Ben,

Thanks for letting me put my engineer cap on today.

In order to calculate the maximum angle - the angle at which the car will scrape the ground, this is what you need to do.

Find out the wheelbase - W

Find out the ground clearance - G

Divide the wheelbase by 2 = W2

Calculate W2/G, then take the inverse tangent of this number (tan-1 on a scientific calculator)

Then take 90 - the angle. 

Then double the angle. 

This will be the angle from horizontal at which the vehicle will have zero clearance when navigating the transition, and therefore the maximum slope that the driveway should be constructed at.  In a real world application, you will want to give yourself some margin.

For example with a wheelbase of 121" and a ground clearance of 5.5":

W = 121

G = 5.5

W2 = 60.5

W2/G = 11

tan-1 (11) = 84.8 degrees

90deg - 84.8deg = 5.19deg

5.19deg X 2 = 10.38deg.

So this means that in this example, if the angle of the flat transition to the driveway is steeper than 10deg from horizontal, the car will scrape the driveway.

(Be aware that this angle would be measured by placing a level on top of the landing and measuring the angle made with the level and the driveway.  Or by placing a device on the driveway that would indicate the slope in degrees.)

This calculation assumes that the lowest point of the ground clearance occurs at the midpoint of the vehicle.  If the lowest point occurs towards the front or back of the vehicle, then this calculation will not work.

Happy calculating!

Antoinette Verdone, MSBME, ATP

Assistive Technology Consultant

ImproveAbility, LLC

Phone/Text: 512-522-1705

Email: xxxxxx@improveability.com

Web: www.improveability.com

Fax: 888-501-1009

Address: 7301 Burnet Rd, Suite 102-265, Austin, TX 78757

DARS Provider# 1-274278960-0-000

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