Tires: tire speed rating, tire speed rating, speed capability

Question
is it safe to go one speed rating down if a vehicle calls for a v rating is it safe and legal to put a h rated on i have over forty years expeience and am ase certified  i say no way please tell me if it is dot legal  thank you

Answer
David,

I tend to think of things as risks.  The word "safe" sounds like an on / off switch:  Either "Safe" or "Unsafe" - and that's not really true.  Using the term "risk" implies a range of values and it is pretty easy to understand that something has more risk than something else.

Going down in speed rating is increasing the risk - and the further down in speed rating you go, the greater the risk.  Tires with high speed ratings not only tend to handle better and grip the road better, but also have more speed capability.  All of these things are capabilities that may never be needed by an average consumer, but having them makes the tire  ......  uh ........ more safe.

But tires with high speed ratings also tend to ride harsher, and wear faster - not things that drivers want.  Did I mention that they also tend to cost more?  So there is some pressure to use lower speed ratings.

I am a firm believer than there is technological barrier at the H speed rating.  Tires with H speed rating are almost required to have a circumferential overlay over the belt package - sometimes called a cap ply.  This restricts the tire tread's growth due to centrifugal forces - basically allowing the tire to survive the stresses generated by higher speeds.  

This overlay also reduces the rate of tire failures way out of proportion to the speed rating increase.  (I have a technical explanation for why this is so, but it is long winded and not suitable for this type of format.

So I do not recommend that anyone use a tire lower than an H rating.

It is understandable that someone would want to replace V or higher speed rated tires with something lower (that has properties they want).  So every time I encounter someone who wants to do that, I point out the increased risk and remind them they they are going the direction of sloppy handling and ask: "Is that really where you want to go?".  I also remind them that there is such a wide variety of tires now available in H speed ratings, that they do not need to go down any further to get what they want.

And to answer your last question:  There are no laws that say you have to replace tires with the same speed rating.

Tires only have to meet minimum requirements - and then they can be used on the consumer level without restriction.  This is not true of manufacturers - and that's a while different set of things - too long for this format.  But speed ratings is not something that the laws cover.

BUT  a good lawyer could take a tire shop to court and make a convincing argument that even though the consumer demanded lower speed rated tires, the shop had the obligation to keep the consumer safe in spite of himself - and that had that happened, the consumer would not have had that accident, so the court should penalize that tire shop by awarding thousands of dollars to the consumer.

For that reason, many tire shops will not apply tires with speed ratings lower than what the vehicle placard says.