Why you need a LSD if you like cornering!

[CSG Mike]

Originally Posted by diss7

Quite simple really, you need it that tight for drifting in the wet, when you're giving it very little beans before wanting both wheels to engage. Having it that tight on decel means it feint drifts like a boss.

Also remember that no matter how tight the diff is, you can always use it like an open diff by pressing the clutch in. I'll often do that say if I need to make a u-turn, I just get enough momentum to do it without power.

I don't disagree that I run it tighter than what would be ideal for circuit. I wouldn't even run a 2 way for a circuit car. I'd be much more inclined to run such a loose decel setting that I might as well run a 1 way. But my point from my previous post still stands, that if its so loose that it NEVER binds/engages on the street, then its probably too loose.

I understand your reasoning now

[CSG Mike]

Originally Posted by ZDan

No, more lockup => more understeer off the gas, more understeer on the gas.

Which is one reason I'm kind of philosophically opposed to tightening up the diff. You're adding work to the tires that is trying to make the car go straight. My approach would be to try to make the car work with as little diff preload/tightness/lockup as possible.

That would depend on what type of slip angle you're holding. A 2 way LSD will exacerbate whichever state you enter the corner in. If you're holding positive slip angle (nose toward center), then it'll promote rotation, whereas if you're holding negative slip angle (nose toward outside), then it'll promote understeer.

[CSG Mike]

Originally Posted by Calum

After reading Mikes first post my only question was, 'why aren't you trying to load up the unloaded tire to prevent the wheel spin instead of ****ing around with the diff? CSG already has the ability to adjust rear roll stiffness.'

Of course, my question has already been answered in that it comes down to personal preference. But along the way I've learned yet more about the artistic side of suspension setup. Thanks guys!

Roll stiffness doesn't necessarily mean that the less loaded tire has more load on it.

For example, stiffer sprung cars roll less, but the total cornering load on the tire under static cornering (ignoring deflection, slip, and alignment) is the same, assuming the cars are otherwise identical (tire size, compound, rims, etc.)

For the above data, we were using stock dampers with Swift springs, to make sure that we were not getting inside tire lift. We were also testing some Swift Spring setups, but that's a different story.

[Calum]

Originally Posted by CSG Mike

Roll stiffness doesn't necessarily mean that the less loaded tire has more load on it.

For example, stiffer sprung cars roll less, but the total cornering load on the tire under static cornering (ignoring deflection, slip, and alignment) is the same, assuming the cars are otherwise identical (tire size, compound, rims, etc.)

For the above data, we were using stock dampers with Swift springs, to make sure that we were not getting inside tire lift. We were also testing some Swift Spring setups, but that's a different story.

what sway bars were you running?

[CSG Mike]

Originally Posted by Calum

what sway bars were you running?

Stock

[ZDan]

Originally Posted by diss7

Also remember that no matter how tight the diff is, you can always use it like an open diff by pressing the clutch in.

A tight/highly-preloaded clutch type will not act like an open diff with the clutch disengaged. It will still induce understeer with the clutch disengaged commensurate with the amount of preload, which is not a function of input torque. Extreme case: welded diff. Crank in some steering angle and try to push the car in neutral. Which is why I prefer as light a preload as I can get away with in a clutch-type diff, and rely on the ramps to give the clamping force under power.

A lightly-preloaded clutch-type *will* act like an open diff with no torque input (clutch disengaged).

[ZDan]

Originally Posted by CSG Mike

Roll stiffness doesn't necessarily mean that the less loaded tire has more load on it.

For example, stiffer sprung cars roll less, but the total cornering load on the tire under static cornering (ignoring deflection, slip, and alignment) is the same, assuming the cars are otherwise identical (tire size, compound, rims, etc.)

He's talking about changing the front/rear roll stiffness distribution. I.e., instead of getting a tighter diff, shift some roll stiffness from the back to the front, which will put more load on the inside rear while cornering.

Tightening the diff as the first response to inside wheelspin can lead to a vicious circle, as tighter diff => understeer => more rear/less front roll stiffness to get back to neutral => increased unloading of the inside rear => tighter diff => ad infinitum

[ZDan]

For the record, I have the highest respect for the CSG guys and do not doubt that they got improved results with the clutch-type diff! I just don't think it's necessary for most who want to track the FR-S/BRZ to be able to put the power down and enjoy excellent handling/cornering. Most people are not going to be at the same level of setup or driving. And also different people and different car setups will have different requirements and desires for how the diff works, even at the same performance level.

I'm at a lower level of car setup and driving skill, and the Torsens in my cars are working great for me. I *hate* inside wheelspin, but I'm not getting it, and I'm not getting any kind of funky behavior on corner entry or exit, so I'm happy

[7thgear]

I'd like to think that I have decent car control skills, but I've never really been able to dictate the car's movements to the extent that is expressed in this video


what makes this car handle the tight corners the way it does, is it raw power? e-brake pulls? Diff magic? Or some of that driver special sauce that only the Finns seems to have


[ame="https://www.youtube.com/watch?v=zJCWR72uHbU"]Onboard Hirvonen/ SSS01 Rally Italia Sardegna 2014 - YouTube[/ame]

[troek]

id say all of the above, lol.

[CSG Mike]

Originally Posted by ZDan

For the record, I have the highest respect for the CSG guys and do not doubt that they got improved results with the clutch-type diff! I just don't think it's necessary for most who want to track the FR-S/BRZ to be able to put the power down and enjoy excellent handling/cornering. Most people are not going to be at the same level of setup or driving. And also different people and different car setups will have different requirements and desires for how the diff works, even at the same performance level.

I'm at a lower level of car setup and driving skill, and the Torsens in my cars are working great for me. I *hate* inside wheelspin, but I'm not getting it, and I'm not getting any kind of funky behavior on corner entry or exit, so I'm happy

Just some anecdotal evidence, but Miatas see good gains by going from Open to OEM Torsen, and HUGE gains by going from OEM Torsen to OSG.

They're so good that clutch type diffs were flat out banned in the Supermiata series; it's worth about 1.25-1.50 seconds at Buttonwillow 13CW on a Miata. This gain was observed to be near universal for anyone who is an intermediate level driver or higher, basically anyone who is comfortable accelerating out of a corner.

Yes, a Miata with ~140hp, that stays WOT for most of the track.


Is the aftermarket LSD necessary? Of course not, but it's a huge "bang for the buck" mod when it comes to cornering, but not one that is quantified on this board.

[DougW]

So which LSD works best for the price Wavetrac has both a torsen and clutch type together maybe making the best or the worst of both worlds?.
DougW

[CSG Mike]

Originally Posted by DougW

So which LSD works best for the price Wavetrac has both a torsen and clutch type together maybe making the best or the worst of both worlds?.
DougW

I'm not exactly sure what you're asking...

[Moto-P]

Originally Posted by neilr

For my own clarification...

I'm reading this as: you can't do this because the car doesn't have a mechanical LSD.

I thought the FR-S & BRZ came standard with a Torsen LSD. Isn't that a mechanical diff? Please clarify if I've missed something obvious.

Src:

___

To clarify this a bit more...

The Torsen is a very worry-free, maintenance-free, LSD design that works very positively for casual and generic need for an LSD for most users casual, and is a vast improvement and advantage over not having an LSD at all. However, because it is fixed to a certain character by design (in a production car's case, the balance of economy of tire wear, and risks for a non-racing user) it is setup very mildly. It has the merit of having almost no additional maintenance, and no more significant wear, or noises associated with racing LSD. It is the perfect choice for manufacturers to equip on production cars.

However, the Torsen (R) has some inherent drawbacks for the serious racing/sports car enthusiast who sacrifice nothing at going faster. These are:

1. the Torsen is not 'tunable' to desired characteristics in operation, like the initial lock up rate, and total maximum lock rate, as well as character in between. ALso they are not ramp-tunable for direction of force varying between full acceleration loads and full deceleration loads.

2. Like CSG Mike had mentioned briefly, they lose the capability to lock up when one wheel loses a load at the tire. While both tires are on the ground, with enough traction at the contact patch, they work very positively. However, when one wheel lifts, or both lifts (as occurs on tracks with crests where the vehicle actually leaves the ground for a split second, the lock is lost, and it takes a brief moment after regaining traction, that the total maximum lock is reached again, an instantaneous loss and delay in regaining lock.

SO, that being said, the mechanical 4 pinion clutch type LSD offers a much more traditional way to lock both wheels, and how that happens can be fine tuned. Ramp angle to cam adjustment provides how much lock takes place and how fast, and also in which load direction. The Torsen is locked as one-way, that is acceleration mode only, so once the throttle is lifted, the lock is released. In the 4 pinion clutch unit, this can be made to occur under deceleration too, so that transition between on and off throttle the axle lock can remain stable and steady. Various clutch setup methods can also tune for how the clutches progressively lock, from mild to hard, and that affects how the car will handle in the transition into various stages of motions a car will go through during a cornering process, from entry to exit. It also affects how the car will behave with throttle and steering inputs as well anytime during that process.

Also if you go back into the reason for having a differential gear, as the name implies, is that wheels travel over different distances and need to spin at different speeds to cover a distance in a turn to prevent binding of tires. Well, this is true for any normal driving conditions, if we can TUNE how that happens, and control when it should happen and when it should be free, this will allow more room and another very important trait where a sports car can be tailored to needs or tastes, skills or conditions of the road.

The Torsen is one of those all-mighty but generic solution that is pre-set at the factory for general consumers, with occasional sports car roles in mind. But a more serious driver will need a bit more suitability of a Mechanical Clutch, 4 pinion LSD as characters will define a handling attribute so much, that it will affect the not only lap times, but even how the suspension, alignment, weight dist, as well as even aerodynamics.... and vice versa.

______

As for how does it FEEL to an avearge user?

Well if you can use a TORSEN to do things like rotate on front tire axis like donuts and drifting, or tucking a line on exit of a corner with throttle inputs... The variables on how that actuates will become more predictable, precise, and controllability more wider.

So overall the mechanical will FEEL smoother, and you will be able to control rotation and acceleration more accurately. This is especially different under turn-in, and braking towards the apex, where 2 way LSD (and any variation between it and 1 way, all collectively named 1.5 but really, is more any fraction of lock rate as percentage of acceleration side) will feel more constant in lock, as the car rotates toward an apex under deceleration, hard on brakes or loose on coasting it will lock the way it is tuned to do.

Sounds like a dream right? There is a reason OEM rarely use clutch 4 pinion, on factory equipment though.

Clutch plates chatter and give noises that are not pleasant to some, especially in a new or luxury car... The maintenance costs are significant for an average Joe, who isn't a motorsports geek, with diff oil changes that are as frequent as engine oil, and annual overhauls and inspection that take more money and time away from driving. And tuning is not something easily done, but requires disassemble and very talented work of a specialist, as setting ring gears is not something easy for a Sunday mechanic, nor is dropping axles and rear ends on your driveway for most.

But if you have the resources, I would HIGHLY suggest you get one. As sports car feel is just as profoundly altered for the better in the same caliber as changing suspension and tires... It's that obvious, if you are an avid driver, or aspiring to become one.