LSD availability- cost, need or other rationale for being included on new cars.

I know that lower power cars (Miata) don't get an LSD with an automatic because it's assumed that it isn't needed/desired the way it is with a manual. However, the automatic Camaros do get an LSD (if I read the spec sheet correctly). Google discussions have led me to believe that:

1. the lower power cars won't usually get tail happy the way, say a 400+ HP Camaro can, so you don't need it as much. If you're likely to spin one tire on an exit, you may need an LSD. In my experience, you can spin a tire on some pretty low powered cars if you drive them hard, so I don't get this.

2. Cost is offset on the automatic by not including an LSD on many cars- higher profits. This makes more sense.

I'm guessing there are a lot of other reasons I don't understand, too. What kind of reasons are usually behind including an LSD or not?

I forgot to mention ABS type e-diffs, which I don't like. They're a factor, too.

Most cars are made to be street cars and not race cars.  For the street, LSD is just added expense, and possibly more dangerous.  For an inexperienced driver, a one wheel spin is no big deal, but breaking the whole back end loose is a disaster.  I think the tendency for lower powered cars to not have them probably has more to do with cost than anything else.

How tail-happy the car is has more to do with the wheelbase than the amount of power, right?  My Miata is pretty eager to spin compared to most of the bigger/longer cars I’ve driven.

There's also the added issues of NVH that a clutch type solution can add, on top of the added maintenance that it entails.

With RWD cars in the snow and ice, it was a more commonly requested addition.

With FWD cars, the improvement in traction in snow and ice made LSD options less critical, especially when manufacturers were working to keep costs low on their mostly-FWD economy cars.

Manufacturers have mostly all moved away from being able to spec cars as they like and instead sell packages.  LSD's and larger engines typically end up in the higher spec versions and not in the lower end vehicles.

With the improvements in tire and suspension technology combined with improvements in stability and traction control solutions, it makes more sense to use the parts that are already implemented (the ABS sensors, pump, etc along with the brakes) instead of adding a rare and expensive to install option for a select few vehicles that also add more maintenance variance and potential warranty claims.

In the case of the Camaro and the like, I suspect that knowing how the product is likely to be used (drag racing for example) and the fact that a LSD is likely already available in the product line (certainly in their truck or SUV lines that share center sections), GM made the option available to their customers.

I don't get it. People want AWD for traction, but no one will pay for a LSD? Yes traction control has improved, but I still think a LSD is better. I remember about a decade ago it cost ~$150 to option a LSD on a F150. That's a complete no brainer anywhere with snow. FWD cars could really benefit from it.

You forget, the average person is a complete moron when it comes to cars.

So they suck up any and all of the sales and marketing drivel, plunk down their hard earned money on whatever fills the emptiness in their lives and they go on down the road.

BTW, a limited slip for an F-150 that is likely using the same diff designed back in the 70’s is cheaper and easier for Ford to produce.  The limited slip for a Focus is not as cheap since the cost won’t have been amortized across enough models for a long, long time.

Snrub said:

I don't get it. People want AWD for traction, but no one will pay for a LSD? Yes traction control has improved, but I still think a LSD is better. I remember about a decade ago it cost ~$150 to option a LSD on a F150. That's a complete no brainer anywhere with snow. FWD cars could really benefit from it.

FWD cars understeer really badly if you have a LSD in it.  

And I also don't agree that it would be a massive improvement in the snow- I've still never lived without snow in the winter, and have had the both for a Miata- snow tires are far superior to LSD, IMHO.  And I've also driven a ton a FWD cars, some with good snow tires, some with factory All Seasons.  Neither would have been better with an LSD in it.

The only time and car I've really needed and LSD was my Alfa, since it had a tendency to lift the right inside tire in the rear, which really reduced getting the power down.  But that's such an extreme case that for 99% of the public, it's a waste of money.

Stefan said:

You forget, the average person is a complete moron when it comes to cars.

99% of the public:

Salesman - "Would you like an LSD?"

John Q. Public - "No drugs are illegal."

Alfa- I’m interested in your comment about FWD cars with LSDs and understeer. I’ve never heard this before. I guess it makes sense though. Is this true for all kinds of LSDs? I’d imagine a clutch type having this problem but a quaife seems like it wouldn’t hurt in that way. 

Of course I drive an under steering torque steering pig of a Mazda. I haven’t found either to be a major but maybe I’m just used to it. I always figured the limited slip was to help with the handling and the traction but maybe it’s just there for traction despite the handling? Is this why Ford used the E-diff in the Focus ST?

I’m learning so much here. 

To the OP I always assumed it was a cost driven decision. Mechanic bits are expensive but programming the ABS system for an E-diff is relatively cheap. 

I will comment that after I had a front LSD (helical) added to my 04 WRX (about 5 years ago), it tended to understeer even worse in both autocross and rallycross (I had already owned it since 2005 before the LSD was put in).

If I had to do it all over again (I'm not going to bother taking it out now), I would probably skip it on my own car.

And to be honest, I can't tell if it helped anything at all in winter (Buffalo snow) driving either.

But, it also wasn't a fancy one, and there was no tweaking of accel/decel on it (if it was even possible on this one), so perhaps some are more effective than others.

Adding a helical LSD to our Civic race car made a nice difference, the car is well balanced.  If anything, when understeering under throttle and hard cornering, if you go for full throttle the car tends to tighten its line up and understeer less than with part throttle.  

Before a car company could sell LSDs, they would need to sell cars (I'm looking at you, Ford).

And they would need to be RWD cars.  This list is old, and it's even shorter now:  Rear Wheel Drive dot Org

AWD cars seem to be popular around here because they're much less hassle than snow tires.

I grew up living in cheap apartments, and I can't for the life of me remember where Dad kept the snow tires for the family sedan during the warmer seasons. 

In reply to Brett_Murphy : Winter snow and Ice

In reply to alfadriver :

Correct. 

Every high powered FWD car I've ever owned suffered without an LSD due to inside wheel spin while accelerating after cornering or if I hit a wet manhole cover while accelerating in a straight line.  Annoying, but if you drive them like a sane person and not a teenager with a turbocharged hatchback, the problem isn't as pronounced.

When an LSD is installed, you have to alter the suspension to introduce oversteer to make the cars more "point and shoot" rather than a traditional line.

Getting a non-LSD FWD car moving uphill in the ice, even with chains, can be damned difficult.  You have to have momentum, anything else and you end up spinning one wheel and drifting back down the hill.  I have the polished spot on my driveway where the wife tried to do this one winter.  I backed it up and increased the momentum while also changing path slightly to get the car into the driveway using a much more soft throttle pedal.

With the advent of modern traction, stability and ABS, these sorts of issues become less annoying since you can balance wheel speed among other things. 

spandak said:

Alfa- I’m interested in your comment about FWD cars with LSDs and understeer. I’ve never heard this before. I guess it makes sense though. Is this true for all kinds of LSDs? I’d imagine a clutch type having this problem but a quaife seems like it wouldn’t hurt in that way. 

Of course I drive an under steering torque steering pig of a Mazda. I haven’t found either to be a major but maybe I’m just used to it. I always figured the limited slip was to help with the handling and the traction but maybe it’s just there for traction despite the handling? Is this why Ford used the E-diff in the Focus ST?

I’m learning so much here. 

To the OP I always assumed it was a driven decision. Mechanic bits are expensive but programming the ABS system for an E-diff is relatively cheap. 

It's just simple physics- LSD prevents the two tires from spinning at different rates, but when you turn a corner, the tires HAVE to spin at different rates to go around different radius circles.  Which becomes worse when you add power, making the LSD more active.  They basically try to un-steer for you.

That kind of compromise may work reasonably well on the track, but autocross turns are much tighter, in general.  And in the real world, where you never are cornering hard enough to unload the inside wheel, it can be incredibly uncomfortable.

Actually, LSD can make understeer worse on a RWD car, too- but normally, the advantages outweigh the losses.  My racecar has pretty much a locked diff, it's so tight, and it made it undrivable at an autocross- it would not turn.

two wheels spinning will loosen things up quicker than one wheel spinning. 8 yrs with Trac Loc.

cost is the only consideration for most things automotive manufacturing related

dumb public, dumb OEM purchasing people, dumber OEM marketing folks and really smart supplier sales staff

alfadriver said:

spandak said:

Alfa- I’m interested in your comment about FWD cars with LSDs and understeer. I’ve never heard this before. I guess it makes sense though. Is this true for all kinds of LSDs? I’d imagine a clutch type having this problem but a quaife seems like it wouldn’t hurt in that way. 

Of course I drive an under steering torque steering pig of a Mazda. I haven’t found either to be a major but maybe I’m just used to it. I always figured the limited slip was to help with the handling and the traction but maybe it’s just there for traction despite the handling? Is this why Ford used the E-diff in the Focus ST?

I’m learning so much here. 

To the OP I always assumed it was a driven decision. Mechanic bits are expensive but programming the ABS system for an E-diff is relatively cheap. 

It's just simple physics- LSD prevents the two tires from spinning at different rates, but when you turn a corner, the tires HAVE to spin at different rates to go around different radius circles. 

I'm confused by this. 

You're describing an LSD more like a locker or welded diff.

I understood an LSD, a clutch-type for instance, allows the wheels to turn at different speeds but the clutches ensure that some power is transferred to the loaded tire vs taking the path of least resistance, the unloaded inside tire?

In reply to z31maniac :

So the entire point of an LSD is to act sometimes as a welded diff, and sometimes as an open diff, right?

Even with a clutch type system, that's the case- so at the times where the clutches are not being forced together (not under load, normally), it turns fine.  When the clutches are forced together (under power, normally), then the two sides want to force the same speed.  And if you are rounding a corner at that time, it will try to stop that by not letting the tires rotate at different speeds.  And that's the core issue with LSD forcing understeer. (of course, if you fully unload that tire, then having them rotate at different speeds isn't a big deal, but you are losing one tires worth of cornering force).  

Clutch systems are a little easier to set up, and modulate how aggressive the limited slip action in, for sure.  But the end game is to act like a locker under certain circumstances.  If you can make sure those times are not when you are going around a corner, great.  If you need a massive version of it mid corner, just as you slightly apply power, you will be dealing with understeer (and there are many ways to deal with that, including loosening up the rear end and using the throttle to manage oversteer).  

alfadriver said:

In reply to z31maniac :

So the entire point of an LSD is to act sometimes as a welded diff, and sometimes as an open diff, right?

Even with a clutch type system, that's the case- so at the times where the clutches are not being forced together (not under load, normally), it turns fine.  When the clutches are forced together (under power, normally), then the two sides want to force the same speed.  And if you are rounding a corner at that time, it will try to stop that by not letting the tires rotate at different speeds.  And that's the core issue with LSD forcing understeer. (of course, if you fully unload that tire, then having them rotate at different speeds isn't a big deal, but you are losing one tires worth of cornering force).  

Clutch systems are a little easier to set up, and modulate how aggressive the limited slip action in, for sure.  But the end game is to act like a locker under certain circumstances.  If you can make sure those times are not when you are going around a corner, great.  If you need a massive version of it mid corner, just as you slightly apply power, you will be dealing with understeer (and there are many ways to deal with that, including loosening up the rear end and using the throttle to manage oversteer).  

Nope. I've never read the point of an LSD to is act as LOCKER, like what the off-road guys want in a street/autoX/track siutation.

In reply to z31maniac :

Limited Slip Differential means that the goal is minimize the speed difference between the two wheels.  So at some point, the goal should be to not have slip.  That's the point.

The different types of LSD do it very differently, where you can tune how that happens, and to what degree.  For most, the clutch system is the easiest to tune so that you don't have too much lock up when you want, but that's at the expense of having totally locked up when you really can deal with it.  Which for most is fine.

Just because clutch systems don't act like a locker or a welded diff doesn't mean they are not trying to get that to happen.

Either way, when you limit the slip between the two tires, you reduce their ability to go around circles of different diameters, which results in understeer.  Again, the clutch set up is easier to tune to compromise understeer and traction for those without a e-diff.  I think you are confusing that last part with what an LSD is supposed to do, in general.

Here's a common use case. There is snow or ice or rain. You are in a FWD car and stopped at an intersection. You are turning right while attempting to accelerate and all the power goes to the inside wheel, resulting in poor acceleration. There is a car coming and you would like to not be hit. You may have misjudged your rate of acceleration because most of your traction experience that day has been in a straight line, with both tires doing useful work. Everyone has experienced this and I have to believe many would appreciate an improvement.

Snrub said:

Here's a common use case. There is snow or ice or rain. You are in a FWD car and stopped at an intersection. You are turning right while attempting to accelerate and all the power goes to the inside wheel, resulting in poor acceleration. There is a car coming and you would like to not be hit. You may have misjudged your rate of acceleration because most of your traction experience that day has been in a straight line, with both tires doing useful work. Everyone has experienced this and I have to believe many would appreciate an improvement.

Modern traction control deals with that just fine.  And with less compromises to how the car drives when the LSD is less than desirable to have.  It also brings up the interesting point that a braking system does essentially the same thing as a clutch LSD does, but in a location that is much easier to do maintenance on than in the diff.  And the braking effort to control slip is considerably less than the braking effort to stop.

BTW, I've never been able to corner in the snow so hard that it will unload the inside tire to any appreciable degree- the slip happens on either tire.

The brake idea to limit slip goes way back to farm tractors.  They had two brake pedal.   It traction got really poor for one wheeel the brake to that wheel was applied .  Providing power to the wheel with traction.

This is the theory in most of todays Traction Controls.

Believe me, it works.   TC and WS80's got me home on ice covered roads.  Hardest part was avoiding less fortunate cars.