I heard that going down on the manufacturer's tire speed rating will affect the handling but will going up from an H to a V do anything such as increasing tread life.
tl dr - There is absolutely no worries about putting a higher rated tire on your vehicle. It just means you can drive your car faster if the car is capable (and the speed limits will allow). You will gain nothing in any other aspect of the tire, such as tire life, treadwear, or what have you. In fact, the higher speed rating doesn't have much to do with cornering ability, either. Just the speed factor of the tire itself.
There is no relationship between the speed rating and the longevity of the tire. Every manufacturer will have different combinations of factors. There is a whole wide range of tires available in many different sizes.
It is widely known how to tell if a tire will fit your car: you look at the size. The size reads something to the effect of: P255/75R-15. It breaks down as:
- P equates to Passenger tire (LT = Light Truck)
- 255 is the width of the tire tread in millimeters
- 75 is the aspect or sidewall ratio as a percentage (in this case, the tire sidewall would be 75% of the width of the tread)
- R is telling us the tire is a radial tire
- 15 is the rim diameter
This same indicator may also look like: P255/75ZR-15 92Y
The Z indicates the tire is speed rated above 149mph (or 240kph). When this speed was introduced, it was thought that there would never be a need to have a tire which would need to go faster. It was soon discovered that there was a need for greater speeds, so W and Y were introduced. You will see the actual speed rating at the end of the 92Y indicator.
225/50ZR16 in excess of 149 mph, 240 km/h 205/45ZR17 88W 168 mph, 270 km/h 285/35ZR19 99Y 186 mph, 300 km/h
The 92 in my above example, indicates the load rating of the tire. The higher the number, the more the tire can individually haul.
(NOTE: LI=Load Index) LI LBS KG | LI LBS KG 71 761 345 | 91 1356 615 72 783 355 | 92 1389 630 73 805 365 | 93 1433 650 74 827 375 | 94 1477 670 75 853 387 | 95 1521 690 76 882 400 | 96 1565 710 77 908 412 | 97 1609 730 78 937 425 | 98 1653 750 79 963 437 | 99 1709 775 80 992 450 | 100 1764 800 81 1019 462 | 101 1819 825 82 1047 475 | 102 1874 850 83 1074 487 | 103 1929 875 84 1102 500 | 104 1984 900 85 1135 515 | 105 2039 925 86 1168 530 | 106 2094 950 87 1201 545 | 107 2149 975 88 1235 560 | 108 2205 1000 89 1279 580 | 109 2271 1030 90 1323 600 | 110 2337 1060
There are more indicators on the side of the tire which are also useful when trying to figure out anything about a tire and how it should behave when on your vehicle. Discount Tire has a great page on this info, but I want to point out one area since you mentioned it, that being tread life. On the side of the tire it will look something like the following:
There are three parts to this being: treadwear; traction; temperature.
- Treadwear: Treadwear is a measurement of the tires durability. The higher the number, the longer the tire should last (under normal conditions). The thing to remember out the treadwear number is it is specific to the manufacturer not to other brands. If you are contemplating a Goodyear brand tire, only compare the number on other Goodyear tires.
- Traction: This measures the tire's ability to stop in a straight line on wet surfaces in a controlled test environment. It doesn't measure the tire's ability to handle in the corner. There are several ratings: AA, A, B, & C. AA is the highest rating.
- Temperature: This measures a tire's ability to withstand heat buildup in the tire. It has measurements of: A, B, & C. A is the highest rating.
Treadwear can be negatively affected, lowering the speed rating substantially and all aspects of the tire's handling. As well, a T-rated tire is manufactured differently from an H-rated tire, so that is why they handle higher speeds differently. Weaves, ply and compound can change ride comfort, handling and wear. Essentially the only thing that is the same is the tread pattern.
Though these changes may not be noticeable to a lay person, tread life may be significantly affected the further from the manufacturer specs you get, which sometimes can lead to cupping. I say this because at my job I have encountered these happenings. Specifically, 2 customers, 1 had V-rated tires and was having a cupping issue that caused a very noisy ride. He had his suspension checked and was found to have no issues, so without a mechanical issue and no apparent cause for cupping, then the only thing left is the fact he had a plu- zero upsized T-rated tire on his V-rated vehicle.
As far as tread wear, there was a 2004 Kia Sedona which came in and had bought S-rated tires on what I believe is an H- or V-rated vehicle and they changed about 3 pairs of these tire over a 2 year period. A 50,000 mile rated tire wears down to the wear bar within 20,000 miles because instead of spending $20 more per tire to get a closer match to their speed rating they throw out their warranty and buy under-rated tires.
UK road regulations only specify a requirement of minimum speed ratings, that of the vehicle to be met, and insurers have no issue whatsoever with higher rated tyres. Many miss the load rating, however, not only for tyres, but wheels, too. Insurers will not cover you if either your tyre load rating, or your wheel load rating is insufficient (lower than specified by vehicle specs - check GCWR, the gross curb weight rating, find the load distribution of your vehicle, select heavier axle, calculate). E.g. 3000kg gross curb weight rated vehicle with 40% front 60% rear weight distribution: 3000kg * 0.6 = 1800kg on the rear axle, divide by 2 = 900kg. Both your wheels and your tyres MUST be load rated at least that. Beware of aftermarket wheel purchases, some sellers will try to tell you it's "fine" to buy a lower weight rated rims, it's not. It's dangerous, and it's an insurance voider.