* Gear Ratio: The rear axle gear ratio significantly impacts RPM at a given speed. Higher numerical ratios (e.g., 3.92, 4.10) result in higher RPMs at the same speed compared to lower ratios (e.g., 3.55, 3.07). Your owner's manual or the sticker on the driver's side doorjamb should specify the axle ratio.
* Tire Size: Larger diameter tires (taller sidewalls or larger rims) will result in lower RPMs at a given speed than smaller tires. Even slight variations in tire size can make a difference.
* Transmission type (automatic or manual): Automatic transmissions might slightly vary in RPM at a constant speed due to differences in torque converter lockup.
To find your RPM:
1. Locate your axle ratio: Check your owner's manual or the driver's side doorjamb sticker.
2. Measure your tire diameter: This is the most accurate way to get a reliable number. There are online calculators that can estimate RPM based on tire diameter, axle ratio, and speed. A quick search for "RPM calculator" will show many options.
3. Use an online RPM calculator: Input the axle ratio, tire diameter, and speed (70 mph) to get an estimate.
Without knowing your specific axle ratio and tire size, I cannot give you an accurate RPM. Expect it to be somewhere in the 1800-2500 RPM range, but it could easily be higher or lower depending on the factors listed above.
