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eLSD Logic?

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Old 10-15-2017, 09:22 AM
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Default eLSD Logic?

Yesterday I took my 2015 V8R Coupe out to a large piece of open tarmac to learn how the car works when DSC is turned off. After reading all about how tail-happy the car is supposed to be, I was expecting to have some lurid sideways moments if I gave it any throttle while not in a straight line. However, I actually never could get the car to go sideways at all! I did smoke some tires, but an outside-the-car observer said they thought it was just spinning one tire at a time. That's certainly how it felt from the driver's seat as well...lots of noise, not much "go", and no feeling of the rear end being loose.

In searching around here on the forum and elsewhere, I've seen many comments about differential problems in these cars, but I have seen no error codes on my car, it was a cold day, and I didn't drive the car for more than a minute at a time (and it was a cold day), so I don't think anything was overheating. I was mostly just in 1st and 2nd gear and under 60 mph and with how cold the day was, had very little grip.

My searching has not turned up any discussion of when the diff closes and opens other than statements that it opens on corner entry and closes when you try to lay down power. Does anyone on this forum have more detail on what the logic is? Is it possible that at lower speeds or in lower gears it just stays open? Or is there some setting I may have chosen that, without realizing, I have disabled the diff? Finally, is this an indication of a fault that I should be hassling the dealer about?

Thanks for any help/info!

Last edited by Driver; 10-15-2017 at 09:28 AM.
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Old 10-15-2017, 05:10 PM
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What you describe is certainly suspicious. I have no problem at all getting my V6S (mech. LSD) sideways doing donuts with the DSC turned off.
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Old 10-16-2017, 05:41 AM
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Is your R, rear or 4 wheel drive?
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Old 10-16-2017, 07:28 AM
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Is your R, rear or 4 wheel drive?
I believe 2015 MY are all rear wheel drive
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Old 10-16-2017, 09:21 AM
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I believe 2015 MY are all rear wheel drive
Yes...RWD.

I plan on giving the local dealer a call today. I bought the car a little over a month ago and it is CPO, so hopefully I can get them to take a look and see if anything looks funny.

The driving I was doing was sort of like mini-road-course driving with almost no straights between "corners" (aka I was wiggling around like crazy trying to unsettle the rear...I didn't go into "let's do donuts" mode, perhaps that my next thing to try). I would have thought that'd be enough to get the rear to dance...I certainly can unsettle the rear on the road sometimes with DSC on, but one doesn't like to get too jolly with that with DSC off until one knows for sure what the car will do.
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Old 10-16-2017, 10:23 AM
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It takes quite a bit of pushing to get it to break loose (contrary to what motoring journalists have brainwashed most people with).
You may want to build up a bit more courage to push a little bit harder.

Top tip that I received form an F-Type proving engineer - not to put too much steering input in during oversteer.

Be interesting to see what the dealer has to say. Check that you haven't lost any oil from the diff. There is a known issue with seals, but I guess you would have spotted an oil patch when left for any period of time?
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Old 10-16-2017, 10:56 AM
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It takes quite a bit of pushing to get it to break loose (contrary to what motoring journalists have brainwashed most people with).
You may want to build up a bit more courage to push a little bit harder.

Top tip that I received form an F-Type proving engineer - not to put too much steering input in during oversteer.

Be interesting to see what the dealer has to say. Check that you haven't lost any oil from the diff. There is a known issue with seals, but I guess you would have spotted an oil patch when left for any period of time?
I've had more than my fair share of spins in cars and enjoy big drifts with a lot of opposite lock...I definitely got both ends of the car sliding at times in this little test, but big hits to the throttle only produced tire smoke (no tail kick out...and I was really trying to make the car spin) and that is when the external observer reported the car one-legging, which I found quite surprising. If anything, I usually overdrive cars and am too aggressive...so I suspect that isn't the issue here.

I'm curious about your hint from the engineer...so if you start losing the tail during a turn, is the tip to not correct too much with opposite lock or not to have too much initial lock in the steering? I'm used to mid-engined cars and true race cars, so I might have been over-jabby with the wheel to get the car to rotate on turn-in. FWIW, I was quite happy with turn in, but then never felt like I could kick the tail out on corner exit by booting the throttle. It just made noise and smoke, but no tail kick and no real launch feeling, so I am theorizing that the diff wasn't locking up. The question is whether it really should have or whether I was giving it inputs that made it think it was still entering a corner (thus leaving the diff open). So, I'd love to hear some more detail on what the proving engineer told you...it sounds like it might match my "fooling it into thinking corner entry" theory.

No oil spots on the floor of the garage that I've noticed previously, but I'll look again. Thanks for the hints!
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Old 10-16-2017, 11:04 AM
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FWIW, this sounds like a somewhat similar story...

https://www.edmunds.com/jaguar/f-typ...tial-fail.html
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Old 10-16-2017, 11:21 AM
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Turns out someone took a series of pics of the car one-legging...so I don't just have to take their word for it.

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Old 10-16-2017, 11:24 AM
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Another interesting pic...this is late part of corner entry. I wonder if the rear having that little in contact with the pavement might confuse the LSD controller as I go to maintenance and "leave-the-corner" throttle.


Last edited by Driver; 10-16-2017 at 11:28 AM.
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Old 10-16-2017, 01:01 PM
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It may be a function of the TVbB. I'm sure you know that the inside wheel has the brake applied a small amount to counteract understeer, it may be trying to 'nanny' too much.

The Jaguar engineer was part of the proving team for the F-Type. He maintained that when you do get the car into OS, it's important not to overcorrect and stressed small application of opposite lock, and slight 'sawing' to maintain a good slide - I'm yet to prove this theory...maybe when the P0's get a little lower! He also did mention about the edif can get hot.

I must admit, looking at the photos, the outside rear, looks a bit 'lame'. Maybe an issue as others have mentioned. I'm sure they can tell you from the OBD faults...if it has flagged any.

Check out these:



or CH with the V8:


Last edited by Tel; 10-16-2017 at 01:05 PM.
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Old 10-16-2017, 01:30 PM
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Did you turn it completely off, as it requires holding button for 10 seconds, or just pressed it once to put it into track mode?
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Old 10-16-2017, 01:34 PM
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Quote:
Originally Posted by Driver View Post
Another interesting pic...this is late part of corner entry. I wonder if the rear having that little in contact with the pavement might confuse the LSD controller as I go to maintenance and "leave-the-corner" throttle.
The car shouldn't lift the rear wheel like that. Is it lowered by any chance? If so, start looking into hackery PO did to it as a likely culprit.
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Old 10-16-2017, 01:49 PM
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Thanks Tel...I don't think the issue is too much correction once in OS...I'm not even GETTING to OS. I think I may have a decent theory on what's going on...

1) Heavy braking
2) VERY tight corner, lots of steering lock
3) From the pictures, I can see me getting onto the throttle a bit before mid-corner and lighting up the inside rear
4) Being the goon that I was trying to be, I stay very aggressive on the throttle all the way to corner exit and down a mini straight. Inside rear smoking the whole way.

I suspect what's going on is the amount of steering lock means the diff will remain open through the corner, even when the throttle starts opening up and spinning the inside rear. By the time I start straightening out the car, the diff COULD close, but I've been so overagressive with the throttle that there's now a >30mph speed difference between inside and outside wheels. Perhaps you don't really want the diff trying to close/lock at that point...unless you really like stopping to pick up diff parts off the ground. So, the computer protects the diff by not closing until the wheels are closer in speed.

Looking at those drifting videos more closely, I think there's a fundamental difference in approach that yields a locked diff. I was getting on the throttle while I had a lot of steering lock in...they are already on the throttle before they turn in (and in some cases, they aren't in as sharp of a corner). The Goodwood video is probably the most telling...you can see a couple instances in there where it looks like the driver has done the same thing I outlined me doing above...and they don't get the diff locked up.

So...I'm now leaning toward "working as intended" as the description of what I have experienced. I still think it might be worth having the diff checked though...
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Old 10-16-2017, 01:56 PM
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SinF,

The DSC was definitely completely off, not just track mode. The giant cloud of tire smoke would tend to agree.

I do not believe the car is lowered. The car was sold to me as CPO from a Jaguar dealer and when I look at the suspension it all looks stock to me. Mind you, in that picture, the car is turning quite hard (look at how rolled over the outside tires are)...I've seen the same rear-tire lift thing in pictures of me driving a Lotus Elise. In the case of the Lotus, I know the reason it's starting to get picked up is that there isn't enough droop in the rear suspension when you're cornering very hard in sharp corners (sadly, it was hard to convince Lotus that the Elise needed a diff...I had quite a back-and-forth with them for a little while...eventually I did get a Toyota diff for the car, but gave up on racing it before I ever managed to find someone willing to put it in). For the Jag...it could be a droop issue or it just could be a sufficiently stiff rear anti-roll bar picking up the wheel.

To my eye, it doesn't look all that surprising...but maybe my eye is stupid.

FWIW, I'm not upset with the car at all. I bought this car to hoon about in and have fun with...and I still have a big grin on my face every time I drive it, even with this eLSD question...

Last edited by Driver; 10-16-2017 at 01:57 PM. Reason: typos
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Old 10-16-2017, 02:03 PM
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Uh...so moral of the story is, I need to find somewhere to try and make 11s. My guess, it'll make 11s just fine.
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Old 10-16-2017, 02:28 PM
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Note that the V6 in the drifting videos has a mechanical LSD.
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Old 10-16-2017, 02:40 PM
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@Driver

I don't think I ever experienced rear wheel lift off like in your picture with my F-type. Maybe I don't drive it hard enough on the track, or maybe it does happen and I am simply oblivious to it. According to in-dash metrics, I had up to 1.12G lateral maxes during cornering on the track.

To me, position of your car during cornering looks like abnormal behavior for F-type. To speculate, you have insufficient rear suspension travel or excessive front compression. Alternatively, you overcooked on trail braking and the picture doesn't show burned rubber and kicked-up grass that about to occur as you plow through the corner. However, if it doesn't feel abnormal and all tires stay on the pavement maybe there isn't an issue.

Keep in mind, my car is V6 and is less front-heavy. So YMMV.

Last edited by SinF; 10-16-2017 at 02:45 PM.
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Old 10-16-2017, 02:49 PM
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It wouldn't surprise me if you're getting some lift-off like that at 1.1G...I doubt I was more than that. You don't really feel the lift off in the car though...that tire isn't generally doing much anyway at that moment.
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Old 10-16-2017, 02:59 PM
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Quote:
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It wouldn't surprise me if you're getting some lift-off like that at 1.1G...I doubt I was more than that. You don't really feel the lift off in the car though...that tire isn't generally doing much anyway at that moment.
You are absolutely correct that rear wheel isn't doing much traction at that point. However, lift-off is a symptom of suspension tune where the stiffness of the rear axle in roll is excessive. Such setup will be prone to earlier and excessive weight transfer.

If you think there is nothing to it, then there is nothing to it. I am dropping the subject.
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