspeed size) or 215/40R18?
According to the tire size calculator, the 45R18 would make my car an extra .6" higher and would cause my speedometer to be off by about 2%. On the other hand, the 40R18 will lower my car a further .4", but would only offset my speedometer by making it around 1% slower.

What are the pros/cons of each and which should I get?

[Kevin@nextmod]

depends if you're lowered. If you are lowered then i'd suggest going 40.

[REZXPERT]

search the threads in this section.. discussed to death

[WeatherB]

search the threads in this section.. discussed to death

That's where you're wrong... Some say 40, while others say 45...

I'm lowered on prokits.

[b]

I am going 225/40/18 on my rims. I need to get new tires as mine are toast.

[WeatherB]

I am leaning towards the 45R18 so that I can minimize the wheel well gap...

[dj_chinaman2097]

I also have the oem speed3 rim + tires and will be dropped on a pro-kit this summer.

From what I've read pro-kits drop the hatches more because of the additional weight. I think those of us with a sedan can get away with the 45 profile since the car weighs less than the hatch.

If you have the oem tires mounted give it a try. If not, play it safe and go 40 with your tires.

[stevenlung]

It doesn't really matter, both are fine

[flylice13]

I would say 225/40/18 as this is the closest you will ever get to the stock size of 205/50/17.

205/50/17 overall diameter = 25.07"
225/40/18 overall diameter = 25.08"
difference of 0.036% slower.

[WeatherB]

I would say 225/40/18 as this is the closest you will ever get to the stock size of 205/50/17.

205/50/17 overall diameter = 25.07"
225/40/18 overall diameter = 25.08"
difference of 0.036% slower.

Hi,

Where are you getting those numbers? When I select the tires from 1010's tire calculator I get:

205/50/17 Overall Diameter = 25.07 in
215/40/18 Overall Diameter = 24.77 in
215/45/18 Overall Diameter = 25.61 in

[stevenlung]

http://www.1010tires.com/TireSizeCalculator.asp

225 will be too wide for your 7" rims

[Kevin@nextmod]

it wont be too wide. It's just one size bigger. Lots of people ran this size in there 7 inch rims. I ran 215 on a 7.5 rim.

[07Speedfreak]

Hi,

Where are you getting those numbers? When I select the tires from 1010's tire calculator I get:

205/50/17 Overall Diameter = 25.07 in
215/40/18 Overall Diameter = 24.77 in
215/45/18 Overall Diameter = 25.61 in

http://www.rims-n-tires.com/rt_specs.jsp

He wrote 225/40/18 not 215/40/18.

[07Speedfreak]

Other good sites to figure stuff out with tire sizes and offsets:

http://www.miata.net/garage/tirecalc.html
http://marksink.com/tire_wheel_offset/offset.html

[flylice13]

Here's how to calculate tire sizes (without using 1010tires or any other site)

Ex. 195/60/15
195 (width)
60 (sidewall height in comparison to the width)
15 (rim size)

195 * 0.60 = 117 (size of one section of the sidewall)
117 * 2 = 234 (all tires have 2 sidewalls to calculate the diameter)
234 / 25.4 = 9.2126 (this is to get it into inches)
9.2126 + 15 = 24.2126" (diameter of the tire)

Hope this helps :D

[Wild Weasel]

http://www.wildweasel.ca/HowTo/Auto/TireCalc.aspx

Go with the 40's. The MS3 uses a taller tire than the regular Mazda3. You're better off getting the correct size for your car, given the option.

[RX9]

you are fine with /45/, even you drop a 1", there is still plently room.

[Wild Weasel]

There's room. They will fit. But your acceleration will suffer, your speedo will be off, etc. etc.

[Unoriginalusername]

http://www.wildweasel.ca/HowTo/Auto/TireCalc.aspx

Go with the 40's. The MS3 uses a taller tire than the regular Mazda3. You're better off getting the correct size for your car, given the option.

I agree, 40 would be my first choice for the 3. I would be tempted to try and squeeze a 225 on if it would fit on the 7" fine

[flylice13]

it probably would. I've seen 235 squeezed on 7" wide rims, so i don't doubt 225's fitment.

[RX9]

235/35/40 into 7"? i dont think so. 235/60/65 will. lol.....

[flylice13]

i've seen it myself...i work with tires day in and day out, lol.