igotanxj
NAXJA Forum User
- Location
- Citrus heights
I see a lot of people are having a hard time with metric tire sizes on this board. I keep reading about people saying I have 235s, or i have 245s or 285s etc... this means nothing. If you want to share the size of your tires you need to list the whole size. 235 or 245 or 285 or whatever is nothing but the tread WIDTH, not height of the tire. We don't say "I run a 12.50" or "10.50" tire when talking about tire heights, likewise, we shouldn't talk about just the tread width with metric sizes. 235/40/17 is a whole different tire than 235/75/17. At the same time, it could be 235/70/17, 235/65/17, 235/60/17 and so on and so forth.
I know, its much easier to talk about tires in inches when talking tire heights. Saying you run 33's or 35's is much easier than listing 3 sets of numbers just to explain the height of the tires, but you really need to if you want a correct definition.
Here's a little explanation:
The first number is the tread width. The second number is the aspect ratio (percentage of the tread width that makes up the sidewall) and the third number is the rim size. For instance, a 235/70/17 is 235mm wide, the height of the sidewall is 70% of 235mm and it fits on a 17 inch rim. For this particular tire size, 235mm equals about 9.25 inches wide. 70% of 235 mm is 164mm or 6.45 inches, so 6.45x2 is 12.9, which is the height of both bottom and top sidewalls, plus a 17 inch hole in the middle means this tire is 29.9 inches tall. Make sense?
For this reason a 235/75/16 is going to be a shorter tire than a 235/75/17.
Sometimes you'll see another set of numbers after the tire size, such as 98T, or 106S, or something different, which are the weight ratings and speed ratings. The numbers 98 or 106 for the weight ratings don't really correspond to anything weight related, they just let you know relatively how much weight your tire is rated for. Speed ratings do actually correspond to a specific speed. If you exceed the speed or weight that your tire is rated for, you could damage your tire, and/or create an unsafe situation. All cars come with a recommended weight rating and speed rating for tires from the factory. You can go above the weight and speed rating that came with your car/truck, but not below. By putting higher weight or speed rated tires on your car/truck, you'll just suffer from a rougher ride, but not much else.
Speed ratings:
M=81mph
N=87mph
P=93mph
Q=99mph
R=106mph
S=112mph
T=118mph
U=124mph
H=130mph
V=149mph
W=168mph
Y=186mph
Z=149+mph
Weight ratings: (Per tire, I skipped a few)
80=992lbs
82=1047lbs
85=1135lbs
87=1201lbs
90=1323lbs
92=1389lbs
95=1521lbs
97=1609lbs
100=1764lbs
102=1874lbs
105=2039lbs
107=2149lbs
110=2337lbs
I hope this clears a little bit of cloudiness with the metric confusion.
I know, its much easier to talk about tires in inches when talking tire heights. Saying you run 33's or 35's is much easier than listing 3 sets of numbers just to explain the height of the tires, but you really need to if you want a correct definition.
Here's a little explanation:
The first number is the tread width. The second number is the aspect ratio (percentage of the tread width that makes up the sidewall) and the third number is the rim size. For instance, a 235/70/17 is 235mm wide, the height of the sidewall is 70% of 235mm and it fits on a 17 inch rim. For this particular tire size, 235mm equals about 9.25 inches wide. 70% of 235 mm is 164mm or 6.45 inches, so 6.45x2 is 12.9, which is the height of both bottom and top sidewalls, plus a 17 inch hole in the middle means this tire is 29.9 inches tall. Make sense?
For this reason a 235/75/16 is going to be a shorter tire than a 235/75/17.
Sometimes you'll see another set of numbers after the tire size, such as 98T, or 106S, or something different, which are the weight ratings and speed ratings. The numbers 98 or 106 for the weight ratings don't really correspond to anything weight related, they just let you know relatively how much weight your tire is rated for. Speed ratings do actually correspond to a specific speed. If you exceed the speed or weight that your tire is rated for, you could damage your tire, and/or create an unsafe situation. All cars come with a recommended weight rating and speed rating for tires from the factory. You can go above the weight and speed rating that came with your car/truck, but not below. By putting higher weight or speed rated tires on your car/truck, you'll just suffer from a rougher ride, but not much else.
Speed ratings:
M=81mph
N=87mph
P=93mph
Q=99mph
R=106mph
S=112mph
T=118mph
U=124mph
H=130mph
V=149mph
W=168mph
Y=186mph
Z=149+mph
Weight ratings: (Per tire, I skipped a few)
80=992lbs
82=1047lbs
85=1135lbs
87=1201lbs
90=1323lbs
92=1389lbs
95=1521lbs
97=1609lbs
100=1764lbs
102=1874lbs
105=2039lbs
107=2149lbs
110=2337lbs
I hope this clears a little bit of cloudiness with the metric confusion.