Brakes & Suspension Forum sponsored by The Tire Rack
|02-08-2002, 09:12 AM||#1|
Join Date: Sep 2000
Location: Los Angeles/MontrealVehicle:
2012 Volvo S60 T5
H-R-W-XYZ....ratings..what do they REALLY mean?
I'm planning on getting a set of Kuhmo 712's this spring, and I can get a good deal on them. The W rated ones are about 40-50 bucks cheaper OVERALL (for all 4) than Z rated.
I know that the ratings are heat ratings for maximum speed (for instance, W is only for 100mph, whereas Z is for 149+ mph (I'm just making those numbers up)).
I rearely go over 100mph, so I dont really NEED Z rated tires....or do I???
Do Z rated tires actually have better GRIP than W rated? I guess they would be more heat resistant, but is the compound actually grippier? What benefit would I have with Z rated? Should I pay the extra cash?
|02-08-2002, 10:13 AM||#2|
Join Date: Mar 2000
Location: Ventura, CAVehicle:
With the 712s, there's some difference between the two. One is a good tire, one gets complaints. Now, of course, I forget which. I believe the W-rated tires are the "good" ones. Something is different about them...search?
|02-08-2002, 10:18 AM||#3|
Join Date: Jun 2000
Chapter/Region: South East
Location: Charlotte, NC USofAVehicle:
Here is a cut and paste from the Tire Rack website. I think it will answer your questions:
P195/60R15 87S - The tire speed rating (S) is the maximum speed for which the tire is rated. For example, the “S” rating identifies speeds up to 112 mph (180 km/h).
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.
In Europe, where selected 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 capabilities 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 “odd” 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 (to reflect its required load) against a large diameter metal drum and run at ever increasing speeds (in 6.2 mph steps in 10 minute increments) until the tire’s required speed has been met.
Speed Rating - Miles/Hour - Kilometers/Hour - Typical Use
N=87 MPH, 140km/h, Spare Tires
P=93 MPH, 150km/h
Q=99 MPH, 160km/h, Winter, LT Tires
R=106 MPH, 170km/h, LT Tires
S=112 MPH, 180km/h
T=118 MPH, 190km/h
U=124 MPH, 200km/h
H=130 MPH, 210km/h, Sport Sedans
V=149 MPH, 240km/h, Sports Cars
Z=149 MPH, 240km/h and over, Sports Cars
W=168 MPH, 270km/h, Exotic Sport Cars
Y=186 MPH, 300km/h, Exotic Sport Cars
*Today, the Z-speed rating is the only speed rating that is still branded “within” the tire size, as in P225/50ZR16. All other speed ratings are shown in the tire’s service description.
When Z-speed rated tires were first introduced, they were thought to reflect the highest speed rating that would ever be required. Since that time the automotive industry has found it necessary to add W- and Y-speed ratings (indicated in the tire’s service description) to identify the tires that meet the needs of new vehicles that have extremely high, top speed capabilities.
P225/50ZR16 149+ 240+
P225/50ZR16 91W 168 270
P225/50ZR16 91Y 186 300
While all Z-speed rated tires are capable of speeds of 149 mph and above, prior to the W- and Y-speed ratings were identified in the service, how far above 149 mph was not identified
|02-08-2002, 10:37 AM||#4|
Join Date: Aug 2001
Chapter/Region: E. Canada
2003 WRX Wagon
You've got it right in that it is resistance to heat buildup from
friction, and the resistance to flying apart from centripetal
acceleration. Traction is traction, based on the UTCQ (?). and
shouldn't matter from one speed rating to the next, but the
higher up the the chain you get, the better the construction of
the tire to resist the effects of speed.
In general (my opinion) nobody needs a Z-rated tire for the
street. You can get a decent tire with anything over a Q-rated
tire. The ratings are also based on continuous use, not just
blasting up to xxx km/h and back down. If you are really into the
"performance" then you can get a H or V-rated tire for less than
|02-08-2002, 10:47 AM||#5|
Join Date: Jan 2001
Location: Paris, FR / Houston, TXVehicle:
2011 STi Sedan SWP
2011 Outback ABP
Just a note: According to Tirerack the Kumho 712 is available in stock 205/55-16 size in V and W ratings.
The W rated version is a bit softer compound (lower treadwear rating) and has slightly stiffer sidewalls than the V rated. Sometimes I wonder if people that complain about Kumho's sidewalls have the V rated, because I have W rated on my 2.5RS and have little or no problems with rollover when auto-xing as long as I bump the pressure up to 40+ lbs.
|02-08-2002, 11:30 AM||#6|
Join Date: Jul 2000
They sell a Z rated Kumho also which I have and beleive totally sux donkey balls. A z-rated tire gives not only improve traction at higher speeds but also better response and road feel.
|02-08-2002, 11:37 AM||#7|
Join Date: Apr 2001
Location: Houston, TXVehicle:
2010 Honda Fit Sport
Great explanation by dsmawd.
Also remember, if a tire only has a "Z" rating without clarification whether it's a "W" or a "Y", it means it has to be designed a few years back at least. Since most tire manufacturers update their tires with better design and material often, I'd NOT get such a "Z" rated tire. Such rating really means nothing other than -
"It's better than a 'V'-rated one from a few years back".
|02-08-2002, 12:49 PM||#9|
Join Date: May 2001
Location: Houston TX USAVehicle:
all the ratings really mean is how fast the tire can go safely.
that said, Z rated tires TEND to have stiffer side walls and more performance oriented tread etc.
|02-08-2002, 02:25 PM||#10|
Join Date: Apr 2001
Location: burlington, vermontVehicle:
1992 vw corrado vr6
silver w/ schrick/quaife
just my $0.02 . . . i had a set of the W-rated 712s, and hated them. soft, soft, SOFT! almost unstable-feeling. i was never happier than the day they came off my car.
maybe i have higher standards? possibly.
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