What tires should I use for highway?

[JohnNeiferd]

I have a 1987 Civic. The stock tires are 175/70R13, they are 22", weigh 28lbs. (including wheels), and have a max pressure rating of 44psi. They are rated for 1047lbs.

I have some trailer tires that are 175/80D13, they are 24", weigh 30.5lbs. (including wheels), and have a max pressure rating of 50psi. They are rated for 1360lbs.

I also have a 175/70R13 trailer tire, that is 23", weighs 28lbs (including wheels), have a max pressure rating of 44psi. They are rated for 1069lbs. But I only have one of these so I guess it's out for now unless I can find another.

These are my options for front tires.

For the back, I put on some small tires that I got off of my father's Wildfire "Truck". The side simply says 4.5-12. They are 21.5". Weigh 20.5lbs. They have a max pressure rating for 58psi. They are rated for 915 pounds. They look like trailer tires.



I can't decide weither I should stay with stock or the 24" because of the following:

Advantages-
Taller tires for lower RPMs.
Skinner for less rolling resistance.
At 65MPH my RPMs will be 3000, which is peak torque.

Disadvantages-
Trailer Tires (tubes, not radial) so that will increase rolling resistance.
Weigh 2.5lbs. more.
I have no exhaust after resonator, so no backpressure. This may have caused the torque curved to move up slightly, so its possible that these tires would move me slightly away from peak torque.


Around town I figure these will decrease fuel economy, but when cruising at a constant speed on the highway (I have college 2 times a week and its a 84 mile round trip) will it increase fuel economy?

The small rear tires should definitely increase fuel economy because they are 10lbs lighter, smaller, and skinnier. But I can't decide how it'd work out with the front tires. So what do you guys think?