[CapriRacer]

First, what you are proposing is a 2 step reduction. There is a "U" between T and H. I'll explain below why you don't find any U speed rated tires in the marketplace.

When car manufacturers specify tires for their vehicle they consider many factors. Obviously top speed and vehicle weight are considerations, but there is more.

As a general rule, the higher the speed rating, the more responsive the tire is to steering input. Generally, T speed rated tires, although more responsive than S rated tires, will not be as responsive as H rated tires. I can almost say without fear of contradiction that even the least responsive H rated tire will be more responsive than the most responsive T rated tire.

This means that you are almost definitely going to lose some of the crispness of the vehicle's handling. In other words, the vehicle will be sluggish in manuevers.

In addition, there is a safety aspect to this that ought to be seriously considered. We engineers tend to think in terms of capability vs risk. In this case we are talking about risk of tire failure vs speed capability. We could also talk about risk of failure vs load carrying capacity.

What is said in engineering circles is that the more capable a product is, the less likely it is to fail. Since tires can be damaged by road debris, punctures, pot hole impacts, cuts, underinflation, etc., they are overdesigned (as is every product), but nevertheless, there still exists a certain amount of risk - and using higher load carrying capacity tires or higher speed rated tires reduces that risk.

Speed ratings are based on a test. The conditions of the test are based on typical European conditions - which means lower temperatures, smoother roads, better maintenance, etc.

It is fairly easy to get a passenger car tire to pass an S rating, and it isn't too much of a stretch to pass a T. But in order to get more speed capability, tires need to have a cap ply - more or less. A cap ply is a circumferentially oriented layer of cords - frequently nylon - that resists the centrifugal forces.

When a cap ply is used, the actual speed capability goes up tremendously - much more than would be indicated by the simple increase in rating from T to H. In fact, there isn't any point in having U speed rated tires - They will easily pass a H rating and maybe even a V, so why bother with U?

This means that an H rated tire is significantly less risky to tire failure than a T speed rated tire - all other things being equal.

Personally, I think H rated tires ought to be the minimum that folks should use on cars (and SUV's, and pickups used on the highway.) Further, if you live on the southern part of the US, particularly AZ, NM, TX, NV, CA, or FL (or anywhere else where it gets hot) then the states ought to require H speed rated tires at a minimum.

I hope you gather that I don't think dropping to a T speed rating is a good idea. You can find plenty of tires with H speed ratings, and you can find one that is affordable and suits your needs.