Science Puzzle
Why Are Racetrack Bends Tilted?
The bends on many racetracks aren't flat. At Daytona in the United States, the track tilts up towards the outside of each turn at 31 degrees: walking across it would feel like climbing a steep hill. The tracks in cycling velodromes tilt even more steeply on the bends, and the curves of railway lines tilt too, though only a little.
What does tilting a bend do for the cars, bikes and trains going round it?
The Answer
The tilt makes the road itself help push the vehicle round the bend, so it doesn't have to rely on the grip of its tyres alone.
Anything moving tends to carry on in a straight line. To follow a curve, something has to keep pushing it sideways, towards the centre of the bend. On a flat road, that push comes entirely from friction between the tyres and the road. Take the grip away, on ice or oil, and the car carries straight on and slides towards the outside of the bend.
A road always pushes straight out from its surface. On a flat road that's straight up, which does nothing to turn you. Tilt the road and its push tilts too, so part of it now points towards the centre of the bend. At just the right speed, the tilt alone provides all the turning push needed, and a car could go round without skidding even if the track were icy. Faster than that, the tyres add the rest. This lets racing cars and cyclists take bends far faster than a flat track would allow.
You use the same idea when you lean into a bend on a bike. Aircraft do it too: to turn, a plane banks, tilting its wings so that part of their lift pulls it round the curve.
The principle: Centripetal force. Moving in a curve needs a force towards the centre of the curve; tilting the surface lets the road's push provide some or all of that force.