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While at the dealership yesterday, I figured I'd start price shopping for new tires (not that I'm ready to buy right now). So, I asked the Parts guy for a price on BFG AT 285/75R16's. He asked me for the speed rating. I've never been asked that before. When I have bought tires from other places, they've never asked me for it. So, what's the speed rating on the tires for the Xterra? And does anyone have a chart of the various levels of speed ratings? I'm not familiar with them.
 

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Taken From: http://www.tirerack.com/tires/tiretech/techpage.jsp?techid=35

Speed Rating

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 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:

225/50SR16 225/50SR16 89S or 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.

225/50SR16 112 mph, 180 km/h
225/50HR16 130, 210 km/h
225/50VR16 in 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:

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.



Related Links:
Calculating Tire Dimensions
Contact Patch
The Plus Concept
Tire Size Conversion Chart
Tire Size Information
 

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Too funny. I just priced new Revo AT's 265/75/16 this morning as my stock tires are heading south fast. $660 installed and balanced. I think after X-mas I will get some new tires. Revo AT's for DD and some Maxxis big horns for OR. I will order the Maxxis on ebay and have a friend mount them. I will balance using equal.
 

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mtdewmike said:
While at the dealership yesterday, I figured I'd start price shopping for new tires (not that I'm ready to buy right now). So, I asked the Parts guy for a price on BFG AT 285/75R16's. He asked me for the speed rating. I've never been asked that before. When I have bought tires from other places, they've never asked me for it. So, what's the speed rating on the tires for the Xterra? And does anyone have a chart of the various levels of speed ratings? I'm not familiar with them.
Stock tires on the OR is a T speed rating. Note the load descript is 114 which equates to 2601 lbs.
 

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mtdewmike said:
snowjunkie said:
syndicate said:
BFG ATs come in different speed ratings?

I don't think they do.

yep they come in "Q" "R" and "S" ratings.
Which rating should I get then? What does everyone else have for the BFG AT's?

Well really you have to gage your need. Speed ratings are based on sustained speed and basically means that you do not want to run at a speed above what the tire is rated for a prolonged period of time or you risk blowing out the tire.

Q = 99mph R = 106 mph and S = 112 mph. Off road speed ratings don't really matter becuase you won't be driving that fast. So my suggestion is decide how much on road driving you are going to do and how fast of an average speed do you intend to drive at. Honestly you could go with the Q rated tire but if there is no price difference I would get the S as I don't see anyone really taking an xterra over 112 mph average speed. Unless of coarse you run the I5 cooridor between LA nd the Bay Area in Cali :cheers:.
 
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