Why need LSD if the TC is so good?

[centurion]

OK my basic understanding first: LSD has the prime use of the outside wheel not down on power if the inside wheel is spinning wildly in an open diff.

But with the TC system on, will the inside wheel spin? If it's spinning, won't the TC take control and brake the inside rear, so the outside rear will regain power.

Aiya, these few days my head all filled with these questions.

 

[satinGHOST|r!der]

Re: Why need LSD if the TC is so good?

I am interested in this qn too. I think TC is more of a power restrainer in a difficult situation whereas LSD, given the skill of the driver, is able to put more power to the ground effectively, and still be able to control the car. I may be wrong but this is my shallow understanding of the 2 main differences

 

[centurion]

Re: Why need LSD if the TC is so good?

I am interested in this qn too. I think TC is more of a power restrainer in a difficult situation whereas LSD, given the skill of the driver, is able to put more power to the ground effectively, and still be able to control the car. I may be wrong but this is my shallow understanding of the 2 main differences

The TC locks the spinning inside wheel, and in an open differential, that would direct torque to the outside wheel. Well, that's what I gather from my open differential remote control car ... therefore, it's not simply a matter of restraining power, it actually locks the spinning wheel and the open diff will redirect power to where there's traction.

 

[Crufty Dusty]

Re: Why need LSD if the TC is so good?

The TC locks the spinning inside wheel, and in an open differential, that would direct torque to the outside wheel. Well, that's what I gather from my open differential remote control car ... therefore, it's not simply a matter of restraining power, it actually locks the spinning wheel and the open diff will redirect power to where there's traction.

Hmm... don't you mean that the open differential redirects power to where there is LESS traction i.e. path of least resistance, opposite of LSD.

Unless you're talking about electronically controlled differential integrated into the system, my understanding of "traction control" is power management on ECU-side to maximize traction by controlling wheel spin, usually on a per-axle basis.

 

[centurion]

Re: Why need LSD if the TC is so good?

Hmm... don't you mean that the open differential redirects power to where there is LESS traction i.e. path of least resistance, opposite of LSD.

Unless you're talking about electronically controlled differential integrated into the system, my understanding of "traction control" is power management on ECU-side to maximize traction by controlling wheel spin, usually on a per-axle basis.

What I mean is that, TC works in such a way as to arrest the spinning of the inside wheel. Once the inside wheel is locked, the outside wheel will regain power. TC is not only engine power, it has relationship with brake also, using ABS sensor. It works like a holistic system.

electronic diff works like LSD but with more intelligence and traction map, different from ordinary TC principle.

 

[Crufty Dusty]

Re: Why need LSD if the TC is so good?

Your definition of "Traction Control" is closer to electronic brake force distribution but with the similar ultimate effect of reducing net torque at the driven wheels. However an LSD does not reduce net torque since it is on the receiving end of the output shaft; it only redistributes torque to the driven wheel(s) that has more available traction. Essentially they don't have to be mutually exclusive and can (and are!) used in concert to achieve the same goal.

 

[centurion]

Re: Why need LSD if the TC is so good?

man all the TC, ASR, EBD. XXX, are so interrelated I'm confused.

 

[powersteer]

Re: Why need LSD if the TC is so good?

LSD will channel torque from the spinning wheel .. the only drawback is slight power loss from friction.

TC brakes the spinning wheel ... more power is lost from that .... thus a less efficient option ... plus, effectiveness depends on programmer and working sensors

 

[satinGHOST|r!der]

Re: Why need LSD if the TC is so good?

LSD will channel torque from the spinning wheel .. the only drawback is slight power loss from friction.

TC brakes the spinning wheel ... more power is lost from that .... thus a less efficient option ... plus, effectiveness depends on programmer and working sensors

So if thats the difference, then how good is an aftermarket LSD that is supposed to work hand in hand with the TC? If so the sensors are orginally calibrated for non-LSD cars?

 

[Crufty Dusty]

Re: Why need LSD if the TC is so good?

So if thats the difference, then how good is an aftermarket LSD that is supposed to work hand in hand with the TC? If so the sensors are orginally calibrated for non-LSD cars?

Generally speaking an LSD-equipped vehicle will have better traction as compared to a similar model without LSD, and depending on the kind of LSD, it may have adverse effects on handling.

But you are right to be concerned about fitting aftermarket differentials onto standard cars. In fact most of the more reputable companies will do some research as to whether it is a suitable mod or not. This is partly why some LSDs can only be fitted with cars without ABS.

 

[satinGHOST|r!der]

Re: Why need LSD if the TC is so good?

Generally speaking an LSD-equipped vehicle will have better traction as compared to a similar model without LSD, and depending on the kind of LSD, it may have adverse effects on handling.

But you are right to be concerned about fitting aftermarket differentials onto standard cars. In fact most of the more reputable companies will do some research as to whether it is a suitable mod or not. This is partly why some LSDs can only be fitted with cars without ABS.

Post march production for cars such as mine, being the 335i, has a welded diff. Gotta remove the whole thing for a complete unit. Way too much work. Still evaluating the possibilities of retro fitting one into the car. You are spot on the effects of LSD on handling. Its completely different from a car without LSD.

 

[powersteer]

Re: Why need LSD if the TC is so good?

So if thats the difference, then how good is an aftermarket LSD that is supposed to work hand in hand with the TC? If so the sensors are orginally calibrated for non-LSD cars?

with LSD, your TC will experience that your car is getting more grippy (less wheelspin), thus kicks in later.

assuming that u are getting torsen, TC will actually work hand in hand to maximise traction, torsen dun work in extreme situations where u have a wheel lift or excessive wheelspin (ie, very low resistance) ... TC will work hand in hand to restrain the spinning wheel.

but if the programmers were to factor in the presence of the LSD during the design stage, that shd work much better ...

 

[powersteer]

Re: Why need LSD if the TC is so good?

Post march production for cars such as mine, being the 335i, has a welded diff. Gotta remove the whole thing for a complete unit. Way too much work. Still evaluating the possibilities of retro fitting one into the car. You are spot on the effects of LSD on handling. Its completely different from a car without LSD.

dun think a mass production car will ever be released with welded diffs ... maybe u mean something else

 

[phil]

Re: Why need LSD if the TC is so good?

for "welded" i think he means a closed unit, not spider gears welded.

errr, traction control controls the throttle i thought, nothing to do with the diff. I know in some cars i have driven with TC, if you floor the loud pedal, car breaks traction, the TC kicks your foot off almost. I thought TC "detunes" a few cylinders till it gets traction again. Another reason why drive wheels must be on the ground for tuning, if off the ground, the TC thinks it has no traction!!

Aftermarket LSD's are most likely just using stronger hemispheres and clutches in the diff. If anything, i would prefer a locker diff over an LSD, much much more control, especially in drifts.

oh, one last thing. Weld the TC button on the off position

 

[powersteer]

Re: Why need LSD if the TC is so good?

for "welded" i think he means a closed unit, not spider gears welded.

errr, traction control controls the throttle i thought, nothing to do with the diff. I know in some cars i have driven with TC, if you floor the loud pedal, car breaks traction, the TC kicks your foot off almost. I thought TC "detunes" a few cylinders till it gets traction again. Another reason why drive wheels must be on the ground for tuning, if off the ground, the TC thinks it has no traction!!

Aftermarket LSD's are most likely just using stronger hemispheres and clutches in the diff. If anything, i would prefer a locker diff over an LSD, much much more control, especially in drifts.

oh, one last thing. Weld the TC button on the off position

TC ... or stability control are usually implemented using various means. some cut spark, throttle .. (reduce engine power), others brakes the spinning wheel.

ahh yes, throw that TC out of the window if u wan purer driving

 

[phil]

Re: Why need LSD if the TC is so good?

brakes the spinning wheel? bugger that, CUT the wires!!

 

[powersteer]

Re: Why need LSD if the TC is so good?

honestly, if u are worried abt interfering with the electronics .. its safer to install a torsen instead of clutch type ...

although the effectiveness is not with the clutch type, the actions are much smoother .. the electronics are unlikely to be screwed that way

btw .. if u wan that LSD in the new elise, u have to tick that TC option too ... so that enforces my view that they are able to work together

 

[phil]

Re: Why need LSD if the TC is so good?

Omar, put an old fashioned 9inch in it!!

 

[powersteer]

Re: Why need LSD if the TC is so good?

honestly, if u are worried abt interfering with the electronics .. its safer to install a torsen instead of clutch type ...
although the effectiveness is not with the clutch type, the actions are much smoother .. the electronics are unlikely to be screwed that way

btw .. if u wan that LSD in the new elise, u have to tick that TC option too ... it has the DBW throttle that cuts power during wheelslips :furious: :laughlik: