Tire size for best RPM at highway speed

Howdy, XJ Folks!
I'm trying to figure out the best tire size for optimizing engine performance. I have an '89 Cherokee with 3.07 gears, 4.0 six and 5-speed manual. I will be driving A LOT this winter in the Northern Midwest. Speed will prob'ly be 55-60 mph max due to conditions and I just don't drive very fast. I will be buying the best set of tires along the "Blizzak" vein. Soft rubber, many sipes, etc. Stock tires were 195/75R 15. Years back on this site I remember seeing 2400 rpm as the most efficient engine speed, in the middle of best torque band. Mr. Loomis sent me some gear ratio info, but I can't find it. I'm currently running 225/75s which will go back on after winter. Sorry so wordy..any ideas? Thanks!
Boomer89

you might get much better results replacing your fuel injectors if you haven't already. If you do, you should have the emission checked to make sure you are in the right A/F ratio range. I did that recently and saw/felt big improvement in performance overall including milage from 240 mi/tank to 280/tank city.

my 2 cents,,,,,,
For a 4.0 automatic,,,,, I would think that about a 29" diamater tires would give you the best highway milage,,, 50-60mph
ONLY IF!
1.you ease up to speed and 2. get your speedometer calibrated ,because you won't be able to determon your actual MPG unless your odometer is correct.
*not sure about manual trans*
just my 2 cents

currently, with 28" tires, i am getting 360 miles out of a tank of gas, (mostly highway), I figure i am getting around 19-20 miles a gallon

The 29 inchers is a commom size. That is right about what came on your Cherokee new.
But what would work best for you would be a hard call across the net.
Things like how much stop and go do you do?
Do you tow much?
Spend much time in the hills?
Are you a pack rat? (run heavy loaded a lot)
If you answer yes to 2 or 3 of these question then I would set (about) 29 inch tires as an upper limit to my ties size.
With the 5 speeds OD and 3.07 I would be very careful about going much bigger. She is pushing the limit now and a larger tire may decrease MPG
around town. But give little or no increase on the open road.
It didn't help me. 245/75/16 LT from 225/75/15 P

uhhhhhhhhh pay attention to the question and look at his gear ratio guys.

stock or smaller.

I have 225 75 16 on a stock 2000xj and turn 2200 at 75 4/0 with auto
and get over 20 mpg on cruise control it does have a flowmaster and a k/n filter in the stock airbox jim

interesting milage and performance chart on page below.
http://www.4wheeloffroad.com/brandpages/jeep/131_0403_jeep_xj_cherokee_mileage/