race. In 1933, Dayton Daily News newspaper photographer Myron Scott of Dayton, United States had covered a race of boy-built cars in his home community and was so taken with the idea that he acquired rights to the event; the national-scale Soap Box Derby grew out of this idea. In 1934, Scott had managed to persuade fifty cities across the United States to hold soap box car races and send a champion each to Dayton for a major race, later held in Akron. Scott later went on to work for Chevrolet. In the UK, gravity racer derbies have recently become more popular, brought to the masses by large events such as the Red Bull Soapbox Race and that held between 2000 and 2004 at the Goodwood Festival of Speed. Now, many small hilly communities organize their own races, such as the Catterline Cartie Challenge in Scotland and the Belchford Downhill Challenge in Lincolnshire, and there are now several dozen known races across the UK. An annual Soap Box Derby has taken place in mid-July at Richard's Castle on the Shropshire/Herefordshire border since 2004. In addition to the local community races, there are a small number of races which attract more serious competitors, such as Cairngorm Soapbox Extreme (held at Cairn Gorm from 2009 to 2012) and the Worlaby Downhill Challenge. These races tend to produce higher speeds than the community races. Gravity racers taking part in Cairngorm Soapbox Extreme in 2011 reached speeds of 70 mph. Physics considerations A gravity racer obtains its energy solely from the force of gravity (assuming no starting push is permitted), which is effectively equal for any combination of racer design and course. However, performance can be greatly affected by the combined effects of various forms of drag and also the moment of inertia of the wheels, and also of course by the skill of the driver in choosing optimal lines. Drag breaks down into aerodynamic drag and rolling resistance. The latter can be minimised by careful attention to the wheel bearings, tyre sizes and pressures, and brakes (to avoid parasitic brake drag). High tyre pressures and narrower tyres will typically lower the tyre contact rolling resistance, usually at the expense of grip. Larger wheels have lower rolling resistance than small ones, and rolling resistance is also proportional to overall weight. If permitted, a 3-wheeler design will have 25% less rotational inertia than a 4-wheeler,