Why you need a LSD if you like cornering!

[Ubersuber]

Originally Posted by Captain Snooze

What does this mean? Not just "better" but "much better". Quality is also subjective.

It means better spring control without messing up the ride.

I think it is accepted that Ohlins makes some of the best shocks out there and makes a set for these cars. I doubt the cost would be warranted unless you did some serious spring rate increases and I don't know if Ohlins makes a shock with stock stroke.

The factory shocks on these cars leave a lot to be desired, especially the rears. They look cheap and they have inadequate rebound control. The ride at the rear of the factory equipped car is poor.

Incidentally, the poor spring control means the drive wheels lose traction more easily than they should, which is the only reason damper quality belongs in this thread. I'd be very interested to read about lap times of a stock car equipped with a lsd as compared to a stock care equipped with B6 Bilsteins.

[Ubersuber]

A consensus emerges: traction out of corners is most affected by roll stiffness.

For rwd moving roll stiffness forwards should improve drive out of the corners.

For fwd the opposite is required.

For awd, all bets are off, the drive force allocation in any awd system designed for the street is fiendishly difficult to design in the first place and successfully modifying one is exponentially more difficult. Just dealing with the centre diff is enough to cause serious headaches, one reason Subaru's rather clever little centre diff is so handy to have in your car. (STi that is)

[Ubersuber]

Originally Posted by acro

Personally i think the Stock LSD is good but even i with limited track experience i have gotten the inside wheel spinning at some points on track. If i could put down more power on corner exit im sure i would be faster. So if i was serious about track times this would be a definite consideration.

A clutch type lsd does not stop the inside wheel from spinning:

http://www.cuscousainc.com/downloads..._lsd_guide.pdf

It limits the spinning to no more than the speed of the outside wheel.

The degree to which the lsd can limit the speed difference between the inside and outside wheels is a function of the difference between the clutch disc friction and tire grip (allowing for the leverage advantage the tire diameter gives to tire grip). Basically, you can wear out the tires first or the lsd clutch discs first...

The extent to which an lsd can be varied should be a caution to anyone deciding to fit one. ALL these lsd lock up and a locked up lsd isn't a very good solution to the torque problem.

The lsd is always trying to speed up the slower moving wheel.

The Torsen divides input torque between the drive wheels in exact proportion to the relative tire grip until the torque bias ratio is exceeded, then it will spin up a wheel, which wheel depends on which tire has most grip as the torsen will eventually spin up the wheel with less grip first.

In theory it is difficult to see how the clutch lsd can outperform the Torsen, especially with only a maxim of 151 lb ft to deal with.

Lap times do not lie but unless nothing else on the car is different from lap to lap they may not tell you useful truth.

[ZDan]

Originally Posted by CSG Mike

Once you drive a S2k/BRZ with a clutch type LSD that's properly tuned, I'm willing to bet you'd change your mind.

If you're in Socal, I'll arrange for it to happen.

Now I just have to arrange to put myself in SoCal

[CSG Mike]

Originally Posted by Ubersuber

In theory it is difficult to see how the clutch lsd can outperform the Torsen, especially with only a maxim of 151 lb ft to deal with.

Lap times do not lie but unless nothing else on the car is different from lap to lap they may not tell you useful truth.

The data there. Novices to pros all universally get faster. I keep using the Miata as an example, because they have so little power. Miatas get faster with a clutch type compared to a torsen. Something on the order of 1.5 seconds on a 2 minute lap. That is HUGE.

Perhaps you should stop theorycrafting, and start actually testing, and you'll discover that your results will curiously match the hundreds of LSD tests that have already been done.

[Ubersuber]

I'm only interested in street applications. But, the theory is interesting nonetheless.

I'm just wondering why Subaru fitted a Torsen.

[Sleepless]

Originally Posted by Ubersuber

I'm only interested in street applications. But, the theory is interesting nonetheless.

I'm just wondering why Subaru fitted a Torsen.

Cost

[Ubersuber]

Originally Posted by Sleepless

Cost

Really? What is the cost difference to an OEM?

[wparsons]

Probably more the maintenance requirements. If people found out they needed a full diff rebuild at ~30k miles they're probably be pretty pissed.

[Dipstik-sportech]

Drivability possibly as well

[acro]

Originally Posted by Ubersuber

A clutch type lsd does not stop the inside wheel from spinning:

http://www.cuscousainc.com/downloads..._lsd_guide.pdf

It limits the spinning to no more than the speed of the outside wheel.

The degree to which the lsd can limit the speed difference between the inside and outside wheels is a function of the difference between the clutch disc friction and tire grip (allowing for the leverage advantage the tire diameter gives to tire grip). Basically, you can wear out the tires first or the lsd clutch discs first...

The extent to which an lsd can be varied should be a caution to anyone deciding to fit one. ALL these lsd lock up and a locked up lsd isn't a very good solution to the torque problem.

The lsd is always trying to speed up the slower moving wheel.

The Torsen divides input torque between the drive wheels in exact proportion to the relative tire grip until the torque bias ratio is exceeded, then it will spin up a wheel, which wheel depends on which tire has most grip as the torsen will eventually spin up the wheel with less grip first.

In theory it is difficult to see how the clutch lsd can outperform the Torsen, especially with only a maxim of 151 lb ft to deal with.

Lap times do not lie but unless nothing else on the car is different from lap to lap they may not tell you useful truth.

In practice it seems the torsen in our cars will not be as efficient as a well tuned clutch LSD. In theory i see no reason y 151 tq would not cause issues and in practice i know it can. so........

[CSG Mike]

Originally Posted by Ubersuber

I'm only interested in street applications. But, the theory is interesting nonetheless.

I'm just wondering why Subaru fitted a Torsen.

Cost. It's a parts bin differential that is used in a TON of Toyota cars.

[Captain Snooze]

Originally Posted by acro

In practice it seems the torsen in our cars will not be as efficient as a well tuned clutch LSD. In theory i see no reason y 151 tq would not cause issues and in practice i know it can. so........

There is a lot hypothesising in my reply but here goes...
I am suggesting that most of the people on this forum are enthusiasts of some sort but most buyers of this car world wide are never going to mod their car. I am suggesting for most buyers, who will never see a track or drift around a roundabout or switch off the nannies, the Torsen is more than adequate and may even have some bragging rights. "Yeah man, my car has one of them Torsens".

[jebuwh]

Originally Posted by Ubersuber

I'm only interested in street applications. But, the theory is interesting nonetheless.

I'm just wondering why Subaru fitted a Torsen.

You're only interested in street applications? Then you care about diffs why?