Growing efficiency Gap: R2 w/ 21" vs. 20" tire sets

[kurtlikevonnegut]

My commute to work is 30 miles and it's almost evenly split between surface roads and freeway. Going 75 for the freeway stretch I got about 2.9 mi/k. Going 70 on the freeway today it was 3.3.

Speed seems to make an even bigger difference on R2 than it did on R1 when it comes to efficiency. In both R1 that I had, 5mph typically resulted in .1 mi/k difference.

*this is on brand new 20s, so assume some reduced efficiency

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[NCSwa]

I think it would be interesting to know what percentage of time is spent in Sport versus All Purpose. I literally keep my R2 in sport like 80% of the time, and only use all purpose if I actually am road tripping (have a condo in the mountains 110 miles from home) it has been on like 3 trips up there and no charging at all - expect once when we did a few day trips while at the condo. The fact that I use Sport all the time is a major upgrade over the R1T I am coming from. I only had a Dual Motor performance so to really get the juice you needed to put in into Sport, but IMO in the softest setting, it just felt way to firm and clunky actually. That is something I Love about the R2, sport is actually a fine daily driver around town.

 

[NCSwa]

I also have lifetime of average of 2.67 mi/kwh and that was after a miserable number from the factory. It was stuck on like .67 for the first 3 weeks. It only had like 18 miles I think at delivery, but took forever to get the numbers up. I would bet I am closer to like 2.90 or so and I have the 21’s and use Sport a bunch. Almost 2k miles

 

[Thebandit]

It is closing actually. It was 0.18 at the beginning of the thread and now it's 0.14.

Down to 0.1 now.

 

[Eric9610]

I drive mine in AP mode all the time.

 

[ksurfier]

So far, the R2 data tell a consistent story: EPA testing predicts the 21-inch setup should be significantly more efficient than the 20-inch, especially at highway speeds, but real-world testing has not shown that advantage. Long-range highway tests have the two setups very close, with the 20s slightly ahead in some cases. Rivian Roamer data also currently favor the 20s, averaging 2.73 mi/kWh versus 2.64 mi/kWh for the 21s, about a 3.4% advantage. While the Roamer data are not controlled for speed, weather, elevation, or driving style, they point in the same direction as the highway tests and opposite the EPA results.

• Late July to early August 2026; 20” highway tests: approximately 259+ miles near 70 mph; roughly 2% to 3% more range than the 21” benchmark, although conditions differed.
• Early August 2026; 21” Out of Spec test: approximately 253 miles at ~70 mph, or about 2.83 mi/kWh.
• August 5 onward; Rivian Roamer: 82 R2s and 52,175 miles; 20” BFGs average 2.73 mi/kWh versus 2.64 for the 21” Pirellis; 20s are 3.4% better.
• EPA expectation: approximately 7.9% highway advantage for the 21s; real-world evidence currently suggests roughly 0% to 3% in favor of the 20s.
• Takeaway: A controlled same-vehicle 20” vs. 21” test is still needed for a definitive conclusion. However, both highway testing and the larger owner dataset suggest the EPA methodology may substantially overstate the real-world efficiency advantage of the 21” package.

 

[tonyg777]

My thoughts are that the 20" A/T design they went with is not as aggressive as some of them on the market. We may be witnessing (actual results instead of the EPA results) that the inefficiencies of the tire they chose is being offset by the smaller wheel size.

Just FYI This is what Gemini has to say about this:

General Principle: Smaller Wheels vs. Larger Wheels
In general automotive physics, downsizing your wheel diameter (e.g., going from 21" to 20" or 19") yields better efficiency ($\text{mi/kWh}$) and longer range. On average, moving down a wheel size improves range by roughly 3% to 7%, though extreme differences (such as moving from a 21" sports setup to an 18" aero setup) can yield improvements as high as 10% to 20%.
The general engineering reasons smaller wheels tend to perform better include:

• Rotational Mass & Unsprung Weight: Metal alloys are denser and heavier than rubber. A larger rim puts more heavy metal further away from the hub axle, requiring more energy to rotate during acceleration.
• Aerodynamics: Larger wheel designs typically feature open spokes for brake cooling, creating turbulent drag at highway speeds. Smaller wheels usually feature flatter, more enclosed "aero" profiles.
• Tire Tread & Compound: Larger factory options (like 21" or 22" rims) are frequently wrapped in wider, stickier summer/performance tires that increase rolling resistance. Smaller options are more often paired with low-rolling-resistance all-season tires.

Important Exceptions to Keep in Mind
While smaller wheels usually mean better efficiency, going down in wheel size does not automatically guarantee higher $\text{mi/kWh}$. The actual result depends heavily on the specific tire mounted to that wheel:
1. All-Terrain vs. Highway Tread
If moving to a smaller wheel (e.g., 20") is done to fit aggressive All-Terrain (A/T) or off-road tires with heavy tread blocks, rolling resistance and aerodynamic drag will increase. In these cases, a smaller 20" wheel with A/T tires can actually be less efficient than a larger 21" wheel wrapped in smooth street/touring rubber.
2. Overall Tire Diameter
Vehicle range is dictated by the outer tire diameter, not the metal wheel size alone. If a 20" wheel setup maintains the exact same outer rolling circumference as a 21" setup using a taller sidewall, the engine gear ratios and speedometer remain identical, allowing the weight and aerodynamic savings to shine through.
Summary Comparison

Factor	Smaller Wheel (e.g., 20")	Larger Wheel (e.g., 21"+)	Impact on Efficiency
Wheel Mass	Lighter overall rotational mass	Heavier wheel structure	Smaller Wins
Aerodynamics	Flatter face / less air turbulence	Open spoke design creates drag	Smaller Wins
Typical Tire	Standard / Low-Rolling-Resistance	Sticky / Wide Performance Rubber	Smaller Wins (unless switching to A/T)
Ride Comfort	Taller sidewall cushions bumps	Shorter sidewall, stiffer ride	Smaller Wins (for comfort)

 

[Captblue]

If that’s the case why wouldn’t they use a 20” efficient road tire?

 

[Dennisis]

If that’s the case why wouldn’t they use a 20” efficient road tire?

So they offer a semi-off-road tire option to go with the adventure theme I imagine.

 

[SuperFeisty]

Why is everyone focused so much on wheel size affecting range vs. evaluating rolling resistance of tires? Is there anyone who switched out their 20' tires to a more efficient tire to see how much more range they get?

 

[dscoti]

To me, efficiency and range really only matters when road-tripping long distances, and then, about

I care about it, I watch it, but I do not obsess about it. I simply deal with it. My regular trips from Las Vegas to SoCal, I won’t bother with it. To see my daughter North of Pittsburgh, PA? I’ll plan the heck out of it, then roll with the punches.

On the other side of that coin, I know most do obsess over it. So they can be themselves, I’ll be myself.

 

[DaveA]

I am consistently at 3.30+ mile/kWh cruising at 70 mph on the highway with 21s. .

 

[richpike]

To me, efficiency and range really only matters when road-tripping long distances, and then, about

I care about it, I watch it, but I do not obsess about it. I simply deal with it. My regular trips from Las Vegas to SoCal, I won’t bother with it. To see my daughter North of Pittsburgh, PA? I’ll plan the heck out of it, then roll with the punches.

On the other side of that coin, I know most do obsess over it. So they can be themselves, I’ll be myself.

I totally agree with this - range doesn't matter much to me. But I do love data and that's why I find this so intriguing. Either way, I'd have bought (and did buy as of yesterday!) the 20s - I like the looks more, like the greater tire options, etc. But I still love seeing this data and find it super interesting.

-Rich

 

[dogwhisle]

I’m glad this thread and data exist. I like the look and slightly softer ride of the 20s, but had planned to order the 21s for road tripping efficiency. I’m going to put my order in for the 20s now, and feel much better about it! Maybe switch to more on-road oriented rubber once these wear out. I’m sure there will be great data on those options by then! Thanks guys.

 

[dscoti]

Agreed! The multiple threads and data are great to have. I’m to the point where I have to just ignore them as they all tend to repeat. The same happens on the Kia and Hyundai EV forums.

When I’m lucky enough to get ours, I’ll add my 2¢ worth after a few trips to SoCal. I’ll probably add our R2 to the mix in rivianroamer. Thanks, Chad, for creating, hosting and maintaining this service.

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