LSD Types and Yaw Behavior

[Flexicoker]

I may be wrong here... but even if you had a low ramp angle Salisbury, if you had no pre-load, it seems like you would still be able to spin the inside rear if it gets light. It would just essentially have a higher bias ratio, and therefore be able to transmit more torque to the outside given the same inside tire load and applied torque as the ATB. If you lift the tire, you're in the same boat as the ATB, unless you're running enough preload.

 

Is that right?

[JMortensen]

That is correct. I've had mine spin going into a steep driveway at an angle as well. They both need some traction to do their thing. Only a spool or a locker will drive a wheel with no traction beyond the breakaway pressure.

[tube80z]

I think we can all agree here, that the ideal solution is to run a spool, a ton of caster, and just lift the inside rear in the air around the corner

 

In my car, if I had the money, I would run a Quaife. My personal opinion is that it is currently the best design out there. I may eat my words if I can't keep the inside wheel from spinning, but thats going to have to wait until I have moneys. I will probably put a CLSD first, because they're easier to get ahold of and cheaper.

 

I've ran a very tight CLSD, a lose CLSD, VLSD, and an open diff. With the preload jacked up a lot (close to spool) I thought the car worked really well for autox (like a big kart). When I started setting the car up more like a sports racer (much stiffer springs, droop limiters, etc.) I found that a loose, almost open diff worked much better and the car was a lot faster.

 

For a while I had a completely open diff in my autox car and it was as only slightly slower than when I ran the loose CLSD. So if you follow a similar setup for your car the Quaife should work well.

 

Cary

[Careless]

*starts re-reading thread after minor brain malfunction*

[johnc]

I too am sold on the Quaife, although I'm really impressed with the OS Giken SuperLoc I put in my 350Z. FYI... I bought two Quaife ATBs and a Quaife Sierra Sequential 5 speed dog box from Craig at Taylor-Race.

[Flexicoker]

=) Its a small world!

 

One of these days I'll get a Taylor Race gearbox in my Z, for umm... testing purposes =)

[260DET]

The inside wheel spin thing with a HLSD is misleading, if the car is set up properly, has adequate tyres and so on the inside wheel will never spin, never.

 

Except where the track surface is loose, wet, whatever.

 

Incidentially the S30 is particularly suitable to use a HLSD in, helps turn in for a start.

[260DET]

Not sure exactly how a S30 should be set up using a HLSD because I no longer race one. But, following on from what I did learn with the S30, perhaps heavier springs at the front than rear and no (or a very light) rear ARB with a heavy front ARB would be a starting point.

 

Anyway, JohnC knows, he had a Quaife in his S30

[johnc]

I'll list exactly what my setup was:

 

FRONT

 

300 lb. in springs.

Penske 8760 triples.

23mm or 25mm ARB depending on the track.

16 x 10 wheels.

275/45-16 Hoosier R4s.

1/4" to 3/4" wheels spacers depending on the track.

28mm bumpsteer spacers.

Monoballed LCA and TC rods.

 

REAR

 

325 to 375 lb. in. springs.

Penske 8760 triples.

16mm or 19mm ARB depending on the track.

16 x 10 wheels.

275/45-16 Hoosier R4s.

No wheel spacers.

Offset monoballed LCA inners.

Quaife HLSD.

 

The wheel spacer and ARB combination were used primarily to get the power down in the back and adjustments were made to keep as much rotation as possible in the car while keeping the inside rear wheel planted. At the time neither I nor my co-driver could stand driving a Z that didn't rotate well. That comes from learning to race a Z with a welded diff. The shocks were our biggest tuning tool and allowed a spring setup that naturally goes against what a Quaife likes. It worked.

[JMortensen]

John, didn't you also send the Quaife out to be preloaded because you were spinning the inside tire in long sweepers?

[johnc]

Yes. One of the Quaifes I had was preloaded by Taylor-Race a bit but the other wasn't. I ended up making enough suspension adjustments that it really didn't matter. I was one of those stubborn guys that didn't want to adjust the car to the diff. Once I got over that, things went a lot better.

[EMWHYR0HEN]

I'll list exactly what my setup was:

 

FRONT

 

300 lb. in springs.

Penske 8760 triples.

23mm or 25mm ARB depending on the track.

16 x 10 wheels.

275/45-16 Hoosier R4s.

1/4" to 3/4" wheels spacers depending on the track.

28mm bumpsteer spacers.

Monoballed LCA and TC rods.

 

REAR

 

325 to 375 lb. in. springs.

Penske 8760 triples.

16mm or 19mm ARB depending on the track.

16 x 10 wheels.

275/45-16 Hoosier R4s.

No wheel spacers.

Offset monoballed LCA inners.

Quaife HLSD.

 

The wheel spacer and ARB combination were used primarily to get the power down in the back and adjustments were made to keep as much rotation as possible in the car while keeping the inside rear wheel planted. At the time neither I nor my co-driver could stand driving a Z that didn't rotate well. That comes from learning to race a Z with a welded diff. The shocks were our biggest tuning tool and allowed a spring setup that naturally goes against what a Quaife likes. It worked.

 

John,

 

Could you share some of your alignment settings when you used the quaife and maybe some alignment/setup with the welded diff. It woud be nice to see the contrast between the two.

[johnc]

The basic numbers are in the alignment sticky on this site. With the welded rear diff I adjusted rear toe depending on the track speed and how courageous I was. Slower tracks got closer to zero toe in the rear. Autocross sometimes got 1/16" total toe out but that was iffy. If the car started to lose the back end you needed hands of lightning to catch it and the run was blown anyway. It did make slaloms interesting...

 

I also think I ran less caster with a welded diff.

 

I was one of those guys that was always adjusting things between sessions at the track. Typically I would show up with a pretty aggressive alignment/shock setting and scare myself silly in the first session or practice. I would back off the settings and then make them more aggressive as the day went on and my tiny puddle of confidence/talent grew.

[johnc]

One issue with running a Quaife ATB is curb hopping. If that's your bag, you need shocks that will keep the car stable over the curbs especially if you're putting down some power.

 

If the rear of the car launches over the curb while you've got your foot down (too much compression damping), the inside rear wheel will go airborn, the Quaife will most likely go open (even with some preload), the inside rear wheel will spin and you'll lose drive on the outside rear wheel, the car will pitch forward and start to spin, and then wham, the inside rear wheel lands and both rear wheels start providing power again - or a stub axle goes boom!

 

Either way, you're going off track in a pretty spectacular way. Been there, done that - once at Streets of Willow and twice at Buttonwillow.

[260DET]

Very interestring article and discussion. All I can say is that for an average amateur driver, me, on road courses (thats Murrican for circuit non oval tracks ) an ATB diff is the go.

 

If that is not practical for some reason then lock it up, plenty of very good lap times have been done with a locked diff.

[drmiller100]

A few thoughts.

When you start discussing power induced Yaw, you should really first decide if you are excluding live axles, and only talking IRS. Was the original article written by someone ignoring live axles?????

 

The comments about caster and differentials I think applied to vehicles with less then an inch of compression travel such as Formula Atlantic and even stiffer purpose built race cars.

 

Are there Z's running less then an 1.5 inches of total suspension travel?

 

On the OBX thread, there is an EXCELLENT picture and description of how Quaiffe works. Pretty cool.

 

Ultimately fast run times come down to grip. The most important grip is acceleration out of a corner, which is why folks run LSD's.

 

At corner entry, it would be nice if the rear tires were free to spin at different rates in order to maximize grip and allow the car to "turn in", rotate, or "yaw". If the rear tires are locked, the car is either pushing or sacrificing maximum grip as the rear tires are fighting each other harder then they need to.

 

If you late apex (as all good autocrossers should), you enter the corner, brake hard, lift on the brakes and turn the steering wheel until the car is about pointed the right direction, then light it off. In this case, the rear tires losing some controlled grip to allow the car to rotate is not the end of the world. But, if you set the car loose enough on entry for these corners, the car gets REALLY exciting in the slaloms, and probably won't corner exit very well.

 

When I was campaigning my V8z in autocross, LSD's were REALLY expensive, so I ran an open diff. I set the suspension for corner exit. Huge front sway bar, really stiff front springs, little rear sway bar, and really soft rear springs.

 

The car pushed like a pig on entry though, so I kept cranking rear brake bias into it until it got really loose. Then I learned to left book brake. Then I learned to trail brake. Then I learned to trail brake, turn in slightly, let the rear brakes loosen the rear of the car up and rotate the car, then power to set the rear end, then roll off the brakes, and power on out of the corner.

 

With an LSD I plan to make the car actually handle.

 

One interesting bit of trivia: only the spool, detroit locker, and cam/pawl can guarantee 100 percent torque application on corner exit, regardless of whether the inside tire is on the ground. Of those 3, only Cam/Pawl free wheels on entry and mid corner.

[HowlerMonkey]

The end result is that you have to change your driving style when comparing most locking type diffs to an open or VLSD diff.

 

Most every locking diff will induce power-on understeer for the basic fact that most locking diffs will fight having both side wheels going a different speed to some extent when power is applied.

 

While testing at any track with a carousel in an r200 equipped car, I've found that the VSLD to have the least power-on understeer but the stock nissan implementation will never carry one through even half a season of Improved Touring racing let alone a higher powered class and many VLSD only last a few laps in classes that don't allow a pumped diff. cooler.

 

I'm sure there are some crazy expensive VLSD out there but I am not aware of them.

 

They just weren't made for long term thrashing.

 

With a VLSD, you can get on the power sooner while a mechanical locking diff. will require you to change your driving style in that you "re-index" your braking/turning/acceleration events to later in the turn to keep the power-on understeer from rearing it's head to the extent it either eats up front tires or hurts your lap times because you encounter understeer as you power out of the corner.

 

This means a change from getting all your braking done in a straight line and powering out to braking deep and putting power down only after you are again going relatively straight.

 

Then you've got the guys who use slip to point the car in while braking late and can get on the power sooner but that technique requires a lot more driver attention and is subject to being hard on rear tires and brakes.

 

I am a lexus tech and lexus uses open diffs. and computerized braking schemes to control yaw and, as said above, will burn up brakes quickly on a road course........but lexus designed the system thinking of the average driver who got in over his head or ran into an unexpected change in road conditions.

 

I'm not sure open diff./electronic controlled braking for yaw control will ever be ironed out for road racing because you need your brakes for..............braking and any braking usage beyond retarding the car's speed is counter productive to brake heat and wear.

[drmiller100]

if you have power induced UNDERSTEER, you are not on the gas nearly hard enough.

 

Power induced understeer is when you are in the middle of a tight sweeper, and you kind of tickle the throttle and ask it nicely to gently speed up.

 

For autocross, late apex is almost always fastest, and in that case you get on the gas so hard you are worried about the back of the car spinning out, and are desperate to feed it more throttle.

 

If you are waiting until later in the corner to brake, turn, and turn, you are early apexing and going slow. The whole point to running a LSD/Spool is to brake earlier, turn earlier, and make the NEXT straightaway even longer under WFO throttle.

[260DET]

..................................................................

 

When I was campaigning my V8z in autocross, LSD's were REALLY expensive, so I ran an open diff. I set the suspension for corner exit. Huge front sway bar, really stiff front springs, little rear sway bar, and really soft rear springs.

 

The car pushed like a pig on entry though, so I kept cranking rear brake bias into it until it got really loose. Then I learned to left book brake. Then I learned to trail brake. Then I learned to trail brake, turn in slightly, let the rear brakes loosen the rear of the car up and rotate the car, then power to set the rear end, then roll off the brakes, and power on out of the corner.

 

..........................

 

In other words, using the steering wheel is not the only way to turn a car in the direction you want. Where the car has a fair amount of power I'm a big fan of the suspension setup you mention, when you have biasable brakes and an accelerator pedal, who needs a steering wheel