The short answer
With a 3.73 axle, going from 265/70R17 to a 35 inch tire makes the axle act like 3.37. To restore stock, regear to 4.13; the nearest common ratio is 4.10. At 65 mph engine speed drops from 2,578 rpm to 2,328 rpm.
Worked example: 3.73 gears, 265/70R17 to 35 inches
| Step | Math | Result |
|---|---|---|
| Acts like (new tires) | 3.73 × 31.61 ÷ 35 | 3.37 |
| Ratio to restore stock | 3.73 × 35 ÷ 31.61 | 4.13 |
| Nearest common ratio | from the list | 4.10 |
| RPM at 65, stock | 65 × 3.73 × 1.00 × 336.13 ÷ 31.61 | 2,578 |
| RPM at 65, 35 in tires | 65 × 3.73 × 1.00 × 336.13 ÷ 35 | 2,328 |
Fewer RPM at the same speed is not automatically bad: highway fuel use and noise can improve, while towing, hills and acceleration can suffer. The tool shows the numbers; how much loss is acceptable depends on the engine, transmission and load. Ratios in the list are common ones; check what is made for your axle. Related: regear chart for bigger tires.
Always confirm the wheel width range for the tire, clearance at full steering lock and suspension travel, and the load index and speed rating for your vehicle. See how to read a tire size, the load index chart and the speed rating chart.
FAQ
What gear ratio do I need for 35 inch tires?
From a stock 265/70R17 with 3.73 gears, about 4.13 restores stock: nearest common ratio 4.10. Your stock tire and ratio change the answer.
Do I have to regear for bigger tires?
Not required. A taller tire lowers the effective ratio, which can reduce acceleration and hill-climbing and make an automatic hunt for gears. Whether to regear depends on the size jump and how you use the vehicle.
How do I calculate engine RPM from tire size?
RPM = mph × axle ratio × top gear ratio × 336.13 ÷ tire height in inches. 65 mph, 3.73 axle, 1.00 top gear, 31.6 in tires is about 2,578 rpm.
What are common axle ratios?
The list includes 3.08, 3.21, 3.31, 3.42, 3.55, 3.73, 3.92, 4.10, 4.30, 4.56, 4.88, 5.13 and 5.38. Check what is made for your axle, and edit the list.