700 mile road trip with R1S Rooftop Tent -- efficiency / range numbers

[Pixelshot]

Not that I'm looking for any attention on the post I made in the "Trip Reports / Journals / Logs", but I posted my experiences with a Thule RTT mounted on the bed of my R1T. It might have some useful info per this discussion.

FWIW. - https://www.rivianforums.com/forum/...trip-indiana-texas-new-mexico-and-back.15699/

Thanks. Sounds like you had similar results (about 1.8 mi/kWh)

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[Pixelshot]

Agree that speed affects efficiency and range, but it's the same whether you're in an ICE or EV. If driving in an ICE SUV (Range Rover, for example) with a roof top tent, your range hit (decrease in mpg in ICE vehicle) would essentially be the same as driving a Rivian with a rooftop tent (assuming cross-sectional areas of both vehicles are generally the same-which they are).

Drag equation doesn't change just because you're in an EV. I can't remember the equation exactly, but the force of drag squares as speed increases... OK, I looked it up. Neglecting minor changes in density of air, Drag= velocity^2/2, assuming the areas of the vehicles are the same (or very similar).
This means that going even a little faster creates a LOT more drag (square of velocity divided by 2) and kills mi/kwh and mpg.
We all hate this law of physics because we want to get where we're going faster! LOL.

Thanks. I've been meaning to TRY and do some math around this but there are so many variables that the margin for error is huge so I'll have to stick with experiential tests. One thing to add is that I find driving the Rivian so comfortable that I don't mind going a bit slower (assuming that we have the extra time).

 

[Pixelshot]

What about having AC on/off. How does that impact the range?

probably some, but not enough to matter for our purposes. Every little thing adds up though.

 

[jjswan33]

Agree that speed affects efficiency and range, but it's the same whether you're in an ICE or EV. If driving in an ICE SUV (Range Rover, for example) with a roof top tent, your range hit (decrease in mpg in ICE vehicle) would essentially be the same as driving a Rivian with a rooftop tent (assuming cross-sectional areas of both vehicles are generally the same-which they are).

Drag equation doesn't change just because you're in an EV. I can't remember the equation exactly, but the force of drag squares as speed increases... OK, I looked it up. Neglecting minor changes in density of air, Drag= velocity^2/2, assuming the areas of the vehicles are the same (or very similar).
This means that going even a little faster creates a LOT more drag (square of velocity divided by 2) and kills mi/kwh and mpg.
We all hate this law of physics because we want to get where we're going faster! LOL.

No disagreement with your statement here but overall what matters is power used to get from point A to point B. So since F is proportional to V^2 as you said at P = F * V this actually means that your power consumption is proportional to V^3. The reduced aero from an RTT will be multiplicative to that.

Since we are talking about aero loss on efficiency I am seeing about 30% loss overall with my setup but that includes two factors. 1. aero loss from the camper I figure is about 15% and 2. aero loss from my Nitto AT tires (vs 21") is another 15%. Of course my camper will be worse than a roof mounted RTT since it also has some aero loss on the sides since it sticks out on either side of the cab a few inches. And yes I see huge differences in efficiency between 65 mph and 75 mph (and wind noise). Overall I have been averaging about 1.6-1.7 mi/kWh. Curious to take a road trips with my 21s this summer so I can isolate just the camper efficiency loss better.

 

[Ash]

Thanks. (can't argue with the channel size thing! - best way to help BTW is to watch, like and comment on the video itself - and share).

I'll bet you won't see much impact on range. Of course there will be some, but with all of the other factors, like hills and wind, you won't be able to single out that small of a difference in aero. would love to know your results! I do know that the thing that will impact the range the most is speed. When we went from 75 to 65 I saw a big jump in efficiency, maybe 20% or more.

I think you're right about not being able to tell. I tried to do some testing for an hour with all the bikes on, but I couldn't get consistent enough speeds at the time to tell. You can see in the photos how much the bikes over the bed stick up in the wind. There's a cost for sure, but I don't think it's worth trying to actually measure it. I'll just assume -20% and plan accordingly.

Thanks again,

Ash

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