Starting to think 2010 Prius has flow separation issues. Comments?

[Daox]

Originally Posted by MetroMPG

How do you know the frontal area was estimated from H x W? I don't see a source in that document.

EDIT: my mistake. I see the note at the top of that page.

But I believe the figures on that page are collected from multiple sources, and the H x W estimate may not apply to all of them. I'll have to ask Daox - he made that page....

Almost all of the frontal areas are calculated from H x W. A few of them were found to be factory specifications, but very few.

[Rokeby]

I'm having trouble getting my mind around the possibility of the Gen III Prius
having worse aero than the Gen II. I'm no fan of the overall Gen III shape/look,
so it would make me happy in a perverse way if worse aero went with it...
That said, I want to believe it's something else.

I take it that the roll-downs are done in "neutral"...

Well, as neutral as a Prius gets; all the bits are still connected through
the PSD, and "neutral" is just a HSD imposed/created electronic condition.

IIRC, on the Gen II, in "neutral" there is just the slightest power being used,
~0.7 HP. I'm guessing that is to overcome drag from spinning the ICE.

Could the Gen III be using a different "neutral" algorithm so that the ICE drag
isn't compensated for?

And then, the Gen III has more aggressive regen if the roll downs were done
in D, in a "blue arrows" coast.

[donee]

Hi Rokeby,

Cd can be better, but the drag worse. The Cd is not that much different between the two. That they could have changed something for the worse, yet still gotten a similar Cd. I think this is the case. Of course, as I have stated, I think its the front slope of the car that is making things worse. One might wonder if the Prius has now been turned into one of these cars with better aero drag going backwards.

The downhill runs were were warp-stealth with the peddle feathered for no regen, and minimum motor.

On the Gen III, its very easy to do this with the accelerator, thanks to the ECO display.

Not so easy on the Gen II. I would feather the peddle so that I was in warp stealth, just above regen.

I have experimented with giving the Gen III significant battery down the hill, and it still does not make up for the difference in speed.

[user removed]

Originally Posted by donee

Hi Rokeby and Clev,

I am thinking Toe-in too. In that the 2010 rolls and rolls below 40 mph, in comparison to the 2006. At the higher speeds, the tires toe out, and if the toe-in setting is dead on zero, this would create scuffing friction on the tires.

The tighter bearings and non-broken in tires would impact the slow speed rolling too. If the car is rolling better at slow speeds, then other than the toe-in issue, its gotta be aero-dynamics.

I have two long slow hills on one of my routes. On the really long hill, I am at 40 mph at the top, and 36 at the bottom 1 1/2 miles later. Both cars do this exactly. On the other hill I crest at 33 mph, and at the base I am doing 35 about 1/2 mile later. Again both cars do this the same.

Slow-Speed down hill coasting wise this car is very very similar to the 2006. In the flats, I think it coasts a little better than the 2006, but I guess that is kinda subjective....

Definitely keep a close eye on your front tires for excess wear on the outer edges. My 2006 Corolla ate up the front tires in 13k miles, and I bought it with 6 miles on the odometer.

After the typical dealer mumbo jumbo, Toyota replaced the tires for free and actually had to tweak the unibody in the rear to get the rear axle properly aligned.

If you really want to know get a reputable (non Toyota) shop to do a thorough 4 wheel alignment check. Be careful of statements like the toe is in specs, when the total toe has a spec beyond the individual wheels. Also if you have the alignment adjusted, tell them to try for minimum total toe at all 4 wheels. Not sure it that is adjustable at the rear wheels, but if so go for minimum total of all wheels.

regards
Mech

[donee]

Hi OM,

Yea, the Prius does that too. We Prius people run our tires at 42/40, or a little higher in general. This will generally result in reasonable tire life. I have my 2010 at 44/42 right now cold, in the morning, before the sun hits them.

The Toe-in spec tolerance on the Prius allows toe-out. Which has been the consternation of allot of Prius drivers. I agree, minimum toe in, without going to toe-out. The rear Prius alignment is only adjustable with shims.

There is a shop near by which the owner races 911's. He has 4 wheel weights capability as well.

[bwilson4web]

Hi,

I do not have direct evidence of higher rolling or aerodynamic drag with my wife's ZVW30. I'm just sharing the following:

• punctured tire - had Firestone patch and bought lifetime alignment. The toe required adjustment. I have yet to correct the passenger side camber, not as vertical as I want, and rear wheel toe and camber. These are on my list of future improvements.
• changed transaxle oil at 5k miles - the subsequent oil analysis did show evidence of sealant and manufacturing tooling material. The straight-line viscosity slope suggests 15k is the initial transaxle oil service life so I'm waiting for 15k miles (another 5k miles to go) before the second change and oil analysis.
• full block - using cardboard and duct tape, there is evidence that full blocking has a small but measurable effect. My plan is an articulating air inlet panel and side, edges to prevent air spillage out of the corners.

One unplanned change were the tires.

I picked up a second nail that hit the patch of the first tire repair. So I bought on sale, four Sumitomo T4s, the recommended, in stock, tires from the Toyota service center and run them at 50 psi (except for the recent cold front.) I'll top them off later today.

Right now, I'm conducting hill climb, maximum speed, gasoline studies with the ZVW30:

• 87 octane, E10, Shell - data collected, crest speed ~91 mph.
• 93 octane, straight gas, Pure - data collected, crest speed ~89 mph.
• 87 octane, straight gas, Pure gas - waiting on fuel exhaustion
• 89 octane, E10, Shell - waiting on fuel exhaustion

Bob Wilson

[donee]

Hi Bob,

So are you saying that the 2010 Prius there is coasting down similar to your Gen 1 Prius from high speed ?

[aerohead]

Originally Posted by donee

Hi All,

I am really starting to think the 2010 Prius has flow seperation issues, in comparison to the 2nd Gen (2004 - 2009). They lowered the rake of the front of the car significantly. The front to back dimension under the hood is much bigger.

I just do not get the coast down performance I was getting from my other car (if you have not heard, my 2006 Prius was totalled by an un-trained SUV driver - lets make SUV drivers pass special training and testing! - and I am now driving a 2010). Even though the low-speed rolling resistance seems just fine, maybe even better! Yea, the car is bigger, but its also a little heavier, and yea its got those big rear-view mirrors, but they have been aero-improved with steped down rim along the back. The 2010 has a nice difuser treatment under the rear bumper. It should be a wash.

On Boundary layers, I think allot depends on vehicle shape. An aero vehicles will have a thin boundary layer, and a bluff body car will have a turbulent boundary layer. So, I think the boundary layer can probably vary by a factor of three from car to car. The thickness of the boundary layer is dependant on the tubulence energy within the air next to the vehicle. Aero-experts does this sound right ?

donee,I took a factory photo of the 2nd-gen Prius and compared to the Streamlining Template and got a very close match.If there is separation over the backlight I would suspect it to be insignificant.
The boundary layer is a function of vehicle length and velocity,and the pressure profile of the pathway the air is following.It is reported by Hucho that around 20-mph,most cars will be in a turbulent boundary layer.
I have the equation to calculate boundary layer thickness although there doesn't appear to be much interest in the formulas already posted.
Our big challenge is flow separation,reducing it,or eliminating it,and Hucho asserts that this can only be accomplished by extending the length of the vehicle,improving its length/height ratio ( fineness ratio ).

[donee]

Hi Aerohead,

Have you done that for the 3rd Generation Prius too? That is what I concerned about. My 2nd Generation Prius did very well down hill above 45 mph. Its the 3rd Gen Prius I have that is not.

The tail of the 3rd is close to that of the 2nd Gen Prius. Its the lead into the peak height that is different between the two cars, I believe.

[bwilson4web]

Originally Posted by donee

. . . So are you saying that the 2010 Prius there is coasting down similar to your Gen 1 Prius from high speed ?

Sorry but I haven't measured the coast down characteristics of either car, yet. However, both have Sumitomo T4s and six of eight tires are 195 width and the other two 175s.

My posting was to suggests some areas that may impact rolling resistance. All I've done for aerodynamics testing with the ZVW30 has been some lower inlet testing in cold weather.

Bob Wilson