I don't understand. The wheels don't care about the power source. If aerodynamic wheels improve effective mileage by 5% that should be 5% even if it was ICE powered meaning a 5% improvement in MPG.
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Aero wheels
- Thread starter richkae
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- Driving Dynamics Model S
A very large percentage of the energy is lost as heat, and any improvement to aerodynamics won't change that. Aerodynamics is simply a smaller percentage of the energy lost on ICE vehicles than it is on EVs.
We're obviously passing each other in the fog.
If I'm behind the car pushing it at 70 mph (say, I'm a taco powered superman) and you come along and say "I've got special rims that'll make it 5% easier" then I'll spend 5% less energy pushing the car. Whatever happens inside me to create the power doesn't matter, that's a black box. Whether I'm efficient and only eat 10 tacos or a taco guzzler and eat 20 to power myself, that number reduces by 5%.
What am I misunderstanding?
@ckessel
I'll try to capture what I think he's saying using made up numbers.
An ICE uses 200 units to go 55mph. Of that 200 units, 1 unit is spent overcoming non-perfect aerodynamics.
An S burns 4 units to go 55mph. Of that 4 units, 1 unit is spent overcoming non-perfect aerodynamics.
The fancy wheels reduce the 1 unit to 0.8 units.
ICE+FW uses 199.8 units, saves 0.1% consumption.
S+FW uses 3.8 units, saves 5% consumption.
I'll try to capture what I think he's saying using made up numbers.
An ICE uses 200 units to go 55mph. Of that 200 units, 1 unit is spent overcoming non-perfect aerodynamics.
An S burns 4 units to go 55mph. Of that 4 units, 1 unit is spent overcoming non-perfect aerodynamics.
The fancy wheels reduce the 1 unit to 0.8 units.
ICE+FW uses 199.8 units, saves 0.1% consumption.
S+FW uses 3.8 units, saves 5% consumption.
I'll take a stab at it, I think I understand what Doug is trying to say:
Out of the gasoline consumed, about 80% (seems like a high number?) gets lost in spillage, smoke and general ICE inefficiencies and actually never makes it far enough down the chain to put power to the wheels. So only the 20% that is actually used to push the car forward benefits from the new aerodynamic wheels. Contrast to EV where (ideally) all spent energy pushes the car forward (except for stereo system use and spillage along the wires) and therefore the 5% benefit has a higher impact.
Doug, sound about right?
Again though, the power source's efficiency is a black box as far as wind resistance is concerned. The EV effectively goes from, say, 100 mpge to 105mpge. A ICE would go from 20 mpg to 21 mpg. The EV is obviously more efficient overall, but the relative improvement from reduced wind resistance should be the same.
ckessel, you are right, doug is wrong.
Sure ICEs are inefficient, but 5% less drag means 5% less output and 5% less total consumption. Thermal loses are still 80% no matter how aerodynamic the vehicle is.
If this wasn't so, aerodynamic vehicles would be *less* efficient than bricks.
Sure ICEs are inefficient, but 5% less drag means 5% less output and 5% less total consumption. Thermal loses are still 80% no matter how aerodynamic the vehicle is.
If this wasn't so, aerodynamic vehicles would be *less* efficient than bricks.
Anyone else see 'aerodynamic 19" wheel' as a bit of any oxymoron?
The wheel options on the Model S are basically boat anchors and all about bling.
17" wheels would get most of the aero benefits of the 19" aero wheels, but also be significantly lighter so you'd get additional efficiency in city driving, too.
I'm disappointed they went through so much effort to make the body aerodynamic (retracting door handles???) then threw it all away on fancy looking wheels.
The wheel options on the Model S are basically boat anchors and all about bling.
17" wheels would get most of the aero benefits of the 19" aero wheels, but also be significantly lighter so you'd get additional efficiency in city driving, too.
I'm disappointed they went through so much effort to make the body aerodynamic (retracting door handles???) then threw it all away on fancy looking wheels.
I'm not. I think they're doing it right by making it an attractive CAR first, and EV second. Remember, they're trying to break the concept of EVs being odd-looking cars with something very eye-catching. 17" wheels would look odd on such a big car (the 19's are already a bit weird looking to my eye). I would be very interested in knowing if they did any tests with 17 inchers though, and what they found.
Let's make it very easy and back track from the model S
The "wheels" decrease the drag by about 6% and for the model S, going from 80/300= 0.2667 kWh/mile to 80/320 = .25 kWh/mile
A gallon of gas has 33.41 kWh/gal and assume 20 mpg. 1.67 kWh/mile. To bump it up just by 5% you have to get 21 mpg.
Also you have to keep in mind that the aero wheels are meant for high speed, they do nothing when sitting in traffic. Consider that some of an ICE car's energy is lost idling
The standard wheel size is 18" for cars in this class (go look at comparable BMWs and Mercedes). 19" wheels are your typical option wheel. Even Mercedes offers a 17" wheel on their "BlueTEC" version.
Rollin' on dubs is purely for show. If Tesla told you how much the 21" wheels reduced efficiency you'd be surprised.
I'm fully aware. This would be the first time I've ever had 21" wheels on ANY car. But I stand by that I think they fit this car very well. The 19's look like 17's and the 21's like 19's on this car. Granted, all I've seen are pictures of the 19's
Regardless of whether they really help or not, there probably aren't any because they look butt-ugly.
goyogi
Member
I'll take the 'performance' wheels and on a long trip slap a 21" clear sticky vinyl disc over the spokes. 
Yeah - it looks good because of the huge fender openings they designed in the car. They had to fill them with something. And the 19" wheels look like crap, too. If they built the 19" wheels with the same design as the 21s it'd look a lot better than the cheap-o looking 19" wheels.
Look at the Fisker Karma for an example of what huge wheels do for efficiency: 22" wheels and the thing sucks down 65 kWh to drive 100 miles according to the EPA. Compare this to 30 kWh / 100 mi for the Roadster, 34 kWh / 100 mi for the LEAF, 36 kWh / 100 mi for the Volt (Can't find the EPA sticker for the iMiev but it's numbers are close to the Roadster's).
From VolkerP in another thread...
It looks like my estimate (25%) was actually too conservative.
JRP3
Hyperactive Member
On an EV with strong regen? The brakes should need less cooling than any ICE, and some ICE's have used moon covers as well. Besides there is still airflow on the inside of the wheel. I agree they could have used a better "picture" on the disk, it looks rather cheesy.
Todd Burch
14-Year Member
If you want super efficiency, get an Aptera...
...Oh wait. Aptera's not around anymore. Maybe the design was too radical to support a sales volume that would actually keep the company afloat?
...Oh wait. Aptera's not around anymore. Maybe the design was too radical to support a sales volume that would actually keep the company afloat?
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