by pup55 » Sat 12 Feb 2011, 18:33:08
$this->bbcode_second_pass_quote('', 'F')or many cars in the USA you can substitute LT (Light Truck) tires for P (Passenger car) of the same size. This would allow you to go from a typical tire pressure of 32 psi to 65 psi, which should give you a significant improvement in fuel mileage
The reason light truck tires have higher pressure ratings is because they were made that way. They have construction differences, such as extra body plies, which will allow them to carry more weight. The higher pressure is so that the tires do not deform as much under heavy load conditions. You may also have discovered that they're much heavier than the similar size and shape passenger tires because of that. Any nominal benefit in fuel economy will be partially offset by the fact that the tire is heavier.
The components are also quite frequently compounded differently because of the differences in service conditions...particularly speed and load related, which are quite different for a truck than they would be for a car, and naturally much much different for aircraft. Truck tread compounds, for example, are almost all natural rubber which runs much cooler than synthetic rubber but gives much worse treadwear, when reasonably equally compounded. Aircraft tires are compounded to solve the problem of what happens when you are flying around in the hold of an aircraft at zero RPM and at low temperatures, and then 5 minutes later hit some hot rough runway in Dallas in the summer.... in other words, they have to withstand having the crap beaten out of them....They're also mostly natural rubber but compounded for higher tear strength, thank goodness.
Also, whether or not you see any improvement in fuel economy with a given set of tires is really heavily dependent on how you drive your car, and over what kind of surfaces. Those rolling resistance tests that they use for the UTQG system are done in a pristine laboratory with regular surfaces with a robot driver and not subject to chaotic conditions such as rain, which could really make a huge difference. Actually, that's not totally accurate. The road tests are done over known routes out in the middle of Texas using human drivers that are told what to do by computer, so it's the next best thing.
It is also quite likely that by putting a type of tire on your vehicle that was not designed for it can give you some surprises, such as reduced treadwear, or, as you have noted, different traction properties.
So your tires might be round, and black, with a hole in the middle, and be very nearly the same size as the manufacturer calls for, and you may indeed get better gas mileage, it is just as likely that you will sacrifice in some other area of performance, and if you have not noticed that, it might very well mean that you never will, all the better, you will be just fine.... but I would not go out of the way to put LT tires on my car to save fuel because a lot of times they're more expensive anyway.