So Much for AWD - Page 6 - PeachParts Mercedes-Benz Forum

thorsen · #76 03-28-2013, 12:06 PM

Quote:

Originally Posted by t walgamuth

We are talking about completely different subjects. Talking about someone sliding off the road because they exceed the grip availalbe happens all the time because the DB does not understand basic physics. What I am talking about is a bit more subtle than that.

He's trying to argue with you on a technicality. You're not going to win.

t walgamuth · #77 03-28-2013, 12:16 PM

Its hard to think of a time BC has ever conceded anything.

rickmay · #78 03-29-2013, 09:16 AM

Quote:

Originally Posted by t walgamuth

Its hard to think of a time BC has ever conceded anything.

Is that yellow bug of yours a formula jr, or a whatchacallit?

I went to University of Denver in the sixties, had a 59 MGA that was serviced by a Brit (was trained in the factory) and half Indian (I call him Indian, as I cannot remember his name, but he was darn proud to be half Cherokee) and both loved messing with cars. We would get a couple of six packs and work on cars in the Indian's garage. He had a whatchamacallit, formula junior race car with a shiny metal bullet-shaped body, and if I remember correctly, it had a 4 cylinder Cosworth engine. I think the engine was mounted aft of the rear axle/transmission.

On some of the warm nights about midnight, he would take this thing out on the Valley Highway (a four land divided expressway, no lights), and we would stand out on his driveway and listen to him go thru the gears, first to to the east, then to the west, and then back home back home. I doubt it took more than four or five minutes total. I want to say that the top end was 120, but could have been as high as 140. On these quiet and warm summer nights, you could probably hear this thing 15-20 miles away.

Brian Carlton · #79 03-29-2013, 10:55 AM

Quote:

Originally Posted by rickmay

Most cars dip in the front when you brake. You will know you have your brakes in tip-top condition when both ends of your Mercedes dip when you hit the brakes. When new, both the front and the back drop pretty much equally. My memory from 33 years ago, says 3-4 inches drop, front and rear. It may take orig pads to do this. "

Congratulations.

You have successfully redefined physics and have figured out how to make both the front and the rear of a vehicle compress their springs equally in a braking situation, despite the fact that the CG of the vehicle forces a significant weight transfer to the front wheels.

In a panic stop, the rear wheels are practically unloaded completely.

You really ought to patent this invention as the automobile manufacturers would be highly interested in understanding how it works.

cmbdiesel · #80 03-29-2013, 12:07 PM

Quote:

Originally Posted by rickmay

I didn't say give it the gas, and I was referring to the driving conditions when the SUV inadvertently challenged the semi in the video I posted earlier. The person lost control of that vehicle because they let up on the gas. For that person, it turned hopeless when they bumped the first truck. In that situation, you want to maintain the pedal and turn the wheel into the direction of the spin. At this point, there is no drag on the front wheels, but there will be more drag on the rear wheels (because they are going sideways a little bit). As far a parking lots go, one can use the parking brake to spin out the car in the parking lot, but one can also put drag on the rear wheels by using the parking brake. In either case, you are reproducing what a rear two wheel drive vehicle does naturally.

We have no way of knowing if the driver of the Nissan Navarra let up on the gas. certainly watching the video, it would appear as if he (Alexander) hit a row of deeper slush/snow and it caused the vehicle to fishtail. This is also the interpretation of the Russian Police in the Omutischi Petushki district, where the incident took place.
You may be excellent at applying a parking brake during a spin, but I would never recommend that course of action to anyone. Far to easy in limited traction situations for the application of any brake (especially a parking brake) to cause lock up and exacerbate the lack of traction.

Quote:

Originally Posted by rickmay

I agree that you choose an appropriate gear, but in the case of my driveway example, one does need a low gear in that case. This from a man who spent many years roaming and skiing the Colorado Rockies.

Again, you may be excellent at this procedure, but as another driver who spent years driving the Colorado Rockies (lived in 'em for many years too, over 5 miles from pavement at 8200') I would recommend to others to be in the tallest gear you can avoid stalling in. Especially in a powerful vehicle.
My old K5 Blazer never saw low range in the snow. Way too much power.
Did use it many times to pull people out of snowbanks and ditches....
My little '51 Willys was way more fun, but much colder....

P.C. · #81 03-29-2013, 12:11 PM

Quote:

Originally Posted by Brian Carlton

Congratulations.

You have successfully redefined physics and have figured out how to make both the front and the rear of a vehicle compress their springs equally in a braking situation, despite the fact that the CG of the vehicle forces a significant weight transfer to the front wheels.

In a panic stop, the rear wheels are practically unloaded completely.

You really ought to patent this invention as the automobile manufacturers would be highly interested in understanding how it works.

The closest thing that I've seen to such a feat involved a '70's Citroen SM.

See it in action at about 1:08 in this clip: http://www.dailymotion.com/video/xc12t4_burt-reynolds-en-citroen-sm-maserat_shortfilms

Volker · #82 03-29-2013, 12:15 PM

Quote:

Originally Posted by P.C.

The closest thing that I've seen to such a feat involved a '70's Citroen SM.

But SM are insane, semi-magical vehicles and not be be used as reference to anything

I always think it easier to consider handling from a basic tire traction aspect, the tire doesn't know what way you are trying to go, it can only develop a force along a single vector, so if you want to slow down, don't turn...

Brian Carlton · #83 03-29-2013, 01:11 PM

Quote:

Originally Posted by P.C.

The closest thing that I've seen to such a feat involved a '70's Citroen SM.

See it in action at about 1:08 in this clip: Burt Reynolds en Citroën SM Maserati. - Vidéo Dailymotion

You can see the capability at 2:03 of the clip under severe braking. But, even the Citroen lifts up the back end at least 6" during that stop.

t walgamuth · #84 03-29-2013, 07:20 PM

Quote:

Originally Posted by rickmay

Is that yellow bug of yours a formula jr, or a whatchacallit?

I went to University of Denver in the sixties, had a 59 MGA that was serviced by a Brit (was trained in the factory) and half Indian (I call him Indian, as I cannot remember his name, but he was darn proud to be half Cherokee) and both loved messing with cars. We would get a couple of six packs and work on cars in the Indian's garage. He had a whatchamacallit, formula junior race car with a shiny metal bullet-shaped body, and if I remember correctly, it had a 4 cylinder Cosworth engine. I think the engine was mounted aft of the rear axle/transmission.

On some of the warm nights about midnight, he would take this thing out on the Valley Highway (a four land divided expressway, no lights), and we would stand out on his driveway and listen to him go thru the gears, first to to the east, then to the west, and then back home back home. I doubt it took more than four or five minutes total. I want to say that the top end was 120, but could have been as high as 140. On these quiet and warm summer nights, you could probably hear this thing 15-20 miles away.

It is a 1985 Reynard Formula Ford. With road race gears it will run 120 I am told, with the autocross gearing it will only go 85 or so but will get there pretty quickly. It has a 1.6 Ford pushrod engine sold here in Pintos with a weber carb and a header, rated about 110 hp in a car that weighs about 900#. We run Hoosier autocross compound slicks capable of about 1.3 to 1.4 G's after they are good and hot. Its a lot of fun.

t walgamuth · #85 03-29-2013, 07:27 PM

Quote:

Originally Posted by Brian Carlton

Congratulations.

You have successfully redefined physics and have figured out how to make both the front and the rear of a vehicle compress their springs equally in a braking situation, despite the fact that the CG of the vehicle forces a significant weight transfer to the front wheels.

In a panic stop, the rear wheels are practically unloaded completely.

You really ought to patent this invention as the automobile manufacturers would be highly interested in understanding how it works.

I will take by your lack of response that you cannot cite any science which will refute my evidence, that you don't own a 4wd vehicle and you have never in fact driven one at the limits of adhesion.

Brian Carlton · #86 03-30-2013, 09:55 AM

Quote:

Originally Posted by t walgamuth

I will take by your lack of response that you cannot cite any science which will refute my evidence, that you don't own a 4wd vehicle and you have never in fact driven one at the limits of adhesion.

My lack of response has already been explained.

You don't have an engineering degree and you are unable or unwilling to make the reach and try to understand the physics of cornering and what occurs at the limit even though it has been carefully and methodically explained to you three times.

Furthermore, you're unable to understand the definition of a "cornering limit".

Finally, your anecdotal evidence of how your 4wd vehicle behaves on a track below the cornering limits of the tires is completely irrelevant to the discussion, and yet you persist with this useless argument.

Therefore, I leave you and all the others who own these vehicles to enjoy your belief that it provides you with "better cornering" at the very limit of adhesion between the tire and the road surface. Hopefully your ignorance won't kill you someday.

BTW, you have many beliefs that are in fundamental opposition to the laws of physics that have been pointed out to you in the past and you refuse to understand your ignorance. This just adds another to that list.

t walgamuth · #87 03-30-2013, 10:08 AM

Quote:

Originally Posted by Brian Carlton

My lack of response has already been explained.

You don't have an engineering degree and you are unable or unwilling to make the reach and try to understand the physics of cornering and what occurs at the limit even though it has been carefully and methodically explained to you three times.

Furthermore, you're unable to understand the definition of a "cornering limit".

Finally, your anecdotal evidence of how your 4wd vehicle behaves on a track below the cornering limits of the tires is completely irrelevant to the discussion, and yet you persist with this useless argument.

Therefore, I leave you and all the others who own these vehicles to enjoy your belief that it provides you with "better cornering" at the very limit of adhesion between the tire and the road surface. Hopefully your ignorance won't kill you someday.

BTW, you have many beliefs that are in fundamental opposition to the laws of physics that have been pointed out to you in the past and you refuse to understand your ignorance. This just adds another to that list.

Having an engineering degree does not automatically make whatever you have an opinion about correct, just as having an Architectural license make anything I think true without proof.

And...I will take your lack of response to mean that you cannot cite any science which will refute my evidence, that you don't own a 4wd vehicle and you have never in fact driven one at the limits of adhesion.

Brian Carlton · #88 03-30-2013, 10:15 AM

Quote:

Originally Posted by t walgamuth

I have another explanation for your lack of response.

Having an engineering degree does not automatically make whatever you have an opinion about correct, just as having an Architectural license make anything I think true without proof.

The difference is the fact that I would not argue with you if you stated that I need a set of 2x12's to span 16 feet when I might have wanted to use 2 x 10's. I probably missed some important variable or definition or live load determination and I would defer to your knowledge on the subject without demanding "proof" from a third party and without arguing things I know very little about. If I wanted proof from a third party, I could just as easily go online and find out the info, but it still would not educate me as to the "why".

BTW, I hammer nails every weekend on the rentals. Does that qualify me to take an "opinion" against a registered architect?

In engineering, as in the physics of architecture, some things are not a matter of opinion. The 4wd vehicle will go off the road and the structure will fall if certain principles are violated.

cjlipps · #89 03-30-2013, 10:35 AM

Quote:

Originally Posted by Brian Carlton

Show me some evidence............any evidence...........that a 4wd vehicle can perform better than a Rwd vehicle at the cornering limit.

I define the cornering limit at the precise speed and angle of turn whereby any additional applied torque to the axle or any further increase in the angle of turn or any additional speed will cause the tire to slide on the surface rather than roll.

You cannot provide any evidence because there isn't any. The only possibility of a 4wd vehicle "cornering better" than a 2wd vehicle is when the vehicle is below the cornering limit and the tire has the capability of accepting torque without sliding. I deliberately wrote "cornering better" in quotation marks because most folks, such as yourself, believe the vehicle is cornering better, when, in reality, it's simply going faster through the turn than an equivalent 2wd vehicle because it is not at its cornering limit.

Isn't "going faster through the turn than an equivalent 2wd vehicle" the very definition of better handling?
I maintain that all else being equal, ie: tires, vehicle weight, driver competence, horsepower, road surface...the 2wd vehicle will reach it's cornering limit at a lower speed than the awd vehicle. I agree that in the mitts of a blundering cretin awd merely serves to increase the speed at which the vehicle gets into trouble. But in the hands of a competent driver awd provides better handling and stability than an equivalent 2wd vehicle on virtually any surface.

Brian Carlton · #90 03-30-2013, 10:48 AM

Quote:

Originally Posted by cjlipps

I maintain that all else being equal, ie: tires, vehicle weight, driver competence, horsepower, road surface...the 2wd vehicle will reach it's cornering limit at a lower speed than the awd vehicle.

This is the fallacy that you and Mr. W will cling to, despite the fact that it is patently false.

The cornering limit of a tire has nothing to do with the torque applied to that tire. In fact, the cornering limit of a 4wd tire can be LOWER than the cornering limit of a 2wd tire because if the tire begins to spin due to the applied torque, its cornering limit, as defined by the force it can withstand laterally (lateral g force) is reduced.

All of the benefits of a driven tire occur BELOW the cornering limit where the applied torque can be useful.