Final answer:
The ideal speed indicates the maximum safe speed given current weather and road conditions, which may be less than posted speed limits. Factors like air drag also play a role, and during the 1970s oil crisis, highway speed limits were reduced to improve fuel efficiency.
Step-by-step explanation:
The maximum speed you can drive given weather and road conditions is sometimes referred to as the ideal speed. This is the maximum safe speed at which a vehicle can operate in current conditions without reliance on friction between the tire and the road. However, to maintain safety and legal compliance, it is important to adhere to posted speed limits and adjust accordingly based on the actual driving conditions.
For example, if conditions are ideal, the maximum speed may be the posted speed limit; however, in poor weather or on bad road conditions, the maximum safe speed will be lower. Several factors can affect the ideal speed, including visibility, the stability and handling of the vehicle, the tire's condition, and the road's surface.
If we consider the impact of air drag at different speeds, it is notable that at highway speeds, over 50% of the power of a car is used to overcome air drag. The most fuel-efficient cruising speed is about 70-80 km/h (about 45-50 mi/h). Following the oil crisis of the 1970s, maximum speed limits on highways were reduced to about 90 km/h (55 mi/h) in part because of fuel efficiency concerns.