Truck racing explained: Overspeed

25. August 2018The long midseason break gives us a good opportunity to explore a term you’ve encountered in many of our reports, a concept not every visitor to truckracing.de / truckrace.info fully apprehends. We’ve received a growing number of enquiries in recent weeks from our vast fan following – more than three million of them at last count – about “overspeed”.
As we all know, the FIA European Truck Racing Championship is a singular species in the motorsport biome – because of the sheer size and mass of the race trucks, and the 160 km/h top speed that they are restricted to.
The causal relationship between the two is important to understand. The trucks, as current ETRC regulations allow them to be built and set up, are actually capable of speeds in excess of 230 km/h. Indeed, a specially set-up SuperRaceTruck-class machine has even been clocked at near 300 km/h on a track expressly prepared for such performance discovery. But because safety is a prime consideration, a speed limit of 160 km/h was written into the regs at the very beginning of the sport.
Should a race truck today, weighing no less than 5,300 kg, crash into a retaining wall or safety fence at 160 km/h, the impact energy, i.e. the kinetic energy of the vehicle dissipated on impact, would equal 5,235 kilojoules. At a speed of 230 km/h the impact energy would be 10,820 kJ. By comparison, a 40 tonne tractor and semitrailer (the standard long haul truck combination on continental Europe) develops 9,877 kJ on a similar impact.
A proposal to raise the limit to 180 km/h has been discussed on several occasions in the past – at that speed the impact energy would be 6,625 kJ.
Translated to Formula 1, an open-wheel single-seater from the world’s premier motorsport series would need to go above 430 km/h to generate the same impact energy as a race truck at 160 km/h. But the fastest an F1 car has ever gone is 370 km/h. To generate the same impact as a race truck at 180 km/h, an F1 racer would need to top 484 km/h!
For several years now, the FIA has used GPS measurements to monitor the speeds of race trucks. The regulation clearly defines infringements and what the consequences for each are. A driver whose truck overshoots the limit for more than 2.75 seconds is awarded a 10 second penalty, i.e. has 10 seconds added to his or her elapsed time at the end of the race. Multiple infringements invite complete disqualification. Likewise overspeeding for 8 seconds continuously or more, or exceeding 170 km/h.
Electronic controls automatically throttle the engine when the truck’s speed touches 160 km/h.
Over the last few seasons the speed limiters have been programmed by the teams to maximally exploit the latitude permitted by the regulation. On long straights, when the trucks hit 160 km/h right at the start, you can clearly hear the roar of the engines suddenly toning down, then a renewed roar resulting from another fuelling boost followed by a few seconds of quiet before the driver begins to brake for the corner. What’s happening here is that the truck is exceeding 160 km/h for a maxiumum of 2.5 seconds before being throttled back to the limit, overshooting again for a very short time, then lifting off, and so on. Fine-tuning the closed-loop control is a work of intricate finesse. Imagine, if you will, the momentum of a 5.3 tonne race truck at 160 km/h – we’re speaking here of adjusting the speed by down to one tenth of one km/h.
Pre-race calibration of present devices does not, however, account for any exceptional changes in tyre pressure over the course of a race.
Free practice is when teams calibrate their speed limiters for the circuit and prevailing or anticipated conditions. Should a truck face headwinds in FP but be helped along by tailwinds during the race, it falls to the pilot to recalibrate the speed tolerance on the fly. If he dials it down a fraction too much, he puts himself at an immediate disadvantage to his competitors; if he doesn’t reduce the speed enough, he just as quickly invites an overspeed penalty or, in the extreme case, exclusion from the final classification.