The concertina theory at Turn one lap one discussed mathematically. With thanks to XL So at 300 kph with 2 cars at a constant and equal speed a gap of 8.33 metres is actually a gap of about one tenth of a second. That same tenth of a second at 80kph is only 2.22 metres. While accelerating a constant time gap will increase in distance creating the illusion of more space. It's still one tenth of a second. When the cars decelerate from 300 to 80 kph that 8.33 metre gap shrinks to only 2.22 metres and that's only if exactly one tenth gap is maintained. Brake half a tenth later and you have 1 metre. Brake a full tenth later and you have contact. With 12 rows of cars maintaining a 1 tenth gap you only have 100 metres in total gaps. As it drops to 80 kph you now have only 26 metres in total gaps and to achieve this all drivers have to maintain 1 tenth gap precisely.. At this point the problem becomes very clear. Lots of cars and space rapidly shrinking to only 25 % of the space we had at full speed. Say the driver in front seeks to maintain a safe gap (in metres) and brakes to achieve this. If on arriving at 80 kph he achieves half the 8.33 metres (so maintains 4.16m) he has doubled his time gap to the car in front and totally consumed the gap to you. If the driver in front brakes even 1 tenth before you so 8 metres before your marker you will have contact. What happens when we all do it? Add to that the fact that on lap 1 turn one with full fuel and cold brakes and tyres, to create some space many wise drivers will add a few metres (lets say half a tenth) to their normal braking marker If conveniently each row adds the exact same half a tenth safety margin, by the time row 12 arrives at the braking zone we have a braking point that has moved towards you by 46 metres. But drivers don't act or react the same, some will allow a bit more, some a bit less, some will see braking as a chance to overtake or a sign of weakness and want to dive into that 2.22 metre gap. And that leaves us with the Race Director each race saying “take care at Turn 1”. Yet it still surprises at least some of us week after week.