How Much Does Speed Impact Range? Testing Rivian R1T at 60MPH, 70MPH and 80MPH

[branden]

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[Donald Stanfield]

I wonder if these percentages hold true with the road tires as well. Like maybe the gap is even closer with more efficient tires.

 

[branden]

I wonder if these percentages hold true with the road tires as well. Like maybe the gap is even closer with more efficient tires.

Probably pretty close. This test is more about aero than anything else.

 

[moosehead]

 

[Bborden]

Hey! Were you in the Millbridge community in Waxhaw a few days ago? I saw a RB R1T in the neighborhood and it made me sad b/c I’m still waiting for mine but happy to see one around

 

[Wentworth]

Fun video to watch, thanks for sharing and driving all of those miles. I’m sure this has been posted elsewhere, but for those that haven’t learned this yet, the drag the motors have to overcome is affected by 1/2 the square of the airspeed of the vehicle. In still air the number that goes into the equation at 60 mph is 1800. At 80 mph the number would be 3200. You can see the equation here: https://www.grc.nasa.gov/www/k-12/rocket/drageq.html

 

[Redmond Chad]

Thanks for the real-world info! So, compared to 60mph, the R1T loses 15% at 70mph, and 24% at 80mph.

The numbers are pretty close to what I'd expect from experience with past EVs. In 2010 I made this chart on Tesla Roadster range-versus-speed (with HVAC thrown in). It shows that the Roadster lost 18% at 70mph and 30% at 80mph. It probably (?) lost a higher percentage to aero than the R1T because it was more efficient to start with.

(The top, dark-green line is expected range at the given speed with no HVAC. The shaded area below it shows how much range can be reduced at that speed given various levels of HVAC - the HVAC's relative effect grows smaller at higher speeds as the aero hit grows and the time spent running HVAC shrinks. Note that the Roadster had a resistive heater and an option to take the top off - so it could use a lot of HVAC energy).

In 2012 I did something similar for the Tesla Model S. It lost 15% at 70mph and 27% at 80mph.

 

[Ladiver]

So, my takeaway is drive faster and get to the next charger sooner! It will take less time to add the kWh lost due to speed than what it will take to get to the charger with less kWh used. Plus you charge faster at a lower SoC.

this is all thrown out the window if the next charger is 300 miles away.

 

[DJG]

So, my takeaway is drive faster and get to the next charger sooner! It will take less time to add the kWh lost due to speed than what it will take to get to the charger with less kWh used. Plus you charge faster at a lower SoC.

this is all thrown out the window if the next charger is 300 miles away.

Yep. This is a helpful reminder when planning trips where you have 250 mi between chargers and you wring your hands about whether you can make it or not. Just account/plan for slower speed and you can just about always make it. Also, a lot of more remote driving will be at lower speed limits anyway. Add in drafting behind a truck and I think you can squeeze out 375+ going 60. There's a big difference just driving on a congested freeway vs. all alone (going same speed in both).

 

[zefram47]

So another way to look at this is 16 min faster to travel the same distance at 80 mph and 7.8 kWh difference. Real-world, you'll take on 7.8 kWh in a shade over 3 minutes at 150 kW. So unless you're really range-constrained on a particular route, you'll still save time by traveling faster. Thanks for doing this, @branden!

 

[branden]

Hey! Were you in the Millbridge community in Waxhaw a few days ago? I saw a RB R1T in the neighborhood and it made me sad b/c I’m still waiting for mine but happy to see one around

Must’ve been someone else

 

[branden]

So another way to look at this is 16 min faster to travel the same distance at 80 mph and 7.8 kWh difference. Real-world, you'll take on 7.8 kWh in a shade over 3 minutes at 150 kW. So unless you're really range-constrained on a particular route, you'll still save time by traveling faster. Thanks for doing this, @branden!

I actually added charging and total trip time to the spreadsheet I have linked in the pinned comment of the video

 

[kylealden]

So another way to look at this is 16 min faster to travel the same distance at 80 mph and 7.8 kWh difference. Real-world, you'll take on 7.8 kWh in a shade over 3 minutes at 150 kW. So unless you're really range-constrained on a particular route, you'll still save time by traveling faster. Thanks for doing this, @branden!

Yep. My general rule of thumb is "never sacrifice driving experience to gain marginal efficiency..." - whether that's Conserve mode (sacrificing ride quality/power/tire wear), slowing down (sacrificing timeliness), etc... "...unless it's necessary to comfortably reach your destination" (e.g. if chargers are too widely spaced to keep a comfortable buffer without mitigations.)

You'll almost always be better off (in terms of time and comfort) just charging a few extra minutes than scraping and saving to preserve a few kWh en-route. Naturally this gets more complex with towing, extreme weather, or extended off-road, but I think the rule above still holds.

From my experience with Tesla, my minimum "comfortable buffer" was around 25-30% (assuming a full-range run), since my Tesla range could easily vary by that much. As I get to know the Rivian I'm much closer to 15-20%, and only that high because I want to keep above 10% for battery health unless necessary.

 

[Yossarian]

Fun video to watch, thanks for sharing and driving all of those miles. I’m sure this has been posted elsewhere, but for those that haven’t learned this yet, the drag the motors have to overcome is affected by 1/2 the square of the airspeed of the vehicle. In still air the number that goes into the equation at 60 mph is 1800. At 80 mph the number would be 3200. You can see the equation here: https://www.grc.nasa.gov/www/k-12/rocket/drageq.html

Don't want to hijack the thread, but have a couple of questions regarding this calculation. In the referenced equation, is variable A the frontal area? If yes, if you were towing, could you include the incremental frontal area of the trailer to get the drag number for the vehicle and trailer combo?

 

[branden]

Yep. My general rule of thumb is "never sacrifice driving experience to gain marginal efficiency..." - whether that's Conserve mode (sacrificing ride quality/power/tire wear), slowing down (sacrificing timeliness), etc... "...unless it's necessary to comfortably reach your destination" (e.g. if chargers are too widely spaced to keep a comfortable buffer without mitigations.)

You'll almost always be better off (in terms of time and comfort) just charging a few extra minutes than scraping and saving to preserve a few kWh en-route. Naturally this gets more complex with towing, extreme weather, or extended off-road, but I think the rule above still holds.

From my experience with Tesla, my minimum "comfortable buffer" was around 25-30% (assuming a full-range run), since my Tesla range could easily vary by that much. As I get to know the Rivian I'm much closer to 15-20%, and only that high because I want to keep above 10% for battery health unless necessary.

I agree with that philosophy - on stretches that I may need range, I’ll run in conserve for the efficiency gain (I need to test to see how much of a difference it actually makes!) but set the height to standard to not sacrifice ride quality. Not really missing much by having less power while driving on the interstate.

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