ksurfier
Well-Known Member
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Points to 2.6 MPK for the R2 w/ 20” wheels at 70 mph:
- The most useful direct observation is the R2’s 2.5–2.6 mi/kWh interstate efficiency at approximately 78 mph on 20-inch all-terrain tires. The overall 2.8 mi/kWh result included substantial lower-speed driving and should not be treated as the vehicle’s highway efficiency.
- The interstate segment had a 5–10 mph tail/crosswind, meaning the R2’s effective aerodynamic airspeed was closer to roughly 68–73 mph for at least part of the drive. Accordingly, the observed 2.5–2.6 mi/kWh is a reasonable real-world proxy for approximately 70 mph in still air.
- The trip included a net elevation gain of approximately 500 feet over 131 miles and rolling hills. This created a modest efficiency penalty, although it was too small to fully explain or materially invalidate the highway result.
- The vehicle was equipped with brand-new 20-inch A/T tires with only 45 miles on them. Several commenters noted that new tires can improve somewhat after a few hundred to approximately 1,000 miles of break-in, so the test may modestly understate mature-tire efficiency.
- The R2 was operated in All-Purpose mode, not a dedicated efficiency or Conserve mode. This supports treating 2.6 mi/kWh as a normal-use estimate rather than a best-case maximum.
- Multiple commenters correctly identified 78 mph as the dominant reason for the relatively low highway efficiency. Because aerodynamic energy consumption rises rapidly with speed, a reduction from 78 mph to 70 mph should produce a meaningful efficiency improvement, but the tailwind already provided much of that aerodynamic benefit during this particular trip.
- A commenter suggested the R2 might exceed 3.0 mi/kWh at 70 mph, based partly on a reported 60–80-mile difference between 70 and 80 mph in an R1S. That is directionally useful, but it is not a direct R2 measurement and likely represents an optimistic upper bound rather than the best central estimate.
- The displayed Rivian efficiency value may itself have some uncertainty. One R1 owner reported that the displayed mi/kWh sometimes differed materially from energy-use calculations, so a controlled test using measured battery energy would be preferable.
- Taken together, the available evidence supports a 70 mph, 70°F efficiency estimate of approximately 2.55–2.65 mi/kWh for the R2 on 20-inch A/T tires, with 2.60 mi/kWh as the best working value.
- Assuming the 21-inch road-oriented setup is 5% more efficient, its corresponding estimate is:
- 20-inch A/T: 2.60 mi/kWh
- 21-inch: 2.73 mi/kWh
- A reasonable uncertainty range is approximately:
- 20-inch A/T: 2.55–2.65 mi/kWh
- 21-inch: 2.68–2.78 mi/kWh
- The clearest current conclusion is therefore: At 70 mph and 70°F, expect approximately 2.6 mi/kWh on 20-inch A/T tires and approximately 2.7–2.75 mi/kWh on 21-inch wheels.
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