FAQ
What is this?
Bomb Hills reads public elevation data and the public road map, puts one on top of the other, and finds every street that goes properly downhill. Then it works out how fast you would get on each one and puts the best at the top.
How accurate is it?
The elevation comes from aerial laser surveys flown by the US Geological Survey. It is accurate to within an inch or two, far better than anything a phone can measure. The grades you see are real.
How fast will I actually go?
Probably a bit less than the number shown. It assumes an 80 kg rider in a tuck, on smooth tarmac, with no wind, from one push. Sit up, ride rough road, or catch a headwind and you will be slower. Treat it as a way to compare hills, not a promise.
Why is a hill I know missing?
A street has to hold at least a 3% grade for at least 400 feet to count. Gentler than that and you coast to a stop instead of speeding up. We also leave out unpaved roads, parking lots, driveways, and anything marked private.
What does Bomb Hills not know?
Quite a lot, and this is the important bit. It knows the shape of the ground. It does not know about traffic, gravel, potholes, blind corners, parked cars, roadworks, whether a street is private, or whether skating it is legal where you live.
The top hill in a town can still be a terrible place to ride. Go and look at it in person, in daylight, before you ride it.
What does "runout" mean?
What happens at the bottom. Uphill is best, because the hill slows you down for you. Keeps dropping means you carry your speed into whatever comes next. Road ends means exactly that, and is worth a look on the satellite view before you commit.
Why does the 3D look so dramatic?
Because we exaggerate it, six times over by default. Stillwater's hills are real but small, and drawn honestly the 3D view is a flat dark sheet that tells you nothing. The numbers in the list are the true ones. Slide the terrain control back to 1x any time you want the honest shape.
Can you do my town?
Check it yourself, free and with no sign-up, on the cities page. Big cities get built in squares about 14 miles across, so you pick the part you actually ride.
We measure how steep the ground gets over short distances, which is what matters for skating. If your square comes back flat, we will say so rather than take your money.
Why the check before the map?
To stop bots hoovering up the data. It does not track you and is not used for advertising. The rest of the site is open.
Where does the data come from?
Elevation and aerial photography from US government surveys, which are public domain. Roads from OpenStreetMap, the volunteer-made map of the world. Nothing is scraped from anyone's private database.