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Old 01-29-2009, 05:51 PM   #1 (permalink)
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4x4 efficiency vs hybridizing?

In all my thoughts about ways to improve my plain-jane Chevy S10, the one thing I am still not sure about is the efficiency of 4-wheel drive.

I POSSIBLY MIGHT trade my 2-wheel drive S10 for a 4-wheel drive version to do my bio-diesel conversion.

What I am mostly wondering about is how and why 4-wheel drive gets such worse economy than simple rear-wheel drive.

Pardon my ignorance here, I have never owned a 4x4. My understanding is that a traditional four-wheel drive has an engine in front which goes to a transmission, then to a transfer case. From there power normally goes straight through to the driveshaft and rear wheels. If the four-wheel drive mode is selected, the power gets split at the transfer case between the rear and the front wheels. I still am not sure of how "push-button" vs locking wheel caps/covers?!? works.

So, is 4-wheel drive less efficient because:

1) it weighs more - transfer case, front half-shafts etc.
2) power is always going through the transfer case - more moving parts, friction, etc.
3) wind resistance - 4x4s always look really jacked up
4) All of the above?
5) Other - something else I'm missing?

Now part of why I am wondering this is that it seems like a 4x4 would be easy to make into a hybrid - gas or diesel runs one set of wheels, and electric runs the other.

For example, could the rear drive shaft be be removed, hook a (powerful/high voltage) motor to the rear differential and let the gas engine run the front wheels?

Does this cause transfer case wear and abuse?
Would you actually make a front wheel drive pickup just by disconnecting the rear drive-shaft?

I have also heard that diesel is rather efficient under load. Does that mean that a 4-wheel drive diesel pickup would take less of an economy hit than a gas 4x4?

Just curious about all this stuff.

Thanks,

-Ben

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Old 01-29-2009, 06:58 PM   #2 (permalink)
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Ben, I think you have it pretty thought out on why 4wd uses more fuel. All of the above.

Creating a fully redundant hybrid with the front and rear wheels driven by completely seperate systems seems like alot of weight and complexity, especially in a truck.

There is power loss in power transmission systems when the torque turns 90*, I seem to recall it's like 92% efficient or something. With a transfer case and front differential there are two additional 90* turns, additional gears in the transfer case and more seals all have losses of thier own that add up.

Using a tansverse engine/transmission in front and an electric in the back might be more efficient. You could use a smaller engine/trans from a car in the front to optimize efficiency, with the electric powering the rear tires, total power output could be equal to the original configuration.

Then again, the complexity issue. Hmmmm.
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Old 01-29-2009, 07:15 PM   #3 (permalink)
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So, is 4-wheel drive less efficient because:

1) it weighs more - transfer case, front half-shafts etc.
Yes. Also keep in mind that the front hubs and are considerably heavier than on a 4x2, so extra spinning weight.

2) power is always going through the transfer case - more moving parts, friction, etc.
Yes.

3) wind resistance - 4x4s always look really jacked up
Yes, they are really jacked up.

4) All of the above?
Yes.

5) Other - something else I'm missing?
You're not thinking about the front differential and differential housing and the beefier springs and shocks needed to handle all that extra weight. Add it all up and you get -
2000 S10 4x2 curb weight: 3,040 lbs.
2000 S10 4x4 curb weight: 3,596 lbs

Not to mention the shorter gears.
2000 S10 4x2 axle ratio: 3.73
2000 S10 4x4 axle ratio: 3.42
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Old 01-29-2009, 07:44 PM   #4 (permalink)
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yeah but the gear ratio is ito set off the tire height.

i can feel the drag when my hubs are locked in.... but a seperate hybrid would be cool, and i have thought hard about it.
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Old 01-29-2009, 08:45 PM   #5 (permalink)
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So 4x4s have bigger tires to get them up in the air to make room for all the front wheel drive stuff, and then lower gearing to match the speeds back up to where they should be?
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Old 01-30-2009, 12:12 AM   #6 (permalink)
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Quote:
Originally Posted by beatr911 View Post
Using a tansverse engine/transmission in front and an electric in the back might be more efficient. You could use a smaller engine/trans from a car in the front to optimize efficiency, with the electric powering the rear tires, total power output could be equal to the original configuration.

Then again, the complexity issue. Hmmmm.
That would be a really creative setup if the complexity issue could be worked out.... electric maybe to get you rolling, then a smaller engine with less hp to keep you rolling.....interesting...BEN...I think we have another project for you


I always enjoy reading threads about the s10's.
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Old 01-30-2009, 12:22 AM   #7 (permalink)
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Quote:
Originally Posted by TestDrive View Post
So, is 4-wheel drive less efficient because:

1) it weighs more - transfer case, front half-shafts etc.
Yes. Also keep in mind that the front hubs and are considerably heavier than on a 4x2, so extra spinning weight.

2) power is always going through the transfer case - more moving parts, friction, etc.
Yes.

3) wind resistance - 4x4s always look really jacked up
Yes, they are really jacked up.

4) All of the above?
Yes.

5) Other - something else I'm missing?
You're not thinking about the front differential and differential housing and the beefier springs and shocks needed to handle all that extra weight. Add it all up and you get -
2000 S10 4x2 curb weight: 3,040 lbs.
2000 S10 4x4 curb weight: 3,596 lbs

Not to mention the shorter gears.
2000 S10 4x2 axle ratio: 3.73
2000 S10 4x4 axle ratio: 3.42

I'd agree with all of that but politely question the last bit about gears. It could be a typo in the source your got it from cause 4x4s almost always tend to have lower gears (higher numerically) than 2x4s. Usually to account for more weight and larger tires the manufacturer will want the motor to rev a little higher at the same speed than the 2x4 which doesn't have to deal with the weight/tire issues. I would guess those two numbers are backwards. Or the numbers could be for an auto vs a manual transmission (alot of times the auto's have different gearing to account for a difference in efficiency).
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Old 01-30-2009, 12:23 AM   #8 (permalink)
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Quote:
Originally Posted by LUVMY02CREW View Post
.interesting...BEN...I think we have another project for you
NOOOOOOOOOOO!

[runs screaming down the hall....]
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Old 01-30-2009, 01:16 AM   #9 (permalink)
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Quote:
Originally Posted by bennelson View Post
So 4x4s have bigger tires to get them up in the air to make room for all the front wheel drive stuff, and then lower gearing to match the speeds back up to where they should be?
No 4x4 r up more cause they are designed to be taken off road And need the clearence

Best set up may be to remove the rear driveshaft and mount a e-motor to it. It would allow more room. And just run the truck in 4 hi so the front drive shaft will power the front wheels with the motor
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Old 01-30-2009, 04:02 AM   #10 (permalink)
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Quote:
Originally Posted by Daveedo View Post
I'd agree with all of that but politely question the last bit about gears. It could be a typo in the source your got it from cause 4x4s almost always tend to have lower gears (higher numerically) than 2x4s. Usually to account for more weight and larger tires the manufacturer will want the motor to rev a little higher at the same speed than the 2x4 which doesn't have to deal with the weight/tire issues. I would guess those two numbers are backwards. Or the numbers could be for an auto vs a manual transmission (alot of times the auto's have different gearing to account for a difference in efficiency).
I totally agree. My 95 Sonoma runs 3.73 gears, the 2WD runs 3.43 gears. With larger tires you need a numerically higher gearing to maintain the same ratio. So the 2WD with 235/75 vs 4WD 31x10.5, both run the same rpm for given speed.

In a solid front axle 4WD you can disengage the hubs, so that no extra parts are moving. 90% of you mileage loss from 2WD to 4WD are stance and higher weight.
In a independent front suspension (IFS) I don't have locking hubs, it locks in at the differential. So I'm always spinning the axleshafts, and when I engage 4WD it connects the axles to the 4WD differential.


I'm looking into a SAS (solid axle swap) and a Cummins QB3.3T. 300ftlbs, with proper gearing on 33" tires, a couple different guys have gotten 34mpg highway. One guy just finished his and first tank was 27mpg, with lots of excessive throttle (gotta enjoy it!). Just need to find all the parts for relatively cheap. Could probably find the motor for under $2000, axles with lockers for under $2000.

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