# What does a tires Speed Rating mean? **URL:** \ **Category:** Factual Questions\ **Created:** [October 19, 2005, 4:27pm UTC](https://boards.straightdope.com/t/what-does-a-tires-speed-rating-mean/326926 "2005-10-19T16:27:11Z")\ **Posts on this page:** 9\ **Page:** 1
**Author:** ![Casey1505](https://avatars.discourse-cdn.com/v4/letter/c/dc4da7/32.png) [@Casey1505](https://boards.straightdope.com/u/Casey1505)\ **Post date:** [October 19, 2005, 4:27pm UTC](https://boards.straightdope.com/t/what-does-a-tires-speed-rating-mean/326926/1 "2005-10-19T16:27:11Z")
I’ve looked around, but don’t understand what they’re telling me. I’m feeling a bit dense today I suppose. I’m considering a set of Wranglers for my truck, and there’s a speed rating of 98S on them. What does that mean? Also, will P225/70R14s fit on my truck? I currently riding on P215/75R14s. There was no one around to ask when I popped in quickly, that’s why I ask here. Thanks ---
**Author:** ![Rick](https://avatars.discourse-cdn.com/v4/letter/r/9f8e36/32.png) [@Rick](https://boards.straightdope.com/u/Rick)\ **Post date:** [October 19, 2005, 4:41pm UTC](https://boards.straightdope.com/t/what-does-a-tires-speed-rating-mean/326926/2 "2005-10-19T16:41:00Z")
[Here is an excellent article on speed ratings](http://www.tirerack.com/tires/tiretech/techpage.jsp?techid=35) [Here is another one](http://autorepair.about.com/cs/generalinfo/l/bldef_760a.htm) As far as the fit goes, the 225/70 should have the same outer diameter as the 215/75, but they will be wider. Not know what your wheelwells look like, I cannot answer your fit question. A good tire shop should be able to. ---
**Author:** ![Mr.Slant](https://avatars.discourse-cdn.com/v4/letter/m/c57346/32.png) [@Mr.Slant](https://boards.straightdope.com/u/Mr.Slant)\ **Post date:** [October 19, 2005, 8:45pm UTC](https://boards.straightdope.com/t/what-does-a-tires-speed-rating-mean/326926/3 "2005-10-19T20:45:05Z")
I’ve heard tell that the higher the speed rating, the stiffer the sidewall, and as a result the handling traits of a vehicle will change as the speed rating changes, even when you are NOT exceeding the speed ratings of either new or old tire. I’m uncertain as to whether this was wholly accurate, as neither of the (admittedly fine) cites that Rick gave seem to mention it. ---
**Author:** ![Harmonious\_Discord](https://avatars.discourse-cdn.com/v4/letter/h/74df32/32.png) [@Harmonious\_Discord](https://boards.straightdope.com/u/Harmonious_Discord)\ **Post date:** [October 19, 2005, 9:23pm UTC](https://boards.straightdope.com/t/what-does-a-tires-speed-rating-mean/326926/4 "2005-10-19T21:23:58Z")
The speed rating is the speed you can drive up to, without exceding the tires design. They’re rated for the speed the manufacturer feels they won’t seperate or blowout at. Don’t buy a tire with a speed rating of 55 if you plan on using the car on the interstate. I don’t know why the government allows the sale of tires under the maximum speed limit. The other numbers are as has been stated by others, width, and radius of the tire. The R means radial tire. Tires can be put on rims for witch they are not manufactured, but then your changing the shape and safety of the tire. Find out the tires traction rating before you buy. I would not go with a rating less than B, and suggest you chose A. That gives you the best ability to keep the car under control in adverse conditions. ---
**Author:** ![bump](https://avatars.discourse-cdn.com/v4/letter/b/7c8e57/32.png) [@bump](https://boards.straightdope.com/u/bump)\ **Post date:** [October 19, 2005, 11:32pm UTC](https://boards.straightdope.com/t/what-does-a-tires-speed-rating-mean/326926/5 "2005-10-19T23:32:19Z")
> [@Casey1505](#): > > I’ve looked around, but don’t understand what they’re telling me. I’m feeling a bit dense today I suppose. > > I’m considering a set of Wranglers for my truck, and there’s a speed rating of 98S on them. What does that mean? > > Also, will P225/70R14s fit on my truck? I currently riding on P215/75R14s. > > There was no one around to ask when I popped in quickly, that’s why I ask here. > > Thanks Speed rating is essentially the speed at which the tire’s rated for sustained use, i.e. highway cruising. S= 112 mph, IIRC. 225/70 R14 will definitely fit a 14" rim- your speedometer may be _slightly_ off due to very minor differences in diameter, but it’s probably not worth worrying about. ---
**Author:** ![snailboy](https://avatars.discourse-cdn.com/v4/letter/s/97f17d/32.png) [@snailboy](https://boards.straightdope.com/u/snailboy)\ **Post date:** [October 20, 2005, 12:26am UTC](https://boards.straightdope.com/t/what-does-a-tires-speed-rating-mean/326926/6 "2005-10-20T00:26:53Z")
Since it hasn’t been mentioned yet, the 98 in 98S is the load index, not the speed rating. It tells how much weight can be put on the tire. I can’t remember the conversion. Also, the most important thing for tire sizes is the wheel diameter (14 in your case). The width also has to be in the same neighborhood or the tire won’t seal. Going from 215 to 225 should be fine, but 215 to 255 might give you problems. I wouldn’t stray by more than 10% without a wider wheel. Also, a wide tire may rub against suspension components, but you usually have more than a centimeter to work with. (Tire width is measured in millimeters.) The profile of the tire (listed in percentage of height divided by width) has nothing to do with the tire fitting on the wheel, but you will want to keep the outside diameter roughly the same if you want your speedometer to be useful. You can find the outer diameter by: tire diameter = wheel diameter + 2 \* (width / (profile / 100)) There are online calculators for this, but it’s not very hard on a regular calculator. Do remember to either convert the wheel diameter to millimeters or the tire width to inches as you can’t mix units. ---
**Author:** ![Rick](https://avatars.discourse-cdn.com/v4/letter/r/9f8e36/32.png) [@Rick](https://boards.straightdope.com/u/Rick)\ **Post date:** [October 20, 2005, 12:27am UTC](https://boards.straightdope.com/t/what-does-a-tires-speed-rating-mean/326926/7 "2005-10-20T00:27:23Z")
> [@Harmonious Discord](#): > > The speed rating is the speed you can drive up to, without exceding the tires design. They’re rated for the speed the manufacturer feels they won’t seperate or blowout at. Don’t buy a tire with a speed rating of 55 if you plan on using the car on the interstate. I don’t know why the government allows the sale of tires under the maximum speed limit. The other numbers are as has been stated by others, width, and radius of the tire. The R means radial tire. Tires can be put on rims for witch they are not manufactured, but then your changing the shape and safety of the tire. Find out the tires traction rating before you buy. I would not go with a rating less than B, and suggest you chose A. That gives you the best ability to keep the car under control in adverse conditions. From my first link > [@](#): > > Beginning in 1991, the speed symbol denoting a fixed maximum speed capability of new tires must be shown only in the speed rating portion of the tire’s service description, such as 225/50R16 89S. The most common tire speed rating symbols, maximum speeds and typical applications are shown below: > M 81 mph 130 km/h > N 87 mph 140km/h Temporary Spare Tires > P 93 mph 150 km/h > Q 99 mph 160 km/h Studless & Studdable Winter Tires > R 106 mph 170 km/h H.D. Light Truck Tires > S 112 mph 180 km/h Family Sedans & Vans > T 118 mph 190 km/h Family Sedans & Vans > U 124 mph 200 km/h > H 130 mph 210 km/h Sport Sedans & Coupes > V 149 mph 240 km/h Sport Sedans, Coupes & Sports Cars > [the article then goes on to discuss XY and Z ratings] Two things here. First off it is obvious that speed ratings are alphabetic **not** numeric. Secondly the lowest rating is M which is above the speed limit in the US with the exception of Montana IIRC. Off the top of my head I don’t recall ever seeing a rating below S. ---
**Author:** ![Casey1505](https://avatars.discourse-cdn.com/v4/letter/c/dc4da7/32.png) [@Casey1505](https://boards.straightdope.com/u/Casey1505)\ **Post date:** [October 20, 2005, 12:46am UTC](https://boards.straightdope.com/t/what-does-a-tires-speed-rating-mean/326926/8 "2005-10-20T00:46:15Z")
The truck’s quick, but it probably couldn’t get to 112 MPH even if it was dropped out of a plane. 😃 ---
**Author:** ![Schuyler](https://avatars.discourse-cdn.com/v4/letter/s/54ee81/32.png) [@Schuyler](https://boards.straightdope.com/u/Schuyler)\ **Post date:** [October 20, 2005, 4:11am UTC](https://boards.straightdope.com/t/what-does-a-tires-speed-rating-mean/326926/9 "2005-10-20T04:11:24Z")
Since traction and temperature ratings came up, I thought I’d throw in a brief bit of information - available lots of places, but handy from the following [NHTSA Report](http://www.nhtsa.dot.gov/cars/rules/regrev/evaluate/807805.html) : > [@](#): > > Treadwear is the wear rate of a tire when tested under controlled conditions. The codes set forth in the UTQGS are two- or three- digit numbers representing a percentage of a standard value when a tire is tested in accordance with specified procedures. The higher the number, the better the treadwear. > > Traction is a tire’s ability to stop on wet pavement under controlled conditions. The codes are one of the letters, “A,” “B,” or “C”, with “A” signifying the highest traction coefficient. > > Temperature resistance is a tire’s resistance to the generation of heat and its ability to dissipate heat when tested under controlled conditions. The codes are one of the letters “A,” “B,” or “C,” with “A” signifying the highest level of performance. Note that the traction rating is for **wet** pavement, so a tire can test well but still not be considered a performance tire for dry-weather handling.