Help figuring ratio

I don't know the tire diameter, but they read 165-15. I'm turning 3450 rpms @an honest 70 mph. Any guess as to what gearing I have?.

165's are approx. 25.4" in diameter. You'd also need your 4th gear ratio however if you have a .89 4th gear and a 3.88 ring and pinion, your approx. speed would be 71 MPH. If you have a .82 4th gear and a 4.12 ring and pinion, you speed would be 73 MPH. How accurate is your speedometer? If you have a GPS, try using the speed form that device and compare the speedometer to the GPS

My GPS and by using those "your speed is" speeding signs I'm really close. I'm off no more than 2 miles an hour....

I think Tire Rack gives wheel diameters in their tire specs for each tire if I'm not mistaken.

keith, heres the formula

rpmx tire dia. divide by mphx336

3450x25.4=87630
70x336=23520

87630 divided by 23520=====3.72 or most likely 3.82, ur speedo is probably off some..