Dont trust those speed signs that tell you your speed they are not calibrated they are just used for slowing the public down in an area where they have received several complaints of speeding. And in the future will probobly have an officer there running radar based on what the sign says it records the speeds of the cars. your best bet is to set the cruise control dead center on say 50mph on a flat road and have an officer with a calibrated radar unit tell you your speed that is if you know one.

 

Don't know any road patrol officers with radar gear...might have to check to see if anybody I know has a contact.

Guess I need to experiment with the Microtuner settings to see which "size" will get me closest to the actual speed with the Yokohama Geolanders. The truck has never been "accurate", even with the stock Wranglers. The Yokos are the same size P265/70-R17, so they're the same as the original equipment tires. I just need to figure out what setting to use in the Microtuner to get it right.

The one I'm currently using is too "tall", the speedo is definitely showing faster than I'm going and the distance is off, too short. I was trying to find a turn at .9 miles a couple of weeks ago...ended up being slightly further, the "next" turn.

I need to get this figured out and get it right...more for the distance than the speed, so that my TripTik directions are accurate.<g>

Anybody got a good setting for the P265/70-R17 in the Microtuner to reduce my experimentation? Gotta' be a way to "calculate" this... I'm switching back to Performance from Tow-Perf this afternoon, so it's a good time to try a new setting.

 

All right, here it is:

At 70 mph, you're going 73,920 inches/minute.
Your tires are 255/70R16, so their circumference is 30*pi = 94.25 inches.
Your tires rotate at (73,920 in/min )*(1 rev/94.25 inches) = 784.3 rev/min.
Your engine should run at (tire rpm)*(rear gears)*(tranny), so

Engine rpm @ 70 mph = 784.3*3.55*0.71 = 1976 rpm.

If you shave 0.25" off the tire tread (0.5" reduction in diameter), you'll get 2010 rpm. 2000 sounds dead on to me.

 

Sorry, I just reread the post and saw I got the tire size wrong. Somewhat humbling, but the math is still good. For 265/75R16s, change diameter to 31.6", and you get ~1870 rpm for 70 mph.