Originally Posted by P. Raz
This is new stuff to me. Most folks talk about going from say a 13" to a 14" tire to gain ground clearance. What you are saying is that another reason might be to reduce sway. One could get a larger rim and smaller profile tire and the diameter would be the same so the tire would fit in the same wheel well.
Yes, that is correct. That is the reason the low profile tires
were developed, to improve driving performance due to the sidewall height, although I think most people choose them for looks if they are not just replacing the same size. Using a low profile tire can increase the possibility of rim damage because the rim is closer to the ground. Wider tires
can increase the diameter as well.
As far as I can tell, the main reason that ST tires are recommended over passenger car tires is the sway issue due to sidewall stiffness. Although a lower profile passenger car tire may have as much sidewall stiffness as a higher profile ST tire. Another reason frequently given is load capacity, however when I was looking for tires it was easy to find passenger car tires with plenty of load capacity. I decided on light
truck (LT) tires because they had very good sidewall stiffness, very high load capacity, much better speed rating and I expect they will have better reliability than ST tires.
The thing that scares me most about ST tires is the speed rating. As far as I know the highest speed rating I have heard is 65 mph while P and LT tires frequently have speed ratings of 130 mph or more. Many people drive close to, at, or above 65 mph and that does not leave much margin. Even driving at 55 mph is using 85% of the speed rating and it would be easy to start going faster down a hill. Using almost anything up close to it's maximum rated level will increase the failure rate compared to using the same thing at half it's rated level. I will be using the LT tires at less than half their load capacity and around half their speed capacity, depending on how fast I get going down a hill.