In 2015 I bought a house on the slope of Paris Mountain in Greenville, South Carolina. A flat spot for the house was bulldozed, creating a steep hill behind the house, leaving a slope from the floor of the garage to the street, so the driveway in between is slanted at about 15 degrees. That turns out to be a lot of degrees. I first noticed that this could be a problem when I drove up from Florida in my 2005 Camry, and after an exhausting day on I-95, finally pulled into the garage. CRUNCH went the bottom of the car, as it ground over the peak caused by the driveway slant.
I learned my lesson and bought an SUV, but being limited in what car one can own by some bothersome geometry is annoying. So I began investigating what modification to the driveway would allow more options. There's currently a small bevel at the join between the slanted and flat concrete, and the idea is to expand that in both directions. How wide would the bevel need to be to allow a Prius to get up the driveway without bottoming out? Or a Chevy Bolt?
The important car dimensions here are the wheelbase (distance between axles) and ground clearance. These are relatively easy to find on the internet, and bulk downloads exist (for a price). One useful data point was that my wife's 2010 Honda Civic just barely touched the concrete, giving me a minimum dimensional set to work from. Initially, I just computed the ratio of wheelbase to clearance and used that to estimate which cars would make it into the garage without the nasty crunch. Anything less than 15.7 was going to be a problem. However, this greatly limits the cars that will work, and that's become an issue lately. We'd like to have the option of getting a small used EV to just drive in town, to complement the Rav4 we share now.
There are two kinds of solutions I've considered. One is remaking the driveway to increase the bevel, and the other is to install a rubber bump in the garage to lift the front of the car as the lowest point passes over the peak.
Given the physical dimensions of the car, the driveway, and the proposed modifications, it's straightforward, but fussy, to do the geometry to calculate the minimum clearance at each point in the driveway as the car comes into the garage. I built a Shiny app to do that, which you can download on Github. (Use at your own risk: no warranties are implied.)
The photo shows a 2" marker placed about 14" behind the edge of the garage slab. By moving the marker until it just brushes the bottom of the car I can get a sense of how well the model conforms to reality. One thing I learned is that the sloped driveway is curved a bit to make a slight hump--it's not perfectly flat, so the results deviate a bit from the model in favor of slightly more clearance.
Another calculation was to find where the plane of the flat garage slab and the plan of the included driveway meet.
Although the driveway isn't perfectly flat, the inclined plane intersects with the horizontal about two inches from the existing edge. This is due to an existing bevel where the two meet. That meeting point is the center of the bevel in the simulation. So it's currently about 2", but because of the slight hump in the driveway it functions more like 3". I didn't try to model the hump explicitly, but that would be the next step in making the app more accurate.
All of this is somewhat approximate, and there's no certainty without actually driving a car into the garage, but this analysis has given me a good idea of how much wider our selection of cars can be if we increase the bevel to about 12" and possibly add a 1" ledge (a secured rubber mat, probably) inside.
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