How it works
A ramp resting on the ground and the deck forms a right triangle. The ramp itself is the long side.
Angle = asin(height ÷ ramp length)
Ramp length needed = height ÷ sin(max angle)
Slope % = height ÷ horizontal run × 100
Breakover angle = 2 × atan(2 × ground clearance ÷ wheelbase)
Height, wheelbase and clearance use inches (or cm); the ramp length uses feet (or meters).
Worked example
A 36 in pickup tailgate with 8 ft ramps, and a 15° comfort limit.
- Angle: asin(36 ÷ 96) = 22°, steeper than 15°
- Ramp length for 15°: 36 ÷ sin 15° = 139 in ≈ 11.6 ft
- A lawn tractor with a 48 in wheelbase and 4 in clearance has a breakover of about 19°, so the 8 ft ramp could also scrape it.
Ramp length needed by height and angle
| Deck height | 10° max | 15° max | 20° max | 25° max |
|---|---|---|---|---|
| 12 in | 5.8 ft | 3.9 ft | 2.9 ft | 2.4 ft |
| 18 in | 8.6 ft | 5.8 ft | 4.4 ft | 3.5 ft |
| 24 in | 11.5 ft | 7.7 ft | 5.8 ft | 4.7 ft |
| 30 in | 14.4 ft | 9.7 ft | 7.3 ft | 5.9 ft |
| 36 in | 17.3 ft | 11.6 ft | 8.8 ft | 7.1 ft |
Safe loading
Secure the ramps to the deck with their straps or pins so they can’t kick out, and set the trailer or truck in park with the wheels chocked. Make sure the ramp’s rated capacity covers the machine plus rider, and remember that weight is concentrated on each ramp under one wheel or track. Drive straight, at a steady speed, with no one standing behind or beside the ramp.
A trailer with a lower deck needs a shorter ramp; dovetail and tilt trailers reduce the angle further. Once loaded, strap the machine down with the tie-down calculator and check the trailer’scargo capacity.
Common mistakes
- Measuring the run instead of the ramp. The ramp length is the sloped length, not the distance on the ground.
- Ignoring the crest. Low vehicles scrape where the ramp meets the deck, not on the slope itself.
- Loading uphill on a slope. Parking on a downhill grade makes the effective ramp angle steeper.
- Unsecured ramps. A ramp that slips off the edge is the most common loading accident.