A ramp's approach angle tells you how steeply the surface rises. What decides whether your car can use it is something else: whether the lowest point of your front bumper clears that rising surface while the tire is still traveling up it. That is a geometry problem with a simple answer.
Degrees to inches
The ramp surface rises by the tangent of its angle for every inch you move forward. In practical numbers:
| Approach angle | Rise per inch | Rise over 24 in of overhang | Rise over 36 in |
|---|---|---|---|
| 6.6 degrees | 0.12 in | 2.8 in | 4.2 in |
| 9.05 degrees | 0.16 in | 3.8 in | 5.7 in |
| 10.8 degrees | 0.19 in | 4.6 in | 6.9 in |
| 17 degrees | 0.31 in | 7.3 in | 11.0 in |
Read the 17-degree row and you can see the problem immediately: a car with 24 in of front overhang meets a surface 7.3 in high by the time the tire reaches the ramp's start. If the bumper sits 6 in off the ground, it touches first.
The two measurements you need
1.Lowest front point, height above the ground
Usually the front lip, air dam or splitter. Level ground, suspension settled, measure straight up. Call this clearance.
2.Horizontal distance from tire to that point
From the front face of the front tire forward to the lowest point. Call this overhang. On most cars it is 20-36 in.
3.Multiply and compare
Overhang x rise-per-inch from the table gives the height of the ramp surface at your bumper's position. If that is more than your clearance, the bumper hits.
The cardboard test, which is faster
Cut a piece of stiff cardboard into a right triangle matching the ramp's profile — or simply prop a straight edge at the ramp's angle against your front tire — and look at where it passes relative to the bumper. Two minutes, no arithmetic, and it accounts for the parts of your front end you did not think to measure.
If you already own the ramps, the real test is better still: with the ramps in place against the tires, kneel and sight along the ramp surface toward the car. You will see the contact point before you find it with the bumper.
Angle and lift pull in opposite directions
A shallower angle means a longer ramp for the same lift, or less lift for the same length. That is why the cheap shallow wedges give only 2-1/2 in of lift, and why a genuinely shallow ramp with 8 in of lift is 56 in long and expensive. There is no way around the trigonometry.
The consequence for a low car is unfortunate: it needs a shallow angle and more lift than a normal car, because it starts closer to the ground. That combination is the expensive corner of the market. Best ramps for low cars covers the options.
Why ramp length matters beyond the angle
Length also determines how much flat area there is at the top. A short wedge gives you a small landing, and a tire parked near its edge is closer to rolling off than one in the middle. Longer ramps give you margin for stopping in slightly the wrong place — which is worth something on a first attempt.