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

[richpike]

Interestingly, both OEM tires are about 36 lb, while the complete 21” assembly is about 62 lb vs. 64 lb for the 20”. That puts the wheels themselves at roughly 26 lb for the 21” and 28 lb for the 20”.

That weight difference is pretty marginal—only about 2 lb per corner, or roughly a 1% effective difference at the vehicle level. In other words, wheel/tire mass is unlikely to explain much of the observed efficiency gap.

So if the 20s are really showing a few-percent advantage, the other variables are almost certainly dominating the apparent difference: temperature, wind, elevation/altitude, average speed, acceleration habits, traffic, route mix, HVAC use, tire pressure, and driving style, among others. That’s why I’d be cautious about calling the current 3–5% gap statistically significant without the individual trip/vehicle data.

But it's more than a 3-5% gap. The 21s should be 7.5% better. They're currently 5% worse. I get what everyone is saying, but this is actually a pretty valid statistical sample (which I'm not a statitician, I am an electrical engineer with a masters in finance - so a fair amount of stats background). Could it change? Pretty much guarantee it will. Will the 21s end up 7.5% better? I think that is HIGHLY unlikely short of a major change (again - Rivian determines Pirelli shipped with the wrong compound, etc).

-Rich

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[DaveA]

I’m doing my part…but not on Rivian Roamer.

 

[ksurfier]

But it's more than a 3-5% gap. The 21s should be 7.5% better. They're currently 5% worse. I get what everyone is saying, but this is actually a pretty valid statistical sample (which I'm not a statitician, I am an electrical engineer with a masters in finance - so a fair amount of stats background). Could it change? Pretty much guarantee it will. Will the 21s end up 7.5% better? I think that is HIGHLY unlikely short of a major change (again - Rivian determines Pirelli shipped with the wrong compound, etc).

-Rich

It’s a little surprising that Rivian continues to ship vehicles on Pirelli tires…at least Goodyear and BFG are now options. I believe the 20” are effectively the same efficiency as 21”, or essentially not statistically relevant difference. More range testing could help…

 

[richpike]

It’s a little surprising that Rivian continues to ship vehicles on Pirelli tires…at least Goodyear and BFG are now options. I believe the 20” are effectively the same efficiency as 21”, or essentially not statistically relevant difference. More range testing could help…

Agreed on all points. Especially the crappy Pirelli tires - genuinely would not be shocked if this ends up being a Pirelli tire issue.

-Rich

 

[jrmbadger]

Had this entire discussion on twitter too - the 20" ATs continue to keep a noticeable gap on the 21s:

At this point, IMHO, there is enough mileage and cars to reduce the impact of variation from location, speed, etc. I don't see the 21s getting to the delta they should have over the 20s (they should be 7% more efficient, not 5% less like it's showing now). Perhaps there is something wrong with that first batch of 21s Rivian got (e.g. wrong compound)?

-Rich

I don't know if its just me, but I was hoping efficiency would be closer to 3 mi/kwhr - maybe 2.8-2.9.

Given the size of the battery(88kwh as I understand it) that means that on 20" tires you are looking at 240 miles of average real world range and on the 21" tires, you are looking at 227.92 miles of average range, in summer, on a brand new battery with essentially 0% degradation. Granted, some of the data may include short trips - which brings down the mi/kwhr (it takes me about 10 miles before the mi/kwhr stabilizes), but still.

A little disappointing.

 

[windshieldfarmer]

I don't know if its just me, but I was hoping efficiency would be closer to 3 mi/kwhr - maybe 2.8-2.9.

Given the size of the battery(88kwh as I understand it) that means that on 20" tires you are looking at 240 miles of average real world range and on the 21" tires, you are looking at 227.92 miles of average range, in summer, on a brand new battery with essentially 0% degradation. Granted, some of the data may include short trips - which brings down the mi/kwhr (it takes me about 10 miles before the mi/kwhr stabilizes), but still.

A little disappointing.

For perspective, I am 34 months into a 36 month lease with a BMW IX50. After 28,500 miles my lifetime efficiency is 2.8 miles per KWh. Usage is 80% suburban and 20% highway. If my new R2 with the 20” ATs averages 2.7 miles per KWH I’ll be a happy camper!

 

[DJFrerichs]

Waaaaaaay too many variables in this data. How do we know how much of these miles if city vs highway for each tire size? We don't and that easily could swing things one way or another. Everyone's different drive and daily traveling lifestyles could easily swing this one way or another regardles of tire size.

 

[ksurfier]

Waaaaaaay too many variables in this data. How do we know how much of these miles if city vs highway for each tire size? We don't and that easily could swing things one way or another. Everyone's different drive and daily traveling lifestyles could easily swing this one way or another regardles of tire size.

Except for the fact that we have 250+ mile drives that seem to suggest essentially the same efficiency, so this suggests that there isn’t a clear winner 20 vs 21 inch…

 

[DJFrerichs]

negative ghost rider.. Someone going +250 city on 20's in the city will perform better efficiency than someone going +250 miles at highway speeds on 21's. Could easily argus the reverse, thus would not trust these at all until additional data of speed, elevation, head wind, etc. data and related use is applied for appropriate apples to apples comparison.

 

[richpike]

Waaaaaaay too many variables in this data. How do we know how much of these miles if city vs highway for each tire size? We don't and that easily could swing things one way or another. Everyone's different drive and daily traveling lifestyles could easily swing this one way or another regardles of tire size.

Except we already have a lot of samples and each of them have a fair amount of miles, so the outliers start to average out. An example - an R2 with 21s signs up today and adds 1,000 miles at 3.75 mi/kWh avg (a HUGE outlier). The 21s would still be behind the 20s by 3%. And behind where they should be by almost 10%. Again, it most likely will change a small amount (which way - who knows), but there is a fair amount of samples and miles now that any major outliers won't impact it much. It would need a total shift in data (again - eg Rivian figures out that the 21s they've been shipping aren't up to spec) to have something like that happen.

-Rich

 

[DJFrerichs]

Except we already have a lot of samples and each of them have a fair amount of miles, so the outliers start to average out. An example - an R2 with 21s signs up today and adds 1,000 miles at 3.75 mi/kWh avg (a HUGE outlier). The 21s would still be behind the 20s by 3%. And behind where they should be by almost 10%. Again, it most likely will change a small amount (which way - who knows), but there is a fair amount of samples and miles now that any major outliers won't impact it much. It would need a total shift in data (again - eg Rivian figures out that the 21s they've been shipping aren't up to spec) to have something like that happen.

-Rich

The only way you can truly prove is to do a same day test between two R2's with different rims/tires sizes on the same roads driving the same speeds and terrain from 100% to 0% to compare results at the end. THAT is when you will be able to confirm Rivian's posted data and what the current RR site is suggesting. Anything beyond that apples to apples testing and comparison has waaaaaaaay to many variables that could swing results one way or another easily. This is the reason for my initial post/ point. Believe what you want to believe, but I don't believe this data is an appropriate "fair" comparison or validation of these two rims/tire types.

 

[mkhuffman]

The only way you can truly prove is to do a same day test between two R2's with different rims/tires sizes on the same roads driving the same speeds and terrain from 100% to 0% to comparis results at the end. that is when you will be able to confirm Rivian's posted data and what the current RR site is suggesting. Anything beyond that apples to apples testing and comparison has waaaaaaaay to many variable that could swing results one way or another easily. This is my point. Believe what you want to believe, but I don't believe this data is an appropraite fair comparison or validation of these two rims/tire types..

100%. I have posted the exact same thing before and it seems to go in one ear and out the other.

There are too many variables that impact efficiency to isolate the difference just to the tires. The same is true for the R1 data in RR, which has a lot more miles to compare. It isn't enough.

You need controlled testing to get a valid result. RR data is the opposite of controlled testing. Chad agrees, and it is his platform.

 

[richpike]

100%. I have posted the exact same thing before and it seems to go in one ear and out the other.


There are too many variables that impact efficiency to isolate the difference just to the tires. The same is true for the R1 data in RR, which has a lot more miles to compare. It isn't enough.

You need controlled testing to get a valid result. RR data is the opposite of controlled testing. Chad agrees, and it is his platform.

All good. Statistically there are always a few people who are completely in the wrong (I kid, I kid).

-Rich

 

[ksurfier]

The only way you can truly prove is to do a same day test between two R2's with different rims/tires sizes on the same roads driving the same speeds and terrain from 100% to 0% to compare results at the end. THAT is when you will be able to confirm Rivian's posted data and what the current RR site is suggesting. Anything beyond that apples to apples testing and comparison has waaaaaaaay to many variables that could swing results one way or another easily. This is the reason for my initial post/ point. Believe what you want to believe, but I don't believe this data is an appropriate "fair" comparison or validation of these two rims/tire types.

I think there’s now a real signal worth investigating.

We haven’t proven the 20” is inherently more efficient, but the claim that the 21” clearly delivers better real-world efficiency is getting harder to support.

If the 21” really has an efficiency advantage, it appears small enough that it isn’t showing up across thousands of miles of owner data or in the two longest 70-mph tests, which matters.

If environmental variation were the whole explanation, we’d expect noisy results centered roughly around Rivian’s predicted ~4% advantage for the 21”. Instead, the aggregate is currently about 12 percentage points in the opposite direction: from an expected ~−4% for the 20” to an observed ~+8%.

That doesn’t prove causation, but it is a legitimate signal.

The best test would be one R2 swapping 20” → 21” → 20”, with repeated 30–50 mile, 70-mph out-and-back runs under similar conditions. That would tell us far more than driving two different R2s from 100% to 0%.

 

[DJFrerichs]

All good. Statistically there are always a few people who are completely in the wrong (I kid, I kid).

-Rich

This is not about stating someone is right or wrong here as we should all be helping each other in support of the brand and what it provides. This is more about making sure people area aware of the information in front of them and if it is fully reliable or not. This kind of miss informative data can cost ya money in the long run if miss understood on how it is calculated and if it is factual in comparison.

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