Highway Cruise RPM Checker

At very low RPM the engine needs near-full throttle to make cruise power, cylinder pressures spike, and knock margin shrinks — older engines suffered bearing and pre-ignition damage; modern ones protect themselves by downshifting constantly or pulling timing, which burns the fuel you thought tall gearing saved. Automatics also unlock the converter to multiply torque, adding slip losses. The tell: a mild hill demands an immediate two-gear downshift.

Torque physics: a 2.0L NA four makes perhaps 130 lb-ft, peaking near 4500 RPM — at 1800 RPM it might offer 90 lb-ft, not enough to hold 75 mph into a headwind without full throttle. Spinning 2800–3000 keeps usable reserve under the pedal. The same displacement turbocharged makes 250 lb-ft from 1700, which is exactly why modern downsized engines pull tall overdrives the old fours never could.

Inside the band, barely — engine friction rises with RPM but BSFC islands are broad and flat; 1900 vs 2100 at cruise is a 1–2% effect, smaller than a roof rack. What kills economy is being OUTSIDE: lugging forces inefficient high-load enrichment and converter unlock; buzzing wastes power on friction. Chasing 200 RPM with a $1500 re-gear has a payback period measured in decades; fixing a 600-RPM mismatch pays immediately.

Your real speed, honestly stated: gearing chosen for an indicated 65 makes a truck that actually travels at 78 buzz forever. Use the speed you genuinely hold on your real highways, add the tire size you'll actually run by year's end, and check the result here. If you split time between 55-mph two-lanes and 80-mph interstates, bias toward the high-speed case — being slightly tall at 55 is gentler than being busy at 80.