I tested drafting 18 wheelers during my road trip (see post “ 8,000 mile roadtrip results”). I’ll walk through my process, key learnings and results.
My configuration: M3, LR, Aero wheels
My drafting process:
1) Drive in the slow lane to wait for the correct type of truck(big square 18 wheeler, good mud flaps on back wheels, driving 5 mph above the speed limit)
2) After truck passes you, pull in behind the truck, increase your speed 3 to 5 MPH above the speed of the truck(this ensures you will maintain the correct distance with the truck)
3) Set the “car follow length” between 1 to 3 car lengths
4) When the truck starts to pass a slower vehicle, slow your speed to match the drafting truck
5) Pass the slower vehicle but leave enough of a gap so you can slide in between the drafting truck and the slower vehicle
1) Don’t bother trying on busy highways because too much interaction is required
2) Attempted drafting in moderate rain but it didn’t save any Wh/mi.
3) Sometimes the truck you are drafting will have a hard time getting into the fast lane in order to pass a slow vehicle. Use your nimble Model 3 to quickly pull out into the fast lane, slow down and flash your lights to let the drafting truck to get into the fast lane. I was able to stay with one truck for over 30 minutes by using this tip. This forms a nice symbiotic relationship.
Advantage of drafting:
1) Reduced my Wh/mi by “11” traveling at 73mph over a 30-mile distance. Reduced from 246 Wh/mi without drafting to 235 Wh/mi with drafting. (Similar road, temperature and speed taken into account)
Disadvantage of drafting:
1) Increased risk of rock damage from drafting truck (ironically, I got a small windshield crack not when I was drafting).
2) Safety issue driving close to truck at high speeds. I have noticed that the Model 3 increases its following distance the faster you are going.