We only give "dumb" answers here.
Your Tire Size has an unloaded circumference of 2689 mm. I'd try reducing that by 3% to account for "squish" (weight on the tire) which gives 2608 mm.
If the speed on your Gryphon reads slower than actual, increase the value. If the Gryphon reads fast, decrease the number. Remember your dashboard speedo will always read 2-3 mph faster than the Gryphon in the 70 mph range. Compare the
Gryphon speed to some known accurate value like from a GPS.
- Jack
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2024 F150 Platinum SCrew 3.5L PowerBoost FX4, Peragon Tonneau Cover, LineX Bed, 35% Window Tint on All Sides and Rear, Full Nose Paint Protection Film, Husky Mud Guards, Lasfit Floor Liners, VIOFO Dash Cam