All this LSD talk, why do most here want LSD?

[Tippy]

My turbocharged Carrera is probably 550-575 hp and does quite fine without LSD. Only a real tight turn in lower gears becomes a problem on a track, but that's on street tires.

If a N/A car ran R compounds, I cannot imagine needing LSD.

Am I missing something other than "nice to have"?

[91133]

Originally Posted by Tippy

My turbocharged Carrera is probably 550-575 hp and does quite fine without LSD. Only a real tight turn in lower gears becomes a problem on a track, but that's on street tires.

If a N/A car ran R compounds, I cannot imagine needing LSD.

Am I missing something other than "nice to have"?

They let you get the power on earlier and harder exiting corners. You probably just need to drive a bit faster.

[wwest]

LSD is a rare bird in a sports car...

Torque sensing diff'l is the name of the game.

LSD is about wintertime "finesse" driving, easy on the throttle.

[91133]

Originally Posted by wwest

LSD is a rare bird in a sports car...

Torque sensing diff'l is the name of the game.

LSD is about wintertime "finesse" driving, easy on the throttle.

Can't agree with that. Different drivers favour one or other of torque sensing and clutch type but my experience and understanding has always been in favour of the clutch type because as soon as you lift a driving wheel off the ground the torque sensing diff becomes an open diff, in order for it to work both wheels must have complete contact with the ground. The clutch type will remain engaged when a wheel lifts under cornering (over a curb for instance).

Racers prefer the clutch type because they are more predictable and also generally adjustable through the number of plates etc.

No expert but just my .02

[Steve@Rennsport]

Originally Posted by Tippy

My turbocharged Carrera is probably 550-575 hp and does quite fine without LSD. Only a real tight turn in lower gears becomes a problem on a track, but that's on street tires.

If a N/A car ran R compounds, I cannot imagine needing LSD.

Am I missing something other than "nice to have"?

Yessir,..I think so.

The REAL value of an LSD is stability. Its much more than just wheelspin control which some people can manage.

Have you noticed how the rear end of your car moves from side-to-side under hard braking during corner entry? The harder you stop, the more the rear end moves around and its quite disconcerting, especially from high speeds. This is due to the rear wheels rotating at different speeds, relative to each other. Open differentials and torque-sensing diffs (which open under trailing throttle) display the same characteristics.

Cars with LSD's keep the rear wheels locked together under trailing throttle at the same speed and this really stabilizes the car at a very critical time. Given a 911's the polar moment of inertial, one cannot always brake to capacity for this reason as such phenomenon makes for some sphincter-tightening moments.

The difference is truly quite dramatic.

Today's LSD's featuring asymmetrical (and adjustable) ramps make huge improvements in handling and allow a driver to fine tune corner entry & exit behavior, as well.

You would be pleasantly surprised how this would improve your car.

[kiwiokie]

^ Very interesting, never thought of that before, thanks for sharing.

[Canada Kev]

My understanding is that the LSD will also tend to stabilize the rear end of a car coming into a corner kinda hot.

With that same idea, it will also result in a front end that wants to understeer a bit, because of the driven wheels being more tied together with the inside wheel not travelling at a slower rate for the shorter path around the corner.

EDIT: Steve beat me to it...

[winders]

Originally Posted by wwest

LSD is a rare bird in a sports car...

Torque sensing diff'l is the name of the game.

LSD is about wintertime "finesse" driving, easy on the throttle.

Too funny.....and wrong.....

[Uwon]

Tippy, I'm with you. For the normal street driver the LSD is just a waste of money. Car will under steer and generally misbehave to some extent. For the track junky, it could make a difference as Steve Wainer so eloquently explained. I would add to his comments that fish tailing when braking can also be caused by improper bais between the front and rear brakes and lousy sway bars, etc. Having said that, I have tracked my 3.4 turbo for ten years at Mosport, a truly challenging high speed track and I don't experience the fish tailing during braking or loosing traction on acceleration. I attribute this to sensible suspension and bias setup. My two cent worth....cheers,
Johan

[JeremyD]

Threshold braking on a bumpy track (like Sebring) will make you a believer. Being able to rotate the car (and not just spin the inside wheel) coming out of a fast corner can also be a confidence builder.

[Uwon]

Originally Posted by JeremyD

Threshold braking on a bumpy track (like Sebring) will make you a believer. Being able to rotate the car (and not just spin the inside wheel) coming out of a fast corner can also be a confidence builder.

Agreed.

[Matt Monson]

What Steve W said. I am a Motorsports manufacturer with a capital M. There's a reason that 90+% of all 911s ever sold didn't come with an LSD from the factory. With the rear engine design the car has great on throttle traction. If you don't race your car, or track it once or twice a year, your money is much much better spent on tires, brakes, and the nut behind the wheel, not necessarily in that order. In short, you don't really need an LSD.

Where an LSD, in a 911, really shows it's stuff is in the braking zone. We are talking pedal to the floor 140mph down to 50mph to drive through a 2nd gear turn. Without it the 911 wouldn't be half the racecar that it is. I'm not kidding. People are very very skeptical when I tell them that half, or more of the time gains they can make by installing one of my LSDs is because of what I can do for them under braking. And then they come back and tell me that I wasn't feeding them some line to make a sale. They tell me I spoke the truth.

Here's an interesting thread for you all to read. The modern GT3 comes from the factory with an LSD, a mud and ice LSD. I rebuild and retune them and consistently, time and time again, find guys 2-3 seconds a lap in DE cars with no other change than the LSD.

How do I do it? Because almost all of the performance gains they are seeing is in the braking zone with greater stability. The factory LSD does all right on throttle. It doesn't do squat (pun intended) under braking. The thread is not for the feint of heart. We are talking 13 pages of reading here:
LSD buster - Rennlist Discussion Forums
And yes, while it's focused on the 997 chassis, it applies to every single 911 ever made.

Have a good evening,

Matt

[jittsl]

Originally Posted by Uwon

Tippy, I'm with you. For the normal street driver the LSD is just a waste of money. Car will under steer and generally misbehave to some extent. For the track junky, it could make a difference as Steve Wainer so eloquently explained. I would add to his comments that fish tailing when braking can also be caused by improper bais between the front and rear brakes and lousy sway bars, etc. Having said that, I have tracked my 3.4 turbo for ten years at Mosport, a truly challenging high speed track and I don't experience the fish tailing during braking or loosing traction on acceleration. I attribute this to sensible suspension and bias setup. My two cent worth....cheers,
Johan

Johan, if you are not fishtailing or tire spinning a turbo after 10 years on Mosport (or any track) it's probably that you have adapted your driving to suit what you have. I'm sure, if you wanted to, you could make it spin a tire by simply getting on it too early. That is probably one of the factors that makes you choose your throttle point and position with your current setup - you know that if you got on it earlier or harder in any given ccrner you would loose forward drive as the car starts to spin or slide. The best set up car in the world will always be faster if equipped with a LSD - its a matter of physics. Tire spin in a non-LSD car has the effect of reducing forward drive to both wheels. Imagine the extreme situation where the inside wheel is spinning completely freely (ie it's off the deck). In this circumstance all drive goes to the free spinning wheel and none goes to the wheel on the ground. In other words - nothing is driving you forward. To avoid this you have naturally adapted (I'm guessing) so that you accelerate at the maximum throttle you can and still avoid tire spin - threshold throttle, if you like. And just like driving skill of threshold braking can be made redundant with a good ABS system, similarily, so too can need for "threshold throttle" be reduced by the inclusion of a good LSD.

My SpecBoxster (by the spec rules and in an attempt to contain costs) cannot run an LSD and after a couple of seasons of club racing it I have gotten fairly adept at making it go around a circuit. Every time I drive my buddies Boxster that does have an LSD I'm reminded of how much pace they really do add.

Just my 2c.

[Carguy59]

All Alfa Romeos have LSD, GTVs anyway. Most expensive sports cars have LSDs, all Porsches should have them. Most 86 944 Turbos have them. You can bet your ass most factory race cars have them.

[Tippy]

Ok, sounds like mostly stability under braking.

Guess I haven't ran the car hard enough to worry about that.

Great input all and of course Steve and Matt.

Matt, appreciate the honesty of your post. Proves you're not just out to sell product, rather help the community.

[Matt Monson]

Tippy,
You are welcome. When I joined PP it was because I am a car guy, and a Pcar guy. The fact that I own a company that makes racing parts for them is secondary to my automotive passion and participation in this community.

Engaging in technical conversations of all natures always come first here. Sometimes my field of expertise puts me in the unique position to offer some specialized insight. Other times I'm just another punter around here trying to help a guy sort out some poorly running carbs. I don't put my company in my signatures because I don't want to be just the Guard guy. I'm a Pelican first.

[fbarrett]

LSD is not always good for winter conditions. I had an LSD-equipped Mercedes-Benz 300SEL 6.3 that could get stuck in an inch of snow or ice on my level driveway. When you gave it throttle (auto transmission), the diff would quickly lock up, so the rear tires both spun. This could also be fun when leaving a red light briskly in the rain; if you weren't careful, the whole rear of the car could jump sideways!

[manbridge 74]

Originally Posted by fbarrett

LSD is not always good for winter conditions. I had an LSD-equipped Mercedes-Benz 300SEL 6.3 that could get stuck in an inch of snow or ice on my level driveway. When you gave it throttle (auto transmission), the diff would quickly lock up, so the rear tires both spun. This could also be fun when leaving a red light briskly in the rain; if you weren't careful, the whole rear of the car could jump sideways!

Truth. A lot of unpaved roads around here are slanted for drainage and LSD vehicles are sliding their rears toward downhill side in adverse conditions. You won't find a lot of 911 type cars out on the road in winter though.

[pksystems]

Originally Posted by fbarrett

LSD is not always good for winter conditions. I had an LSD-equipped Mercedes-Benz 300SEL 6.3 that could get stuck in an inch of snow or ice on my level driveway. When you gave it throttle (auto transmission), the diff would quickly lock up, so the rear tires both spun. This could also be fun when leaving a red light briskly in the rain; if you weren't careful, the whole rear of the car could jump sideways!

You'd prefer 1 of your rear tires was spinning in snow? (Open diff).... More likely to get moving if 2 tires are trying to get you going.

I'm putting lsd in front, and rear of my winter beater DD. The quaife torsen front I'm going to use tho sounds like it won't help much in the white stuff... once a wheel lifts or has near zero traction it acts like an open diff. Clutch type rear should lock tho and help plow through snow.

[manbridge 74]

Not all cars have the same dynamics in the white stuff.

My AWD 1993 Celica Alltrac has open diffs front and rear. The diffs aren't the limit in snow. The low ride height is what stops me after about 6" hardpack as the tires get raised up once the body starts to rest on snow. The fluffy dry stuff becomes a hazard at about 10-12" because the front of car is knifing enough snow up on windshield to limit speed to around 20mph.

I do have a OE Jap domestic market rear torsen waiting to be installed for this car but I think its advantage lies in smooth roads and hard cornering as it was never (according to factory) meant to be an off-road vehicle like a Jeep.