The Prius Experiment

[Blacktree]

I was using mpg data as a point of comparison. Granted, I'm comparing a Prius to a Jetta. But the "A/C penalty" for the Jetta was about 12% worse fuel economy. For the Prius, the A/C penalty seems to be closer to 15%.

But I have to admit, that comparison was based on only 2 fillups in the Prius. So maybe I jumped to a conclusion. This latest fillup seems to be closer to 12% A/C penalty.

Side note: If I can reach 60 mpg with the A/C running all the time, that would be awesome! With the latest fillup coming in at 57.5 mpg, that might actually be feasible.

[ps2fixer]

I've been running AC a little here, 82-90ish temps outside and AC set to around 80-82. It drops the instant right away, but once it runs a bit it seems to have a pretty low effect on overall mpg. I'm one that normally drives with the windows down, so I guess I'm more used to being hot in a car. I've hit 50-55mpg for most longer trips with ac on according to the scan gauge. I wasn't going as slow in those cases so not a great comparison. It seems like driving a little faster offsets the AC "tax" a little, less time it's on, less fuel used. It's probably quite a balancing act for speed vs ac draw over time to work out the best speed for the given situation and such.

I wouldn't mind hitting 60mpg for somewhat "normal" driving, ac on would be a nice bonus. I think it should be possible though.

[Drifter]

A/C has a pretty high start-up cost as it tries to lower cabin temperature (about 2,000 watts on my 2010 after being parked in the sun on a very hot day). Over the course of a half an hour, it gradually decreases to 300-500watts where it stabilizes (much less energy to maintain temperature than lower it). So the A/C penalty on road trips will be a lot less than the A/C penalty for a trip across town. Or for a car that is garaged vs a car that lives outdoors.

Tire/wheel alignment is interesting too. My hypothesis: Older bushings flex more which allows the alignment to change as road forces are applied. When power is being applied, the wheels try to pull forward as the chassis lags behind, toeing in. When power is removed, the force of rolling resistance acts like a brake on the wheel/tire and it shifts rearward in the wheel well (toeing out).

If you're operating steadily on the highway, you can just set the alignment to minimize drag when the suspension is flexed for that much power. If you're pulsing and gliding, you'll be shifting back and forth so newer bushings will make more of a difference.

[ps2fixer]

I think your theory is correct. My 1997 Corolla on the way home from around 3hr away only got 33mpg for the trip, by far the worst tank I ever had and I could only go 60mph max with it. It had a lot of problems though....

Rear struts completely blown out, tire had no resistance on bumps so this is why the max speed was 60
Alignment was about a half a turn of the steering wheel off

I did a basic tune up, rear struts, new rear tires + alignment and I think that's all and my mpg since has been 38-44mpg. It all adds up, and ironically the front end still had issues, inner tie rods were sloppy and strut mounts made a ton of noise on bumpy roads. I put 80k miles on it that way and it didn't change lol. It was a city beater car though, it was nothing special. I orig wanted it as a temp car, but it worked so I drove it for like 3-4 years.

[Blacktree]

Originally Posted by Drifter

Tire/wheel alignment is interesting too. My hypothesis: Older bushings flex more which allows the alignment to change as road forces are applied.

The tire wear pattern seems to support this. The tires have more wear on the outside edges. At first glance, it may look like underinflation. But the tires were inflated properly. And that wear pattern is only on the front tires.

So the worn suspension bushings were allowing extreme toe-in changes during acceleration and braking. That resulted in alternating inside / outside edge wear, as the tires shifted back and forth.

The tires still have plenty of tread left. So I'll increase the tire pressure a little bit, to balance out the wear pattern. And I'll move those tires to the back of the car. That should help get more usable life out of them.

[redpoint5]

Here's my front tires on a 2012 Prius, taken in 2016. That's also when I noticed extreme resistance trying to turn the front wheel when it was off the ground. Don't know if that's normal or not.


I believe the wear was the inside edge, which is abnormal considering how I corner.

[Blacktree]

When I was replacing the control arms, I also checked the brakes. I was able to turn the hubs by hand (with the wheels removed) without much difficulty. I'm guessing maybe your brake calipers were dragging, or the wheel bearings were bad?

[ps2fixer]

With that bad of tread wear, the alignment was bad. Cars go out of alignment over time from the bumps and such. I doubt just a sloppy front end would do that unless it was extremely bad.

My corolla I put 80k miles on the tires with bad inner tie rods but I had the alignment done to 0 (no offset for accounting for road crown, so naturally pulls slightly to the right), and the tread wore just fine. My Tacoma on the other hand I put new tires on and the alignment was way off, I was super busy with work and never had a chance to get the alignment done, 10k miles and the front tires were worn just like the pics above. The front end was tight, just out of alignment.

[Blacktree]

The pizza pans are installed! I was afraid they might look goofy. But as luck would have it, they're almost the same color as the car. So they blend in nicely.





The pizza pans are attached to the trim rings with stainless steel nuts & bolts. The stainless hardware was more expensive, but shouldn't rust. I don't want rust stains all over my wheels.

Now I can acquire fuel economy data while working on the Bimmer.

[redpoint5]

Originally Posted by Blacktree

When I was replacing the control arms, I also checked the brakes. I was able to turn the hubs by hand (with the wheels removed) without much difficulty. I'm guessing maybe your brake calipers were dragging, or the wheel bearings were bad?

Thanks for that response despite it not exactly being on topic...

My Gen III always got 50 MPG, which was lower than my expectation. It had been in a front-end collision, so who knows what damage went undetected by me. Seemed to coast at I expected though.