Another significant issue in 2007 was the reduction in permissible fuel from 22 litres to 21 litres, causing engineers to introduce ECU control over maximum revolutions, where internal friction losses are highest, and leaning out the fuel-air mixture in sections of the track where maximum power is less necessary. Observers noted that the 800 cc machines were not using proportionately less fuel than the 990s because with their lower power output the smaller machines were using full throttle more of the time for a given circuit.
New tire regulations introduced in 2007 limited the number of tires any rider could use over the practice and qualifying period, and the race itself, to a maximum of 31 tires (14 fronts and 17 rears) per rider . This introduced a problem of tyre choice vs. weather (among other factors) that challenges riders and teams to optimize their performance on race day. This factor was greeted with varying degrees of enthusiasm by participants.
'No fuel on the motorcycle may be more than fifteen °C (15 °C) below ambient temperature. The use of any device on the motorcycle to artificially decrease the temperature of the fuel below ambient temperature is forbidden. No motorcycle may include such a device.' This stops an artificial "boost" gained from increasing fuel density by cooling it.
MotoGP-class motorcycles are not restricted to any specific engine configuration. However the number of cylinders employed in the engine determines the motorcycle's permitted minimum weight; more cylinders attracting more weight as a form of handicap. This is necessary because, for a given capacity, an engine with more cylinders is capable of producing more power. If comparable bore to stroke ratios are employed an engine with more cylinders will have a greater piston area and a shorter stroke. The increased piston area permits an increase in the total valve area, allowing more air and fuel to be drawn into the engine, and the shorter stroke permits higher revs at the same piston speed, allowing the engine to pump still more air and fuel with the potential to produce more power but with more fuel consumption too.
From 2007 onwards and for a minimum period of five years, FIM has regulated in MotoGP class that two-stroke bikes will no longer be allowed, and engines will be limited to 800 cc four-strokes.
