QuestionI have three questions you may be able to help me with. First, I am replacing the tires on my daughter's '04 Mazda 3 and want the best overall I can find. Can you direct me to a source for comparisons. Consumer Report isn't complete. I wanted to put Michelin Xs on it but the dealer told they're not the correct speed rating and won't install them.
Second, it seems like most new cars require speed rated tires. Why? The standard installer’s response has been that the cars are designed for speed rated tires citing vehicle manufacturers. This implies that these cars are designed to operate at these tire speeds, a selling point. The tire maximum rated speeds are far above any posted US speed limit, far beyond the driving skill of most drivers, and from a green perspective, using EPA formulae, probably produce the worse possible economy and greatest potential air pollution emissions possible. And the price, the softer compounds used wear much faster resulting in shorter (~50%) tread life, more tires sold.
Third, what speeds are today's cars really designed for, the tires max rating or somewhere within legal limits? Race cars and their tires are designed to perform at 150+ mph. I don't believe their design includes equal performance in the 30 to 60 mph range. I believe the same necessarily holds for cars intended for everyday use on our highways. If designs are for within legal limits, why do so many cars require speed rated tires?
AnswerAl,
First, there are a number of sources for comparisons for tires on the internet. What comes immediately to mind are Tire Rack and 1010tires. Both of these retailers provide areas for feedback - and you may find that valuable, especially if you factor in that folks that like their tires are much less likely to post than folks that don't.
Some background on Speed Ratings:
As a general rule, tires with higher speed ratings have better handling characteristics - and that sells cars. But cars have been gradually getting more powerful and therefore capable of higher speeds. Car manufacturers feel that if a car is capable of 120 mph - and most of them are - then it ought to have tires that are capable, too. And in order to be sure they are capable, they are generally overspecified - in this example 130 or 140 mph.
But there is another aspect that kind gets lost. When cars are designed, every components is overspecified. Every nut and bolt is much stronger than it needs to be. What this does is provide a greater level of safety or looking at it the other way - lowers the risk of a failure.
As my professor used to say "Overdesign / Underutilize."
While it may not be obvious that the bolt that holds the engine to the chassis is 3 times what the calculations say it needs to be - and how often have we heard about those breaking - it is much more obvious in tires that they are overspecified (underutilized). And in spite of that we still hear about tires failing. The load carrying capacities and the speed capabilities all add to a tires ability to do what it is suppose to do without failure, but the closer you get to the "rating", the more likely a tire failure will occur. This is one of the lessons learned from the Ford/Firestone situation.
So if you don't want to compromise the safety of your daughter's car, you should use the speed rating as specified by the vehicle manufacturer.
I can understand that V and higher speed ratings seem like overkill - and I somewhat agree - and knowing what I know - and it would take another half hour of typing to explain it - I think the general public ought to be using H rated tires at a minimum.
