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

[tivoboy]

Received my notification to order this morning. I had a Sept/Oct window. Ordered the 20" wheels based on the discussion and evidence in this thread. Thanks, folks. Hope the data dump tomorrow doesn't throw all of the prior analyses into question.

The data dump tomorrow will probably show that the 21” are 8-10% more efficient.




;-0

Sponsored

 

[ksurfier]

Received my notification to order this morning. I had a Sept/Oct window. Ordered the 20" wheels based on the discussion and evidence in this thread. Thanks, folks. Hope the data dump tomorrow doesn't throw all of the prior analyses into question.

There’s no meaningful difference in efficiency between the 20” and 21” options, certainly not enough to matter. For example, even if there’s a 10% advantage on the 21” tires at 70 mph, that’s only going to add around 20 miles of range. If driving/using 70% (80 to 10), 20” would get ~180 miles and 21” ~190 miles…EPA and rumors call it ~7% better, so prob. less than a 10 mile range penalty for having 20” instead of 21”, seems like a very easy call to me…

 

[dfairris]

Thanks. I see your point, but please be mindful that yesterday you promised me roughly 2% difference, if any at all. I'm holding you to that. (-:

 

[ksurfier]

Thanks. I see your point, but please be mindful that yesterday you promised me roughly 2% difference, if any at all. I'm holding you to that. (-:

You have much bigger things to worry about (and also benefit from).
Assuming you typically drive at ~6,500' elevation, you will likely see a nice 0.3-0.4 increase in efficiency (maybe 3.2, on average ~12% or so). Your cold weather penalty will likely put you in ~2.5 MPK range...all that said your average will still likely fall into several percent of the mean.

 

[dfairris]

Thanks. Assuming mpk is on the vertical axis. What's on the horizontal? And which tire is black and which is red?

 

[iamnid]

How is it more available exactly? There's only 1 choice for for 20" or 21" since you're not going to replace a single busted 20" tire with something other than what Rivian puts on and have 1 tire different than the other 3.

I have more than twice now, with my past two vehicles, ended up with an unpatchable flat. Since the other three were a few years old at that point, I just replaced all four tires while I was at it, rather than replacing just the one or two (on same axle). Nice to have multiple options.

 

[NCBob]

While anecdotal, it appears that the R2 with 20" wheels may in fact be slightly more efficient that the 21" setup. Some say that it's just the 21" crowd is driving faster, which might be true, interesting none-the-less:

As reported here: Rivian Tires: Compare & Review for R1T, R1S & R2

Tire	Miles	Vehicles	MpV	MPK	Range
20"	9184	12	765	2.74	241
21"	5579	11	507	2.53	223

Update 3, August 19: Will the 21" R2 Catch Up with the 20"?

Tire	Miles	Vehicles	MpV	MPK	Range
20"	36820	49	751	2.77	244
21"	30482	49	622	2.70	238

A month into this little tire science experiment, the good news is that the picture is getting clearer. The bad news is that our famous “70 mph” test was apparently a 66 mph test wearing a 70 mph nametag.

The RivianTracker/Out of Spec run took 3 hr 51 min, which works out to about 65.7 mph. Its 2.80 mi/kWh result actually fits the developing speed curve very well and points to roughly 250 to 260 miles at 65 to 66 mph and around 235 to 245 miles at a true 70 mph.

That mostly settles the bigger range question. The R2 appears capable of roughly 240 to 250 miles of real highway range, with normal interstate charging legs more like 210 to 225 miles. July’s 256 mile runs look more like deliberate range demonstrations, while August owner data around 200 to 225 miles probably better represents how people will actually road trip.

Which brings us back to the increasingly silly tire mystery.

EPA certification says the 21s should be roughly 7 to 8% more efficient on the highway. So far, the real world has stubbornly declined to cooperate. Roamer still has the 20s slightly ahead overall, although those averages mix speed, elevation, weather, HVAC, trip length, driving style, tire mileage and probably the phase of the moon.

That does not prove the 20s are inherently more efficient. But we also haven't seen convincing evidence yet that the 21s are actually 7 to 8% better at freeway speeds.

At this point I think the realistic question has narrowed considerably: Are the 21s actually 2 to 3% better, maybe 5%, or will they eventually reveal the full EPA predicted 7 to 8% advantage?

If speed matched data eventually show the 21s winning by several percent, great. I'll update the conclusion. If more real world testing keeps putting the two packages surprisingly close together, that gets harder to explain away too.

Either way, more comparable highway runs with actual average speed, tire mileage and conditions will tell us far more than another fleet average or another “70 mph” test conducted at 65.

Update 2, August 17:
A month into R2 testing, the efficiency debate has narrowed considerably. My first test drive was around July 16, when the main question was simply how much real-world highway range the R2 loses relative to EPA estimates. Subsequent testing established a fairly consistent speed curve, with efficiency around 3.0+ mi/kWh near 60–65 mph, ~2.7 near 70 mph, and roughly 2.3 or less approaching 80 mph.

The discussion then shifted to 20-inch vs. 21-inch wheels. EPA data suggest the 21s should have roughly a 7–8% highway efficiency advantage, but the real-world tests collected so far have generally shown the two much closer than that, with some 20-inch results slightly better. The larger Rivian Roamer dataset has also not shown an obvious 21-inch advantage in its raw averages, although those data contain major uncontrolled variables.

Where things stand now: the key question is no longer whether speed matters; it clearly does. The remaining question is whether, after controlling for speed, elevation, trip length, weather, and other variables, the 21s actually deliver the ~7% freeway advantage suggested by EPA testing, or whether the real-world difference is materially smaller.

Update 1: The latest Rivian Roamer data now cover 82 R2s and more than 52,000 miles, with the 20” BFGoodrich Trail-Terrain setup averaging 2.73 mi/kWh versus 2.64 mi/kWh for the 21” Pirelli Scorpion MS, a 3.4% real-world efficiency advantage for the 20s; that is notable because it runs opposite to the EPA data, which imply roughly an 8% highway advantage for the 21s and an even larger advantage at sustained 70–80 mph based on the road-load coefficients. The gap has narrowed from the earlier smaller-sample data, which suggests some early noise is averaging out, but the 20” result has remained remarkably stable around 2.73 mi/kWh as the mileage has increased. Because the Roamer data are not controlled for speed, weather, elevation, HVAC use, or driving style, they cannot prove the 20” setup is inherently more efficient, but combined with the individual highway tests showing little or no clear 21” advantage, they increasingly suggest that the EPA/coastdown testing may overstate the real-world efficiency benefit of the 21” wheel/tire package, potentially because real-world wheel aerodynamics, turbulence, and yaw effects are not fully represented by the certification road-load model.

	R2 >130 mi (6 trips)	Out of Spec R2	Out of Spec R1S Dual Max
Distance	139 mi avg	253 mi	359 mi
Time	~2h 18m	3h 51m	5h 25m
Implied avg speed	61.2 mph	65.7 mph	66.3 mph
Efficiency	2.60	2.77	2.51
Energy used	53.7 kWh	91.4 kWh	143.0 kWh

Does anybody have any sense of the difference in road noise between the A/T and the A/S on the R2? I've got a gen 1 R1T with A/T tires and I get a LOT of road noise. When my number comes up on the R2 waitlist a difference in road noise will probably be the deciding factor for me when it comes to wheels.

 

[mkhuffman]

Received my notification to order this morning. I had a Sept/Oct window. Ordered the 20" wheels based on the discussion and evidence in this thread. Thanks, folks. Hope the data dump tomorrow doesn't throw all of the prior analyses into question.

"Data dump" with the usual AI slop. I am sorry you chose the 20s based on this bogus thread - if you care about range, that is.

The 20s are probably better for those going off road, or for those who like the appearance and don't care about range.

But if you think you are smarter than Rivian and can actually do something they couldn't do during their own testing, then the AI slop has won. So sad.

 

[dfairris]

I may be making a mistake, and so may come to regret it. But, I didn't have a sense at all that the numbers were AI generated. The data come from real-world observations, no? Now, there may be good reasons to discount them -- biased observation, spurious correlation, etc. -- but still real-world observations. Am I missing something?

 

[ksurfier]

I may be making a mistake, and so may come to regret it. But, I didn't have a sense at all that the numbers were AI generated. The data come from real-world observations, no? Now, there may be good reasons to discount them -- biased observation, spurious correlation, etc. -- but still real-world observations. Am I missing something?

Check out the data on RivianRoamer.com:
20” still leads the 21” by ~2% with more than 100,000 miles logged:

 

[r2fb]

I have more than twice now, with my past two vehicles, ended up with an unpatchable flat. Since the other three were a few years old at that point, I just replaced all four tires while I was at it, rather than replacing just the one or two (on same axle). Nice to have multiple options.

You will also have more options when the 21's are a few years old. Or you can spend $1.2k on some lightweight Enkeis and then get tires for them.

 

[ksurfier]

Thanks. I see your point, but please be mindful that yesterday you promised me roughly 2% difference, if any at all. I'm holding you to that. (-:

It’s miles (approx) for each tire group…

GOATEE

 

[dogwhisle]

I propose that part of the reason the 21s are underperforming is that Rivian did not actually run the certification tests on this setup. The EPA does not require every wheel/tire combination be certified separately. I bet they ran the numbers on the Premium standard setup on the more aero-wheel 20s with Pirellis they intend to be their mass-market seller (same 330 range). I’m sure this setup will prove to be more efficient than the 21s. Then they just applied this same rating to the 21s on the Pirellis with the donked-out high-drag wheels and called it a day. The Premium on 20s could be a pleasant surprise.

 

[VandalSibs]

It’s miles (approx) for each tire group…

GOATEE

I initially understood your quest for data to see about efficiency on this whole subject. Data is fun! But you then started posting new threads whenever you wanted to make a new point instead of continuing in your first one.

Then today comes the whole "GOAT" thread and imagery that you decided to bestow on yourself, which you don't seem to be giving up on after that thread was locked.

Maybe take a step back and look at how ridiculous you appear to the other users of this forum...

 

[VandalSibs]

I propose that part of the reason the 21s are underperforming is that Rivian did not actually run the certification tests on this setup. The EPA does not require every wheel/tire combination be certified separately. I bet they ran the numbers on the Premium standard setup on the more aero-wheel 20s with Pirellis they intend to be their mass-market seller (same 330 range). I’m sure this setup will prove to be more efficient than the 21s. Then they just applied this same rating to the 21s on the Pirellis with the donked-out high-drag wheels and called it a day. The Premium on 20s could be a pleasant surprise.

There was a thread when the EPA certification was first found that showed testing done on both the 20" and 21" wheels:

https://rivianforums.com/forum/thre...-capacity-charging-rate-efficiency-etc.57814/

Sponsored