LSD

[Mozart]

My apologies in advance, as I suspect that this has been covered before.
Please review the merits and downsides of the Lotus LSD, or refer me to a previous post that will give me the guidance that I need. I am planning on purchasing a 2008 Exige S240 in the months ahead. Thanks.

[fzust]

LSD is really useful for AutoX to power out of corners rather than spin the inside wheel. Less important for trackdays and honestly NOT having one builds in a bit of safety as the car will not tend to snap oversteer under power. If you are hardcore at autox it is a must have, otherwise not necessary. My $0.02

[ace10]

easiest search is as follows:

advanced search, titles only, use "lsd*"
good luck.

[Z-dculus]

LSD is bad for you

also, i still don't understand the "snap oversteer" concept. if anything i think it would add to understeer, not oversteer (cause the car to push)


oh yeh, and there's only 26 of us

[TimMullen]

Originally Posted by Z-dculus

LSD is bad for you

also, i still don't understand the "snap oversteer" concept. if anything i think it would add to understeer, not oversteer (cause the car to push)

LSD does tend to promote understeer (unless tweaked out of the suspension). But the snap oversteer happens because of the affect of the LSD.

With an open differential, if the inside tire gets unloaded, it can start spinning - the outside tire continues to provide some amount of traction and keeps the car under control. But with an LSD, the car can corner at a higher level. When the inside tire gets unloaded, it is not free to spin, and the car can continue to put power down on the road. Ultimately, that can get to the point that you suddenly overcome both tires ability to keep traction, and then there is nothing to stop the spin.

The car can corner at a higher level before it reaches the point at which the car can "snap oversteer", but there is no "loose it one one side" It's all or nothing, and unfortunately, loss of "all" means the rear is spinning.

I see this all the time in my Miata for instance, when driving in the snow. Instead of going around a corner like the other cars with one tire spinning, my Miata is sliding "tail out" around the corner. Same with my truck. Plenty of traction up to a point, then sideways...

[fitfan]

at vir i was not really getting it right through the fast esses, and got the second one all wrong, and was starting to drift (in a bad way) into the next...

Thankfully i did not have LSD - otherwise it would have grabbed and i would have never been able to catch it fast enough, not me... or i would not have been in that situation in first place - open diff is more predictable - lsd can catch, and send you quickly either in the direction the rear tires are pointing (the other way), which would cause a spin if your pointing the wrong way. or the scenario Tim describes.

if your "really" good - go for it.

if your really that good - you probably don't need it!

if your a normal human - i thinks it safer (on the track) with out it. i just putter around for fun, i don't car if my laps time are 2 seconds faster or slower - as long as i am driving may car home, learning, and having fun.

auto'x = a differnt story, some of the best driving skills - but i get lost with all thoose cones laying around...

at most road courses there are very few corners where you would "use" it. i think the negatives out weigh the positive (traction). unless you are very competitive and can utilize it to the cars advantage at the limit. - no way i could. i have enough trouble as it is!

[elise/europa]

Sorry, but like many thread, the context is not present. General question without detail of the future usage.

It depends of so many thing, including the max. curve speed and minimum curve speed on the same track.

[Z-dculus]

Originally Posted by TimMullen

LSD does tend to promote understeer (unless tweaked out of the suspension). But the snap oversteer happens because of the affect of the LSD.

With an open differential, if the inside tire gets unloaded, it can start spinning - the outside tire continues to provide some amount of traction and keeps the car under control. But with an LSD, the car can corner at a higher level. When the inside tire gets unloaded, it is not free to spin, and the car can continue to put power down on the road. Ultimately, that can get to the point that you suddenly overcome both tires ability to keep traction, and then there is nothing to stop the spin.

The car can corner at a higher level before it reaches the point at which the car can "snap oversteer", but there is no "loose it one one side" It's all or nothing, and unfortunately, loss of "all" means the rear is spinning.

I see this all the time in my Miata for instance, when driving in the snow. Instead of going around a corner like the other cars with one tire spinning, my Miata is sliding "tail out" around the corner. Same with my truck. Plenty of traction up to a point, then sideways...

another great techsplanation. Thanks Tim!

[Rugbyduck]

Originally Posted by TimMullen

LSD does tend to promote understeer (unless tweaked out of the suspension). But the snap oversteer happens because of the affect of the LSD.

Don't believe this crap. Once you learn how to drive the car with LSD you'll have no problem. It's more about weight distribution and using the brakes and throttle the way you should.

[SteveLevin]

While the points about the LSD v. non-LSD are true, I have to really, strongly suggest that anyone who is relying on that difference pull their pace back overall -- the truth is, what you are saying is "I'm not comfortable recognizing the limits of my car."

And there's nothing wrong with that, it's doggone healthy IMO. But what I'm trying to say (and trying not to sound like a prat in saying so) if you are getting that close to the edge and not recognizing it, I strongly suspect you are that close to the edge in cornering and braking forces and quite likely not recognizing that you ARE near those limits.

Steve

[Mozart]

Thanks to all for their most helpful insights! Truth be known, my Exige may never end up seeing all that much track time, and I am probably not going to return to the the AX circuit anytime soon. So, my Lotus will more than likely be ordered without this option.

Here is a confession - I am also an early 911 nut and presently own two '72 cars. Each has a factory ZF LSD tucked into its 915 tranny. Are any of you both modern Lotus AND early Porsche tech savy enough to compare and contrast the LSD's in these two seemingly very different beasts?

[fpitas]

To sum up: people who have it like it, those who don't think it's got to be bad. Either way, you should realize that it's a b*tch to install later. 10 hours, or something like that.

[Clovis]

Get the LSD. Especially with the power of the 240. If you enjoy powering out of corners, you're going to want it. Inside rear wheel spin/hop is annoying and hard on drivetrain components.

[fpitas]

Originally Posted by Clovis

Get the LSD. Especially with the power of the 240. If you enjoy powering out of corners, you're going to want it. Inside rear wheel spin/hop is annoying and hard on drivetrain components.

That's my advice too, unless you're really pinching pennies. A lot of people who don't have it theorize about the disadvantages, but those who have converted non-LSD to LSD (like Randy) have only good things to say.

[TimMullen]

Originally Posted by Rugbyduck

Don't believe this crap. Once you learn how to drive the car with LSD you'll have no problem. It's more about weight distribution and using the brakes and throttle the way you should.

No, an LSD does tend to promote under steer. That is not necessarily a bad thing. You can adjust the tendencies out of the suspension, or change your driving habits to allow for it - some people's driving habits would actually work better with it than without.

But the simple fact is that an LSD physically tries to make the car go straight. With an open diff, one side of the rear is free to rotate at a different speed than the other, as in a sharp turn. With and LSD, both sides are "locked" together, which tries to make the car go straight (picture the front wheels off the ground and both rear wheels turning at the same rate - which way is the car going to so?).

Again, it's not a bad thing. My Miata, for instance, has a Torsen LSD. In a tight corner, if I start adding power, the Torsen start "locking" and the car tends to want to "plow" straight ahead slightly. Backing off the accelerator slightly (lessens the Torsen's locking), and the front tucks in nicely and the car turns sharper. But that Torsen is tending to promote under steer when it's being used.

I even knew of one guy that had a Europa autocrosser that someone had installed a LSD in. The car would go in an absolute straight line under power (knocked down lots of cones). He had to replace the diff with a regular one, and his car became competitive (it never was spinning it's inside rear wheel).

There are times and places where an LSD is invaluable. There are times and places where it isn't of much help. Whether it's good or not, depends on how YOU are going to use YOUR car, and how YOU drive with or without an LSD.

Originally Posted by fpitas

To sum up: people who have it like it, those who don't think it's got to be bad. Either way, you should realize that it's a b*tch to install later. 10 hours, or something like that.

No. Some people like it because it's right for the way they use the car. Some people don't need it and are better off without it. If you are using your car for autocross and you are serious about it, you may want it. If you are using your car for extensive track use on tight twisty tracks, you may want it. If you are not competitive, use it primarily for street, may run in the rain, snow, low traction conditions, etc., you may not want it. It all depends on what YOU need, and what YOU prefer.

Originally Posted by fpitas

That's my advice too, unless you're really pinching pennies. A lot of people who don't have it theorize about the disadvantages, but those who have converted non-LSD to LSD (like Randy) have only good things to say.

Randy is one of those people that have extensively tuned his suspension to take advantage of an LSD, has the driving skills to require an LSD, and is competitive enough to be able to use it to his advantage on the track/course. He is also knowledgeable enough to know what to adjust to implement the LSD.

Other's are not. Some of us that don't have and LSD are quite aware of it advantages and disadvantages have have decided that it is not necessary or something that we don't feel the need for. Everything in life is a trade off, and some people have different priorities that make an LSD either necessary or un-necessary. But it's not something that there is only one answer to - it depends on each specific situation.

[fitfan]

i would agree - powering out of corners - you want LSD, - thats why its so good for auto'x - but i have no experiance in how "much" or "soon" it locks

its the high speed esses that would give me fear that thing might twitch...

that said - i have a 190hp elise, and have not driven an exige s in fear and anger with LSD. i have had a few pucker moments and my engineer brain is saying open diff saved me from my lack of skill. but like i said - i haven't compared the two in thoose kind of circumstances. certianly not a limit in my car - driver error!

[elise/europa]

Me, I have tendance to say that the LSD is changing the understeer and oversteer of the car.

Typically, in very rought summary, you are adjusting the suspension according to the lateral G force. The effect of the LSD is more specific to the geometric radius of the curve. At one point, you can adjust the car perfectly the suspension for a specific curve with the LSD. The point, what going on on the next curve with a different radius curve. Last year, my Lotus Europa was equipped with a LSD, and I removed it because of that. I agree that for Auto-x, the curve speed is more constant and all a time a low speed, but on some race track where the minimum curve speed is at 40, and maximum curve at 120, the story can be something else.

It is all a time a gain and lost somewhere. Depends of the application.

[Clovis]

Inside wheel spin when you are trying to go fast is no fun, even on the big tracks. See 6:40-7:00.