Shift Speed Comparator
Compare theoretical shift speeds in every gear for two tire sizes. See how much faster each gear runs out at your shift RPM.
Compare theoretical speeds across gears.
Shift Speed Comparator: Tire Size Inputs
Compare two tire sizes here. Use the formulas and reference tables below for this tool's specific calculation.
How Shift Speed Comparator Works?
The Shift Speed Comparator works by calculating the road speed at the shift RPM in every gear for two tire sizes and listing the gap. The tool uses 4 steps.
Enter the gear ratios
Type every forward gear ratio, for example 4.70, 2.99, 2.15 … 0.85 for an 8-speed.
Enter axle ratio and shift RPM
Type the axle ratio (3.73) and the shift point (5,500 RPM).
Enter 2 tire sizes
Type the stock tire (31.61 in) and the new tire (35.0 in).
Compare gears
The comparator lists the shift speed in each gear for both tires and the gap in mph and km/h.
Shift Speed Comparator Formula
The Shift Speed Comparator formula is V_shift = RPM_shift × D ÷ (G_n × A × 336.13), applied to each gear n and each tire.
V_n = RPM_shift × D ÷ (G_n × A × 336.13)ΔV_n = V_n(D₂) − V_n(D₁)RPM_after = RPM_shift × G_(n+1) ÷ G_n- G_n
- Ratio of gear n
- RPM_shift
- Engine speed at the shift
- D
- Tire diameter (in)
Worked example
In 1st gear (4.70) with a 3.73 axle at 5,500 RPM, a 31.61 in tire reaches 29.5 mph and a 35 in tire reaches 32.7 mph. The engine drops to 3,499 RPM after the shift to 2nd on both tires.
Shift Speed Comparator Conversion Table
The Shift Speed Comparator conversion table compares shift speeds in 8 gears for a 31.61-inch and a 35-inch tire.
| Gear | 31.61 in tire | 35.0 in tire | Gap (mph) | Gap (km/h) |
|---|---|---|---|---|
| 1st (4.70) | 29.5 mph | 32.7 mph | +3.2 mph | +5.1 km/h |
| 2nd (2.99) | 46.4 mph | 51.3 mph | +5.0 mph | +8.0 km/h |
| 3rd (2.15) | 64.5 mph | 71.4 mph | +6.9 mph | +11.1 km/h |
| 4th (1.77) | 78.3 mph | 86.7 mph | +8.4 mph | +13.5 km/h |
| 5th (1.52) | 91.2 mph | 101.0 mph | +9.8 mph | +15.7 km/h |
| 6th (1.28) | 108.3 mph | 119.9 mph | +11.6 mph | +18.7 km/h |
| 7th (1.00) | 138.7 mph | 153.5 mph | +14.9 mph | +23.9 km/h |
| 8th (0.85) | 163.1 mph | 180.6 mph | +17.5 mph | +28.2 km/h |
What is Shift Speed Comparator?
A Shift Speed Comparator is a tool that compares the speed at which each gear runs out for two tire sizes. Taller tires stretch every gear, so each shift happens at a higher road speed.
A stretched gear feels slower to accelerate. The engine spends more time in each gear, and the force at the wheels drops by the same percent as the diameter gain.
Transmission control units decide shift points from vehicle speed. Uncorrected tire size changes make an automatic transmission shift at the wrong engine speed.
What are the uses of Shift Speed Comparator?
There are 4 main uses of the Shift Speed Comparator, including race gearing and automatic transmission tuning.
Race gearing
Check which gear the car uses at the end of a straight.
Automatic transmission tuning
Set shift tables after a tire change.
Merge and pass checks
See which gear covers a 50–70 mph (80–113 km/h) pass.
Tire choice
Compare the acceleration effect of 2 tire heights.
Related Speedometer & Distance Tools
View All 134 Subtools →Estimate speed changes after tire resizing.
Estimate road speed from indicated speed.
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Calculate a tire-size correction multiplier.
Tabulate indicated and estimated actual speeds.
Estimate distance recording differences.