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  #1  
Old 05-13-2011, 10:09 AM
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Why does the Toyota Prius get much better MPG then the Lexus CT 200h?

So the Toyota Prius and Lexus CT 200h both have the same drivetrain.

The drag coefficient on the Prius is 0.25
The drag coefficient on the CT 200h is 0.29

The weight of the Prius is 3042 lbs.
The weight of the CT 200h is 3130 lbs.

Yet Gas Mileage Varies Big Time

The Prius gets 51 in the city and 48 on the highway
The CT 200h gets 43 in the city and 40 on the highway

Can anyone please explain the huge difference in Fuel Economy?

Last edited by henk4; 05-15-2011 at 10:04 PM.
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Old 05-13-2011, 10:27 AM
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I think a difference of .04 in the drag coeffecient is semi-large. They also may not have the same frontal area.
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Old 05-13-2011, 10:39 AM
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yes, the relevance of 0.04 ( sounds a small number ) is that it means the CT has 16% MORE DRAG.

Check out the higway figs especially --- 20% better , close enough as kitdy says for small change in frontal area to account for the rest
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Old 05-13-2011, 11:01 AM
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But at EPA cycle speed, which I think is like 65mph or something like that, we are not talking huge number here....

It might be the car is geared differently, or just that the car had different tuning in terms of how it behaves at normal drive cycle....

BTW I saw one of these the other day, the car is a lot smaller than I thought....
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Old 05-13-2011, 11:04 AM
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Not to mention different tires, suspensions, engine ECU maps, aerodynamics (which is much more complex than just Cx), gearbox management and so on and so forth.

The two tires/wheels available on the Prius make a 5% difference in fuel consumption (the larger wheels are worse in this regards).

The difference in mileage between the Insight and the CR-Z is 15%.

No wonder these two are different as well.
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Old 05-13-2011, 11:05 AM
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Drag starts from low speeds.

Just dip the clutch and see how it slows down.
Then try the same with a wind and see how it slows down quicker.

There's a lot of drag at 65mph
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Old 05-13-2011, 11:10 AM
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Tires friction is quite relevant as well, maybe more than drag at low speeds (65 mph is not that slow).
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Old 05-13-2011, 11:18 AM
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100 lbs would do a bit of difference too. Think about it, you have another person with you in the car.

In America's case, you'd have about 1/3 of an extra person in the car.
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Old 05-13-2011, 11:33 AM
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I drove a CT. It was pretty boring and crappy, but it was the first hybrid I had ever driven so I was quite thrilled.
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Old 05-13-2011, 11:49 AM
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Quote:
Originally Posted by Matra et Alpine View Post
Drag starts from low speeds.

Just dip the clutch and see how it slows down.
Then try the same with a wind and see how it slows down quicker.

There's a lot of drag at 65mph
But it will be a bigger contributor as the speed increases, and the city cycle driving, which is done largely below 55 mph, drag will not be the main contributor, at least I don't think to the tune of 8mpg.

CT was designed to be more of a hybrid to the tune of CR-Z, as in maybe less boring(doubtful) and with some sacrifice of pure mileage performance in order to look more exciting, with the big wheels and tires. I'd guess the extra inertia from that probably hurt its MPG performance too....
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Old 05-13-2011, 12:07 PM
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Get a low friction car and a low wind and see the difference in each direction.

MAN the kind of things teachers got us to do as kids to learn the reality of a physics lesson. WHere are those kind of lessons now

but yeah, lots of other variables involved !!!!
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Old 05-13-2011, 03:27 PM
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Great responses thanks....Both vehicles have the same CVT trans and they both wear low rolling resistance tires.

Just seems like quite a difference.

Last edited by henk4; 05-15-2011 at 10:02 PM.
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Old 05-13-2011, 03:42 PM
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Quote:
Originally Posted by Matra et Alpine View Post
Get a low friction car and a low wind and see the difference in each direction.

MAN the kind of things teachers got us to do as kids to learn the reality of a physics lesson. WHere are those kind of lessons now

but yeah, lots of other variables involved !!!!
Mulsanne's Corner Race Car Aerodynamics Database: 2001 Mazda RX-7 and RX-7 R2

RX-7 arguably less aerodynamic than a Prius, produces ~300 lb of drag at 150mph. Drag quadruple with speed, at 75 mph you are looking at 70-80 lb of drag. Do you get 8 MPG less with a kid sitting in your car?

I wouldn't be surprised though if the CoD is not the only measure that the CT is less efficient than the Prius, its not the sole contributor to actual drag force a car is carrying.

Plus big wheels and tires you are accelerating that every time you stop and go in the city cycle....
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Old 05-13-2011, 06:01 PM
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Quote:
Originally Posted by RacingManiac View Post
I wouldn't be surprised though if the CoD is not the only measure that the CT is less efficient than the Prius, its not the sole contributor to actual drag force a car is carrying.

Plus big wheels and tires you are accelerating that every time you stop and go in the city cycle....
I think that's probably the answer. Despite the similar drivetrain they are in the end very different vehicles, therefore the difference in offficial figures.
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Old 05-13-2011, 08:50 PM
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Being that I know nothing about drag coefficients other than the fact that lower is better, I was really surprised to actually see the different numbers put into a percentage. 16% is a fairly sizeable improvement.

Quick question for the American members on here, as we're talking about low fuel consumption cars, is the Golf Bluemotion or Fiesta Econetic available in the United States? I ask only because (give or take) 50mpg for the Prius or Lexus seems pretty dismal when you could be talking about 60+ mpg where the Volkswagen or Ford are concerned.
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