TedxGS

iTrader: (1)

Hi, i am a bit confused about the Y and Z for 275/30YR19 and 275/30ZR19 after the 30. What is the Y and Z? Thanks!

meZoom!

this question belongs in the wheels/tires section.

but anyway, the y and z are speed ratings for the tires.
Y=300km/h (186mph)
Z=240km/h (149mph)

How fast are you trying to go?

TedxGS

iTrader: (1)

Thanks for the reply and sorry about not posting it in the correct area. Well my current tires use the Z but I need to change my rears and on tirerack they sell the one with the Y. My front tires are still good and are the Z. So basically my question is it ok to have the Z in the front and Y in the back? I hope I didnt confuse anyone. hope to hear from someone soon. thanks.

rominl

iTrader: (4)

oh boy, we need 200mph though, what do we do then?

TedxGS

iTrader: (1)

bump^ anyone know?

Eternity3G

Sorry... never was faced w/ the 200+mph question as most passenger cars are only capable of ~150-180mph... and most drivers aren't capable of handling vehicles even at that speed safely...

But, here's some info courtesy of the rack....

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

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.
W 168 mph 270 km/h Exotic Sports Cars
Y 186 mph 300 km/h Exotic 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.
225/50ZR16 in excess of 149 mph, 240 km/h
205/45ZR17 88W 168 mph, 270 km/h
285/35ZR19 99Y 186 mph, 300 km/h

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 99Y 186 mph, 300 km/h
285/35ZR19 (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.

meZoom!

Yes, it's perfectly ok for street use to mix different ratings like that. Nothing adverse should happen under the maximum load and speeds listed for them.

TedxGS

iTrader: (1)

thank you zoom. that was the answer i was looking for!!!