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Thread: Ultimate tire write-up!!!

  1. #1
    Full Throttle Extreme! 93camaro_zzz's Avatar
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    Oct 2004
    Oxnard, Califonia, USA

    Post Ultimate tire write-up!!!

    OK here is the "everything you want to know about tires" write-up. Just wanted to write up something so everyone can read, and have a better understanding of it all. Take a deep breath, this is going to be long.


    Tires basically come in two forms of sizes. Standard and metric. Most cars and light trucks come with metric sized tires these days. Only really heavy trucks (18 wheelers) and some heavy duty light trucks come with Standard. Metric is sized in a fashion measuring first the width of the tread, then the aspect ratio, and then a letter or two, and then the size of rim it fits on. Here is an example:


    In this example the 275 is the width of th tire in millimeters, then 40 percent of that 275 width measures the height of the tire from where it meets the rim to the tread of the tire measuring along the sidewall, then the "Z' is the speed rating, then "R" stands for radial, and then 17 means it fits on a 17" rim. Now there is some controversy in this. For example, one myth, is that all 275/40R17 tires are the same in size. This is not true, it is actually up to the manufacturer to determine where to measure the width. There is no government standard or anything. Here's what I mean... Some manufacturers measure the 275 from the farthest outward point, to the opposite farthest point, with the tire off a rim, and uninflated of course. Then some measure the actual tread, which is measured also with the tire off the rim, and the tire uninflated. The tread would be measured where the tread would start curving into the sidewall. Basically the part of the tire that would actually be touching the road. So obviously the manufacturers that measures it the second way, will actually have a slightly wider tire. I dont remember all the manufacturers that did their sizing the second way, but I do remember some. They include Yokohama, BFGoodrich, and Michelin, and all of their subsidies and sister companies. The only ones I remember that did it the first way, were Goodyear, Kuhmo and Falken. You can probably notice that the first three (Yokohama, BFGoodrich, and Michelin) are usually more expensive then the other ones are. Like I will probably reiterate through this write-up, price is important on tires. Some people say, "Wow, look! A tire that is cheap, and pretty good or high performance. In very little cases this is true. I will also mention about size, that size does matter. If you throw an oddball size on your car, then your speedo could be off. There is a GREAT tire size calulator on the internet, and it is right here:

    It will show you the comparison of two tire sizes, and tell you how much your speedometer will be off between the two. Now if you go there and compare say the 245/50-16 tire, and the 275/40-17, it says they are EXACTLY the same size. Thats why alo t of Z28 and SS guys go to that tire size, because there car's came factory with the 245 tire. But if you compare the 275 tire to the 235/55-16 tire, it actually says this:

    Speedometer reading with non-stock tire is 2.0% too fast. When your speedo reads 60mph, you are actually traveling 58.8mph.

    Thats why a 285/40-17 tire is actually closer to the stock V6 size of 235/55-16. It is 0.8% too fast, and when traveling 60mph, you are actually traveling 59.5mph. Alot closer. Basically it comes down to if you're getter a tire that is actually larger in diameter, cause thats what matters to the speedomter, your speedometer will be faster (stock-60mph compared to non-stock-90mph). And obvioulsy the opposite is true.

    Standard tires are measured (for example) 31x10.50-15. With the first number being the actual diameter of the tire in inches, the next being the width of the tread, with the same myth as metric occuring sometimes, and the last number is of course the rim size the tire fits on. Like I said before standard tires usually go on trucks, trailers, and maybe some old cars. Ive seen them on old volkswagen's and such. You can always times the width of the tire by 25.4 to get metric. So 10.5 x 25.4 in our example to find out that it is actually 266.7 or basically a 265 metric width tire. Alot of standard tires will also have a load rating. (I.E. "B" load range or "C" load range) This is obviously the max load the tire could hold compared to its max pressure rating. Alot, actually I would say most standard sized tires will not have a speed rating.


    If you look at the side of your tire, you will see many things on it. Lots of numbers, letters, and all kinds of stuff!

    Speed rating:

    The speed rating is specified by a letter on the side of the tire. You can find it either sometimes in the size of the tire like earlier. (275/40ZR17) so the "Z" would be the speed rating in that example, or if it is not there, it will be on the side of the tire in this form: "91Z" Which will be the load rating and then the speed rating right afterwards. Now the speed rating is actually a measurement of the maximum sustained speed of a tire. Now, not that is advised, but you techinically could take an S-speed rated tire (112mph) to more than that speed, because that tire has been tested to withstand 112mph at a fixed period of time (its somthing like 2 hours). This is why my friend took his chevelle to 135mph on an S speed rated tire, and it did not explode. But dont try that at home. Anyways, here are the speed ratings and there speeds:

    Q = 99 MPH
    S = 112 MPH
    T = 118 MPH
    U = 124 MPH
    H = 130 MPH
    V = 149 MPH
    Z = 149 MPH and over
    W = 168 MPH
    Y = 186 MPH

    Now about "Z" rating. When Z-speed rated tires were first introduced, they were devoloped to reflect the highest tire speed rating that would ever be required, in excess of 149 mph. While Z-speed rated tires are capable of speeds in EXCESS of 149 mph, how far above 149 mph was not identified. This ultimately caused the automotive industry to add W and Y speed ratings to identify the tires that meet the needs of new vehicles that have extremely high top-speed capabilities.

    Load rating:

    The load rating is represented in a two digit number. It is simple, and just resembles the relative load capability of an individual tire. For example, an 87 load rating can hold 1,201 pounds. Here is a list of them:

    80 990
    81 1018
    82 1047
    83 1074
    84 1102
    85 1135
    86 1168
    87 1201
    88 1234
    89 1278
    90 1323
    91 1356
    92 1389
    93 1433
    94 1477
    95 1521
    96 1565
    97 1609
    98 1653
    99 1708
    100 1764
    101 1819
    102 1874
    103 1929
    104 1984
    105 2039
    106 2095
    107 2149
    108 2205
    109 2271
    110 2337
    111 2403
    112 2469
    113 2535
    114 2601
    115 2679
    116 2750
    117 2833
    118 2911
    119 2999
    120 3080
    121 3197
    122 3308
    123 3410
    124 3528
    125 3638

    There we go.

    Treadwear, traction, and temperature:

    There is another bit of information that is on the side of tires. It might look something like this: 400/AA/A or maybe it just looks like this: Treadwear 400 Traction AA Temperature A. The first thing to remember when reading about this, is these specifications are manufacturer tested or tested by an independent company hired by the manufacturer. They are not government tested only government monitored. So all 400/AA/A tires are DEFINETLY not the same!


    This number is a comparison of the said tire, and a tire treadwear rated "100" by the same company or independent tester. So this means, somewhere in like the back of a Michelin wearhouse, there is this tire rated with a treadwear of 100. So you take a Michelin tire with a treadwear of 400, and it will last 4 times as long as that 100 rated tire. So what does this all mean? This means, it will give you an idea of how long the tire will last. For example, what if yokohama uses a drag slick (not long lasting) as their 100 tire, and michelin uses a really hard tire as their "100" tire, . They would definetly be two completly different ratings for their use of the treadwear number.


    The traction rating is measured by one of four letters. C, B, A, or AA. C of course being the worst, and AA being the best. A tire has to have at least C to be sold in the US. Most of your Z and higher speed rated tires will have an AA rating, but it is not bad to have an A. This number is devoloped from how the tire operated in WET conditions. Some people just take this as the general traction rating, like how much traction does the tire have. This is proven by looking at alot of popular drag radials. Some drag radials will have C as a traction rating. Because they obviously dont have good wet weather traction, but have excellent dry traction.


    The rating for temperature measures how the tire will react to a sustained speed for a prolonged period of time. Will it stay cool? Or overheat? The temperature could have 3 ratings, measured as letters, including C, B, and A. As the same as traction, C being the worst, and A being the best. I will relate back to my drag radial example in traction, to say that some drag radials might have C as their temperature rating, and this does not mean they are a bad tire. It is a tire for a specific use. Drag radials are supposed to get hot, so they can stick at a track, this is how they were designed.

    Thats about it right now. I might update this occasionally, when I get time, or learn something new. Hope everybody learned something, I had to do alot of research for this.
    2000 Pontiac TransAm WS-6 MN6 370ci Twin turbo
    1999 Camaro Z28 - Auto, lid, catback (Daily)
    2006 GSX-R 750
    Jordan - 1995 Chevy Camaro 3.4 5 speed (Sold)

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  3. #2
    Dead on
    Join Date
    Feb 2005
    Very nice writeup. Very nice indeed.
    94 Firebird Formula LT1 (sold)
    Current bests:
    RT: .0006 60': 1.792 1/8 mile: 8.128 @ 85.85 1/4 mile: 12.854 @ 107.40

  4. #3
    Join Date
    Dec 2005
    That clears alot up. Thanks for the info.

  5. #4
    Full Throttle Extreme! FloydSummerOf68's Avatar
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    Oct 2004
    Missouri City, Texas, USA
    Nicely done.
    So what I now know, is that the #'s and letters don't mean a damn thing when comparing tires
    '11 CTS-V Coupe
    '12 SRT8 Charger
    V6 Firebird - 12.2 on 100 shot and 13.5 Cam only - GONE

  6. #5
    Mod Squad HAZ-Matt's Avatar
    Join Date
    Oct 2004
    TX Med Ctr
    Oh but tires get even more fun than that. If you use a tire diameter calculator and then look at how the computer is programed, you will find that the values are not the same I wish I knew what GM used for their dynamic tire diameter calculations.
    2001 Formula
    2000 Firebird - sold

    FI Moderator

  7. #6
    Light Throttle
    Join Date
    Jun 2005
    in hell (a.k.a central texas
    ok 93camaro_zzzz thanks alot for the write up and also if you wanna keep the same rim on there thats stock then you can get the 255/50-16 from BFG and its 140 plus shipping new on jegs
    1998 Camaro
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    simulated Dual Exhaust with turndowns.... sounds like a beast

  8. #7
    Well, on the subject of tires, can you tell me why I have 3 different tire pressure gauges and each one gives a different reading in the same tire? I guess tire pressure is not a real exact science.

  9. #8
    thanks for the info

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