Mixing classes with BOP

That is the problem: the average gap between two classes in our catalogue is 14.8 %, seven times what BOP can move. Which is why the correct answer for most mixes is that it cannot be done, and knowing it early saves a season of arguments.

Out of 269 measured pairs

In the recipe, each line is prefixed with the class it applies to. The first slows the faster class; the second, when it appears, speeds the slower one up — it only shows on the “at the limit” pairs, where slowing the faster car down is no longer enough.

• The gap varies a lot from track to track

  The average deviation from the pair’s mean is 1.9 percentage points. For mixable pairs, that variation is the same size as EVERYTHING BOP can move. A single value for a whole season is worthless.

• And that variation is real, not missing data

  This was the check to run before drawing conclusions: the deviation is 1.82 points on tracks with fewer than 30 laps and 1.95 on those above 30. It does not shrink with more data, so it is not sampling noise.

• But track geometry does NOT explain it

  The correlation between the gap and corners per kilometre is -0.086 over 369 observations — that is, none. Monza (1.90 corners/km) and Spa 2022 (5.62) produce practically the same gap. The idea of a BOP per “track family” — fast, technical, balanced — sounds right and does not work here.

• What you can do instead

  Use the table’s average as a starting point and, if it matters to you, measure it at your specific track. There is no shortcut from layout type. The exception is very distant pairs — a formula car against a GT — where the layout matters a great deal; but those cannot be mixed anyway.

1. 1

   Run a stint per class, with no BOP

   Same track, same weather, no traffic if you can. You need at least a dozen valid laps per class or the number means nothing.

2. 2

   Compare medians, not records

   The best lap is set by the best driver that day. The median holds up better when someone has a good afternoon.

3. 3

   Apply the starting point and restart the server

   BOP takes effect at startup. Edit the list with the session running and nothing changes — you will measure the same thing twice.

4. 4

   Repeat and adjust by half the difference

   If you fell short, do not double the adjustment: add half of what is missing. Overshooting and coming back is slower than closing in from below.

5. 5

   And validate in a race, with traffic

   Two cars with the same lap time can still produce a bad race if one claws back a lot on the straights. Equal lap time is the requirement, not the goal.

How it is measured, and what it does not cover

• Where the numbers come from

  From laps recorded on our servers: 18,062 valid laps, cross-referenced with the car each driver used and its class. Invalid laps, nonsense times and the test account are discarded, and each class×track pair needs 12 laps and 3 drivers to count.

• It is race data, not lab data

  Inside each number sit free setups, drivers of different standards, traffic and drafting. That makes it good for deciding whether a mix is viable, not for fine-tuning a tenth.

• The equivalence probably understates it

  The power-to-weight slope comes from comparing different classes, where the power difference arrives bundled with different aero and tyres. The real reach of BOP is most likely somewhat SMALLER than the figure here, not larger.

• What is missing

  Measuring each lever car by car, under fixed conditions and without traffic. Until then, the starting-point column is an honest derivation and not a measurement.

The 56 groups where EVERY pair within them is measured and can be balanced: 41 of two classes, 13 of three and 2 of four. A working with B and B with C is not enough: if A and C are not measured, the group is not listed here.

There is no group of five classes or more with data to back it.

• Can I mix GT3 with GT4 by putting ballast on the GT3s?

  No. The measured gap between GT3 and GT4 is over 7 % of lap time and BOP reaches around 2 %. Even with maximum ballast and power cut to the limit, they are still two different races on the same track. They can run together as separate categories, each with its own classification, but not equalised.

• What about the two GT3 generations against each other?

  That one works, and it is the best-documented mix of all: seventeen tracks. It needs the power limit plus a few kilos of ballast on the faster generation, so it is tight but it fits. It is the best place to start if you have never used BOP.

• Why slow the fast car instead of speeding up the slow one?

  Two reasons. First, range: slowing down has both power and ballast available, while speeding up only has power, so it reaches less. Second, a slow car is usually slow because it lacks grip, and more power makes it worse rather than closer. And it is easier to explain “I gave you ballast” to a driver than “I gave your rival more power”.

• Does the same BOP work all season?

  No, and this is the most common mistake. The gap between two classes moves almost two percentage points from one track to another, which is as much as the whole BOP margin. What you cannot do is guess the correction from the type of track: you have to measure it where you are going to race.

• How often is this table updated?

  When there are enough new laps to change something, and always with the measurement date visible. If Reiza touches a class’s physics or tyres, the earlier numbers stop being valid and it has to be measured again: they are not carried over.