Did BoP Work?
SRO changed the Balance of Performance during the weekend at eight of nine 2026 GT World Challenge Europe rounds. We measured what each weight change did to pace.
Balance of Performance is how SRO keeps ten different GT3 cars within reach of each other. It sets a minimum weight and a power level for every model, and it can change them at any point in a race weekend. Fans argue about it constantly. Almost nobody measures it.
In 2026 SRO changed the BoP weights during the weekend at eight of the nine GT World Challenge Europe rounds so far, 35 times in all. Every change was a natural experiment: same track, same weekend, one brand heavier or lighter. We compared each brand's pace before and after.
8/9
Rounds with a change
mid-weekend
35
Weight changes
5 to 20 kg each
11/14
Heavier, then slower
brands
0.10%
Cost of 10 kg
of lap time
How often did SRO change the BoP during a weekend?
Nearly every weekend. SRO publishes a BoP before each event, then revises it once it has seen the cars run. At the Sprint rounds the revision usually landed after the first qualifying session and before Race 1. At the Endurance rounds it landed after qualifying and before the race. Misano was revised twice.
| Round | Took effect | Weight changes |
|---|---|---|
| R2 Brands Hatch | Before Race 1 | Porsche +10 kg |
| R3 Monza | Before Race | Audi +5 kg |
| R4 Spa 24 Hours | Before Race | Aston Martin -5 kgLamborghini -5 kgFord -5 kgMercedes-AMG -10 kgMcLaren -10 kgBMW -10 kgPorsche -15 kg |
| R5 Misano | Before Race 1 | BMW +20 kgAudi +20 kgPorsche +15 kgMercedes-AMG +10 kg |
| R5 Misano | Before Race 2 | Porsche -10 kgLamborghini -10 kg |
| R6 Magny-Cours | Before Race 1 | Mercedes-AMG +20 kgAston Martin +10 kgBMW +10 kgLamborghini -8 kgPorsche -10 kgMcLaren -10 kgAudi -10 kg |
| R7 Nürburgring | Before Race | Ferrari -5 kgAudi -10 kgFord -10 kgCorvette -20 kg |
| R8 Zandvoort | Before Race 1 | Porsche +15 kgMcLaren +10 kgFerrari +10 kg |
| R9 Barcelona | Before Race 1 | Porsche +10 kgMercedes-AMG +10 kgAston Martin -10 kgBMW -10 kgMcLaren -15 kgLamborghini -15 kg |
Misano had two revisions. Paul Ricard published one weight table only, so a change there would not show. Barcelona's revision notice is missing from the noticeboard, but its revised weight table says it follows a revised BoP.
How we measured it
- ◆Weights come from the stewards' bulletins, which list every car's BoP minimum weight and are re-issued whenever the BoP is revised. Power and restrictor changes are not published there, so this story measures weight only.
- ◆Pace is each brand's fastest car as a percentage gap to the fastest car in the session. We averaged it over the sessions run before the revision (practice and qualifying) and the sessions after it.
- ◆Timing: noticeboard documents are numbered in the order they are posted, so we know which sessions ran under which weights.
- ◆The control group: races and qualifying are run differently from practice, so every brand's pace shifts after a revision. We measure each changed brand against the brands SRO left alone at the same revision.
- ◆Limits: one best lap per car per session, no lap-by-lap data, and a small sample of 35 changes. Barcelona's qualifying was wet. Leaving Barcelona out does not change the result.
Did added weight slow a brand down?
Mostly, yes. Of the 14 times a brand gained weight, it lost pace against the unchanged brands 11 times. Of the 21 times a brand lost weight, it gained pace 14 times. Taken at face value, every 10 kg added cost about 0.17% of lap time.
Weight added, pace lost: SRO's changes moved brands the right way
Each dot is one brand at one mid-weekend BoP revision. Right means weight added; up means the brand got slower than the brands SRO left alone.
- Brand at one revision
- Trend
How much of that is real?
Less than the raw numbers suggest. SRO adds weight to the brands that look fastest in practice, and a brand that looks fastest in one session tends to look less dominant in the next one anyway. Statisticians call this regression to the mean. The brands SRO slowed were the ones that had been quickest before the change (a correlation of -0.46), so part of their slowdown would have happened without any BoP.
Once we account for how fast each brand was before the change, the effect shrinks but does not disappear: 10 kg costs about 0.10% of lap time, or roughly a tenth of a second on a 1:40 lap. It comes out between 0.09% and 0.11% in the Sprint rounds, the Endurance rounds and the season without Barcelona. If the weight changes did nothing, a link this strong would turn up by chance about once in a hundred tries.
So BoP works, and in the direction SRO intends. But around 40% of what looks like a BoP effect in the timing sheets is the field settling down on its own. That matters every time a team blames a result on its weight.
Which brands did SRO adjust most?
Porsche was adjusted most often, seven times across the season, and ended up 15 kg heavier in net terms. Mercedes-AMG started every round as the heaviest car on the grid and took a net 30 kg more from mid-weekend changes. Lamborghini never had weight added during a weekend: its four changes were all reductions, 38 kg in total.
Mercedes-AMG was the heaviest car at every round
BoP minimum weight in kg at the start of each round. Darker cells are heavier. The small figure is the change SRO made during that weekend.
| Brand | R1END | R2SPR | R3END | R4END | R5SPR | R6SPR | R7END | R8SPR | R9SPR |
|---|---|---|---|---|---|---|---|---|---|
| Porsche | 1330 | 1325+10 | 1315 | 1330-15 | 1325+5 | 1320-10 | 1325 | 1315+15 | 1330+10 |
| Mercedes-AMG | 1350 | 1345 | 1350 | 1350-10 | 1335+10 | 1335+20 | 1350 | 1340 | 1345+10 |
| McLaren | 1320 | 1315 | 1320 | 1320-10 | 1310 | 1315-10 | 1305 | 1310+10 | 1325-15 |
| Aston Martin | 1300 | 1285 | 1290 | 1305-5 | 1285 | 1280+10 | 1300 | 1290 | 1295-10 |
| Audi | 1315 | 1315 | 1315+5 | 1300 | 1305+20 | 1305-10 | 1305-10 | 1310 | 1295 |
| BMW | 1320 | 1300 | 1315 | 1320-10 | 1310+20 | 1305+10 | 1320 | 1310 | 1320-10 |
| Lamborghini | 1320 | 1315 | 1320 | 1325-5 | 1315-10 | 1305-8 | 1325 | 1320 | 1320-15 |
| Ferrari | 1320 | 1315 | 1320 | 1325 | 1325 | 1325 | 1325-5 | 1320+10 | 1330 |
| Ford | 1315 | 1320 | 1325-5 | 1320-10 | |||||
| Corvette | 1320 | 1330 | 1325 | 1330-20 |
Three calls worth a closer look
- ◆Mercedes-AMG at Magny-Cours (+20 kg): the biggest single addition of the year went to the fastest brand of the weekend, 0.02% off the session best before the change. Afterwards it was 0.44% off, the largest drop of any brand against the unchanged field.
- ◆BMW at Magny-Cours (+10 kg): the exception that proves the point. BMW gained weight and still got much faster, from 1.66% off to 0.35%. It had been the slowest brand in practice and first qualifying, which is exactly the kind of number that bounces back on its own.
- ◆Corvette at the Nürburgring (−20 kg): the biggest break of the year went to the slowest brand, 1.48% off before the change. In the race it was 0.82% off, still behind but much closer.
The spread between the fastest and slowest brands narrowed after six of the nine revisions. That is the outcome BoP is designed to produce, although racing and practice sessions spread the field differently, so it is only supporting evidence.
What it means for 2027
SRO's mid-weekend changes did what they were meant to do, by about a tenth of a second per 10 kg. That is a small number with big consequences in a field covered by a few tenths. The next step is the one the data cannot yet take: SRO also changes power, and those figures are not published in the bulletins. Until they are, any verdict on BoP, including this one, sees only half of the picture.
For how pace turned into results this season, see Fast on Saturday, Invisible on Sunday and Four Leaders, One Champion.
// Data and sources
BoP minimum weights from the stewards' bulletins of the 2026 GT World Challenge Europe, rounds 1 to 9. Session times and classifications from the official noticeboard documents. Analysis by Apex Insights. See every team's pace on the GTWC team pace page.