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Do you mean on the Gravity? If so, all three wheel sets have both staggered widths and diameters.
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Gravity EPA docs are here.
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Do you mean on the Gravity? If so, all three wheel sets have both staggered widths and diameters.
No, I'm quoting the video posted which is about a Model 3 Performance.
A small correction, the OEM 20" PZ4 tires are all season but they are wider and much stickier than the OEM 18" tires (70-0 braking 163ft vs. 178ft skidpad .92g vs. .84g)
I think the same will hold true for the Gravity, if you put sticky tires on the 20/21 rims it will get similar efficiency and performance to the 22/23 tires.
I don't need to watch the OOS video to see that the smaller wheels appear more aerodynamic than the larger wheels. Do they have the same tires mounted? The only way to prove your point is to compare two wheels that have rims that are identical (except one is larger) and tires that are identical. It is almost impossible to do that comparison.
Tires that are the same brand and model but have a smaller sidewall will have different rolling resistance. It is even possible the tire compound is different betweent he two sizes due to load requirements, which also impacts rolling resistance. And then there are the rims: I have yet to see a OEM (Tesla or otherwise) make identical rims in two different sizes. You can find that in after-market rims, so you could do a test by comparing two identical aftermarket rims in two different sizes. That is not what OOS did, right?
If you did that test, everything exactly the same except wheel size, what would be the results? I suspect the smaller wheel would win because it would be more aerodynamic. A larger sidewall means lower rotational resistance. But if the rim is super aerodynamic, the difference could be so small that it is unmeasurable. OOS did not do this test. Did they?
Why do you fail to understand that wheel size is not the variable that matters?
There are three variables that matter: aerodynamics, rolling resistance and weight. That is it. Of course, those variables are loosely correlated with wheel size. A smaller wheel is likely to be lighter and more aerodynamic. But a smaller wheel with the wrong tire can be worse because of rolling resistance. And you can have a very aerodynamic rim that is larger than a smaller one with poor aerodynamics. And a larger wheel that is lighter than a smaller wheel. Rivian has clearly demonstrated that wheel size is not a relevant factor related to efficiency.
Wheel size isn't what matters at all. Focus on what does, and then you can understand why the EPA results for the 21/22 vs. the 22/23 wheels are so similar. It makes sense to me.
I agree with most of what you said but the 21/22 and 22/23 data is fake. There is a 0% chance that all three coefficients are exactly the same to 4 digits (F0 F1 F2 in post #19).
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I have some (long out of date) experience with homologating motorcycles in the USA. There's a lot of interesting data produced during the process, but the rules are both a bit arcane and also leave lots of room for interpretation for what's required in the testing. When I was involved, the process required an engineer who also had a law degree. The data tends to be interesting, but also doesn't do a good job of telling vehicle owners what they'd really like to know about a vehicle. I don't know how the regulations have changed in the last 30 years, but it certainly used to be true that one didn't have to separately test every variation.
You are right. It doesn't seem possible that they have identical results down to four digits.
It could be they were able to demonstrate no material differences between the wheels using the EPA test cycle and a rule allowed them to use the same data for both. Or the data is just made up. I don't think it is the latter, but it could be. Not sure how they get away with making up data.
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Huh? The Pirelli PZ4 is a max performance summer tire.
Oops, you are right and those are the tires in the video. And strengthens the point that it's not at all a fair comparison.
For some reason I thought they were all season. There is an OE all-season option (PZ MS, not PZ4):
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www.caranddriver.com
“Our test employed nearly identical Goodyear Eagle GT ultra-high-performance all-season tires in all five sizes, inflated to manufacturer-recommended pressures.”
“What’s immediately apparent from the results is that as the wheel-and-tire packages get larger and heavier, acceleration and fuel economy suffer. Neither is a huge surprise, but we measured a 10-percent drop in fuel economy”
Holy cow! Another fake article claiming smaller wheels are more efficient! Crazy how they even used the same tires for each size wheel. Blasphemy!
That's a much better test. I can quibble a little with the results though. First they're testing an ICE vehicle which is much more affected by wheel/tire weight, they have a difference of 54lb vs. 40lbs from biggest to smallest. It's too bad they didn't measure highway effficiency (which should not be be affected by wheel weight.) Second the tire performance is very different even though they're all the same model tire.
"We say that the tires were nearly the same because the 15-, 16-, and 17-inchers have a lower speed rating (V, or a top speed up to 149 mph) than the 18- and 19-inch tires’ W-rating (up to 168 mph)."
The V rated tires got 0.83g,.85g,0.85g and 23.3mpg,22.9mph, 22.8mpg
The W rated tire got 0.89g,0.88g and 21.9mpg, 21.1mpg
It seems that there's a significant difference in the tire compound and the stickier tires get worse efficiency.
Maybe we can compromise and agree that larger diameter wheels are usually less efficient primarily because of the design choices made for larger diameter tires?
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This article is 15 years old. So much has changed about tire design and construction in these 15 years that I don't really know how far its observations go at this point.
There are so many variables at play here. Some things remain the same. As wheel diameter increases, more of the rotational mass of the tire/wheel combo does migrate further out from the center of rotation, and that will inevitably mean more energy is required to start the wheel rotating (as when accelerating) and to stop it (as when braking). That will affect mileage both with ICE and EV cars. However, EV cars pick up a bit of advantage here, as braking a larger wheel with regenerative braking will make more energy available to recharge the battery instead of all being lost to heat as in an ICE car. But many other things affect that exchange, and I don't know how significant it really would be even in the optimal circumstances.
This discussion about how all the factors at play (diameters, weight, tire rolling resistance, tire compound, etc.) affect range could go on all day without any resolution.
But I think one thing is clear. The wide difference in Gravity range between the Hankooks and the Pirellis has a lot more to do with the tire design and construction (and maybe a little with the aerodynamics of the wheel faces) than it does with the wheel diameter differences. If Hankooks could be had in the sizes for the largest Gravity wheel set, I suspect the bulk of the range difference between the wheel options would disappear. "Car and Driver" had to vary the wheel diameters by four inches to get a 10% change in mileage. With the Gravity, we're talking a 17% range drop over a 2" diameter change.
What is your point? That bigger rims are always less efficient than smaller rims? If that is your point, you are clearly mistaken.
There is no need to repeat all the previous posts I have made about this. You can read those and see that I agree smaller rims and wheels tend to be more aerodynamic and lighter than bigger rims and wheels. But just because it is smaller does not automatically mean it is more efficient. It is 100% proven with data and real world testing that bigger rims/wheels can be more efficient than smaller ones. As mentioned before.
Sigh.
Here is another data point: when I replaced the tires on my Mach-e, I replaced them with the Hankook iON SUV tires the Gravity uses on the smallest rim. But I didn't replace them with the same size tire. I went up a size, making the tread wider. I kept the same aspect ratio, so the result was a taller tire than the one it replaced. I now had a bigger wheel on my car!
Did my efficiency decrease? Nope. Just the opposite. I gained 7% efficiency at highway speeds. With a bigger wheel! Oh, no!
Of course the Hankook is a insanely efficient tire. But I think rotational air residence decreased since the rim was actually rotating a little slower. At high speeds, the bigger tire sidewall meant the fastest part of the wheel was bigger, and more aerodynamic.
I have no way to know for sure if aerodynamics improved enough to make a measurable difference. It is possible all of the improvement was due to lower rolling resistance. But it makes sense the bigger wheel would have lower rotational air resistance.
Bigger is often better.
Did my efficiency decrease? Nope. Just the opposite. I gained 7% efficiency at highway speeds. With a bigger wheel! Oh, no!
Of course the Hankook is a insanely efficient tire. But I think rotational air residence decreased since the rim was actually rotating a little slower. At high speeds, the bigger tire sidewall meant the fastest part of the wheel was bigger, and more aerodynamic.
I have no way to know for sure if aerodynamics improved enough to make a measurable difference. It is possible all of the improvement was due to lower rolling resistance. But it makes sense the bigger wheel would have lower rotational air resistance.
Bigger is often better.
It’s kind of hilarious how nuanced you’re making this out to be. No sh** sometimes bigger wheels can be more efficient than smaller ones…which only comes down to tire selection. Which you like to make apparent from Rivian’s range 22’s being more efficient than their 20 setup. I mean, I would hope an all season or summer tire would be more efficient than an all terrain tire.
Did you change your computer in your Mach e? If not, then your calculation is wrong and has to be adjusted.
Look at this Lucid air they tested and got over 500 miles.
Maybe they wanted to use an OEM tire setup?
They do actually make Hankook iON tires for the 21" size 245/35R21. It would interesting for someone to compare. They'd also have to run a set of front wheels in the rear since the 21" OEM wheels are wider in the back.
edit: actually the 21" wheels are 0.5" wider in the front and 1.5" wider in the back so you'd need to find a narrower set of wheels with similar aero to the 19's.
But then why didn’t Lucid contact a tire manufacturer and ask for the most efficient tire for their 21’s on the air so they could achieve the 500 plus range or 5mi/kwh? Because everyone here is arguing against me saying larger wheels are more efficient. Why not just have a very efficient tire on the 21’s?
Why did Lucid go to a 19” setup? Why are all the records on the Air with the smaller wheels setup? I thought larger wheels are more efficient here.
Absolutely nobody is saying that.
Marketing and not wanting to have too many tire wheel combos.
Automakers put high performance tires on their big wheels. It's silly because there really isn't a performance advantage to super low profile tires (there is a huge performance advantage to the sticky tires though)
All I'm saying is that wheel size has almost nothing to do with efficiency.
What affects efficiency (most to least)
- Tire compound and tread design
- Aero
- Weight
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Because with 1111HP, I don’t want efficient. I want traction.
And if I want efficient, I’ll get the 19s.
But that isn’t because smaller wheels are always more efficient.
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