Following George Russell's disqualification from the Belgian Grand Prix, Sky Sports F1 strategy expert Bernie Collins analyses the key questions arising from the incident.
Russell appeared to have pulled off a glorious victory when he held off Mercedes team-mate Lewis Hamilton in the closing stages to take the chequered flag at Spa.
However, the remarkable one-stop strategy that the Brit pulled off ultimately appeared to cost him, as his W15 came in 1.5kg under the 798kg minimum weight limit after the race.
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Mercedes team principal Toto Wolff said he suspected that the issue had been caused by Russell making one rather the two stops that his rivals went for, with the lack of rubber on his heavily worn tyres explaining the reduction.
Wolff apologised to Russell for the error, but Mercedes did at least have the consolation of Hamilton inheriting his 105th grand prix victory.
After the race, former Aston Martin head of strategy Collins explained what might have gone wrong for Mercedes and how the team are likely to address their error.
What factors led to Russell disqualification?
In advance of qualifying, as that's when the car is in parc ferme, the team will have to estimate the lightest the car will be through qualifying and the lightest it will be in the race. In qualifying, it's easy because you estimate, normally, for a dry tyre.
When we look at the race, it's the end of the race when the car is the lightest because you should have used all your fuel, engine oil, driver drinks and the plank is worn and in this case, the tyres are worn. We try to get an estimate for what all those numbers add up to at the end of the race and what it will be.
Normally the strategists and tyre engineers, together, will look at what the strategy might be, how many laps you are likely to do on a tyre, and that will dictate the tyre wear, so how light you expect the tyres to be at the end of the race, which is part of the total car weight.
In this case, George has done double the expected number of laps on that tyre set. Even if there was margin in there or allowed for a one-stop, they probably haven't allowed for a one-stop pitting on lap 10, so it's a significantly longer stint than anyone would have expected in tyre wear rate.
In Spa, there's no in-lap. Normally, drivers try to pick up rubber, that's just a safety net for car weight. That doesn't exist in Spa. The normal get out clause you have is not there.
To add to that, if you have a load of pickup on your tyres, the FIA can ask for a different set of tyres to be fitted to the car, if they think that other set of tyres are lighter but they very rarely do it.
Would Russell have gained an advantage from reduced weight?
The amount by which Russell was under the limit, 1.5kg, is probably worth about half a tenth per lap, so it's small.
If it is tyre wear, then it's only the laps where the tyre is lighter where he's gaining, so the final few laps of the race.
He had fuel on board, so the car was never actually underweight during the race, if you think of it like that, so I don't necessarily think he's gained. If he has, it's small.
Surely Mercedes would have considered one-stop implications?
They will have considered a one-stop but at a much more optimum stop lap, something like lap 20.
So it's those extra 10 laps that he's done on that tyre, which have maybe affected the fact they didn't take all the margin for what they had done.
Equally, Friday was different conditions, different wind. They did nowhere near this number of laps on Friday.
All of those little estimations they have done, have had them over a bit, in terms of the margins they are taking.
Will Mercedes be concerned by another disqualification?
Lewis Hamilton was disqualified after finishing second in last season's United States Grand Prix due to excessive wear on the plank beneath his car.
In my opinion, it's pretty worrying this is their second disqualification in two years. The first thing the car needs to be is legal.
That's a sign that they are being pushed by their competitors and are keeping the margins very fine.
If the car was 1kg overweight, the engineers would try and push that. They are pushing the limits of the technical regulations, as every team does, you try to get the car as light as you can.
This, and the plank, is an indication that where in the past they have been risk averse and were winning everything. Now they haven't, they are trying to push these fine margins in order to get it right and in this case it's had them over again.
What will Mercedes do going forward?
I think the team will look at all of the legality things. The tyre stuff, they probably finish every race with what they think is acceptable margin and in this race they have not.
What they need to be careful of is overreacting to this one race, which is very outside to normal, because of the new tarmac, the lack of Friday running and all these things.
They can't just overreact at the next race and put a massive allowance for tyre wear in the car, or else they will be too slow throughout the race.
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