Will using a higher speed rated tire do anything for the car?

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.