Tire rating info I didn't know "Z" is not the higest speed rating...
#1
Drifting
Thread Starter
Tire rating info I didn't know "Z" is not the higest speed rating...
While shopping for tires I learned something new to me. I am sure many of you already know this but I didn't until today. This was taken from the Tirerack.com site:
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
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
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CorvetteBrent (04-28-2020)
#3
Le Mans Master
just finishred that lesson on tires
we have 2 Y speed rated tires but no (Y) speed rated ones....
Been in the shop with them using the tire machine also.... the fun and joy of teaching high school auto tech
we have 2 Y speed rated tires but no (Y) speed rated ones....
Been in the shop with them using the tire machine also.... the fun and joy of teaching high school auto tech
#5
Race Director
the thing i have never read about is how long those speeds can be sustained. while Y tires are much less common than W tires people have still exceeded 200mph on Y tires with no issue. what i've been curious about is how they come up with those numbers. like what testing is involved
#6
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I knew about the W rated tires, but did not know about the Y rated ones. Thanks for the info.
#7
Team Owner
Just once, I'd like to be able to get my car in the range of where I'd need "Y" speed rated tires......and furthermore, to think my first brand new car, a Chevelle with a 454 engine, came with tires that had no speed rating!!
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CorvetteBrent (04-28-2020)
#8
Race Director
so i found the answer to how speed ratings are determined. apparently ratings are what a tire can sustain for at least 2hrs
It might help if I explained “speed ratings.” The rating does not tell you how fast the tire can go, rather how long it can be expected to last at a sustained speed.
The biggest safety issue with respect to tires is heat. An underinflated tire will generate more heat; a worn tire will generate more heat because there is less tread to absorb the heat. A brand-new tire will generate heat as the sidewall flexes not only when the when the car goes up and down over bumps and during cornering but principally as it rotates.
A tire, depending on size, will rotate in the 750-900 times per minute range at highway speeds. With each rotation, it goes from compressed at the bottom where it contacts the road to expanded at the top where centrifugal force pushes it out. This constant movement as the sidewall flexes generates heat. Too much heat and the sidewall will blow out.
The more weight or pressure there is on a tire, the greater the forces acting on the sidewall and the amount of heat generated. Those big pieces of tire you see along the highway are a result of heat. Most often they are treads thrown from retreaded tires when heat built up to the point that it caused the adhesive used to bond the tread to the tire to give up
Heat is tire enemy No. 1. With this in mind, there is a rating system that tells us the maximum speed at which a tire can run for two hours without failure. The chief reason for these ratings is the unrestricted speeds of the German autobahn.
The ratings run from M for 130 km/h to Y for 300 km/h. In North America, where the maximum legal limit is 75 mph or 122 km/h in some U.S. states, virtually every passenger car tire sold exceeds that limit.
The S rating you mention is 180 km/h, T 190 km/h and H 210 km/h. So on the surface, there is no need to buy a tire with a higher rating. But it is not that simple. Vehicle loads and inflation pressure directly affect how much a tire will flex and the amount of heat generated, so there is a need for safety margin. And, during the development process, suspension engineers designate a tire size and speed rating – often higher for cars that may see use on the autobahn.
That rating also takes into account the size or depth of the sidewall, the “profile” of the tire. A lower profile means a stiffer sidewall and less flex and heat. Tires rated for extremely high speeds, without exception, have a very short sidewall. Tires with a low speed rating tend to have very deep sidewalls that will flex a lot more and create more heat. And tires with a higher speed rating have a stiffer sidewall and are more responsive to steering input and better under severe braking.
The bottom line – you should stick within a pretty narrow range of that original speed rating – incorporated into the design of the vehicle.
The ratings
M 130 km/h
N 140 km/h
P 150 km/h
Q 160 km/h
R 170 km/h
S 180 km/h
T 190 km/h
U 200 km/h
H 210 km/h
V 240 km/h
Z 240 km/h plus
W 270 km/h
Y 300 km/h
The biggest safety issue with respect to tires is heat. An underinflated tire will generate more heat; a worn tire will generate more heat because there is less tread to absorb the heat. A brand-new tire will generate heat as the sidewall flexes not only when the when the car goes up and down over bumps and during cornering but principally as it rotates.
A tire, depending on size, will rotate in the 750-900 times per minute range at highway speeds. With each rotation, it goes from compressed at the bottom where it contacts the road to expanded at the top where centrifugal force pushes it out. This constant movement as the sidewall flexes generates heat. Too much heat and the sidewall will blow out.
The more weight or pressure there is on a tire, the greater the forces acting on the sidewall and the amount of heat generated. Those big pieces of tire you see along the highway are a result of heat. Most often they are treads thrown from retreaded tires when heat built up to the point that it caused the adhesive used to bond the tread to the tire to give up
Heat is tire enemy No. 1. With this in mind, there is a rating system that tells us the maximum speed at which a tire can run for two hours without failure. The chief reason for these ratings is the unrestricted speeds of the German autobahn.
The ratings run from M for 130 km/h to Y for 300 km/h. In North America, where the maximum legal limit is 75 mph or 122 km/h in some U.S. states, virtually every passenger car tire sold exceeds that limit.
The S rating you mention is 180 km/h, T 190 km/h and H 210 km/h. So on the surface, there is no need to buy a tire with a higher rating. But it is not that simple. Vehicle loads and inflation pressure directly affect how much a tire will flex and the amount of heat generated, so there is a need for safety margin. And, during the development process, suspension engineers designate a tire size and speed rating – often higher for cars that may see use on the autobahn.
That rating also takes into account the size or depth of the sidewall, the “profile” of the tire. A lower profile means a stiffer sidewall and less flex and heat. Tires rated for extremely high speeds, without exception, have a very short sidewall. Tires with a low speed rating tend to have very deep sidewalls that will flex a lot more and create more heat. And tires with a higher speed rating have a stiffer sidewall and are more responsive to steering input and better under severe braking.
The bottom line – you should stick within a pretty narrow range of that original speed rating – incorporated into the design of the vehicle.
The ratings
M 130 km/h
N 140 km/h
P 150 km/h
Q 160 km/h
R 170 km/h
S 180 km/h
T 190 km/h
U 200 km/h
H 210 km/h
V 240 km/h
Z 240 km/h plus
W 270 km/h
Y 300 km/h
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CorvetteBrent (04-28-2020)
#10
Burning Brakes
Good info, I didn't know that either. Now the question I have is what is the number before the "Y". I have 345/25ZR20 100Y. What is the difference in a 99Y and 100Y?
#11
Race Director
based on what? the sidewalls are the areas that fail during high speed. every test i came across pointed to heat as being the reason tires failed during high speed
#12
Race Director
http://www.discounttire.com/dtcs/infoLoadIndex.dos
tires like the new michelin pss have incredibly high load ratings for such a low profile tire, probably because they have such rugged sidewalls
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CorvetteBrent (04-28-2020)
#13
Team Owner
I just pulled a small nail out of one of the tires on my Z-28. The tires are a few years old, but have maybe 3000 miles on them, at the most. No, I'm not happy about having a patched tire on the car, but I'm certainly not going to replace them.....I can't get just one, because the manufacturer has recently discontinued them, and secondly, one new tire and one old tire, on the rear end of a car with a limited slip diff can cause problems.
#14
Le Mans Master
I agree that heat is the biggest issue with speed ratings. I was a senior engineer for an auto manufacturer and dealt with Goodyear as our supplier. I have witnessed some of the speed testing during qualification of our tires. There can be several strategies in the design of the tire to reduce heat buildup in the tire, one of them is like racebum stated that a short stiff sidewall can help.
This link shows some diagrams of good and bad repairs with some discussion.
http://www.tirerack.com/tires/tirete....jsp?techid=77
This link shows which manufacturers allow repairs vs. the speed ratings.
http://www.tirerack.com/tires/tirete...jsp?techid=225
This link is to a specific Goodyear policy.
http://www.goodyear.com/cfmx/web/gov...e/psb_9811.cfm
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CorvetteBrent (04-28-2020)