LexusRules

sorry at first i thought i saw 245 all around

Mr Johnson

wwest: I'm afraid I don't understand. With an open differential, like on our cars, braking the only wheel that has power reduces traction on the only wheel that has it. With a LSD you'll actually try to get the other wheel involved in moving the car. That's why I'm saying it doesn't add anything. Now with a torsen diff braking a wheel that's loose will cause the other one to move.

In any case I completely agree that the ideal setup (probably used by the racers) is to have a LSD with TRAC (foot braking). If I'm missing something please let me know.

Peter

willard west

something...

Trac: according to Lexus the TRAC ECU applies the brakes to the driven wheel wherein it detects "impending" wheelspin, literally forcing the engine torque to the opposite wheel, presumably the one that will still turn AND has roadbed adhesion. And in the meantime you have just "slowed" the wheel that was entering the "spin cycle" back down below below the point where its "driving" force, torque, was threatening to overcome its ability to adhere to the roadbed.

For myself, I just can't buy that "impending wheelspin detection" bit. I think it is likely a wording mistake taken from ABS activation on "detection of impending lockup".

How would you go about detecting impending wheelspin, isn't that a lot like predicting the future?

But that is an implementation detail that really doesn't matter detection of actual wheelspin will suffice.

The shortcoming of a simple open diff'l is this, it will route all of the available engine torque to the wheel or wheels with the LEAST level of traction. This clearly would reduce the amount of torque available overall to the lowest common denominator.

How much torque does it take to turn a freely "spinning" wheel?

Now throw in a mechanical LSD, Limited Slip Diff'l, across the open diff'l.

Limited Slip diff'l: If I'm wrong here I'm sure some of you will let me know. I believe the most typical mechanical LSD implemenation, the one most commonly encountered by the "masses", is one implemented with "wind-up" clutch paks.

The driven wheel which spins/turns the fastest "winds-up" the clutch activation mechanism toward the side with the most traction. Notice that it does NOTHING to reduce the spin rate of the tractionless wheel, so here again the available torque is limited to the lowest common denominator.

And I would NEVER suggest combining an electronic TRAC system with a mechanical LSD.

LexusRules

i belive lexus does this with some of their IS300's that have LSD option and VSC.

willard west

VSC, vehicle stability control...

If under steering.. will actuate the appropreate rear brake to facilitate correction.

If over-steering, will actuate the appropreate front brake to facilitate correction..

TRAC, Traction control...

Will apply the brakes to any DRIVEN wheel wherein wheel slippage is detected to be impending.

Both VSC and TRAC rely on the ABS hardware for base implementation.

VSC can be implemented indendent of TRAC and if the IS has a mechanical LSD implementation then the electorically implemented TRAC would likely not be included.

But the more likely scenario, much better overall performance, would be ABS, VSC, and TRAC. As a general rule, once ABS is made available, mechanically implemented LSDs would not be cost effective, nor is their performance likely to be as good as TRAC.

///MDex

If anyone is curious like I was about some basic principles of what is taking place, here's a decent starting point:

http://www.howstuffworks.com/differe...tm?printable=1

Mr Johnson

willard west: Sorry, didn't mean to put words in your mouth. WRT to LSD and TRAC though, I don't know about how Lexus implements it on the IS300 but it seems like a good idea to me. Why wouldn't you want to have the mechanical piece add as much traction as possible by shifting the TQ to the other wheel, so that both are driving you forward, and then when you have exhausted *that* call on the TRAC to slow things down and keep things under control. Didn't you earlier agree that a LSD would let you spin both wheels? As far as the swapping of power left/right/left (the military step...) I think that could be handled pretty easily with decent programming of the TRAC.

Alas I'm too lazy to head over to the website you mentioned but I'd love to hear how an open diff car with TRAC could provide more traction than one with a LSD and a good right foot (My example here would be how people were sure Audio Quattros wouldn't be as fast as other rally cars of that time. Putting power down to more wheels sure did help them win races. If that's wrong analogy let me know.)

Regards,

Peter

Brahms

Thought I'd resurrect this thread years later to ask GS430 owners what make/size of tires they use for wet conditions.

It rained pretty hard here (SF Bay Area) recently and I took a pretty harmless left turn at an intersection and almost completely lost control of the back end. Loud beeping from the VSC, etc. Luckily, the streets were pretty much vacant--which, come to think of it, is pretty remarkable for this part of the country. Anyway, any advice would be appreciated.
2001 GS430

firelizard

iTrader: (1)

I've not had issues with wet weather traction on either the Michelin Primacy all seasons I had on my stock wheels, the Hankook W409 winter tires I use, or the Bridgestone Potenza RE760 Sports I have on my 18" Prodrives. Obviously the Bridgestones work the best, at least while the weather is warm. Despite that I drove to work and back on wet roads just above freezing temperatures and the Potenzas were still sure footed. Either your tires are shot, or it's driver error.

2002 GS430, VSC/Trac/ABS disabled.

Brahms

Ha! Driver error and bad tires are both possibilities. But with respect to driver error: I'm not generally a leadfoot and I'm not sure what I did wrong, presuming it was my fault. I didn't power through the turn, or anything like that. I do keep all traction/stability control systems on, by default, and drive with the ECT set to 'ECON.'
Tires still have a little under half of their life left.