Confession

[hyde]

Re: FWD all the Time

Throw this into the mix: unless the vehicle has locking axles front and rear, the vehicle really does not have 4 wheel drive, only 2 wheel drive-1 wheel on each axle.

you mean one on each side? I don't get that, select trac sends %48 to front %52 to rear on FT. (although this feels more like 40/60)

My mom's 05 GC has 2 options. Full Time 4WD (AWD?) and 4lo. No 2WD. Must not be a problem...

That's actually no problem at all, it is Quatra-Trac ? or Quatra Trac - II or something like that I think..

 

[kjpilot]

Being in 2wd does not mean there is any drag on the front tires. The amount of drag would be VERY, VERY little. Not enough to notice a difference in tire wear. The entire drivetrain is turning at all times, so putting the tcase in fulltime does not turn anything that wouldnt be turning in 2wd.

Master Yoda says: Underestimate the power of the Force, you must not!

Of course, the force in this case is friction, or drag. Everything is turning regardless of 2wd or 4wd, that is true. But whether or not the front tires are putting power to the pavement makes a big difference. It's just physics, I'm not just making things up! I read i in a text book, & went out to test it in our 2001 Grand Cherokee. I Drove the same circuitous route of about 15 miles, once in 2wd once in full time 4wd in close succession. Using the overhead computer, the difference was about 1 MPG better in full-time 4wd.

All other things being equal, when in 2WD the engine only has to turn the rear wheels. This results in "drive-train" drag. This typically saps 10-25% of the engines power, & explains why horsepower & torque are higher when measured at the flywheel and lower at the drive wheels. Now switch it to AWD, & the ENGINE has to turn additional parts of the t-case, the front driveshaft, the diff, the axles, & the wheels. All these parts have inertial weight & and mechanical friction which adds to the drive-train drag. If this were the only aspect of the issue, it would be more efficient to drive in 2WD.

This is where all other things become unequal. As we said, everything turns when driving in 2wd as well as AWD, & it takes energy regardless of why it is turning. In 2wd, the power from the rear wheels has to do this, in AWD, the power from the engine does this directly. The biggest difference between these two is the rubber & the road. If the engine turns the 4 wheels directly there is not as much "surface friction" as there is when the engine has to add all the power through the rear wheels to indirectly push the rest of the drive-train.

The difference isn't much, but it is measurable.

Tokyo Joe, I emphasized full-time above, because the same is not true with part-time. the added mechanical drag of the wheels being locked together makes the difference there.

 

[kjpilot]

And increased tyre wear?

Which of these 2 tires will disappear first?

1) the one being dragged across pavement against its will

2) the one which is rolling freely across the pavement

There should be less tire wear with 4wd.

#-o ](*,) #-o

I thought about this, & My reasoning is off! Tire wear should actually be the same in 2wd as FT 4wd. The difference is that the wear is more evenly distributed across all 4 tires.

In other words, you will loose the same amount of rubber in 2wd or FT4wd. In 2wd it is probably close to 90% from the rear & 10% from the front, and in FT4wd it is 48% from the front & 52% from the rear. But the end result is 100% regardless of t-case setting.

 

[hyde]

Only if I can find a way to fix the transfer case BANG, I don't think I would ever switch back to 2WD. Sometimes the bang is embarrassing.

 

[Jeger]

Being in 2wd does not mean there is any drag on the front tires. The amount of drag would be VERY, VERY little. Not enough to notice a difference in tire wear. The entire drivetrain is turning at all times, so putting the tcase in fulltime does not turn anything that wouldnt be turning in 2wd.

Master Yoda says: Underestimate the power of the Force, you must not!

Of course, the force in this case is friction, or drag. Everything is turning regardless of 2wd or 4wd, that is true. But whether or not the front tires are putting power to the pavement makes a big difference. It's just physics, I'm not just making things up! I read i in a text book, & went out to test it in our 2001 Grand Cherokee. I Drove the same circuitous route of about 15 miles, once in 2wd once in full time 4wd in close succession. Using the overhead computer, the difference was about 1 MPG better in full-time 4wd.

All other things being equal, when in 2WD the engine only has to turn the rear wheels. This results in "drive-train" drag. This typically saps 10-25% of the engines power, & explains why horsepower & torque are higher when measured at the flywheel and lower at the drive wheels. Now switch it to AWD, & the ENGINE has to turn additional parts of the t-case, the front driveshaft, the diff, the axles, & the wheels. All these parts have inertial weight & and mechanical friction which adds to the drive-train drag. If this were the only aspect of the issue, it would be more efficient to drive in 2WD.

This is where all other things become unequal. As we said, everything turns when driving in 2wd as well as AWD, & it takes energy regardless of why it is turning. In 2wd, the power from the rear wheels has to do this, in AWD, the power from the engine does this directly. The biggest difference between these two is the rubber & the road. If the engine turns the 4 wheels directly there is not as much "surface friction" as there is when the engine has to add all the power through the rear wheels to indirectly push the rest of the drive-train.

The difference isn't much, but it is measurable.

Tokyo Joe, I emphasized full-time above, because the same is not true with part-time. the added mechanical drag of the wheels being locked together makes the difference there.

That really doesnt make sense...would be like saying that your rear bicycle tire has more friction/traction while pedaling than it does while coasting. It doesnt add up.

Can you explain what you mean in a different way perhaps?

 

[thecause17]

Being in 2wd does not mean there is any drag on the front tires. The amount of drag would be VERY, VERY little. Not enough to notice a difference in tire wear. The entire drivetrain is turning at all times, so putting the tcase in fulltime does not turn anything that wouldnt be turning in 2wd.

Master Yoda says: Underestimate the power of the Force, you must not!

Of course, the force in this case is friction, or drag. Everything is turning regardless of 2wd or 4wd, that is true. But whether or not the front tires are putting power to the pavement makes a big difference. It's just physics, I'm not just making things up! I read i in a text book, & went out to test it in our 2001 Grand Cherokee. I Drove the same circuitous route of about 15 miles, once in 2wd once in full time 4wd in close succession. Using the overhead computer, the difference was about 1 MPG better in full-time 4wd.

All other things being equal, when in 2WD the engine only has to turn the rear wheels. This results in "drive-train" drag. This typically saps 10-25% of the engines power, & explains why horsepower & torque are higher when measured at the flywheel and lower at the drive wheels. Now switch it to AWD, & the ENGINE has to turn additional parts of the t-case, the front driveshaft, the diff, the axles, & the wheels. All these parts have inertial weight & and mechanical friction which adds to the drive-train drag. If this were the only aspect of the issue, it would be more efficient to drive in 2WD.

This is where all other things become unequal. As we said, everything turns when driving in 2wd as well as AWD, & it takes energy regardless of why it is turning. In 2wd, the power from the rear wheels has to do this, in AWD, the power from the engine does this directly. The biggest difference between these two is the rubber & the road. If the engine turns the 4 wheels directly there is not as much "surface friction" as there is when the engine has to add all the power through the rear wheels to indirectly push the rest of the drive-train.

The difference isn't much, but it is measurable.

Tokyo Joe, I emphasized full-time above, because the same is not true with part-time. the added mechanical drag of the wheels being locked together makes the difference there.

Do you have any facts other than what you read in a text book and a 15 mile loop of driving? I think if you're goign to make claims such as this then do an actual study which all variables taken into consideration and a much longer milage slice. Not just 15 miles. You didn't even use a gallon of gas, let alone be able to say what the difference in gas milage is. Ever notice how much gas milage fluctuates on your EVIC when you first reset it? It takes a while for it to settle down to a more stable reading...longer than 15 miles. Early on you can just hit the gas and make it drop or put it in neutral and watch it climb. If you're going to make actual claims, try driving a known milage(that uses much more than less than a gallon of gas) in the same temp, same humidity, and the exact same driving routes, in both 2WD and Full-Time.


You are giving the same speculation you did in this thread...

http://www.jeepkj.com/forums/viewtopic.php?t=4565


In the meantime, I'm going to go drag my front two tires across the pavement against their will. \/

 

[kjpilot]

Do you have any facts other than what you read in a text book and a 15 mile loop of driving? I think if you're goign to make claims such as this then do an actual study which all variables taken into consideration and a much longer milage slice. Not just 15 miles. You didn't even use a gallon of gas, let alone be able to say what the difference in gas milage is. Ever notice how much gas milage fluctuates on your EVIC when you first reset it? It takes a while for it to settle down to a more stable reading...longer than 15 miles. Early on you can just hit the gas and make it drop or put it in neutral and watch it climb. If you're going to make actual claims, try driving a known milage(that uses much more than less than a gallon of gas) in the same temp, same humidity, and the exact same driving routes, in both 2WD and Full-Time.


You are giving the same speculation you did in this thread...
http://www.jeepkj.com/forums/viewtopic.php?t=4565


In the meantime, I'm going to go drag my front two tires across the pavement against their will. \/

Well lets see...
Setting aside my college degree in aviation, and my career as a pilot & flight instructor, I guess I know nothing about physics; especially friction & drag on moving object :-s

I didn't go into specifics above, because I was already using alot of room. I did my circuit on an interstate highway at night, with minimal traffic, using cruise control. I did not reset the computer until I was at a stabilized speed. I did a circuit (notice the first 5 letters are the same as in circular) so I would negate the effects of wind, differing road conditions and grade. I did the circuits one right after another so the weather conditions were as identical as possible, & to allow the cruise setting to remain untouched. Of course, I did not use instantaneous MPG, but average MPG.

Using the set-up I described above, you'd be suprised how fast the EVIC settles down. If the EVIC has a sample rate of once per second (I think it's higher) then the average readout I observed was taken across 900 samples per circuit (15 miles at 60mph =15 minutes x 60 seconds.) That's a pretty good sample, especially when merely testing a statement in a physics text, rather than working on my own research.

Your math is off, as 15+15=30 and that leads to slightly less than 2 gallons. And your reasoning is backward- your rear tires are pushing your front tires. the force that is generated is called drag. Feel free to continue pushing, you are only loosing .5-1.5 mpg... no big deal!O

Please, prove me wrong. I am not a push-over, but in the face of overwhelming & accurate evidence contrary to what I believe, I will change my outlook!

 

[thecause17]

Well lets see...
Setting aside my college degree in aviation, and my career as a pilot & flight instructor, I guess I know nothing about physics; especially friction & drag on moving object :-s

I didn't go into specifics above, because I was already using alot of room. I did my circuit on an interstate highway at night, with minimal traffic, using cruise control. I did not reset the computer until I was at a stabilized speed. I did a circuit (notice the first 5 letters are the same as in circular) so I would negate the effects of wind, differing road conditions and grade. I did the circuits one right after another so the weather conditions were as identical as possible, & to allow the cruise setting to remain untouched. Of course, I did not use instantaneous MPG, but average MPG.

Using the set-up I described above, you'd be suprised how fast the EVIC settles down. If the EVIC has a sample rate of once per second (I think it's higher) then the average readout I observed was taken across 900 samples per circuit (15 miles at 60mph =15 minutes x 60 seconds.) That's a pretty good sample, especially when merely testing a statement in a physics text, rather than working on my own research.

Your math is off, as 15+15=30 and that leads to slightly less than 2 gallons. And your reasoning is backward- your rear tires are pushing your front tires. the force that is generated is called drag. Feel free to continue pushing, you are only loosing .5-1.5 mpg... no big deal!O

Please, prove me wrong. I am not a push-over, but in the face of overwhelming & accurate evidence contrary to what I believe, I will change my outlook!

This isn't an airplane...and I know how fast the EVIC settles down, my girlfriend's Grand Cherokee has one. That is not a good sample. You may view it as one, but it would be nothing as compared to let's say, a 150 mile sample.

I could care less about your degree, I went to school with plenty of people who have the same piece of paper I do, but couldn't work their way out of a paper bag. You're still basing it out of a book, and not testing. I never called you a push over, so don't throw name calling around...instead of speculating, test it. As far as circuits go, I have a degree in Electronics Engineering Technology...big whoop.

And it's not 30 miles, it's two seperate instances, for comparison, not adding together. You did 15 miles in each mode, if you're going to add the milage together, than you have to average your gas milage too. If you can't perform a proper test then don't bother posting information that's not accurate.

I'm not going to argue about it any further, obviously you would rather me try and prove you wrong than back up your speculation. Believe me, if my Jeep had Select-Trac, I would not hesitate to put together a proper test of this and graph the results, but since I don't and you do, it's up to you, and you won't either.

Take it easy, don't work too hard. =P~

 

[hyde]

Too bad KJs don't have instant mpg to check anything, but even so, it is pretty hard to get the same instant mpg at same road, it depends on whole lot other things than just drag. Engine is hot/cold, road conditions, wind (especially on neutral), heck even sitting position..

What I would say is that 1mpg is well worth the pleasure and handling of 4x4FT on my kj. I do 12 miles to work in the morning, that takes almost 40 minutes.. so, imagine.

 

[thecause17]

Too bad KJs don't have instant mpg to check anything, but even so, it is pretty hard to get the same instant mpg at same road, it depends on whole lot other things than just drag. Engine is hot/cold, road conditions, wind (especially on neutral), heck even sitting position..

Yeah, there are a lot of variables, including driving habits. I had a rental Malibu a while back, and just sitting at a light you could watch it's readout change, and at the same token out on the highway it would change as the grade of the road changed, early on.

Sometimes I wish I had Selec-Trac...My old Explorer had a system similar to the Quadra-Trac II and I like that a lot, I think Id like the Selec-Trac even more.

 

[chetos]

Re: FWD all the Time

Throw this into the mix: unless the vehicle has locking axles front and rear, the vehicle really does not have 4 wheel drive, only 2 wheel drive-1 wheel on each axle.

you mean one on each side? I don't get that, select trac sends %48 to front %52 to rear on FT. (although this feels more like 40/60)

My mom's 05 GC has 2 options. Full Time 4WD (AWD?) and 4lo. No 2WD. Must not be a problem...

That's actually no problem at all, it is Quatra-Trac ? or Quatra Trac - II or something like that I think..

You can actually feel that difference? [-o<

 

[hyde]

When the rears spin, yes. Not the %4 but %20. Just drive through unfinished pavement, stop and try to get go, you will notice rear spin way more than %4.

 

[kjpilot]

This isn't an airplane...and I know how fast the EVIC settles down, my girlfriend's Grand Cherokee has one...

wtf.gif

Sorry, You thought I was being adversarial. I wasn't.

Your reply is so full of holes, errors and illogical comments that I cannot reply to them with out insulting you. I tried 3 times, and I can't do it. So I won't.

If you have a degree even loosely based in science, you should recognize that I took someone's theory & tested it. I observed it to hold up, under the parameters that I outlined. You think The experiment should be more extensive. Do something about it! This stage is called peer review, & if you have found your way out of the bag, you know this is how the scientific process works!

Of course now you are a biased source, because if your test agrees with mine then your pride is at stake.:-$

BTW-Circuit 1: 15 miles at 16mpg=0.9375 gallon; Circuit 2: 15 miles at 15mpg =1.0 gallon; Circuit 1+Circuit 2=1.9375 gallons, or "slightly under 2 gallons" over a 30 mile course idea.gif

 

[desertkj]

This isn't an airplane...and I know how fast the EVIC settles down, my girlfriend's Grand Cherokee has one...

wtf.gif

Sorry, You thought I was being adversarial. I wasn't.

Your reply is so full of holes, errors and illogical comments that I cannot reply to them with out insulting you. I tried 3 times, and I can't do it. So I won't.

If you have a degree even loosely based in science, you should recognize that I took someone's theory & tested it. I observed it to hold up, under the parameters that I outlined. You think The experiment should be more extensive. Do something about it! This stage is called peer review, & if you have found your way out of the bag, you know this is how the scientific process works!

Of course now you are a biased source, because if your test agrees with mine then your pride is at stake.:-$

BTW-Circuit 1: 15 miles at 16mpg=0.9375 gallon; Circuit 2: 15 miles at 15mpg =1.0 gallon; Circuit 1+Circuit 2=1.9375 gallons, or "slightly under 2 gallons" over a 30 mile course idea.gif

Just curious kjpilot, I've been biting my tongue for a long time, but why is every one of your posts condescending and dripping with disdain? Everyone here is trying to be insightful and provide opinions and discussions, while you treat everyone else like an inferior being. I would greatly appreciate it if you would show a little more respect.

 

[Jeger]

Being in 2wd does not mean there is any drag on the front tires. The amount of drag would be VERY, VERY little. Not enough to notice a difference in tire wear. The entire drivetrain is turning at all times, so putting the tcase in fulltime does not turn anything that wouldnt be turning in 2wd.

Master Yoda says: Underestimate the power of the Force, you must not!

Of course, the force in this case is friction, or drag. Everything is turning regardless of 2wd or 4wd, that is true. But whether or not the front tires are putting power to the pavement makes a big difference. It's just physics, I'm not just making things up! I read i in a text book, & went out to test it in our 2001 Grand Cherokee. I Drove the same circuitous route of about 15 miles, once in 2wd once in full time 4wd in close succession. Using the overhead computer, the difference was about 1 MPG better in full-time 4wd.

All other things being equal, when in 2WD the engine only has to turn the rear wheels. This results in "drive-train" drag. This typically saps 10-25% of the engines power, & explains why horsepower & torque are higher when measured at the flywheel and lower at the drive wheels. Now switch it to AWD, & the ENGINE has to turn additional parts of the t-case, the front driveshaft, the diff, the axles, & the wheels. All these parts have inertial weight & and mechanical friction which adds to the drive-train drag. If this were the only aspect of the issue, it would be more efficient to drive in 2WD.

This is where all other things become unequal. As we said, everything turns when driving in 2wd as well as AWD, & it takes energy regardless of why it is turning. In 2wd, the power from the rear wheels has to do this, in AWD, the power from the engine does this directly. The biggest difference between these two is the rubber & the road. If the engine turns the 4 wheels directly there is not as much "surface friction" as there is when the engine has to add all the power through the rear wheels to indirectly push the rest of the drive-train.

The difference isn't much, but it is measurable.

Tokyo Joe, I emphasized full-time above, because the same is not true with part-time. the added mechanical drag of the wheels being locked together makes the difference there.

That really doesnt make sense...would be like saying that your rear bicycle tire has more friction/traction while pedaling than it does while coasting. It doesnt add up.

Can you explain what you mean in a different way perhaps?

I am still trying to make sense of that, (in the bold) maybe you could tell me where you read this?