Endurance races run multiple categories of car simultaneously on the same circuit. The format is deliberate, and the speed difference between classes is a competitive element rather than an inconvenience.
The economics of a mixed grid
A long race needs a full grid to be worth staging, and few manufacturers will build top-category prototypes at any given time. Relying on one class would leave the field thin.
Additional classes based on production cars are far cheaper to campaign, which lets privateer teams and amateur drivers enter events they could not otherwise reach.
The mixed field also gives manufacturers two routes to participate, since a production-based programme carries direct marketing value that a prototype does not.
What the speed difference creates
Faster cars catch slower ones continuously, so a leading car spends much of the race negotiating traffic rather than running in clear air.
Lap times therefore depend heavily on where a car finds itself relative to slower traffic, which introduces variation unrelated to the car's own performance.
Over many hours the effect averages out somewhat, but a badly timed sequence of traffic in a critical stint can cost more than a pit stop.
The protocols that make it work
Cars carry distinct lighting so drivers can identify class at a distance in darkness, since closing speed is difficult to judge from mirrors alone.
Slower drivers are expected to hold a predictable line and to yield without braking suddenly, which is more important than yielding quickly.
Race control issues warnings for unpredictable behaviour, because the primary safety risk in a mixed field is a slower car making an unexpected movement.
Driver rating and stint rules
Amateur categories use a driver rating system that classifies competitors by experience and results, with rules requiring a minimum share of driving from lower-rated drivers.
This keeps amateur classes genuinely amateur rather than allowing teams to hire professionals and enter the category for an easier trophy.
It also makes team strategy partly about scheduling, since the required driving time must be completed regardless of conditions or race position.
Why the format has spread
Multi-class racing gives spectators several contests in one event, so a race can be compelling even when the outright lead is settled early.
It also spreads the cost of staging a long event across many more entrants, which matters when a race occupies a circuit for a full day.
The consequence is that endurance racing rewards a different skill set from sprint racing, where consistency in traffic matters as much as outright pace.
