Smaller wheels highway question?

[aerohead]

Originally Posted by Phase

Do you think engineering explained had credibility?

https://youtu.be/NYvKxsYFqO8?si=4L4M45SEzCVrZW_H

Skip to 7:30 in the video. He straight up states that Tesla itself has different ranges submitted legally for each tire size at a STEADY STATE speed also.

Explain that too, regardless of your beef with Wayne

We can circle back to him later.
I just looked at ' ars TECHNICA's' website on the new Prius:
Toyota Motor Company told them that the LE, with 17" wheels/tires is the only Prius with Cd 0.27.
The Limited and XLE are 'more like Cd 0.29'. That's from the horse's mouth.
It's something about both the tire's frontal area, and the ventilation drag of the more 'open' spoke pattern of the alloy wheels, just like Tesla, just like Lucid Air, just like KIA, Just like Genesis, just like Hyundai.......................
It's not about 'killer' mass.
SAE INTERNATIONAL wasn't even informed, with respect to their report on the 2023 Prius.
I don't have enough time to get into 'Engineering Explained', so that will have to be for Monday.
As 'consumers', our biggest beef ought to do with the Munroney stickers on new cars. In a perfect world, they'd provide official drag coefficients and projected frontal areas for the specific model they're affixed to, allowing the potential customer to 'do the math.'

[Phase]

Originally Posted by aerohead

We can circle back to him later.
I just looked at ' ars TECHNICA's' website on the new Prius:
Toyota Motor Company told them that the LE, with 17" wheels/tires is the only Prius with Cd 0.27.
The Limited and XLE are 'more like Cd 0.29'. That's from the horse's mouth.
It's something about both the tire's frontal area, and the ventilation drag of the more 'open' spoke pattern of the alloy wheels, just like Tesla, just like Lucid Air, just like KIA, Just like Genesis, just like Hyundai.......................
It's not about 'killer' mass.
SAE INTERNATIONAL wasn't even informed, with respect to their report on the 2023 Prius.
I don't have enough time to get into 'Engineering Explained', so that will have to be for Monday.
As 'consumers', our biggest beef ought to do with the Munroney stickers on new cars. In a perfect world, they'd provide official drag coefficients and projected frontal areas for the specific model they're affixed to, allowing the potential customer to 'do the math.'

Do you have any break downs on why the new Prius has so much higher drag coefficients than the previous models? Many casual people think it “ looks” the most aerodynamic of any prius but clearly it’s not

I’m just curious to what you’d say pops out to you visually

[Andyinchville1]

I have a 2003 Jetta Wagon TDI (5 speed) and on factory steelies and ecopia 195-65R15 tires @ 44 psi I used to average about 47 - 48 MPG ..... I switched to lightweight wheels (Volk TE 37) and larger tires (215 - 75R15 Hankook tires at 51 psi ( I'll have to look at the model) ) and got basically about 9 percent better fuel mileage .... I attribute this to the overdrive effect of the tires .... I had weights of the wheel / tires before but I misplaced them unfortunately .... I have about a 1.5" lift on the front end to help level the car when unladen .... my take (at least on my car) ... larger tires for an OD effect can be helpful for MPG if your engine can pull the extra load .... despite a lift of 1.5" I still had MPG gains so extra lift does not always hurt ? (unless of course I may have gotten MORE mpg's without lift?..... Hopefully this is some food for thought).
Andrew

NOTE : Car is modded .... it would be nice to try steelies and the ecopias again in factory size to see MPG comparison now since I may have done some modding along the line before the final larger tire size (current size)....

[aerohead]

Originally Posted by Phase

Do you think engineering explained had credibility?

https://youtu.be/NYvKxsYFqO8?si=4L4M45SEzCVrZW_H

Skip to 7:30 in the video. He straight up states that Tesla itself has different ranges submitted legally for each tire size at a STEADY STATE speed also.

Explain that too, regardless of your beef with Wayne

Wow!, that's an old one.
From Jason's data:
1) The tire circumferences are essentially the same, so, fundamentally, either size tire's sidewalls and tread blocks are deforming at equal surface-feet-per-minute rates. Only a difference in tire construction could explain a difference in R-R.
2) All-season radials have the lowest R-R of all tires.
3) Touring tires have the next-best R-R characteristics.
4) High-performance tires have the worst R-R. The lower aspect-ratio, larger wheel tires may be high-performance, hence, higher R-R.
5) 'Wider' tires would increase frontal area, at a fixed ground clearance. Jason never specifies if this 'condition' exists with the Tesla 3 tires. So it remains an unknown quantity.
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6)Rob Palin, aerodynamicist for all Tesla Vehicles, excepting the original Lotus Elise-based Roadster-I, tested Tesla's different Wheel/tire combos in Germany on the Autobahn, at up to 141-mph ( 247-km/h ) in 2018, and reported his findings @ 'Tesla Model 3 Aerowheels', at electrek.co.
7) Mechanical efficiency varied by 10%.
8) Range varied by 5%.
9) Cd varied from zero at low-speed, to 3% @ top speed.
10) Bjorn Nyland did the same thing, at posted speed on the Interstate, from Tesla's Hawthorne, California offices, with a Dual-Motor, Long Range Model 3.
11) He saw a delta-10% difference in efficiency also.
12) Range in energy consumption between, 186-Wh/Mi, and 179-Wh/mi, Delta-3.9%.
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This tire issue involves a multivariate problem involving the simultaneous solution for both linear, and non-linear equations, which even with a Masters Degree in Mechanical Engineering, Jason shied away from.
And we never actually learn from the video what 'mechanism' is attributed to the explanation for the difference in Tesla's submitted EPA documentation, only 'hypotheticals.'
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So, on to the 2024 Prius...................................

[aerohead]

Originally Posted by Phase

Do you have any break downs on why the new Prius has so much higher drag coefficients than the previous models? Many casual people think it “ looks” the most aerodynamic of any prius but clearly it’s not

I’m just curious to what you’d say pops out to you visually

I went to TOYOTA's website for the 2024 Prius, and found some pertinent info to add to what we've talked about so far:
A) If the roof apex has been moved rearwards 2-inches, then Toyota has 'shortened' the roofline of the new car, a direct violation of aerodynamics writ large.
B) Even if the entire 1-inch lengthening of the new car is added to the rear, the roofline is still 'stunted.' It's more 'bluff.'
C) The rocker panels on the new car are 'mutilated' by the designer's horizontal character line embossed into the sheet metal, creating a pressure 'kink.' Another violation of 'aerodynamics'
D) The new car body has been widened in the rear, adding 'haunches' for 'stance', and in so doing, destroyed some of the car's facility for pressure recovery; the most important thing with 'aerodynamics.'
E) Both the 17" and 19" tires are P195s, so the frontal areas are identical, and no potential for a difference in drag there.
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BIG NEWS!
F) The Prius SE is the 'ONLY' Prius with Cd 0.27.
G) The Prius Limited & XSE are Cd 0.29.
H) The non-SE cars are 'taller' ( greater ground clearance ), exposing 0.4-inches more tire face to the air.
I) The non-SE cars are 'wider'.
J) Their CdAs are greater
K) Although the new car is reported to be 1-inch greater in length ( 181.1" ), the out-going Prius is 182.9" in length.
L) The engine in the new Prius has an identical 'Brake Thermal Efficiency' ( BTE ) as the out-going model.
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Without a set of blue-prints for the cars, I'm hamstrung, and can't say anything definitive, aerodynamically.

[Phase]

Originally Posted by aerohead

I went to TOYOTA's website for the 2024 Prius, and found some pertinent info to add to what we've talked about so far:
A) If the roof apex has been moved rearwards 2-inches, then Toyota has 'shortened' the roofline of the new car, a direct violation of aerodynamics writ large.
B) Even if the entire 1-inch lengthening of the new car is added to the rear, the roofline is still 'stunted.' It's more 'bluff.'
C) The rocker panels on the new car are 'mutilated' by the designer's horizontal character line embossed into the sheet metal, creating a pressure 'kink.' Another violation of 'aerodynamics'
D) The new car body has been widened in the rear, adding 'haunches' for 'stance', and in so doing, destroyed some of the car's facility for pressure recovery; the most important thing with 'aerodynamics.'
E) Both the 17" and 19" tires are P195s, so the frontal areas are identical, and no potential for a difference in drag there.
--------------------------------------------------------------------------------------
BIG NEWS!
F) The Prius SE is the 'ONLY' Prius with Cd 0.27.
G) The Prius Limited & XSE are Cd 0.29.
H) The non-SE cars are 'taller' ( greater ground clearance ), exposing 0.4-inches more tire face to the air.
I) The non-SE cars are 'wider'.
J) Their CdAs are greater
K) Although the new car is reported to be 1-inch greater in length ( 181.1" ), the out-going Prius is 182.9" in length.
L) The engine in the new Prius has an identical 'Brake Thermal Efficiency' ( BTE ) as the out-going model.
--------------------------------------------------------------------------------------
Without a set of blue-prints for the cars, I'm hamstrung, and can't say anything definitive, aerodynamically.

I was reading some scientific studies last night stating that a more slanted windshield angle allows for better attached airflow over the roofline and rear. With this info, that would mean the back of the new Prius has better attached flow on the hatch. Maybe this explains why the spoiler is much smaller than older Priuses?

Knowing the back of the new Prius is shorter and wider, I’m assuming we can drop the CD significantly if the new Prius with a simple tapering extension

I don’t know exact numbers, but I’m guessing even adding just a foot longer tapered box cavity that’s on the sides and roofline would make a huge difference On the cars drag.

You’re pretty much saying that extending the roofline out even just a little bit and continuing down would make a drastic difference?

[freebeard]

I was reading some scientific studies last night stating that a more slanted windshield angle allows for better attached airflow over the roofline and rear.

Two dimensional thinking in a three dimensional world. But your conclusion is plausible.

[Vekke]

#1 Smallest wheel is usually almost always most energy efficient. (same tire outer diameter is kept)

#2 steel wheels fit over bigger brakes. So sometimes you can fit 1" smaller steel wheel vs aluminum wheels. Steels wheels are also more aeroydynamic as there is not poles to twist the air. --> you need to use wheelcovers to get best aero. many stock ones are good enough.

#3 Wheel or tire weigth impact to consumption is going to be minimal. In a city you migth get 1% better FE but you cannot measure it. So buying expensive ligthweigth wheels is usually waste of money. If you get them cheap go for it if they are also aerodynamic. or can be made aerodynamic. Best option is ofcourse ligth and aerodynamic wheel.

#4 bigger tire diameter lower RR and lower wheelwell drag but increases drag (ground clearance. These usually is similar impact so in most cases no gains to either direction. Migth give little good in selected wisely the rubber compound that has low rolling resistance.

#5 tire rolling resistance is very important specially on heavy vehicles.

#6 narrow tires lower drag, but I recommend installing them to wider wheels. It boost performance on all areas.

My video series on the matter on youtube:

https://www.youtube.com/watch?v=MQlJ...wi9ZNdEUozH7bs

[COcyclist]

Originally Posted by Andyinchville1

I have a 2003 Jetta Wagon TDI (5 speed) and on factory steelies and ecopia 195-65R15 tires @ 44 psi I used to average about 47 - 48 MPG ..... I switched to lightweight wheels (Volk TE 37) and larger tires (215 - 75R15 Hankook tires at 51 psi ( I'll have to look at the model) ) and got basically about 9 percent better fuel mileage

I am curious how you measured your miles, before and after. A change in tire diameter should throw off your odometer. I have used a GPS and found the VW speedometer/odometer to be slightly off even with the original tire size. That said, a taller tire should make your mpg worse on the factory odometer, right?

[Phase]

Originally Posted by Vekke

#1 Smallest wheel is usually almost always most energy efficient. (same tire outer diameter is kept)

#2 steel wheels fit over bigger brakes. So sometimes you can fit 1" smaller steel wheel vs aluminum wheels. Steels wheels are also more aeroydynamic as there is not poles to twist the air. --> you need to use wheelcovers to get best aero. many stock ones are good enough.

#3 Wheel or tire weigth impact to consumption is going to be minimal. In a city you migth get 1% better FE but you cannot measure it. So buying expensive ligthweigth wheels is usually waste of money. If you get them cheap go for it if they are also aerodynamic. or can be made aerodynamic. Best option is ofcourse ligth and aerodynamic wheel.

#4 bigger tire diameter lower RR and lower wheelwell drag but increases drag (ground clearance. These usually is similar impact so in most cases no gains to either direction. Migth give little good in selected wisely the rubber compound that has low rolling resistance.

#5 tire rolling resistance is very important specially on heavy vehicles.

#6 narrow tires lower drag, but I recommend installing them to wider wheels. It boost performance on all areas.

My video series on the matter on youtube:

For low rolling resistance tires like the ecopias, on the Prius the 17 inch tires are 195 wide but if you downsize to the 16 inch wheels, the width increases to 205. It’s very small though

My big debate is which wheels will be best, 17s with 195 or 16s with 205s even if rolling resistance is the same…