Three-Way 275/60R20 Efficiency Comparison: Ram/AS, Ram/AT, OEM/AS

[Proxy]

@sub Drag is proportional to the square of speed. However, energy is proportional to the cube of speed.

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[ksurfier]

Do you know temp, air density, and wind speed/direction for all tests? Without that info the numbers can’t be compared, my data indicates a 0.1 MPK drop between 55 and 60 mph (OEM 20” Rim).

 

[Riviot]

I think you are underestimating the impact of slight differences in speed.

A) Ram 2363s with Pirelli AS+3, 2.29 mi/kWh @ 55 MPH average
C) OEM "Staples" with Pirelli AS+3, 2.15 mi/kWh @ 60 MPH average

Wind drag increases with the square of the speed.

5MPH may not seem like a lot. But it is. Wind drag is 60^2 / 55^2 = 1.19x more at 60MPH than 55MPH. You are going 9% faster, but there is 19% more wind drag.

By my math, if you got 2.15 at 55MPH, you would expect 2.15 * 60/55 = 2.35 at 60MPH if 100% of your energy was going to wind drag which is very similar to what you got at 60MPH in the Ram wheels.

Based on your data, I would give the OEM wheels the win.

Average speed dropped as I sat at the light for an extra 2 minutes, but highway speed was steady across the board.

 

[HaveBlue]

What's interesting about the results is that external variables quickly make a difference but wheels and tires are pretty close to each other. Meaning if we stay reasonable for wheels and tires, there shouldn't be major differences.

 

[SeaGeo]

FWIW, 2363 AT and OEM AS were hours apart. Ran the loop, had dinner, changed tires, ran it again.



Ugh y'all are gonna make me do it again?! Killing me!

Douglas Fur (heh, I like that spelling better) supervised wheel changes but did not ride along for any.



Ram AS had 2773 miles

Ram AT had 7500 miles

OEM AS had 6300 miles

You can run at the same time against the OE setup if you meet up with one of us on the east side of the Sound. No need to remove tires or wheels.

It was good meeting you this weekend!

 

[Riviot]

Do you know temp, air density, and wind speed/direction for all tests? Without that info the numbers can’t be compared, my data indicates a 0.1 MPK drop between 55 and 60 mph (OEM 20” Rim).

No, I wasn't that sciencey in my loops. I controlled as many factors as possible, but alas, there's always something...

Again, speed was constant 66mph on the highway. Average varied due to stoplight wait times. I watched the speed drop the longer I waited, efficiency and power were unchanged.

 

[usofrob]

If anything, being stopped longer would have used more energy from HVAC and computers, etc.

 

[Riviot]

If anything, being stopped longer would have used more energy from HVAC and computers, etc.

Again, I monitored trip meter info (average speed, total energy, etc etc etc) during stops. Only speed and duration changed, HVAC use seemed minimal.

 

[Riviot]

I hesitated to post these in OP, because they literally only tell half the story. But this halfway data also made me suspect OEM had something against it on that run, not sure what...

Halfway point altitude was net gain from the start, hence lower lower than round trip.

Regarding someone's question on wind, it's a round trip. Any gains one direction are losses the other direction. Net zero impact.

Only other impact I could see would've affected both Ram AT and OEM AS: weight gain. A semi-full frunk water tank after camping and new gear shuttle, maybe +200lbs, but I think we learned in Out of Spec tests weight add has a negligible impact on efficiency.

 

[usofrob]

Again, I monitored trip meter info (average speed, total energy, etc etc etc) during stops. Only speed and duration changed, HVAC use seemed minimal.

My point was just that the highest efficiency run was also stopped longer. So, given the same speeds while driving, it should have used a tiny bit more energy causing it to be less efficient. It implies more evidence that the RAM wheels are more efficient.

However, running round trip helps to balance the energy usage, a round trip test will always be more efficient with no wind. I'm sure doing this test was a pain, and I wouldn't suggest doing it again, but if you wanted to do a test, I'd suggest doing it with 2 vehicles at the same time. Maybe even swap the wheels between vehicles and do it again to eliminate any possible vehicle differences. Then you's still have treadwear differences, but you can't win them all (without $$$ support).

 

[Riviot]

I have to rescind my update, I just realized I didn't have the RTT on, so of course it's going to be more efficient... I'll put the RTT back on after washing the truck tomorrow and give it yet another go... Ugh.

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