Hi All

I am about to replace the tyres on my 04 Coupe.

The following are a good price at the mo

GOODYEAR F 1 GSD 3 Eagle - 225/40R18 92Y XL fronts

GOODYEAR F 1 GSD 3 Eagle - 255/40R19 96Y XL rears

(Price of the tyres above are £480 UK pounds plus fitting.)

Question is that the rears are not stock size (255/35), does this
make a big difference or not.

Can you go to a different size ie 235/35R19.

I am also assuming that the 96Y / 92Y are important factors.

Any other suggestions for replacements would be greatly appreciated ie Vredestein Ultrac Sessanta's, Avon ZZ3's.

Many thanks for any help guys - the forum is a great place for information.

 

An aspect ratio of 40-v-35 will not make a difference. Maybe an extremely small speedometer diff at most. Aspect is the percent of a tires sidewall hieght to the width of the tread. About 13 mm.

Following info from tirerack.com



How to Read Speed Rating, Load Index & Service Descriptions




Using a P195/60R15 87S tire size as our example, the 87S at the end of the size represents the tire's service description. A service description identifies the tire's load index and speed rating. Service Descriptions are required on all speed rated (except for Z-speed rated) tires manufactured since 1991.
The first two digits (87S) represent the tire's load index and are followed by a single letter (87S) identifying the tire's speed rating.
Load Index
P195/60R15 87S - The load index (87) is the tire size's assigned numerical value used to compare relative load carrying capabilities. In the case of our example the 87 identifies the tires ability to carry approximately 1,201 pounds.
The higher the tire's load index number, the greater its load carrying capacity.
89 = 1,279 pounds
88 = 1,235 pounds
87 = 1,201 pounds
86 = 1,168 pounds
85 = 1,135 pounds
A tire with a higher load index than that of the Original Equipment tire indicates an increase in load capacity. A tire with a load index equal to that of the Original Equipment tire indicates an equivalent load capacity. A tire with a lower load index than the Original Equipment tire indicates the tire does not equal the load capacity of the original.
Typically, the load indexes of the tires used on passenger cars and light trucks range from 70 to 110.
Load IndexPoundsKilograms
Load IndexPoundsKilograms71761345911356615727833559213896307380536593143365 07482737594147767075853387951521690768824009615657 10779084129716097307893742598165375079963437991709 77580992450100176480081101946210118198258210474751 02187485083107448710319298758411025001041984900851 13551510520399258611685301062094950871201545107214 99758812355601082205100089127958010922711030901323 60011023371060

Speed Rating
In Germany some highways do not have speed limits and high speed driving is permitted. Speed ratings were established to match the speed capability of tires with the top speed capability of the vehicles to which they are applied. Speed ratings are established in kilometers per hour and subsequently converted to miles per hour (which explains why speed ratings appear established at "unusual" mile per hour increments). Despite the tire manufacturer's ability to manufacturer tires capable of high speeds, none of them recommend the use of their products in excess of legal speed limits.
Speed ratings are based on laboratory tests where the tire is pressed against a large diameter metal drum to reflect its appropriate load, and run at ever increasing speeds (in 6.2 mph steps in 10 minute increments) until the tire's required speed has been met.
It is important to note that speed ratings only apply to tires that have not been damaged, altered, under-inflated or overloaded. Additionally, most tire manufacturers maintain that a tire that has been cut or punctured no longer retains the tire manufacturer's original speed rating, even after being repaired because the tire manufacturer can't control the quality of the repair.
Over the years, tire speed rating symbols have been marked on tires in any of three ways shown in the following examples:
225/50SR16225/50SR16 89Sor 225/50R16 89S

Each of these was an acceptable method of identifying speed ratings.
Early tires had their speed rating symbol shown "within" the tire size, such as 225/50SR16. Tires using this type of branding were not to have been produced after 1991.
225/50SR16112 mph, 180 km/h225/50HR16130, 210 km/h225/50VR16in excess of 130 mph, 210 km/h

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:
M81 mph130 km/hN87 mph140km/hTemporary Spare TiresP93 mph150 km/hQ99 mph160 km/hStudless & Studdable Winter TiresR106 mph170 km/hH.D. Light Truck TiresS112 mph180 km/hFamily Sedans & VansT118 mph190 km/hFamily Sedans & VansU124 mph200 km/hH130 mph210 km/hSport Sedans & CoupesV149 mph240 km/hSport Sedans, Coupes & Sports Cars

When Z-speed rated tires were first introduced, they were thought to reflect the highest tire speed rating that would ever be required, in excess of 240 km/h or 149 mph. While Z-speed rated tires are capable of speeds in excess of 149 mph, how far above 149 mph was not identified. That 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.
W168 mph270 km/hExotic Sports CarsY186 mph300 km/hExotic Sports Cars

While a Z-speed rating still often appears in the tire size designation of these tires, such as 225/50ZR16 91W, the Z in the size signifies a maximum speed capability in excess of 149 mph, 240 km/h; the W in the service description indicates the tire's 168 mph, 270 km/h maximum speed.
225/50ZR16in excess of 149 mph, 240 km/h205/45ZR17 88W168 mph, 270 km/h285/35ZR19 99Y186 mph, 300 km/h

Most recently, when the Y-speed rating indicated in a service description is enclosed in parentheses, such as 285/35ZR19 (99Y), the top speed of the tire has been tested in excess of 186 mph, 300 km/h indicated by the service description as shown below:
285/35ZR19 99Y186 mph, 300 km/h285/35ZR19 (99Y)in excess of 186 mph, 300 km/h

As vehicles have increased their top speeds into Autobahn-only ranges, the tire speed ratings have evolved to better identify the tires capability, allowing drivers to match the speed of their tires with the top speed of their vehicle.