Why George Russell’s car was underweight – and it is not the reason you think

Mercedes made a genuine mistake rather than something more sinister and their winning tyre strategy contributed to the disqualification

George Russell’s disqualification after ‘winning’ the Belgian Grand Prix will have been a tough one to take. Unfortunately, as soon as it was announced that his car was being investigated for being underweight, a disqualification was almost inevitable.
The official process is that every car is weighed in parc fermé after the race and must have a minimum weight of 798kg to remain legal, once the fuel is drained from the car. Most cars would probably come in at just over 800kg. Russell’s car weighed exactly 798kg before a mandatory fuel sample (or three lots of 0.5kg of fuel) was removed for testing. This meant his car was 1.5kg underweight in the final reckoning. Would Lewis Hamilton have passed him without this? I do not think it would have made a great difference to the result.
The first thing to say is that this was a genuine mistake from Mercedes – they were not trying to gain a competitive advantage. If you go back to 2005, Jenson Button’s BAR team were disqualified and banned from two grands prix for running a ‘hidden’ fuel tank. This was in the days of in-race refuelling. They had extra (unused) fuel in the secondary tank at the car’s final pit stop to act as ballast and ensure the car met the weight limit. This meant that the car could run underweight for much of the race. That clearly contravened the regulations, but Russell’s car being underweight is a different issue entirely.
Of course, weight of fuel is critical in Formula One. Most cars are run on a marginal fuel load as teams want the cars to be as light as possible. You would be annoyed if you had 6kg of extra fuel in the tank as it would cost you so much race time. But you obviously must be within the regulations. Mercedes’ error was not simply about fuel, though, as the 798kg limit is with the car being ‘dry’ or drained of fuel, though the reality is that it is not possible to get every last drop from the car.
How did it happen then? Perhaps surprisingly, the ‘missing’ weight would likely have come from the tyres – in two ways. Firstly, Russell used an unexpected one-stop strategy to ‘win’. Even tyre manufacturer Pirelli did not believe stopping once to be viable. Russell made it work but that extra tyre wear would certainly have contributed to his disqualification.
In being used for 34 laps – 16 more than team-mate Hamilton – Russell’s hard compound tyres would have been more worn and thus lighter. The difference in tyre weight could have been as much as 0.2kg per tyre, adding up to 0.8kg – more than half of the critical 1.5kg.
Additionally, Spa is unusual in that the drivers do not complete a full cooldown lap. Because the track is so long, the drivers cross the finish line, go around turn one and then head the ‘wrong’ way into the pit-lane. This deprives them of the opportunity to collect tyre ‘pick-up’ – the discarded worn tyre rubber off the racing line.
This is an important way that drivers and teams ensure they are over the minimum weight. In Hungary, for example, you could pick up 5kg of rubber if you wanted (see below). If you have any blatant pick-up, the FIA reserves the right to clean that off but generally they do not. It all mounts up, even though you are talking only about 1.5kg – the weight of a bag of sugar.
There are probably a few people whose responsibility this is. Each driver will have a team of data analysts and engineers on the pit wall looking at various data points like brake temperature, tyre temperatures and pressures, engine temperature and fuel usage and so on. The team as a whole will shoulder the blame for this one, however hard it is to take. It was unfortunate but meant that Russell had to say goodbye to a stunning victory in a painful manner.