Why are speed factors a bad way to measure your growth as a racer?

Many racers think that looking at their speed factors over time is a good way to measure how much faster they have become. However, there is a fatal mistake in doing this: all speed factor calculations throw out a certain amount of "bad stages". And generally, the more stages there are in a rally, the more they throw out. The idea is to ignore stages on which the racer has a flat, or gets stuck in a ditch, or spins.

So a speed factor is really much more a measurement of "typical maximum potential speed". And here is where that fails when considering the use of speed factors as a measure of a racer's growth: the algorithm is designed, by it's vary nature, to ignore your mistakes, it does this by dropping your bad stages. But it's the continual reduction in the number of mistakes made that is actually the measure of a racer's improvement! So the very thing you want to measure, it ignores!

Let's look at two racers:
1. Marvin McCrashALot goes fast on Stage 1, crashes on Stage 2, and then goes fast on Stage 3.
2. Steve Steady goes fast on Stage 1, and fast on Stage 2, and fast on Stage 3.

Marvin McCrashALot gets a speed factor that is the average of speeds on SS1 and SS3. Steve Steady gets a speed factor that is the average of speeds on his best two stages, let's say that's SS1 and SS2. It doesn't matter which two we pick for Steve Steady, since they're all fast. So Marvin McCrashALot and Steve Steady both have the same "fast" speed factor. However, Steve Steady wins the race, every time. We all know people that go very fast... and crash a lot. They're almost always beaten by more consistent racers with a slightly lower speed factor.

Now while it may seem unfair that Steve Steady and Marvin McCrashALot have the same speed factor, remember, speed factors were not designed to measure the worth of a racer. These algorithms were built to create a start order that would result in the least amount of passing so that everyone gets a fair shot at an empty road. Speed factors do a very good job of that.

In the game of determining if you are improving as a racer, the best measure is "are you moving up in the overall ranking". Speed factors are a specialized mathematical tool to manage start orders and reseeds, and because they ignore mistakes, they are a poor way of measuring a racer's growth in the sport.