QuestionI am having a disagreement with a friend who said speed ratings only apply to high speeds and as long as the size is right s will replace v rated tires. I told him that tire was engineered for that cars suspension not only for speed but for handling and steering response and anything less is a safety issue. Who is right?
AnswerDan,
I had a college professor who use to say "Overdesign / Underutilize". What that means is that it's the design engineer's responsibility to design a product so that it exceeds the minimum, and it's the user's responsibility to use the product below its capability.
Unfortunately, too many folks think they are vehicle engineers and try to rethink what the vehicle engineers spent a lot of time deciding was appropriate for the vehicle.
I can understand that a V rated tire on a sedan makes little sense. But going below H isn't a good idea. The short version is that the speed rating test takes place at 77F temperature at the rated load and the rated pressure for 10 minutes at the speed being rated. There are a lot of things that would cause someone familiar with this test to say - "I'm not using those conditions, so I need to specify a tire with more capability than the speed rating suggests" This is particularly true for the temperature and the inflation pressure. Besides, the test takes place on a new tire and we all know that rubber deteriorates over time.
Plus, as you mention, as the speed rating goes up, the tire is usually more responsive and has better grip - all of which improves the handling. So using a lower speed rating makes a car more sluggish, especially in emergency maneuvers - just when you need it most.
I see all these things as safety issues - especially the speed capability. This is something that a novice to vehicle design should not change without a great deal of understanding.
