MPP's Rivian Towing Journal

Hey everyone,

I'm going to make a little towing journal here to document our current efficiency with different configurations so that we can compare in the future. The goal long term is to modify our 26' Featherlite trailer to be more aerodynamic. CFD suggests a significant reduction in drag, that should equate to around 30% more range.

The eventual changes include a flat floor, rear diffusers, tire covers and a front overhang. The low hanging fruit will be the rear diffusers to start.



We took our Hybrid 350z to the racetrack yesterday, which is ~160km (100mi) away from our shop.

The average efficiency started out around 1.125 mi/kWh but dropped down to around 1.00 mi/kWh later on in the drive. We're guessing that is due to the battery getting warm and the compressor starting to ramp up to cool the battery.

On the drive back we had a similar efficiency - it wasn't super comparable due to differences in traffic.

From a 100% charge, we used 92 kWh to cover the 97 miles. The arrival state of charge was 28%.

The figures for this trip:

• 60psi truck tires (MPP Mega Terra with K03's - not the most efficient setup)
• 80 psi trailer tires
• ~8000lbs trailer + load
• 110km/h average efficiency around 1.01 mi/kWh once the battery was hot - NO DRAFTING!
• No modifications to the trailer

Next week we have a long trip planned to Lime Rock for a race with this 350z as well as our Model 3 Challenge where we'll have 12 Tesla Model 3's all racing together. We're going to be towing down with both the Rivian and the Cybertruck so it will be interesting to compare the efficiency and overall experience across both trucks. Considering the larger battery and faster charging with the Rivian, we expect it to do better.

We're even going to swap trucks half way between chagers as needed to stretch it between V3 Superchargers!

• 

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Thanks for doing this! I have been considering aero mods myself. Let me know if you need any help testing.

What is the efficiency of the truck at those speeds when not towing? That would give a better delta baseline.

About 2.05 mi/kWh

Cool. Signing on for updates.

What software do you use for the modeling? And the models themselves?

Also interested in the simulation software.

Thanks!

Everything is modelled in Solidworks (the same program we use for software design), except for the Rivian itself, which I got from the internet. We use Blender to mesh the solid files (the trailer) with the mesh (the Rivian STL downloaded from the internet).

The CFD software is an online service called AirShaper, which is very powerful at taking poor quality meshes (like a Rivian STL downloaded on the internet!) and converting that into a useable mesh for CFD.

The above simulations are done with a very low quality mesh to save on costs, but even still the differences between the different trailer models were astounding. The drag of the truck and trailer dropped by around 50% with all of the aero modifications.

Run 1 was the truck and trailer in the original configuration:

The red areas are areas of low pressure - in other words pockets of still or turbulent air (drag). We want to get rid of the red clouds!

Frontal Aera 6.445 m2
cd 0.569



Run 2 was with a flat bottom to the trailer:

Frontal Area: 6.446 m2
cd: 0.502 (-12% drag from baseline)



Run 3 was with a flat bottom and rear diffuser panels:

Frontal area: 6.447 m2
cD: 0.409 (-28% drag from baseline)



Run 4 added a smoothed leading edge to the trailer to help smoothly reintroduce flow under the trailer:

Frontal Area: 6.447 m2
cD: 0.388 (-32% drag from baseline)



Run 5 added a complicated "5th Wheel" style nose that hangs over the tailgate and blends airflow from the truck cab into the trailer

Frontal Area: 6.447
cD: 0.303 (-47% drag from baseline)

The runs were done in order of how hard it would be to physically make the upgrades to the trailer - and it seems the rear diffuser panels are the easiest to do and yield a strong result.

As you can notice, each change helps a little bit, and it's all fairly intuitive stuff. I'm sure making further improvements from here on out would be much more difficult.

Now before you might ask "it would be interesting to see X" or "do a run with X configuration" please keep in mind that each run costs money and this was more to get an idea of the rough scale of the improvements that can be made - the tests above were done at low resolution, the truck scan quality is low - among other things - so none of this is super precise!