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Old 01-14-2009, 10:39 AM   #1 (permalink)
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Default 2010 Prius same drag coefficient as original Insight

Is this possible?

http://autos.aol.com/article/detroit-au ... 0709990001

Honda Insight vs. Toyota Prius
Detroit Auto Show Hosts Battle of The Green Giants
While the roof is the same height, the peak roof height has been shifted back almost four inches. The move gives the Prius a more wedge-like shape for improved interior room and reduced aerodynamic drag. According to Toyota, the Prius achieves an aerodynamic drag coefficient (Cd) of just 0.25
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Old 01-14-2009, 01:41 PM   #2 (permalink)
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Default Re: 2010 Prius same drag coefficient as original Insight

quoting said article:

"Even though the 2010 Prius is slightly larger and carries more features than the outgoing car, its combined mpg rating is expected to increase to 50 mpg, up from 46 mpg for the 2009 model. Toyota achieves this mileage using a 98-horsepower 1.8-liter four-cylinder engine running on the ultra-efficient Atkinson cycle. The engine's extra size enables it to make more torque (105 lb-ft), and although it runs counter to conventional thinking, the additional torque enables the engine to get better highway fuel economy (because the engine can run at lower engine speeds). The motor portion of the Prius hybrid system produces a peak 80 horsepower, and when combined with the engine, results in a maximum powertrain output of 134 horsepower. Acceleration should be more than ample."

If they cut 700lbs off the current curb weight of 2921lbs, and gave it a smaller atkinson cycle engine, They could probably build an affordable 4 seater sized similarly to the yaris, with the ability to run in all electric, maybe even a 5spd.. what, maybe 70mpg?
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Old 01-14-2009, 06:41 PM   #3 (permalink)
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Default Re: 2010 Prius same drag coefficient as original Insight

I think the Prius-III has an even larger frontal area than the Prius-II did.
Preliminary Frontal Area of Prius-III
looks like somewhere under about ~2.6 m^2

Total Aerodynamic drag is Cd times Frontal Area.

So to have better Aerodynamics your combined Cd * Frontal Area has to be less.

The Insight-I had 0.25 * 1.9 = 0.475
Prius-II had 0.26 * 2.16 = 0.5616 ( ~18% worse than the Insight-I , even while the Cd is only ~4% worse. )

Of course the preliminary numbers might be off slightly... but we know it is a bigger car than the Prius-II was... a Bigger car = a bigger frontal area.... with the Cd = to Insight-I ... in order to have as good of Aerodynamics, it also have to have equal or less frontal area as well.... which it won't.

Still nice car... nice stuff... but... not more Aerodynamic than the Insight-I.... sorry folks.
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Old 01-15-2009, 02:29 AM   #4 (permalink)
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Default Re: 2010 Prius same drag coefficient as original Insight

If the 2010 has same cd as Insight 1. Than I guess that means the rear retracted/skirted wheels
and underbody panels are mere cosmetics. Huh?
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Old 01-15-2009, 06:07 AM   #5 (permalink)
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Default Re: 2010 Prius same drag coefficient as original Insight

Quote:
Originally Posted by lenwardus
If the 2010 has same cd as Insight 1. Than I guess that means the rear retracted/skirted wheels
and underbody panels are mere cosmetics. Huh?
nope... it means they might have been able to get down to a Cd of ~0.249 with them... and they didn't think the increase in aerodynamics was worth the cosmetic effect.
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Old 01-15-2009, 09:54 AM   #6 (permalink)
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Default Re: 2010 Prius same drag coefficient as original Insight

I think lenwardus is suggesting in his comment that the wheel splats (side panels) and under body panels on the original Insight (vintage Insight - first generation Insight) do not really affect aerodynamics so much since the new Prius can match the drag coefficient number without using wheel splats.

I tend to disagree... Time changes everything... Toyota had 10 years to come up with a different design that would match the drag coefficient as the original Insight. If Honda wanted to redesign the outer shell of the first generation Insight, I'm sure that they could change a few things here and there that could beat the original cd without using wheel splats.

But just like IamIan was saying, the cd is now the same but the frontal area of the Prius is much larger than the original Insight so it still would take more power to push the car through the air.

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Old 01-15-2009, 11:21 PM   #7 (permalink)
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Default Re: 2010 Prius same drag coefficient as original Insight

I think it shows that aerodynamics is a lot more complicated that it might appear at first glance.

For example, the Prius and Insight II are longer than the Insight, so their rear wheels are further back. The distance from the front of the car to the rear wheel is about 3 meters on the Insight and about 4 meters on the Prius. According to a chart in an aerodynamics book I have, the turbulent boundary layer at 3 meters is perhaps 4 cm thick, while at 4 meters it's about 5.5 cm thick. That might be enough to put the wheel well on the Prius into an area where the boundary layer is thick enough that the spats don't help very much.
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Old 01-17-2009, 08:10 PM   #8 (permalink)
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Default Re: 2010 Prius same drag coefficient as original Insight

Think this may fit better in our Hybrid/Alt Fuel News forum...
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Old 01-19-2009, 12:08 AM   #9 (permalink)
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Default Re: 2010 Prius same drag coefficient as original Insight

The CDxFA on my old '67 Europa (type 46) was .5068. .29x1.7477

In the past the frontal area of a car was measured all the way to the ground since undercar turbulence was like a solid. The early Europas had a full belly pan, so that may have helped. The car got 39 mpg at 75 mph on 39 cents per gallon 100 octane gas. A penny a mile with an archaic Renault rocker box motor. At a gvw of 1320 lbs with the cast iron engine, I wonder how a Civic Hybrid transplant would work.
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Old 01-21-2009, 08:32 PM   #10 (permalink)
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Default Re: 2010 Prius same drag coefficient as original Insight

Occasionally I park my 2000 Insight next to a Prius and I have a hard time believing a newer Prius more aero than the old Insight. I tend to think Toyota didnt really fudge the numbes, but cleverly manipulated them.

An example:

Back in about 1969 Honda started making the 750 4-cylinder motorcycle. They claimed that any one rolling off the assembly line would do like 10.5 seconds in the quarter mile (dont remember the exact time). I Had a hopped up Norton and went to the drags and quite a few of my buddies had the 705 Hondas - ported, polished, lightened, bigger tire, re-geared, etc. and no one could not get near the time advertised for a stock one.

We got notified that the Honda racing team was coming to the local dealership (GN Gonzales in Baton Rouge, La was the largest in the US at the time) and we decied to find out how they did it.

This little guy comes walking by about 4' tall, probably weighed 65-70 pounds. He was the drag race rider. What they said was that they pulled really did pull a bike off the end of the assembly line, just enough gas to make the run in the tank, got 4 sumo wrestler size guys, one each side of front wheel, one each side of rear wheel, picked the bike up over their heads (at the starting line), rider revved motor in 2nd gear until it was about to blow.

Then they didnt drop it, they slammed it down as hard as they could from about 8' in the air.

It shot out with this 65 pounds guy about 50 feet before it hit the ground, by this time the motor was back revved up near blowing rpm in 3rd and he was off.

I would say that 20 pounds of that guy's 65 pounds were kahunas. Can you imagine doing that?

I will lay odds that when the tested the new Prius, it was with heated air, low barometirc pressure, wiped down with Rain-X or whatever else it takes to get nice munbers.

Besides, if it has a lower aero coefficeint, it would get better gas mileage --- Simple math.

Sorry, dont believe it...... Joe Mayers
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