Joe, I have faith that Eric (DTS) will nail down a LSD for the S-Type.

 

I was always under the impression that our dsc systems apply's the brakes in order to keep power to both wheels. Same system as the e55,c32,etc... which are all truely open diff cars. People install lsd's aftermarket for $$$$. I really can't believe our cars are don't have some type of lsd, ive read numerous times it does.

 

Correct me if I am wrong, but I believe that "Dynamic Stability Control" is intended more for maintaining traction during breaking and cornering rather than during heavy acceleration.

Applying a brake to one wheel while you are trying to accelerate, while wheel is losing traction/spinning out, is not the best way to optimize acceleration. Limited slip allows the power to be proportionately applied to both wheels so one wheel will not brake loose and still lets both wheels apply power to the ground.

In general you only need a LSD when accelerating and during cornering under power. If cornering hard, as in autocross, and the inside tire lifts up off the ground, resulting in less traction, the other wheel will still get proportionately more power.

 

I don't recall EVER reading (from anyone credible) that our cars have LSD and indeed they do not. I do recall a lot of people wanting one or hoping they already have one.

 

LSD can be useful in bad weather when traction is spotty. I don't care about stoplight drag racing, just getting home when the weather turns bad.

The 'Traction Control' feature is new to me, and the info in the user's manual isn't very specific other than to say there is a switch to disable it if desired. Does this actually apply selective braking to one wheel when it breaks loose? How effective is it in poor traction (snow/slush/ice) conditions? What are the down sides other than reduced acceleration (which doesn't matter in bad weather)? Would the LSD mod really be worth the $$/hassle for bad weather driving or is this more of a high performance nice-to-have?

 

The LSD interest is for high performance and better launch from zero, mainly for the STR. TC is OK for bad weather but even the 3.0 is RWD with a bit much power to be good in snow/ice. Fit winter tyres for those conditions.

 

On a RWD vehicle, a good clutch plate type LSD in the hands of an experienced snow driver will beat "traction control" hands down every time in deep snow, or on ice.

On rutted ice covered secondary roads, the traction control makes the car feel squirrely because it tries to correct for every little thing, whereas an experienced driver will let the car wander a little bit because it is not necessary to be arrow straight at all times.

 

+1

This is the issue with the traction control on the STR. It's rather clumsy feeling IMHO and makes me completely lift, not a good reaction on my part!

Those of us who learned to drive without it or ABS (ancient ones ... LOL) are perhaps a bit more in tune with a cars "natural" behavior. Though I wouldn't necessarily want to try and out perform a good ABS system. My track car still has ABS and it saved my **** once while racing a guy to the corner next to me who wen't straight off in a huge cloud of blue smoke.

Some LSD should improve the driving!

 

I just had a drive today in bad conditions. BTW, I am an experienced RWD snow driver, lived for 7 years near the shore of lake Superior, where we never saw pavement for 6 months out of the year.

Today was pretty bad, not that much snow; only a couple of inches, but it fell on pavement that was above freezing, making for a thick slush all over everything. Changing lanes is really dicey when it is like that. You can hydroplane at 30 mph.

TC worked OK, but felt weird, and acceleration was slower than I would expect. I tended to let off acceleration when TC kicked in; it still felt like a spinning wheel with a conventional diff. ABS got a good workout today; I wouldn't be without it! I think I like the feel of 'posi' or LSD better, but don't know yet if it is worth the $$ for the mod. My tire tread is most definitely not appropriate for these conditions; regular tread, and only about a year of tread depth left. I do think that I need at least an all-season tread. I drove very conservatively and had no trouble, but wouldn't want to chance it in deeper snow. I have a 4WD vehicle for that.

 

To be more clear, there are several different combinations of stability and traction control systems at play here. "DSC" describes several of them in one.

The DSC system in my '03 STR may be different than that of an '00 3.0,

With DSC on, you will have a 'stability' program which manages vehicle yaw through turns, it will modulate wheel speed of individual wheels through the ABS,

DSC will also have a 'traction' program managing wheel-spin at the drive tires by way of the ecu/throttle control. This is how it works on most 'traction control equipped' cars out there.

DSC will also have another form of 'traction' control, in which the ABS will try and slow down the spinning drive-wheel through the brakes,

This is what you could call a faux electronic differential. A cheap band-aid solution to an open diff car like the STR. Pretty common to see used on modern performance cars that are still open diff equipped.

Then you take for instance a true electronic differential, such as Ferrari eDiff which allows the stability program to intelligently vector torque to individual wheels!

---

With that said, ABS, Stability, Traction, controls of DSC are there to keep car rolling safe and predictably. An LSD upgrade is of little benefit if all you're doing is going about your daily commute with the right tires on.

For me personally, I want to be able to switch off the DSC and really wring this car out the way it deserves, with plenty of tail-out smokey drama. An LSD, for me personally in my own STR, is as desirable as another 100+ hp.


An LSD would have the added benefit of having the DSC system 'work less' in its effort to 'slow down' spinning wheels, making this car all that quicker off the line.

I was considering selling my STR come spring, but this potential for an LSD upgrade has me rethinking that...

 

That could very well be...
but I don't have enough info at hand.

The only things I *recall* from reading the owner's manual are the brief description of TC and that it can be disabled, and 'Sport mode' for the transmission. I have both enabled.

When I first drove on slippery roads about a month ago, I just remember it feeling so strange, like the rear end was a bit squirrely.

It seems odd to me that Jag would omit LSD on this type of car; It couldn't be more than a few hundred $ worth to include the feature as OEM. This is a funny place to economize unless they actually thought that TC was really just as good as LSD for essentially no cost.

 

Various (most?) of the models do not have the accelerometers that the STR has.

GT42R - good summary. The CAN messages include "torque reduce".

 

We can anticipate a LSD for the S-Type.

 

Contrary to popular belief, a limited slip differential does not effect wheel traction on slippery surfaces such as ice, rain or snow. The 'clutch' discs are designed to lock the two output shafts when both rear wheels are on dry pavement and have good traction. Once one wheel loses traction, the clutch discs release and the differential works like all non-LSD units.

 

Hogwash.

You've got it backwards. Use a search engine to find advanced articles on clutch type lsd's that includes a discussion on ramp angles. Ramp angles determine the rate of engagement and rate of release.

Newport Beach doesn't get much snow. Snow drivers who have driven with these lsd's for decades know full well that they improve traction on ice and snow. Even for small jobs like getting out of a rutted parking spot. Alternatively, ask any experienced mudder. There is a reason these two markets pay extra to get lsd capability and it isn't bragging rights or theory. It's because they work in inclement conditions as described.

 

Ditto to plums. Both wheels recieve power all the time in wet and snow. It's on dry pavement that power to either wheel is limited when one wheel spins during a turn, etc.

 

Based on the number of LSD units I worked on over the years, I believe there is much mis-information on the subject.

I have no desire to debate this issue, but would be interested in knowing how many differentials either of you have disassembled and reassembled?

I hope you enjoy the season and holiday with your families and friends.

 

Just to confirm some earlier posts here regarding Quaife QDF3W:
Racing Green Jaguar. - S-Type 1999 onwards, Differential, Limited Slip

 

NBCat you are 100% completely wrong. As has been said, you have things completely backwards. A LSD works to move torque from the spinning wheel to the wheel with traction. My credentials are that I work for Jaguar and worked with the people that developed the eDiff on the later XFR. That is a LSD with electronically controlled lockup clutches. Note, the S Type including R has no LSD. The Traction control program reduces throttle opening to reduce wheelspin, and brakes wheels to recover from slides.

 

Nbcat: I've disassembled and assembled many, many diffs for many different types of racing and street cars. And you are absolutely wrong in your assertions. In low traction situations, an LSD should never overcome the force required to separate the clutches, resulting in both wheels turning equally, with equal torque.
It is only in dry, hi traction situations that the wheels might have enough traction that they can overcome the clutches and turn at different speeds, like in a turn.