Tire Talk
What do the numbers on the sides of my tires mean?
Typically, you will see something like 195/60HR14. The 195 is theoverall width of the tire in millimeters, the tread is usuallynarrower. Now much narrower depends on the tire's design. Each tiremake and size is measured on a reference rim of the manufacturer'schoosing. If they measure P275/60R15 on a 7x15 rim and you trymounting it on an 8x15 rim, your tire will have differentdimensions than they claim.
The 60 is the "aspect ratio". This indicates the height of thesidewall of the tire relative to the overall width. Our exampletire has a sidewall height of 0.60 * 195 = 117mm. If the aspectratio is omitted, it is probably 80, but may be 78.
The 14 is the wheel diameter in inches. The R stands for radial,and the H is a speed rating indicating the highest speed at whichthe tire, when properly inflated and carrying an appropriate loadmay safely operate. There are almost as many speed ratings as thereare letters in the alphabet, and they basically go in 10 km/hincrements. The most common ones are:
S: up to 180 km/h (112 mph)T: up to 190 km/h (118 mph)H: up to 210 km/h (130 mph)V: up to 240 km/h (150 mph)Z: above 240 km/h (150 mph)
Recent changes to the method for specifying tire sizes move thespeed rating to a different part of the designation. You maytherefore find designations like 195/60R14 88H. The 88 indicatesthe per-tire load associated with the speed rating. Exceeding thisload in continuous operation at the rated speed is considereddangerous practice. What follows is a table showing a number of"load indexes" and corresponding maximum per-tire loads:
load index max load (kg)50 19051 19588 56089 580
Note that the usual mass versus weight confusion occurs in thistable.
In some cases, the letters P or LT may be found in front of a tiresize. The LT designation indicates "light truck", and the Pdesignation indicates "passenger car". If no letter is given, thenthe application of the tire is passenger car usage. These lettersonly appear in the US market. The LT designation is principally ofinterest to owners of light trucks and other utility vehicles. Forthe owner of a passenger vehicle, there is no meaningful differencebetween a tire with a P designation and one with no designation atall.
There is an additional set of ratings on tires for temperature,traction, and treadwear. Temperature and traction are graded A, B,and C (with A the best and C the worst). Treadwear is a numericrating. These values are of limited value, as they are assignedsomewhat arbitrarily by tire manufacturers and are thus not usefulin comparing different brands of tires.
Additionally, the designation M+S (mud and snow) means that thetire is at least somewhat applicable to use in mud and snow, andshould be taken as a indication that at least some thought wentinto designing a tire which could be used in winter conditions. Notall M+S tires are much good in winter, though. Some might workduring winter in San Francisco but not in Toronto, for example.Tires with an M+S designation may have their speed rating reducedby 20 km/h (about 12mph).
Tire Talk: What do the numbers on the sides of my tires mean? [sticky?]
Re: Tire Talk: What do the numbers on the sides of my tire ... (S13GUY)
Man oh man. Thanks for posting info, but most of this is already covered in the links of the existing stickies..
some corrections:
-M+S does NOT designate (per se) good snow or mud use. ALl it designates is the tread design had a blockier design with side channels, etc. THis was done by the RMA (Rubber Mfr Assoc.) back in the 60's I believe. THe new correct way to look for a 'winter' capable tire is the RMA "severe" duty symbol. Its a little mountain and snowflake, this designates it had a quotient of 110 or better in snow/mud testing compared to a standard tire (rating of 100..).
-If aspect ratio is omited its actually an 82, not 80. People think its 80 because its simplifies the math.... ANd it can vary by MFR to some extent. Simple solution? dont drive a car made in the time when radials were new :p
-THe first numbers designation is "section width", the distance from the farthest point on one sidewall to the other on the specified measuring rim.
I'll add an intersting fact here, for my own ammusement:
-Mounting a tire on a wheel less that the measured with will result in effectively increasing the aspect ratio, and vice versa.
anyways, thanks for the informative posts. I'm not going to sticky this because its covered in finium in the links already in the sticky.-Chet
some corrections:
-M+S does NOT designate (per se) good snow or mud use. ALl it designates is the tread design had a blockier design with side channels, etc. THis was done by the RMA (Rubber Mfr Assoc.) back in the 60's I believe. THe new correct way to look for a 'winter' capable tire is the RMA "severe" duty symbol. Its a little mountain and snowflake, this designates it had a quotient of 110 or better in snow/mud testing compared to a standard tire (rating of 100..).
-If aspect ratio is omited its actually an 82, not 80. People think its 80 because its simplifies the math.... ANd it can vary by MFR to some extent. Simple solution? dont drive a car made in the time when radials were new :p
-THe first numbers designation is "section width", the distance from the farthest point on one sidewall to the other on the specified measuring rim.
I'll add an intersting fact here, for my own ammusement:
-Mounting a tire on a wheel less that the measured with will result in effectively increasing the aspect ratio, and vice versa.
anyways, thanks for the informative posts. I'm not going to sticky this because its covered in finium in the links already in the sticky.-Chet