Smaller wheels highway question?

[Phase]

Originally Posted by oil pan 4

Stuff that works on electric cars don't work on gas powered ones.
Gearing and motor rpm isn't as important on an electric motor.

Okay so why is there a 4 mpg gain across the board on the new Prius when dropping down from their 19 inch to 17 inch wheels?

About the same 4 mpg difference when comparing the Ioniq hybrids 17 inch vs 15 inch wheels. Seems like higher end hybrids all gain about 2 mpg average for every inch you drop in rim size while keeping the total wheel radius the same

[Ecky]

Using the Tesla Model 3 as an example, the 2023+ models with 18" wheels use the Michelin ePrimacy in 235/45r18. The models with 19" whels use the Hankook Ventus S1 EV03 in 235/40r19.

Michelin says the following about the ePrimacy:

MICHELIN e·PRIMACY: eco-designed, made to last.

Reduce fuel consumption, CO2 emissions[1] and extend battery range[2][3] with MICHELIN e.PRIMACY, an eco-designed tyre, made to last.

• MICHELIN eco-designed summer tyre for fuel, hybrid and electric vehicles
• Lowest fuel consumption and CO2 emissions in its category[1][2]
• Extended battery range for electric vehicles[2][3]
• Long-lasting safety, from the first kilometre to the last
• Excellent longevity[4]

The ePrimacy has no treadwear rating, but based on its reported lifespan, I'd wager it would be around a 600, give or take.


Hankook says the following about the Ventus S1:

The best balance between wet and dry performance.

The Hankook has a 280 treadwear rating, and is an Ultra High Performance tire.

~

So, in the case of the Tesla, the 18" vs 19" is apples to oranges. The tire mounted on the 18's is a LRR eco tire, while the 19 gets a high performance tire.

In the case of the G5 Prius, the 17" get BluEarth-FE AE30, while the 19" get BluEarth-GT AE51. Just going by the names, the 17" is a F(uel)E(fficient) tire, while the 19 is a G(rand)T(ouring) tire.

[Phase]

Rolling resistance isn’t as important on the highway. I’m just trying to figure out if downsizing an inch and also choosing a lighter rim will hurt or benefit highway driving.

[Ecky]

Originally Posted by Phase

Rolling resistance isn’t as important on the highway. I’m just trying to figure out if downsizing an inch and also choosing a lighter rim will hurt or benefit highway driving.

At 62mph, rolling resistance is still in the ballpark of 25% of the total energy needed to move a vehicle. It drops to ~20% at 75mph.

Sure, that's smaller than aero, but it's still significant. Also, the EPA "highway" test averages less than 50mph, and includes a fair amount of accelerating and decelerating, which may account for part of what you see in the highway rating.

[Phase]

Originally Posted by Ecky

At 62mph, rolling resistance is still in the ballpark of 25% of the total energy needed to move a vehicle. It drops to ~20% at 75mph.

Sure, that's smaller than aero, but it's still significant. Also, the EPA "highway" test averages less than 50mph, and includes a fair amount of accelerating and decelerating, which may account for part of what you see in the highway rating.

What I’ve noticed a lot with my heavier snow tires and getting worse mpg besides rolling resistance is when accelerating. It’s very rare that I’m on a perfectly flat road with cruise control and no traffic. There’s always some type of accelerating or coasting going on with highway driving, whether it being going over a small hill or someone pulls in front of you and then speeds back up or going around someone to pass and so on. The throttle is always changing

[oil pan 4]

Originally Posted by Phase

Okay so why is there a 4 mpg gain across the board on the new Prius when dropping down from their 19 inch to 17 inch wheels?

About the same 4 mpg difference when comparing the Ioniq hybrids 17 inch vs 15 inch wheels. Seems like higher end hybrids all gain about 2 mpg average for every inch you drop in rim size while keeping the total wheel radius the same

My bad didn't realize it was smaller wheel with same size tire.
For 4mpg it seems like it could be worth it if you sell your old wheels to cover most or all of the cost.

[freebeard]

https://tiresize.com › tiresizes › 155-70R19.htm
155/70R19 Tires - TireSize.com
155/70R19 tires have a diameter of 27.5", a section width of 6.1", and a wheel diameter of 19". The circumference is 86.5" and they have 733 revolutions per mile. Generally they are approved to be mounted on 4-5" wide wheels. Specs may vary by manufacturer. learn more. Visualizer / Alternate Sizes
..versus
https://tiresize.com › tiresizes › 165R15.htm
165R15 Tires - TireSize.com
Tires Education 165R15 Tires 165R15 tires have a diameter of 25.4", a section width of 6.5", and a wheel diameter of 15". The circumference is 79.7" and they have 795 revolutions per mile. Generally they are approved to be mounted on 4-5.5" wide wheels. Specs may vary by manufacturer. learn more

[Phase]

Originally Posted by oil pan 4

My bad didn't realize it was smaller wheel with same size tire.
For 4mpg it seems like it could be worth it if you sell your old wheels to cover most or all of the cost.

I’m just trying to get someone to explain why highway mpg is still higher with a smaller wheel based on the epa and testing, but then everyone else says bigger wheels and inertia are better on the highway. Conflicting data

[Piotrsko]

Not necessarily conflicting. It is however a case of not being able to look at all the data and compute a solution so you are resolved to only look at one aspect: a increase in efficiency giving a reduced fuel consumption, which you can measure. You can calculate drag, pretty sure it isn't measureable with the accuracy you could calculate.
Possibly a GPT analysis writing a program in a quantum computer could with a couple billion lines of code....

Your tire change has altered some sort efficiency either in the engine or in the aero flow, which may or may not be representative or duplicated in another vehicle, even the same as yours.

[freebeard]

Data produced by the nut behind the wheel?