Tommy
Established Member
I know but not enough for an impact, provided the gap between car and lorry is greater than the distance travelled in the reaction time. The car will stop quicker than the lorry, 50m* as opposed to 120m*, say, so from the car's point there would be an initial rapid closing of the gap - but not enough for a collision - then the lorry would appear to accelerate away from the car even though both are hard braking, hopefully ... in theoryBut the lorry will already be in the process of stopping, which is happening during your reaction time.

57mph is approx 25m per second, so if reaction time is =1, or <1, then no collision would occur, if gap is 25m or above, as in the 3rd option in the diagram above, 15m would be pushing it unless you had very quick reactions.
Perhaps I got my maths/physics wrong**, but I've thought about this a lot as I do slipstream on motorway often.
* figures I got online, though there is lots of conflicting data.
** maybe braking is not linear, for example.
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