Calculating Tire Size
#1
Calculating Tire Size
I often see people inquiring about metric tire sizes and what they are equivalent to in inches. For those who do not know how to convert a metric tire size to an inch equivalent I wanted to post this. Hopefully you can find it helpful.
Let’s use a common stock tire found on the F150:
275x65x18
275 = width in mm
65 = aspect ratio, this is the side wall height as a percentage of the tires width
18” = rim size in inches
To convert this tire to standard units (inches) use the following steps:
(NOTE: I round to the 100th place)
1. Convert the width in mm to inches: 275/25.4 = 10.83" (25.4 mm = 1 inch)
2. Calculate the sidewall height: 10.83 x .65 = 7.04" (don’t forget the decimal as this is a %)
3. Calculate final tire height: (total sidewall = sidewall x 2) 7.04" x 2 = 14.08". Now add your total sidewall height to your rim size, 14.08"+18" = 32.08"
This means a 275x65x18 is ~32.08x10.83x18
Hope this helps.....
Let’s use a common stock tire found on the F150:
275x65x18
275 = width in mm
65 = aspect ratio, this is the side wall height as a percentage of the tires width
18” = rim size in inches
To convert this tire to standard units (inches) use the following steps:
(NOTE: I round to the 100th place)
1. Convert the width in mm to inches: 275/25.4 = 10.83" (25.4 mm = 1 inch)
2. Calculate the sidewall height: 10.83 x .65 = 7.04" (don’t forget the decimal as this is a %)
3. Calculate final tire height: (total sidewall = sidewall x 2) 7.04" x 2 = 14.08". Now add your total sidewall height to your rim size, 14.08"+18" = 32.08"
This means a 275x65x18 is ~32.08x10.83x18
Hope this helps.....
Last edited by mdhawkin; 06-11-2010 at 11:44 PM.
#4
Thanks, glad it helps, I know a lot of members are often confused by the metric sizes. Sure you can go to a website and type in the numbers and get a conversion, but its always nice to know how the values are derived. Makes it easy to quickly put sizes into perspective.
#5
Also note that some tire manufacturer's sizes vary somewhat. A BFG may be smaller then say a Toyo in the same shown size. Also a mud terrain can be larger then an all terrain or a highway tread tire due to the large lugs on the mud tires even though they are shown as the same size. This can make a big difference in whether a tire can fit OK or have some rubbing.
#6
Also note that some tire manufacturer's sizes vary somewhat. A BFG may be smaller then say a Toyo in the same shown size. Also a mud terrain can be larger then an all terrain or a highway tread tire due to the large lugs on the mud tires even though they are shown as the same size. This can make a big difference in whether a tire can fit OK or have some rubbing.
#7
Good info for manual ratios. I always use the Wallace Tire height chart to figure the size out, Its automatic.
http://www.wallaceracing.com/tire-aspect-calc.php
http://www.wallaceracing.com/tire-aspect-calc.php
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#9
Thanks Jack, its actually been around for a while and I have shared the link when applicable, I think its lack of visibility came from me not including "HOW TO" in the title. Hopefully now it can serve its original purpose.
#10
hey can somebody please tell me the (MM) of my 285/70 R17. i mesured and its basically 32 inches tall. im not good with math and i got a edge so i want to add the tire size to adjust my gauges. i wanna say its right about 2xxx. its all throwing me off. if somebody knows what im talking about please email at future_ndn@yahoo.com and let me know the MM. thank you!
#11
hey can somebody please tell me the (MM) of my 285/70 R17. i mesured and its basically 32 inches tall. im not good with math and i got a edge so i want to add the tire size to adjust my gauges. i wanna say its right about 2xxx. its all throwing me off. if somebody knows what im talking about please email at future_ndn@yahoo.com and let me know the MM. thank you!
#14
This is my favorite online tire calculator, it allows you to compare two different tire sizes
http://www.miata.net/garage/tirecalc.html
http://www.miata.net/garage/tirecalc.html