Tire speed rating T vs. V and brands

  #1  
Old 08-26-2010, 05:28 PM
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Question Tire speed rating T vs. V and brands

I will be replacing my Michelin Energy MXV4 S8 tires soon, 56,000 miles so far. I was considering the Michelin Hydroedge GreenX for replacement, but Michelin does not recommend it because of the speed rating difference. The MXV4 S8 is V rated (149 mph)and the Hydroedge is T rated (118 mph). There is a lot of controversy about speed ratings and handling. I can't find info on exactly what handling issues are possibly compromised. Anyone have experience with this? I was also considering the general Altimax HP which is V rated but not an LRR tire. I use General Altimax Arctics for winter driving, which if I remember correctly are H rated, with no apparent issues. Since the car will never be driven at T and V speeds, what are the true issues? Anyone have the General Altimax HP or the Hydroedge on their Camry hybrid? What tires would others recommend for summer use since I have dedicated snow tires? Thanks all!
 
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Old 08-27-2010, 10:23 PM
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Default Re: Tire speed rating T vs. V and brands

My opinion, I think the whole speed rating thing is 80% smoke and mirrors, and 20% fact. The ratings are governed by basic tests that last only a few minutes at the speed being rated, and are self administered by the tire mfrs. I suspect the ratings as far as the mfrs are concerned are mainly about how they differentiate, construct, and market their product lines then what most people will actually experience in real life driving conditions.

As far as auto mfrs, once they pick a tire for a car, suddenly that tire's speed rating becomes God's word on the matter for some tire dealers. One tire store will happily put a "T" rated tire on my heavy Sienna with tons of loading capacity and a powerful V6 engine that can go as fast or faster than my TCH, but claims, literally, "What, are you trying to kill yourself?" when I considered putting the "T" rated Michelin Energy Saver on my gently driven TCH. Although in the end I picked the "H" rated Primacy MXV4 GreenX tire, I didn't get it from that tire dealer telling me I was going to kill myself...

I do however, pay attention to load ratings on the tires...
 
  #3  
Old 08-27-2010, 10:38 PM
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Default Re: Tire speed rating T vs. V and brands

Keep in mind that the car's computer is tied to the recommended speed rating on the label on the door post.

If they recommend a tire rated to 118 MPH, the computer will cut off the engine around 108-110. So, buying a 149 MPH tire is money wasted.

A better piece of data to look at are the temperature, traction and treadlife ratings. Get a temperature and traction rating as high as possible. Treadlife is a general guideline, not exact at all. I would personally go with a traction rating of A or AA and a temperature rating of A over any other tire that had lower ratings.

Joe
 
  #4  
Old 08-28-2010, 06:13 AM
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Default Re: Tire speed rating T vs. V and brands

Generally a high performance tire will have a short sidewall (this also increases the response on turn in) to generate less heat, a wider tread design and a "stickier" compound to increase braking, acceleration and lateral grip. The compounds are greatly influenced by the carbon black and silicon content and are formulated for the tire speed rating.

The OEM tire for the TCH was rated for a speed that the car can NEVER attain. It was chosen for its low rolling resistance, not the speed rating. Any tire rated at or over the maximum speed of the car would be safe under any conditions. If you do not drive near the maximum speed of the car for sustained periods at the maximum load the car is capable of carrying, you could safely run a tire rated below a cars rated speed.

As for the cars speed being tied to the speed rating on the door post, i will respectfully disagree. The engine rpm, MG1 and MG2 rpm, available horsepower and torque and several other factors set the maximum speed of the car. The manufacturer then chooses the tire based upon that maximum speed and the load ratings that the car is capable of carrying. There are cases where the top speed of the car is limited by the computer but this is a safety issue and recommended by the feds. Generally that self enforced limit is usually 155mph in this country although the European versions of that same car will often not be limited.
 
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Old 08-28-2010, 06:20 AM
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Default Re: Tire speed rating T vs. V and brands

It's a safety issue. The tires are designed to be safe up to a certain speed. That means, they are engineered to withstand certain amounts of force. If you go faster than the tire is engineered for, the tire may "fail". Shortly afterward, the entire car will likely be destroyed in the wreck, and the driver and passengers may be injured or killed.

The tire rating is not based only on a test. The tires are engineered for the loads that will be generated by operating at that speed. The engineers calculate the stresses, test the materials individually, do computer simulations, and finally test prototypes. Because the simulations are so good any more, the prototype tests are really just a formality, but they are still required by the DOT regulations.

An unmodified TCH is able to go 130 mph, IIRC. If the tire is designed to be safe at 110 mph, but could "fail" at 120 mph on rough road or in a high-G maneuver, a driver who decides to drive at maximum speed would be in danger.

In Europe, it is illegal to fit a tire on a car if the tire speed-rating is less than the maximum speed of the car. That is for safety reasons.

Also, many insurance policies require that the car must be fitted with tires that have speed rating at least as high as the maximum speed of the car. If the accident is due to tire failure, and you have lower-rated tires on the car, your insurance could refuse to cover the claim.

A 130 mph car really requires tires with speed rating at least "H". The "V" rating is probably not actually needed. For more info, see http://en.wikipedia.org/wiki/Tire_code

I have the "H" rated Michelin Primacy MXV4 on mine. They make less noise than the previous Michelin Energy MXV4 tires.
 

Last edited by SteveHansen; 08-28-2010 at 06:25 AM.
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Old 08-28-2010, 08:26 AM
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Default Re: Tire speed rating T vs. V and brands

I wonder what the MPG would be on a Camry hybrid doing 130 MPH?

Seriously, all good comments. What I said before is that the computer's speed limiter is tied to the OEM recommended tire. Some cars, such as the Corvette, will have different max speeds programmed into the computer, based upon the tire that comes on a particular car. Buy a car with an option package that includes a higher rated tire, and the computer is programmed accordingly.

As for speed ratings, buy the tire that fits your needs, not what the tire jock in the big box store is pushing this week. The tire's max speed rating is less significant than is the driver's ability and the road conditions. More than 97% of American drivers should never drive over 75-80 MPH; they don't have the training for it, and most of our lousy roads weren't built for those speeds. The dynamics of what can happen in an emergency driving situation at 60 MPH vs. 85 MPH is just too much for the average American driver to handle. For example, can you imagine making an emergency lane change at 85 MPH on some of the interstates in this country with their expansion strips heated up in the summer heat?

Now, if you take a professional driver, or someone with a Bob Bondurant certification or an SCCA license, and that is a different matter. Of course, all you have to worry about then are the idiot drivers around you fiddling with their iPod or texting someone.....
 
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Old 08-28-2010, 07:12 PM
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Default Re: Tire speed rating T vs. V and brands

Interesting conversations. I checked the speed rating on the General Altimax Arctic, it is Q, which is 99 MPH. I use these for my winter tire.

I checked the door post on my car and the only info is the tire size and inflation. No mention of speed rating. If it was that critical I would think they would have to post it on the door post with the other info? There is also no info regarding the speed rating in the owners manual, at least online when I looked it up. With that being the case I don't see where it would matter as long as you are within the limitations of the tire. The General Altimax HP comes in a V rating, but it is not a LRR tire. I am concerned how much I will give up in the mpg category.

Great conversation, keep the info coming. If someone has something different on the speed rating listed for the car please advise. Also where can I find it?

Thanks all.
 
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Old 08-28-2010, 07:40 PM
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Default Re: Tire speed rating T vs. V and brands

SanAntanio Joe, I like your comment about the general public not driving beyond 75-80 MPH because they have not been trained for it. Most of the public is not capable of driving at posted speed limits. They prove it every day. I say this because I was trained in high speed and pursuit driving. Most of the public can't negotiate a curve in their own lane, turn a corner correctly, signal properly, etc. They consider themselves good drivers, I consider them lucky drivers because the people around them have been attentive enough or lucky enough to avoid them. Others drive beyond their ability, and their vehicles ability, and they are not aware of it, again, they are lucky.

Off subject, but I couldn't resist. Back to the questions posed.
 
  #9  
Old 08-29-2010, 12:28 AM
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Default Re: Tire speed rating T vs. V and brands

Originally Posted by SanAntonio Joe View Post
... More than 97% of American drivers should never drive over 75-80 MPH ....
While I agree that most drivers shouldn't drive that fast, I also notice that "should" and "do" are two different words. In my daily commute, I usually drive between 70 and 75 mph. Every day, numerous vehicles pass me like I am standing still. The faster ones have to be going at least 85. Most days, I see the results of at least one collision on the shoulder. And, every day, I see the remains of blown tires on the road.

I think the tire speed issue should not be decided by how the owner intends to drive the car on a routine basis. It should rather be decided by how the car might be driven, even once, by anyone. Imagine driving to the hospital with a relative in urgent need of medical care. Or, imagine how some of your younger relatives might drive when they borrow your car. The only actual limit is, how fast the car can go at full throttle.
 
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Old 08-29-2010, 04:00 AM
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Default Re: Tire speed rating T vs. V and brands

Max Load for each energy mxv4 S8 H-rated tire is 1521 lb.

max load for each energy saver a/s T-rated tire is 1477 lb. That's 44 lb. less for the saver a/s tire.

The 2007 TCH weighs about 3750 lbs and has a weight distribution F/R, 57/43. That comes to F 2137, R 1613.
Each front would carry 1068.5 lb. and the rear tire would carry 806.5 lb.

Max load for the a/s tire is 1477. The TCH load is 1068.5 or 408.5 below the max load. The S8 oem tire would be 452.5 below the max load.

Not sure if this matters, but I did want to have a look see.
 

Last edited by rburt07; 08-29-2010 at 04:08 AM.

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