Dallas weather and LSD - Page 2 - Lexus IS Forum
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post #16 of 20 (permalink) Old 12-09-2005, 12:22 PM
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Quote:
Originally Posted by evolver
Out of technical curiousity, how to determine quantitively that "some level of stability"? Ice is not enough but dry concrete is sufficient. Where is the threshold? How to define it?

You probably want to spend some time reading up on the coefficient of friction. A quick link that I found using Google is, http://www.school-for-champions.com/...ctioncoeff.htm

A rubber tire on dry asphalt has a very high coefficient of friction (~.8), whereas a tire on ice has a very low coefficient (~0). Wet ashphalt may only have a coefficient of .25. Obviously there is an infinite level in between.

The fact that the genteman's car was slowly creeping forward says that there was some traction, however small... maybe .05 coefficient.
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post #17 of 20 (permalink) Old 12-12-2005, 11:03 AM Thread Starter
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Originally Posted by HoustonLex
You probably want to spend some time reading up on the coefficient of friction. A quick link that I found using Google is, http://www.school-for-champions.com/...ctioncoeff.htm
Thanks for the hint but having a PhD degree in Material Science I think I know what the friction coefficient and the nature of friction are

I probably should rephrase my question though. In its original form it sounds too theoretical, I guess. Let me put it this way: "What are the driving conditions that the stock LSD is designed for?"

We have already excluded icy pavement and other flavors of loosing traction by one or both wheels. In such conditions LSD behaves as if was an open diff. Is it correct?

Ideally, it would be very interesting to know how the torque distribution changes depending on the traction ratio between the wheels. Two scenarios are the most interesting -- when the ratio is gradually decresing (one wheel is loosing traction), and when the ratio increases (one of the wheels regains traction). Is there a threshold at which the torque distribution has a change in behavior in both direction? Or does it have a hysteresis of some sort?

"Howstuffworks" only has an explanation that a housewife can understand... I could not find any other, more scientific, description anywhere.

+rep for willingness to help and spending time to do so

Last edited by evolver; 12-12-2005 at 11:10 AM.
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post #18 of 20 (permalink) Old 12-12-2005, 11:22 AM
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Stock LSD is not meant to be a all-weather device. It is designed for spirited driving in near ideal conditions. The whole purpose of LSD is to put the torque on the outside wheel during cornering since that wheel has the larger contact patch and therefore more traction. Also, that allows the car to push itself through the corner at a faster rate of speed.

However, LSD acts like LSD in all conditions. An open diff would behave differently in icy conditions, although I did mean to ask the original poster whether traction control was on or off when he conducted this experiment?

For example, I would expect an open diff to put power to the wheel with the ice first (path of least resistance), and then I would expect traction control to apply the brake on that wheel. The new path of least resistance should be the wheel with traction, and away you go.

I have never conducted this experiement, but have driven my open diff IS on icy parking lots with no problems, so I assume this is what was happening behind the scenes.

I would expect the same outcome of the LSD too, provided traction control was on.

regarding your last question, that is well above my understanding of LSD, although it would make for one hell of a project.
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post #19 of 20 (permalink) Old 12-12-2005, 11:30 AM Thread Starter
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Quote:
Originally Posted by HoustonLex
I would expect the same outcome of the LSD too, provided traction control was on.

regarding your last question, that is well above my understanding of LSD, although it would make for one hell of a project.
I had traction control turned off for that particular experiment. I did not want automatic braking and throttle control to interfere with LSD bahavior.

Yeah, that could be a very interesting project. Too bad I do not have time and resources for that...
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post #20 of 20 (permalink) Old 12-12-2005, 01:01 PM
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Quote:
Originally Posted by evolver
I had traction control turned off for that particular experiment. I did not want automatic braking and throttle control to interfere with LSD bahavior.

Yeah, that could be a very interesting project. Too bad I do not have time and resources for that...
You're expriment just verifies that with a Torsen, when one wheel has zero traction, you're SOL.

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