LSD a disadvantage on the track????

[xtn]

Originally Posted by MikeW

When God starts making cars, I'll consider them perfect and quit trying to think for myself.

Hmph. I'm sure his designs would be wonderful, but he hasn't shown much in the way of QC in a while.

xtn

[TimMullen]

Originally Posted by JeffYoung

The best LSDs, if I understand the LSD gurus correctly, are clutch packs that are set up to free wheel under coast/braking, and then "lock" under acceleration.

Nope. You have the backward. Torsen type of LSDs "coast" with no power being applied, and "lock" when under power/acceleration. Torsens vary the tendency to induce understeer depending on the power being applied (the amount of "lockup" depends on the amount of power)

Clutch pack type of LSD are "locked" all the time - they tend to induce oversteer all the time, constantly.

[fpitas]

And just to complicate the situation, Torsens don't really lock in the conventional sense, they direct torque. The RPM of the two driven wheels can be very different:

http://en.wikipedia.org/wiki/Torsen

[JeffYoung]

TIm, probably wasn't totally clear (because in part I don't fully understand it).

I have an ATB unit (a Quaife) in my race car. It, as you say, only locks under acceleration, or reallly one wheel is receiving more torque than the other. THe advantage to the Quafie is no understeer on turn in, the disadvantage is if you lift a wheel (so that no torque is applied to in effect), then the ATB doesn't work.

The clutch pack works even when curb hopping, but as opposed to locked, the ramp angles and clutches can be set such that resistance on entry under deceleration is LESS than on acceleration, effectly giving you teh best of both worlds.

Most racers I run with swear by custom clutch pack designs that are set up with the proper amount of breakaway torque -- enough to lock under acceleration, but not too little to lock on turn in.

Clearer?

[fuse]

Just chiming in here a little about LSD and some differences I know of on track.

The Torsen LSD in the Lotus, is the same type for 3rd gen RX7, and 1.8 liter Miata. When I race SpecMiata, a 1.6 liter car gets a Viscous LSD and a 1.8 liter car would get a Torsen LSD per rules. What we found was that the Torsen has more driveline parasitic lost due to the torque sensing design. It is particularly good going deeper into a corner trail braking better than a Viscous LSD. During corner exit, the Viscous unit launches of the corner better than Torsen...but not as good as a locked rear end. (We welded one locked for testing...an old school practice when you don't have LSD, it works, but a handful to drive.) So in SpecMiata, both types of LSD have different advantages and works itself out pretty well. A Viscous LSD is likely in need of a rebuild after a season of racing (I did) but a Torsen is very durable wear and tear perspective, it will last a very long time. Both types produced much better lap times compared to open diff. The Viscous made noises during turns maneuvering like in parking lots or paddocks. The Torsen just is nice and quiet.

I also had an S1 Motorsport Elise which had the Quaife unit in it. I am not sure if it is a 1-way, 1.5-way or 2-way LSD. The difference is 1-way = acceleration only, 1.5 way = acceleration and partial deceleration, and 2-way = acceleration and deceleration. I believe the unit that was in the Motorsport Elise is a 1.5-way. This type works very well, better than Torsen and Viscous. It does however work very quickly, so if you are not familiar or not ready, it can bite you very quickly. My very first warm up lap in my Motorsport Elise resulted in a spin as I put my right rear tire on freshly painted curb and got on the power coming off that corner onto a straight. I never knew what happened, just that I was going backwards when I squeeze on the power. Granted, cold slicks + painted curb + lightweight mid engine car...the effect was much more significant than other cars I have driven with the same type of LSD...but it shows how it can be trouble some on streets when you often have unpredictable surfaces.

I've not autox before, so I don't really know what the courses layouts are like and how tight the corners are and how much you would trail-brake and the need to launch off the corners...but I believe Elise Torsen LSD will allow you to drive smoother and should result in better times. It should not have any ill effect on the street. It will change how the car feels as it is working all of the time except when 1 wheel has lost all traction (ie, 100% torque difference between left and right) which I would guess why there are some understeer comments...I would imagine when you are in a turn, and the rear diff is working properly providing grip, allowing you to apply more throttle and more speed, eventual resulting in understeer at the limit.

Don't forget understeer/oversteer condition varies, you can have corner entry, mid corner, and corner exit understeer/oversteer and you are never going to get the car to be perfect in every corner and every part of the corner. You adjust and set up the car to the way you like to drive, the way you can get the best lap time, and if racing, how and where you want to be fast to pass or avoid being passed.

I didn't get LSD as the car is very good without it when I drove my friends Elise on the track...and when I want to get one I would probably go with a clutch-type given that this is not my daily driver anyway. (Just a few areas on the track that it was less than ideal, but few enough that you'd just drive around it...not racing wheel to wheel and just don't need that advantage.)

[EXigeS]

I have the factory LSD and love the way the car drives on the track; from some of the threads last year I was expecting terrible understeer on and off power but it absolutely doesn't exist (front camber of just under 2degrees helps i'm sure).

[LotusUSA]

LSD is ok. Just don't overdose.

No. pls don't ban me. I was just kidding.

[Patricko]

Originally Posted by cgomez

Have any of you tried driving fast a non-LSD car in the rain or winter? It's just no fun, watching the engine rev up with little control over the rear and no power oversteer attitude.

Yes, 1,700 miles mostly in the rain Wettest June in 500 years in England

It was loads of fun

I am still smiling

[cgomez]

Is a lot more fun when you have a LSD and can lay down some nice opposite lock black lines while still having forward thrust. Better for lap times too ...



...and I haven't stopped smiling for a second

[jacks1071]

Originally Posted by grecomfs

Am contemplating an Exige S for track/DE events. I'm being told that LSD option is good for autocross but is a disadvantage on the track. Can anyone here confirm/refute/explain? Thanks in advance and thanks for the great forum!!

I think whoever told you that BS was on LSD....

The LSD is awesome everywhere, I wouldn't own a car without one.

[robains]

You want Limited Slip Differential in most cases. Agree with XTN -- inner wheel doesn't spin as freely as the outer which can make the front wheels work harder which can result in understeer.

But as has been pointed out, you can adjust the weigh balance, tire stagger/pressures, diff oil, to address any understeer from the LSD. But every race series I've ever participated in I've also had LSD and adjust the packing accordingly -- there are many levels of "slip". Bare in mind this is "limited slip" the diff still slips, it's not a locker.

If you want more or less slip, try experimenting with Redline shock proof oils (super light weight to heavy weight) and you'll soon "feel" how these fluid differences are affecting your slip -- just do a U turn or a tight circle -- you'll hear it and feel it (sounds like a grinding/clicking noise). I played around with oil weights all the time to adjust the desired level of slip when racing.

LSD is more noticeable with more TQ -- Exige S would almost always benefit from LSD but even a Elise/Exige would benefit also -- still enough TQ with given weight.

But to answer the question, track or autoX -- I would always want LSD.

Rob.

[TimMullen]

Originally Posted by jacks1071

The LSD is awesome everywhere, I wouldn't own a car without one.

In general I would agree, however the Elsie is a different animal than most cars. I love the LSD in my Miata. I haven't missed it at all in the Elise. Then again, I'm not heavily into tracking the cars. There are advantage and disadvantage to an LSD. And those differ depending on the car.

Originally Posted by robains

But as has been pointed out, you can adjust the weigh balance, tire stagger/pressures, diff oil, to address any understeer from the LSD. But every race series I've ever participated in I've also had LSD and adjust the packing accordingly -- there are many levels of "slip". Bare in mind this is "limited slip" the diff still slips, it's not a locker.

The oils should have little to no effect on the LSD that is installed by the factory in the Elise/Exige. It is a Torsen type of LSD, and it's "locking" capabilities are based on the physical properties of the angles of the work gears in the LSD. They do not depend on the friction of clutch packs, etc. They do not depend on friction, and different oils should not change that - at least not to any really noticeable effect.

[Conan]

All I know is I wish I would have had an LSD in the car on Saturday. I would constantly get inside wheelspin coming out of T7 at Grattan, and could feel the acceleration flatten out. Then once I got the wheel straightened out, the spinning tire would suddenly bite the asphault and the car would lurch forward. That CAN'T be good for the rear to link.

[robains]

Tim,

I'll disagree with you somewhat -- Torsen uses worm gears to sense torque and all gears are subject to friction and the oils used to manipulate that friction will modify the level of sensing.

But I do agree, that the oil differences are not as significant on Torsen.

Conan,

If you're spinning the unloaded wheel that much you might want to consider increasing the spring rates or notch up the shocks or play around with weight transfer (ride heights).

Just curious, how many of you are actually scaling your Lotus and setting ride heights, caster, camber, front/rear toe, etc. etc. before going to the track (and/or at the track)? Pretty important steps -- we're talking seconds in lap times not just 1/10ths.

Rob.

[JeffYoung]

I've had the car corner weighted, and a "full" track alignment done consisting of each available adjustment. With 4k on teh A048s on my first track day, unlimited wheel spin in turn 1 at VIR in 3rd gear.

Put new A048s on the rear, wheel spin gone, but the fronts are shot so the car now pushes like a beeyatch.

Need to get "real" track tires. Not so impressed with the squealers, I mean A048s. Never heard R compounds squeal like that.

[Conan]

Originally Posted by robains

Conan,

If you're spinning the unloaded wheel that much you might want to consider increasing the spring rates or notch up the shocks or play around with weight transfer (ride heights).

Just curious, how many of you are actually scaling your Lotus and setting ride heights, caster, camber, front/rear toe, etc. etc. before going to the track (and/or at the track)? Pretty important steps -- we're talking seconds in lap times not just 1/10ths.

Rob.

Good to know. I currently have the base suspension, so I can't adjust anything other than toe and camber. I do plan on getting an adjustable suspension soon. Maybe next spring-ish.

[robains]

Jeff,

Hoosiers -- might wanna consider a separate set of wheels to mount them on. I rarely get more than one weekend out of Hoosiers. Or some shaved Proxies RA1 -- they last longer but not as sticky as Hoosiers.

I don't know for sure yet since I haven't tried Hoosiers on the Exige S yet, but almost always Hoosiers have required me to go up in spring rates.

Conan,

Toe and camber is a start (they adjust together not separately). If you do move up to ride height adjustability be sure to corner weight it with you in the car (or at least your approximate weight in the driver seat)

Rob.

[S2Lola]

I'm not suggesting that they are the same, but look at formula fords for example (lightweight, mid engine, lots of rubber) - some similarities to our cars. FFs use an open diff, but are extremely efficient at putting the power down due to extremely adjustable suspension and big sticky tires.

Having driven them for the better part of 15 years, I don't think a well-sorted FF would be quicker with a LSD.

So, to our cars. IF one were to work on dialing in the suspension to the nth degree (like we do on our FFs), maybe it makes sense that once at that point and LSD would be of little value. However, many of us aren't about to go to that degree of work - for those folks, maybe an LSD is an easier way to go faster without a lot of work?

Just rambling.....

BT

[robains]

Perhaps not the best of comparisons as the usage of differential (seeing as these are not F1 cars):

http://www.f1technical.net/articles/30

F1 drivers (Schumacher in particular) would constantly adjust the differential during a race (along with other parameters) -- corner specific. It can directly affect the balance of the car and even braking.

For sure the best solution -- so I guess the answer to LSD or not to LSD is -- it depends