Will taller rear tire size help lower engine rpm on the road, especially on the highway? I have a 373 rear that screams on the highway . I would like to take longer trips but it is not a hwy car. I know a change of gears would make a difference.It would be much easier to change tires

yep!

going from a 26" tire to a 28" tire will drop your rpm a couple hundred, but it will throw the speedo waaaay off, and if you don't know how much, you will get a speeding ticket out of it eventually.

so going from a 245/60 /15 to a 275/60/15 should fit and drop the rpm may 200 rpm or so

If you want to see more than a couple of 100 RPM drop you need to change the rear or go to an overdrive trans. Here you can play with this and see the speedo error from changing tire sizes. http://www.miata.net/garage/tirecalc.html

I changed from my stock, D-70/14 redline's to 9.50/14 Mud&Snow's right after I bought my car.

Went from a 25.3" to 5" tall tire to a 29.5" tall tire by raising my rearend up about 4" using coil-over shock overload springs.

Speedometer went from 3070/3050 or so rpm at 70 mph to 82!!!

AND I got a ticket and that's what the Trooper said I was running..

She topended out to 145 mph just as smooth as can be back then..

pdq67

PS., M-20 and 3.31's car!!!

My Camaro with 3.73's and 27.5" tall tires is 3000ish at 65mph. Hope that helps.

on the hwy I am going about 55- 60 @ 3000 with 245/60 /15- 3.73

it is alot easier and cheaper to get larger tires. Rear is 1 -2 years on rebuild.
I hate having all the people pass me by because of the high RPM on the motor on hwy