Drafting Impact on Efficiency?

[Greg29]

On a recent road trip I decided to see the impact of "drafting" on my efficiency in order to skip a SuC. I found a truck going between 70 and 75 mph and followed it for about 50 miles using the closest (setting 1) following distance for TACC. Non-scientific for sure but I estimated a 20% to 25% or so improvement in efficiency during my study.
A police officer friend says there is no way TACC can follow closely enough to benefit from draft. That I needed to be closer than TACC would allow. I'm frankly not willing to follow any closer than that at those speeds.
What do the scientists on this forum say? Is there a rule of thumb following distance to benefit from drafting based on size of vehicle being followed?

 

[DirtyT3sla]

Here's an "as scientific as it gets" study from myth busters. You can probably find the video on youtube. It was a huge savings.

 

[Greg29]

Here's an "as scientific as it gets" study from myth busters. You can probably find the video on youtube. It was a huge savings.

Very helpful, thanks. If I had to guess I would say TACC 1 setting is about a 1 second following distance or about 100 feet at 70mph. Sound about right?

 

[KArnold]

I had a similar experience for about 60 miles. Simply anecdotal as I didn't write down specifics at the time but I remember arriving at the scheduled SC with 11% more SOC than I had planned. And I'm historically pretty good at getting a close "arrival SOC" plan with ABRP tuned to my car/conditions.

 

[brkaus]

Remember part of the savings in many cases is the slowing down part.

I have set at 4 behind trucks when I was low and felt it helped. No measure though.

 

[maximizese]

Unfortunately for my friend who drove his Bolt from southern California to Sedona, Az last weekend, he came across one of the biggest fears for EV drivers...no fast-charging available at a crucial stop. He called from Blythe after the Chargepoint DC charger was offline. I saw on the Plug Share app that EV Connect had a DC fast-charger about 1.5 miles away...that charging station wasn't working either. He had to drive back to the Chargepoint location and level 2 charge for almost 6 hours to make it to the next available EVSE. ABRP told him to charge to 81% SOC and to not exceed 76mph. He was bored out of his mind and asked me if he should leave at 78% SOC.

I told him to study his energy graph and to not exceed 76mph AND to draft behind a big box truck when he could. I told him he didn't have to ride the bumper or tailgate and that even following 5-8 car lengths would help reduce the air turbulence. At the halfway mark, he told him he had about a 14% buffer and he was amazed at how much of a difference going 65-70mph behind a truck made on his range. It was his 4th roadtrip over 3 years and he's thinking of waiting a few years before attempting another one...next time I'll loan him our Tesla.

 

[Rockster]

The Mythbusters chart seems accurate. I noticed a benefit from following an 18-wheeler on the farthest TACC setting on my Model S.

 

[Babaron]

I draft all the time and I can tell you from experience that it definitely has a noticeable positive impact on efficiency.

As mentioned, slowing down even a little also has a considerable impact.

NOTE: If not already installed, you should strongly consider paint protection film if you plan to draft a lot.

 

[SSedan]

Drafting definitely helps and you do not need to be dangerously close.

I can only guess anyone who doubts is either always in heavy traffic or is a fast driver in an unpopulated area and always out front.

It doesn't have to be a semi either, a minivan or SUV work pretty well too.

 

[Snerruc]

You can get a drafting benefit from vehicles other than a large truck. You will benefit from a pickup pulling an enclosed trailer, or even a large suv. Being in a train of vehicles also helps.

 

[JustADude]

I got about 130wh/km in my 2015 S driving at around 95kmh while drafting on AP setting 1

 

[tomauto15]

If you don't care about rock chips, by all means, get right up on that butt of the car in front. Be ready for a brake check from the vehicle ahead.

My favorite draft trailers are the liquid carrying trucks. A cylindrical trailer design gives absolutely the cleanest air to follow behind without any of the "buffeting" of a square trailer. It is a very smooth airflow.

https://www.wabashnational.com/imag...nd-sliders---1315x690/walker-1---1315x690.jpg





The downside, of course, is getting a face full of tractor-trailer bumpers. Not all trailer bumpers are built to the same standard...So is it really worth it?

 

[SSedan]

As many of us are saying you don't have to tailgate to see meaningful benefit.