View Full Version : Changing tire size and type on my M6
My factory Conti's are a bit worn, they are noisey on some freeway surfaces, and lack wet/cold weather traction IMHO.
My thoughts were to change to a Ultra Preformance All Season tire, but the only fitments I found on Tire Rack are 245/45/19 and 275/40/19, which are narrower by 1/2 inch and taller by 1/2 inch, 1) will they fit the M6 19" stock wheels, 2)will the +1 size in Circum. cause any problems ?
I know this might sound sacrilegious to some but I have my reasons, I live in Cleveland and we get 6 months of winter, 3 months of cold/wet spring/fall , and maybe 3 months of nice summer weather, I would just like a colder compound tire to extend my driving .
I don't track my car and love it's sporty GT style, so the larger side wall should afford a smoother ride, but I will loose some of the cars sharp turn-in ability I know this and I'm OK with it.
I guess down sizing to a 18 inch wheel will allow me more selection of tire brands, but I will miss the looks of the stock M6 wheels, and also will the 14.7 " rotors of the M6 fit inside a 18" rim?
I was told this is the forum to get the right answers so thanks in advance guys.
DR.Z
Richard in NC
11-23-2007, 06:16 AM
Michelin Pilot PS2s are a great 3 season tire. Although they are not recommended for cold weather, I ran them in the 20s and 30s with no issues. I did notice a greater tendency to spin the tires on take off but never intended to run them at their max in the cold anyways. PS2s are also among the best in the wet along with Goodyear F1s. Then in the winter run winter tires if you must, but I'd park the car. Some 18 inch rims should work and are recommended for winter sets.
I use tire rack a lot for exploring options. They do show some 18 inch rims as a winter option.
If you really want all season, a possible option is the Pilot A/S. You WILL sacrifice some performance and feel year around with them. The performance area you'd hate to miss the most is braking distance as there would be some difference with lesser tires.
Tire Rack shows these sizes available http://www.tirerack.com/tires/Sizes.jsp?make=Michelin&model=Pilot+Sport+A%2FS.
You could probably go within 10mm or 5 aspect difference and maintain the same rims and look and no issues. Although, compare diameters. Too much difference could result in speedo error.
Welcome, Dr. Z. I saw you had posted elsewhere and didn't get direct answers. So I followed you to your website and sent you an e-mail.
I also have an M6. The stock tires on an M6 are 245/40f, 285/35r. So, what you are proposing is to replace what you have with a good all-weather tire which is -1. (We're usually used to +1.) It is, as you point out, not as wide as the stock tires and it rides a bit higher.
The answer, I believe, is that you can do it. The biggest problem in changing out the profile is that we tend to move in the + direction, getting wider and lower. That can create clearance issues, although the tires will still fit on the wheels, usually up to +3. You should not have a problem moving -1. However, some of our technical geniuses will come on the board after they have had their turkey leftover breakfasts, and will give you more technical responses, including citations to Internet resources with calculators of the differences between tires in either a - or a + direction. (Such as this one: http://www.miata.net/garage/tirecalc.html )
BHR4CE1
11-23-2007, 08:50 AM
You should not have a problem moving -1. However, some of our technical geniuses will come on the board after they have had their turkey leftover breakfasts, and will give you more technical responses, including citations to Internet resources with calculators of the differences between tires in either a - or a + direction. (Such as this one: http://www.miata.net/garage/tirecalc.html )
Sounds logical to me. The only think I have heard is that it is important to keep the overall outside diameter of the tire the same as the stock one so the Speedo/Odo will register the same.
Disclaimer...I am no TECHNICAL GENIUS, but I did stay at a Holiday Inn Express last night (no, not really).
cobradav
11-23-2007, 08:58 AM
I also did a cursory check on Tire Rack. Staying with the 19 in and ULTRA HIGH Performance A/S sure did not provide a lot of options... but what I did find was only about .6 to .8 inch difference in diameter over your OEM Contis. SInce the section width and tread width are narrower by about the same amount this should not provide any issues with clearance. Furthermore, BMW recomends staying within 3% of OEM diameters and the 0.8 inch is just that (OEM being 27 inch diameter). This is more for their speedometer calcs but also applies to other safety and performance issues as well. I also noticed only a 1-2 pound penalty going to an A/S tire in this size. I also think you would find more tire options by going DOWN to HIGH PERFORMANCE or just plain PERFORMANCE A/S tires.
So in summary you could stay with your OEM 19 wheels to retain the "look" and light weight and still go to the desired size you indicate. I am not a fan of going to 18 inch unless it is just for winter setup and you would switch back to summer tires for half the year. I would also suggest you consider the PS2 as a alternate as MalibuBimmer suggested. I just switched to them from my OEM Bridgestone RFT tires. While I am not convinced I them any better, they really do have considerable more wet grip than my OEM tires did. But not sure how well they could do your cold WX.
And welcome. You do realize we require pictures posted of all our members :greet:
Richard in NC
11-23-2007, 10:45 AM
And welcome. You do realize we require pictures posted of all our members :greet:
I second that welcome :cheers: and its the car we want pictures of....
:bmw: says hello....
Now give us some pics!
Going with PS2's sounds like a great idea.
If they provide good wet traction I'll be happy.
I have no plans to drive the M6 in snowy conditions, I have other rides for that.
I just wanted to drive it as much as possable and the PS2's should provide 6 to 7 months of use, plus sharp handling on the warm dry days.
It is snowing so I didn't want to pull it out of the garage, I took a shot of it in the garage and will upload later.
DR.Z
Going with PS2's sounds like a great idea.
If they provide good wet traction I'll be happy.
I have no plans to drive the M6 in snowy conditions, I have other rides for that.
I just wanted to drive it as much as possable and the PS2's should provide 6 to 7 months of use, plus sharp handling on the warm dry days.
It is snowing so I didn't want to pull it out of the garage, I took a shot of it in the garage and will upload later.
DR.Z
Welcome again Dr. Z. Sounds like a good compromise. I guess we helped you by answering your questions. We'd love to see more of you in the future. We look forward to the pics. We are photo whores.
BHR4CE1
01-06-2008, 07:19 AM
I just came across this little tidbit while surfing around on the net at http://www.502motorsports.com. It might come in handy to some of you...
If you're in the market for new tires, all of the variables in tire specifications and the confusing jargon you might hear from tire salesmen or "experts" might make your purchase rather stressful. Or maybe you just want to fully understand the tires you already have, the concepts at work, the significance of all of those sidewall markings. What does all this stuff mean in regular terms?
In this article, we will explore how tires are built and see what's in a tire. We'll find out what all the numbers and markings on the sidewall of a tire mean, and we'll decipher some of that tire jargon. By the end of this article, you'll understand how a tire supports your car, and you'll know why heat can build up in your tires, especially if the pressure is low. You'll also be able to adjust your tire pressure correctly and diagnose some common tire problems!
What All the Numbers Mean
Each section of small print on a tire's sidewall means something:
The tire size branded on the sidewall provides a significant amount of information about the tire's intended purpose, dimensions, load capacity and high temperature/high speed durability.
Our primary example will be based on variations of the 225/50R16 size, although other sizes will appear where appropriate.
Service Type
Most tire sizes begin with a letter or letters that identify the type of vehicle and/or type of service for which they were designed. The common indicators are as follows:
http://www.502motorsports.com/ho_a6_ci2_l.jpg
P225/50R16 91S
P = When a tire size begins with a "P," it signifies the tire is a "P-metric" size that was designed to be fitted on vehicles that are primarily used as passenger vehicles. This includes cars, minivans, sport utility vehicles and light duty pickup trucks (typically 1/4- and 1/2-ton load capacity). The use of P-metric sizes began in the late 1970s and they are the most frequently used type of tire size today.
225/50R16 92S
If there isn't a letter preceding the three-digit numeric portion of a tire size, it signifies the tire is a "Metric" size (also called "Euro-metric" because these sizes originated in Europe). While Metric tire sizes are primarily used on European cars, they are also used on vans and sport utility vehicles. Euro-metric sizes are dimensionally equivalent to P-metric sizes, but typically differ subtly in load carrying capabilities.
T125/90D16 98M
T = If a tire size begins with a "T," it signifies the tire is a "Temporary Spare" ("space saver" or "mini spare") that was designed to be used temporarily only until a flat tire can be repaired or replaced.
LT245/75R16 108/104S
LT = If a tire size begins with "LT," it signifies the tire is a "Light Truck-metric" size that was designed to be used on vehicles that are capable of carrying heavy cargo or towing large trailers. This includes medium and heavy-duty (typically 3/4- and 1-ton load capacity) pickup trucks, sport utility vehicles and full-size vans. Tires branded with the "LT" designation are the "little brothers" of 18-wheel tractor-trailer tires and are designed to provide substantial reserve capacity to accept the additional stresses of carrying heavy cargo.
7.50R16LT 112/107Q, 8.75R16.5LT 104/100Q or 31x10.50R15LT 109Q
LT = If a tire ends with "LT," it signifies the tire is either an earlier "Numeric", "Wide Base" or "Flotation" Light Truck size designed to be used on vehicles that are capable of carrying heavy cargo and towing trailers (Numeric sizes), use 16.5-inch diameter rims (Wide Base sizes) or are wider, oversized tires designed to help the vehicle drive on top of loose dirt or sandy surfaces (Flotation sizes). This includes light, medium and heavy-duty (typically 1/2-, 3/4 and 1-ton load capacity) pickup trucks and sport utility vehicles. Tires branded with the "LT" at the end of their size designation are also the "little brothers" of 18-wheel tractor-trailer tires and are designed to provide substantial reserve capacity to accept the additional stresses of carrying heavy cargo.
195/70R15C 104/102R
C = If a Euro-metric sized tire ends with a "C," it signifies the tire is a "Commercial" tire intended to be used on vans or delivery trucks that are capable of carrying heavy loads. In addition to being branded with the "C" in their size, these tires are also branded with their appropriate Service Description and "Load Range" (Load Range B, Load Range C or Load Range D).
ST225/75R15
ST = If a tire size begins with "ST," it signifies the tire is a "Special Trailer Service" size that was designed to only be used on boat, car or utility trailers. ST-sized tires should never be used on cars, vans or light trucks.
Section Width
Following the letter(s) that identify the type of vehicle and/or type of service for which the tire was designed, the three-digit numeric portion identifies the tire's "Section Width" (cross section) in millimeters.
P225/50R16 91S
The 225 indicates this tire is 225 millimeters across from the widest point of its outer sidewall to the widest point of its inner sidewall when mounted and measured on a specified width wheel. This measurement is also referred to as the tire's section width. Because many people think of measurements in inches, the 225mm can be converted to inches by dividing the section width in millimeters by 25.4 (the number of millimeters per inch).
225mm / 25.4 = 8.86"
Sidewall Aspect Ratio
Typically following the three digits identifying the tire's Section Width in millimeters is a two-digit number that identifies the tire's profile or aspect ratio.
P225/50R16 91S
The 50 indicates that this tire size's sidewall height (from rim to tread) is 50% of its section width. The measurement is the tire's section height, and also referred to as the tire's series, profile or aspect ratio. The higher the number, the taller the sidewall; the lower the number, the lower the sidewall. We know that this tire size's section width is 225mm and that its section height is 50% of 225mm. By converting the 225mm to inches (225 / 25.4 = 8.86") and multiplying it by 50% (.50) we confirm that this tire size results in a tire section height of 4.43". If this tire were a P225/70R16 size, our calculation would confirm that the size would result in a section height of 6.20", approximately a 1.8-inch taller sidewall.
http://www.502motorsports.com/tire-cutaway-big.jpg
Internal Construction
A letter (R in this case) that identifies the tire's internal construction follows the two digits used to identify the aspect ratio.
P225/50R16, P225/50ZR16
The R in the P225/50R16 91S size identifies that the tire has a Radial construction in which the tire's body plies "radiate" out from the imaginary center of the wheel. Radial tires are by far the most popular type of tire today representing over 98% of all tires sold.
If the R in the size was replaced with a D (225/50D16), it would identify that the internal tire body plies crisscross on a Diagonal and that the tire has a "bias ply" construction. Tires using this construction are for light truck and spare tire applications.
If the R in the size was replaced with a B (225/50B16), it would identify that the tire body plies not only crisscross the tire on a diagonal as before, but that they are reinforced with belts under the tread area. This type of tire construction is called "Belted." Tires using this construction are practically extinct.
Speed Rating
Today, the only tires that continue to include the speed rating "in" the tire size (P225/50ZR16) are Z-speed rated tires. In this case, following the two digits used to identify the aspect ratio are the letters ZR to identify the tire's speed rating (Z) and its internal construction (R). Since 1991, all other speed ratings are identified in the tire's Service Description (which will be covered shortly).
Tire and Wheel Diameter
P225/50R16 91S
The 16 indicates the tire and wheel diameter designed to be matched together.
Tires that have a rim diameter expressed in inches (P225/50R16, as well as 8, 10, 12, 13, 14, 15, 17, 18, 19, 20, 22, 23, 24, 26 and 28) are called "inch rim" sizes, are the most common type of tire size and are used on most cars, minivans, vans, sport utility vehicles and light duty light trucks.
While not as common, two additional "unique" types of tire/wheel diameters are still in use today.
Tires and wheels that have a rim diameter expressed in "half" inches (8.00R16.5LT, as well as, 14.5, 15.5, 17.5 and 19.5) are used on some heavy-duty trailers, heavy-duty light trucks and box vans.
Tires and wheels that have a rim diameter expressed in millimeters (190/65R390, as well as, 365 and 415) are called millimetric sizes. Michelin initiated millimetric sizes for their TRX tires that saw limited use on many different car models in the late 1970s and 1980s.
Michelin PAX System run flat tires have been introduced as an integrated wheel/tire system on a very limited basis as Original Equipment (O.E.) in North America. An example PAX System size of 235/710R460A 104T expresses tire and wheel dimensions in millimeters (235 mm Section Width, tire Overall Diameter of 710 mm and a 460A mm rim diameter, with the "A" in 460A signifying these tires feature ¿asymmetric¿ beads in which the outside bead (450 mm) and inside bead (470 mm) are actually different diameters.
All of these "unique" tire/wheel diameters were developed specifically because the tire and wheel design or intended vehicle use required them to be different than conventional tires and wheels. All of these tires and wheels feature bead profiles that have a different shape than traditional "inch rim" sizes.
Tires and wheels with unique rim diameters should never be combined with traditional "inch rim" tires and wheels.
It is critical that the tire and wheel diameters are always confirmed to match before the tire is mounted on the wheel.
Uniform Tire Quality Grading
Passenger car tires also have a grade on them as part of the uniform tire quality grading (UTQG) system. You can check the UTQG rating for your tires on this page maintained by the U.S. National Highway Traffic Safety Administration (NHTSA). Your tire's UTQG rating tells you three things:
Tread Wear: This number comes from testing the tire in controlled conditions on a government test track. The higher the number, the longer you can expect the tread to last. Since no one will drive his or her car on exactly the same surfaces and at the same speeds as the government test track, the number is not an accurate indicator of how long your tread will actually last. It's a good relative measure, however: You can expect a tire with a larger number to last longer than one with a smaller number.
Traction: Tire traction is rated AA, A, B or C, with AA at the top of the scale. This rating is based on the tire's ability to stop a car on wet concrete and asphalt. It does not indicate the tire's cornering ability. According to this NHTSA page, the Firestone Wilderness AT and Radial ATX II tires that have been in the news have a traction rating of B.
Temperature: The tire temperature ratings are A, B or C. The rating is a measure of how well the tire dissipates heat and how well it handles the buildup of heat. The temperature grade applies to a properly inflated tire that is not overloaded. Underinflation, overloading or excessive speed can lead to more heat buildup. Excessive heat buildup can cause tires to wear out faster, or could even lead to tire failure. According to this NHTSA page, the Firestone Wilderness AT and Radial ATX II tires have a temperature rating of C.
chuck92103
01-06-2008, 09:58 AM
I have been reluctant to change to a different tire on my 645. The original OEM run flats have approx. 30k miles on them. I have approx. 5-10k miles left on them. :shock: It must be something to do with the tread compound.
By other reports, all the other tires yield less than 20k miles. I am not even sure if the Bridgstone RE050 non flat version would wear as long.
I just came across this little tidbit while surfing around on the net at http://www.502motorsports.com. It might come in handy to some of you...
If you're in the market for new tires, all of the variables in tire specifications and the confusing jargon you might hear from tire salesmen or "experts" might make your purchase rather stressful. Or maybe you just want to fully understand the tires you already have, the concepts at work, the significance of all of those sidewall markings. What does all this stuff mean in regular terms?
In this article, we will explore how tires are built and see what's in a tire. We'll find out what all the numbers and markings on the sidewall of a tire mean, and we'll decipher some of that tire jargon. By the end of this article, you'll understand how a tire supports your car, and you'll know why heat can build up in your tires, especially if the pressure is low. You'll also be able to adjust your tire pressure correctly and diagnose some common tire problems!
What All the Numbers Mean
Each section of small print on a tire's sidewall means something:
The tire size branded on the sidewall provides a significant amount of information about the tire's intended purpose, dimensions, load capacity and high temperature/high speed durability.
Our primary example will be based on variations of the 225/50R16 size, although other sizes will appear where appropriate.
Service Type
Most tire sizes begin with a letter or letters that identify the type of vehicle and/or type of service for which they were designed. The common indicators are as follows:
http://www.502motorsports.com/ho_a6_ci2_l.jpg
P225/50R16 91S
P = When a tire size begins with a "P," it signifies the tire is a "P-metric" size that was designed to be fitted on vehicles that are primarily used as passenger vehicles. This includes cars, minivans, sport utility vehicles and light duty pickup trucks (typically 1/4- and 1/2-ton load capacity). The use of P-metric sizes began in the late 1970s and they are the most frequently used type of tire size today.
225/50R16 92S
If there isn't a letter preceding the three-digit numeric portion of a tire size, it signifies the tire is a "Metric" size (also called "Euro-metric" because these sizes originated in Europe). While Metric tire sizes are primarily used on European cars, they are also used on vans and sport utility vehicles. Euro-metric sizes are dimensionally equivalent to P-metric sizes, but typically differ subtly in load carrying capabilities.
T125/90D16 98M
T = If a tire size begins with a "T," it signifies the tire is a "Temporary Spare" ("space saver" or "mini spare") that was designed to be used temporarily only until a flat tire can be repaired or replaced.
LT245/75R16 108/104S
LT = If a tire size begins with "LT," it signifies the tire is a "Light Truck-metric" size that was designed to be used on vehicles that are capable of carrying heavy cargo or towing large trailers. This includes medium and heavy-duty (typically 3/4- and 1-ton load capacity) pickup trucks, sport utility vehicles and full-size vans. Tires branded with the "LT" designation are the "little brothers" of 18-wheel tractor-trailer tires and are designed to provide substantial reserve capacity to accept the additional stresses of carrying heavy cargo.
7.50R16LT 112/107Q, 8.75R16.5LT 104/100Q or 31x10.50R15LT 109Q
LT = If a tire ends with "LT," it signifies the tire is either an earlier "Numeric", "Wide Base" or "Flotation" Light Truck size designed to be used on vehicles that are capable of carrying heavy cargo and towing trailers (Numeric sizes), use 16.5-inch diameter rims (Wide Base sizes) or are wider, oversized tires designed to help the vehicle drive on top of loose dirt or sandy surfaces (Flotation sizes). This includes light, medium and heavy-duty (typically 1/2-, 3/4 and 1-ton load capacity) pickup trucks and sport utility vehicles. Tires branded with the "LT" at the end of their size designation are also the "little brothers" of 18-wheel tractor-trailer tires and are designed to provide substantial reserve capacity to accept the additional stresses of carrying heavy cargo.
195/70R15C 104/102R
C = If a Euro-metric sized tire ends with a "C," it signifies the tire is a "Commercial" tire intended to be used on vans or delivery trucks that are capable of carrying heavy loads. In addition to being branded with the "C" in their size, these tires are also branded with their appropriate Service Description and "Load Range" (Load Range B, Load Range C or Load Range D).
ST225/75R15
ST = If a tire size begins with "ST," it signifies the tire is a "Special Trailer Service" size that was designed to only be used on boat, car or utility trailers. ST-sized tires should never be used on cars, vans or light trucks.
Section Width
Following the letter(s) that identify the type of vehicle and/or type of service for which the tire was designed, the three-digit numeric portion identifies the tire's "Section Width" (cross section) in millimeters.
P225/50R16 91S
The 225 indicates this tire is 225 millimeters across from the widest point of its outer sidewall to the widest point of its inner sidewall when mounted and measured on a specified width wheel. This measurement is also referred to as the tire's section width. Because many people think of measurements in inches, the 225mm can be converted to inches by dividing the section width in millimeters by 25.4 (the number of millimeters per inch).
225mm / 25.4 = 8.86"
Sidewall Aspect Ratio
Typically following the three digits identifying the tire's Section Width in millimeters is a two-digit number that identifies the tire's profile or aspect ratio.
P225/50R16 91S
The 50 indicates that this tire size's sidewall height (from rim to tread) is 50% of its section width. The measurement is the tire's section height, and also referred to as the tire's series, profile or aspect ratio. The higher the number, the taller the sidewall; the lower the number, the lower the sidewall. We know that this tire size's section width is 225mm and that its section height is 50% of 225mm. By converting the 225mm to inches (225 / 25.4 = 8.86") and multiplying it by 50% (.50) we confirm that this tire size results in a tire section height of 4.43". If this tire were a P225/70R16 size, our calculation would confirm that the size would result in a section height of 6.20", approximately a 1.8-inch taller sidewall.
http://www.502motorsports.com/tire-cutaway-big.jpg
Internal Construction
A letter (R in this case) that identifies the tire's internal construction follows the two digits used to identify the aspect ratio.
P225/50R16, P225/50ZR16
The R in the P225/50R16 91S size identifies that the tire has a Radial construction in which the tire's body plies "radiate" out from the imaginary center of the wheel. Radial tires are by far the most popular type of tire today representing over 98% of all tires sold.
If the R in the size was replaced with a D (225/50D16), it would identify that the internal tire body plies crisscross on a Diagonal and that the tire has a "bias ply" construction. Tires using this construction are for light truck and spare tire applications.
If the R in the size was replaced with a B (225/50B16), it would identify that the tire body plies not only crisscross the tire on a diagonal as before, but that they are reinforced with belts under the tread area. This type of tire construction is called "Belted." Tires using this construction are practically extinct.
Speed Rating
Today, the only tires that continue to include the speed rating "in" the tire size (P225/50ZR16) are Z-speed rated tires. In this case, following the two digits used to identify the aspect ratio are the letters ZR to identify the tire's speed rating (Z) and its internal construction (R). Since 1991, all other speed ratings are identified in the tire's Service Description (which will be covered shortly).
Tire and Wheel Diameter
P225/50R16 91S
The 16 indicates the tire and wheel diameter designed to be matched together.
Tires that have a rim diameter expressed in inches (P225/50R16, as well as 8, 10, 12, 13, 14, 15, 17, 18, 19, 20, 22, 23, 24, 26 and 28) are called "inch rim" sizes, are the most common type of tire size and are used on most cars, minivans, vans, sport utility vehicles and light duty light trucks.
While not as common, two additional "unique" types of tire/wheel diameters are still in use today.
Tires and wheels that have a rim diameter expressed in "half" inches (8.00R16.5LT, as well as, 14.5, 15.5, 17.5 and 19.5) are used on some heavy-duty trailers, heavy-duty light trucks and box vans.
Tires and wheels that have a rim diameter expressed in millimeters (190/65R390, as well as, 365 and 415) are called millimetric sizes. Michelin initiated millimetric sizes for their TRX tires that saw limited use on many different car models in the late 1970s and 1980s.
Michelin PAX System run flat tires have been introduced as an integrated wheel/tire system on a very limited basis as Original Equipment (O.E.) in North America. An example PAX System size of 235/710R460A 104T expresses tire and wheel dimensions in millimeters (235 mm Section Width, tire Overall Diameter of 710 mm and a 460A mm rim diameter, with the "A" in 460A signifying these tires feature ¿asymmetric¿ beads in which the outside bead (450 mm) and inside bead (470 mm) are actually different diameters.
All of these "unique" tire/wheel diameters were developed specifically because the tire and wheel design or intended vehicle use required them to be different than conventional tires and wheels. All of these tires and wheels feature bead profiles that have a different shape than traditional "inch rim" sizes.
Tires and wheels with unique rim diameters should never be combined with traditional "inch rim" tires and wheels.
It is critical that the tire and wheel diameters are always confirmed to match before the tire is mounted on the wheel.
Uniform Tire Quality Grading
Passenger car tires also have a grade on them as part of the uniform tire quality grading (UTQG) system. You can check the UTQG rating for your tires on this page maintained by the U.S. National Highway Traffic Safety Administration (NHTSA). Your tire's UTQG rating tells you three things:
Tread Wear: This number comes from testing the tire in controlled conditions on a government test track. The higher the number, the longer you can expect the tread to last. Since no one will drive his or her car on exactly the same surfaces and at the same speeds as the government test track, the number is not an accurate indicator of how long your tread will actually last. It's a good relative measure, however: You can expect a tire with a larger number to last longer than one with a smaller number.
Traction: Tire traction is rated AA, A, B or C, with AA at the top of the scale. This rating is based on the tire's ability to stop a car on wet concrete and asphalt. It does not indicate the tire's cornering ability. According to this NHTSA page, the Firestone Wilderness AT and Radial ATX II tires that have been in the news have a traction rating of B.
Temperature: The tire temperature ratings are A, B or C. The rating is a measure of how well the tire dissipates heat and how well it handles the buildup of heat. The temperature grade applies to a properly inflated tire that is not overloaded. Underinflation, overloading or excessive speed can lead to more heat buildup. Excessive heat buildup can cause tires to wear out faster, or could even lead to tire failure. According to this NHTSA page, the Firestone Wilderness AT and Radial ATX II tires have a temperature rating of C.
Sounds like a technical genius to me.
I have been reluctant to change to a different tire on my 645. The original OEM run flats have approx. 30k miles on them. I have approx. 5-10k miles left on them. :shock: It must be something to do with the tread compound.
By other reports, all the other tires yield less than 20k miles. I am not even sure if the Bridgstone RE050 non flat version would wear as long.
What's the reason why runflats last that long? :dunno: