LT metric tires are the little brothers of the over the road truck tires. They are designed to use high pressures to carry the load. Using high pressure, instead of just larger, is an efficient way to carry load in a tire – less material and therefore less cost. The downside is that the ride is worse. But part of what comes along with this efficiency is that all the rubber components are designed to work at high load concentrations and therefore, don’t work as well in high flex situations.
Passenger car tires are designed to be use at low pressures – and therefore flexible – which promotes a good ride.
If you do a side by side comparison, you’ll find that even if the numbers are the same, the LT metric tire requires 15 psi more inflation pressure to carry the load (once you deduct 10% from the P metric to account for using the tire in a Light Truck application). This is because of the way in which the tires are designed: LT metric = high load, low flex.
I do not recommend interchanging the 2. You should be able to find what you want in the type that came on your vehicle.
Fuel economy: Too many variables. There is going to be more difference between tires than between the types of tires.
But you should be aware that a tire is all about compromise and tires with good rolling resistance have poor traction or wear (or both). The reverse is also true.
Personally, if you have to worry about fuel economy, you need a different vehicle, not different tires.
