Tire size

[SharkDiver]

Hey all,
Im going to get 2 new all season tires for my ms3.My front tires are almost bald.Im looking at the GY F1 all season for the front.If I go with a 225-40R18 will there be a problem?Ive read that the 225 will not rub but Im not sure what the 40 means.I know the stock uses 45 so does this mean my new tire tread will be a hair wider then the stock 45s.They also have a 215-35R18 or a 225-45R18.ANy sugestions?
Thanks

 

[Powerslave]

ive got 235 40's with no problem

 

[SharkDiver]

Thanks for the reply..What does the 40 mean anyway?Does 40 mean I will have less tread to the road then a 45?I want the widest tire possible for my wheel and without rubbing when I turn the wheels all the way.
Thanks

 

[Powerslave]

...

 

[major error]

from http://www.tirerack.com/tires/tiretech/techpage.jsp?techid=46

Section Width

Following the letter(s) that identify the type of vehicle and/or type of service for which the tire was designed, the three-digit numeric portion identifies the tire's "Section Width" (cross section) in millimeters.

P225/50R16 91S

The 225 indicates this tire is 225 millimeters across from the widest point of its outer sidewall to the widest point of its inner sidewall when mounted and measured on a specified width wheel. This measurement is also referred to as the tire's section width. Because many people think of measurements in inches, the 225mm can be converted to inches by dividing the section width in millimeters by 25.4 (the number of millimeters per inch).

225mm / 25.4 = 8.86"
​

Sidewall Aspect Ratio

Typically following the three digits identifying the tire's Section Width in millimeters is a two-digit number that identifies the tire's profile or aspect ratio.

P225/50R16 91S

The 50 indicates that this tire size's sidewall height (from rim to tread) is 50% of its section width. The measurement is the tire's section height, and also referred to as the tire's series, profile or aspect ratio. The higher the number, the taller the sidewall; the lower the number, the lower the sidewall. We know that this tire size's section width is 225mm and that its section height is 50% of 225mm. By converting the 225mm to inches (225 / 25.4 = 8.86") and multiplying it by 50% (.50) we confirm that this tire size results in a tire section height of 4.43". If this tire were a P225/70R16 size, our calculation would confirm that the size would result in a section height of 6.20", approximately a 1.8-inch taller sidewall.​

 

[SharkDiver]

After reading some more I think I may know now.The 225 is how wide the tread is and the 40 is how much side wall you will have on the tire.So If I went with a 235 instead of a 215 that would mean the 235 has a wider tread to the ground.So Im guessing that the larger the first number the wider my tire tread will be.Is this right?

 

[SharkDiver]

Thanks for the reply major..I think I understand now.

 

[aaronc7]

235/40 is closer to stock diameter (i think a bit smaller), but its gonna be wider so you have a greater chance of rubbing (lots of ppl have it though i think) 225/40 is quite ab it smaller and you'll have no problems. 225/45 is larger and know of people that rub with that, with people in the back. I'm debating between 235/40 and 225/40 for my next tires

 

[SharkDiver]

Thanks..After reading I think I will go with a 235-40ZR18 in a GY F1 all season.IF anyone thinks I will have a problem just let me know.Im not ordering the tires for a week or so.I have a local shop that is pretty much matching tirerack prices so thats kinda nice.
Thanks

 

[Powerslave]

sorry about my post i edidted and went to lunch without reading... if you look at the edge of the rim how close is it to the ground thats th 40 number the smaler the number the less space between the rim and the ground and the 235 is how wide the tire is 235 is fatter than 225 and a 235/40 is acutally a better fit than a 225/40 cuase the wider the trie the taller so the 235 and the 40 wash with the 215/45

 

[Hirudin]

I hate how tires are measured! I refuse to believe that this ridiculous system of ratios and mixed metric/standard measurements is the best way to go...

The first number, say 225, is the width of the tire in millimeters. The second number, say 40, is the ratio of width(100%):sidewall. In this case, the sidewall is 40% of the width (225*0.4=90), or in this case: 90 mm. The last number, say 18, is the diameter of the rim, in inches for some reason...

So, since the second number is a ratio based on the width all "40s" aren't the same size. Compare some 215/40s with 235/40s, since they both have "40" in the size you'd think they would have the same size sidewall. But the 215s have a sidewall of 86 mm and the 235s have a 94 mm sidewall, 8 mm larger.

On top of that, not all tires conform to the sizing. I don't have any specifics, but 2 different brands of 215/45 18s might have a different overall diameter. According to www.tirerack.com, the stock Mazdaspeed3 tires have a 25.7" diameter. When buying new tires you'll want to use this number as a guide.

 

[Sacrilicious]

say, what size wheels are you putting the tires on? 235/40/18 is a very wide tire, so it's a very tight fit. our stock wheels are pretty darn narrow for use with 235/40/18 tires, but if you get wider wheels, you're going to need an offset as close to 52.5mm as possible. even then, i don't know if you're going to be able to fit tires of that size into our fenders without rubbing a little bit when you make a big turn. i would do some major searching around in these forums, since this is definitely not a tire size that gets an easy OK from most...=d

 

[SharkDiver]

Thanks for the replys all.I can say I understand what the sizes mean now,Before I had no idea.Anyways Im using the stock wheels.I will keep reading and searching to make sure I order a size that will work.If its going to be to close I will just go with the 225 instead.I just want to get the most rubber to the road with the stock wheels.

 

[Sacrilicious]

Thanks for the replys all.I can say I understand what the sizes mean now,Before I had no idea.Anyways Im using the stock wheels.I will keep reading and searching to make sure I order a size that will work.If its going to be to close I will just go with the 225 instead.I just want to get the most rubber to the road with the stock wheels.

ya, i went through all this research too, and i came to the conclusion that i just didn't want to deal with all the garbage and risk necessary to get the biggest tires i can onto my car. when my stockers go, i'm going to get 225/40/18s onto my stock wheels and just call it a day...=d

 

[SharkDiver]

After reading Ive found that a few people have 235/40/18 on there stock wheels and have no problems.So I ordered 2 GY all season 235/40/18 yesterday and should have them installed next Thur..Next summer I will change the rear tires to the same size.

Thanks

 

[redspeed]

Can't you use 235/35/18?

Edit: Nevermind, I check some sites and that size is expensive.

 

[Blang]

What size tire and offset would be good for a set of 18x8 rims without rubbing?

 

[2ManyCars]

Here is what I have heard over the last few weeks and from speaking with some shops...

18 x 7.5 (Stock Rims) = 215/45/R18 - 225/40/R18
18 x 8.0 = 235/40/R18

Some folks are running 235/40/18s on stock rims but I've seen and heard that is risky not because of rubbing but because it impacts the rigidity of the sidewalls of the tires. Discount Tire would not even test-fit 235s on my stock 7.5 rims...

 

[pmeilakjr]

Stock rim size

I'm 100.0% sure the stock rim size of the MS3 is 18 x 7.0 and putting a 235/40 tire on that size of a rim is not advisable (tire specs call for a minimum of a 8.0" rim) however, it is doable. My concern would be there is a lot more stress on the tires sidewall. For dailing driving probably not an issue but for spirited or track driving I have to wonder.

Cheers!

Peter

 

[SharkDiver]

I just had the tires installed today and they fit perfect.No rubbing at all and Wow they sure are fat..Im happy I went with the 235 now because I was worried about rubbing but its all good.