why dont more people have an LSD?
10-11-2011, 08:56 PM
#26
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10-11-2011, 11:56 PM
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10-12-2011, 02:06 PM
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2001 SLK320 Firemist Red
I had to search the web to understand whats going on.. the power is following the path of least resistance. As the right wheel gets braked more... its the path of more resistance so the power shifts to the left. Since my truck doesnt have brake activated traction control... the drive wheel is always the wheel of least resistance so the power never shifts to the left and the right wheel just spins and spins. And here I thought I understood how an open diff works.
that explains why the quaife offers such low rewards in straight line acceleration. I couldnt make any sense of their published figures. I figured they would be really high rewards since the wheels dont spin... The MB system works so well.. like you said.. its a psuedo lsd.
that explains why the quaife offers such low rewards in straight line acceleration. I couldnt make any sense of their published figures. I figured they would be really high rewards since the wheels dont spin... The MB system works so well.. like you said.. its a psuedo lsd.
since the biggest issue I have with my E55 is initial takeoff wheelspin.
Somebody please correct me if this is wrong, but I'm thinking the LSD
will help stop spin in two situations: in hard cornering, and when
there is a large traction differential between the left and right drive tires.
So in a straight line with both wheels having *equivalent* traction,
the only thing that will help stop the spin is better traction, i.e. stickier
tires or a better road surface. LSD will have no effect in such a case.
Is this true?
10-12-2011, 04:38 PM
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This is what I have come to understand.. Im sure its not 100% correct.. but it is correct enough for me to decide an LSD is not needed for my purposes.
An open diff sends power to both rear wheels when going in a straight line. When it meets a situation where there is more or less resistance on a wheel... the power follows the path of least resistance. In most cases the right rear wheel begins to spin. As the the Benz traction control brakes the spinning wheel.. it is no longer the path of least resistance and the power shifts to the left hand side. This happens very quickly but as you can see from the video I posted... there is some lag and loss of forward momentum.
With a limited slip, the transfer of power is mechanical via clutches or gears inside the diff. Due to the quality of the LSDs most often discussed on these boards... this happens much faster than the traction control system operates. These LSD's also do it at different rates of power. 60/40 or 100% (quaife) transfer of power are common. The lsd shifts the power with out the need for the brakes to engage and often does it faster/better than the traction control.
So why get an LSD on a car equipped with a traction control system as sophisticated and as fast as the e55 amg? The motor will continue to put power to the rear right tire's drive shaft even while the brake is clamping down on it and that could result in broken axle splines, particularly in higher powered cars. Not to mention that you dont really want to be applying the brake to something you want to be moving you forward. In the case of a track car... the lsd shifts power more efficiently and more predictably than a traction control system while still maintaining forward power. A tire under brake tends to slide where as a tire under power tends to grip.
If you watch what happens to individual wheel speeds as a car goes around in a circle and how propulsion helps or hampers that activity... its more clear why an LSD is a good thing. In a situation where I want to go faster in a straight line and what should I do with $2500.00... the money is much better spent on some other mod.
Will an LSD help you do anything you want to do better.. yes. But it is not as big of an improvement on this car as compared to a pick up truck with no traction control.
An open diff sends power to both rear wheels when going in a straight line. When it meets a situation where there is more or less resistance on a wheel... the power follows the path of least resistance. In most cases the right rear wheel begins to spin. As the the Benz traction control brakes the spinning wheel.. it is no longer the path of least resistance and the power shifts to the left hand side. This happens very quickly but as you can see from the video I posted... there is some lag and loss of forward momentum.
With a limited slip, the transfer of power is mechanical via clutches or gears inside the diff. Due to the quality of the LSDs most often discussed on these boards... this happens much faster than the traction control system operates. These LSD's also do it at different rates of power. 60/40 or 100% (quaife) transfer of power are common. The lsd shifts the power with out the need for the brakes to engage and often does it faster/better than the traction control.
So why get an LSD on a car equipped with a traction control system as sophisticated and as fast as the e55 amg? The motor will continue to put power to the rear right tire's drive shaft even while the brake is clamping down on it and that could result in broken axle splines, particularly in higher powered cars. Not to mention that you dont really want to be applying the brake to something you want to be moving you forward. In the case of a track car... the lsd shifts power more efficiently and more predictably than a traction control system while still maintaining forward power. A tire under brake tends to slide where as a tire under power tends to grip.
If you watch what happens to individual wheel speeds as a car goes around in a circle and how propulsion helps or hampers that activity... its more clear why an LSD is a good thing. In a situation where I want to go faster in a straight line and what should I do with $2500.00... the money is much better spent on some other mod.
Will an LSD help you do anything you want to do better.. yes. But it is not as big of an improvement on this car as compared to a pick up truck with no traction control.
10-12-2011, 05:45 PM
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"I'm thinking the LSD will help stop spin in two situations: in hard cornering, and when there is a large traction differential between the left and right drive tires."
when you turn, the outside wheel is moving faster than the inside wheel. How lsd or traction control will help depends on what wheel is spinning and which direction you are turning. Lets say you are turning right in the rain and your rear right tire begins to spin. Traction control will brake that tire... the idea is to slow the spin down so that the tire can get traction again. in this scenario it is unlikely the other wheel will get power. The brakes will most likely allow the tire to regain grip and stop spinning. The LSD will transfer the power to the other wheel. Less power to the spinning wheel slows it down and allows it to get traction while the other wheel continues to power the car through the turn.
On the street... either option is great. On the track at high speeds with the shifting weight of the vehicle coming into play.. an LSD not only provides a means to transfer power with out the brakes it also helps control the shifting weight of the vehicle through the turn. In a right hand turn the weight of the car gets pushed left. There is a tendency for the wheels on the inside to lift and lose traction. With a limited slip, the outside wheel gets power and effectively pushes the car back down on the ground.
"So in a straight line with both wheels having *equivalent* traction,
the only thing that will help stop the spin is better traction, i.e. stickier
tires or a better road surface. LSD will have no effect in such a case."
think about it like this.... all the power goes to one wheel and it starts to spin.... with a limited slip the power is mechanically transferred to the other tire effectively doubling your contact patch (the amount of tire on the ground) In off road trucks there is something called locking which forces both wheels in the rear to spin at the same rate at the same time. this is great for traction and propulsion but terrible for turning... remember that when you turn the outside wheel must spin faster than the inside wheel. SO an lsd allows both tires to be used for propulsion and also allows them to move at different rates.
Traction control is braking one tire causing the other tire to gain power by default (it may or may not actually get power). What ends up happening.. and you can see it in the video.. the traction control causes the car to sort of shuffle left right left right as it moves forward. SO to answer your question... yes, sticker tires, wider tires, better road surface reduce wheel spin.
Either an LSD or traction control dont really prevent wheel spin... they answer the question of... if there is wheel spin, what will I do with it..... shift power to the other side... or brake the wheel.
when you turn, the outside wheel is moving faster than the inside wheel. How lsd or traction control will help depends on what wheel is spinning and which direction you are turning. Lets say you are turning right in the rain and your rear right tire begins to spin. Traction control will brake that tire... the idea is to slow the spin down so that the tire can get traction again. in this scenario it is unlikely the other wheel will get power. The brakes will most likely allow the tire to regain grip and stop spinning. The LSD will transfer the power to the other wheel. Less power to the spinning wheel slows it down and allows it to get traction while the other wheel continues to power the car through the turn.
On the street... either option is great. On the track at high speeds with the shifting weight of the vehicle coming into play.. an LSD not only provides a means to transfer power with out the brakes it also helps control the shifting weight of the vehicle through the turn. In a right hand turn the weight of the car gets pushed left. There is a tendency for the wheels on the inside to lift and lose traction. With a limited slip, the outside wheel gets power and effectively pushes the car back down on the ground.
"So in a straight line with both wheels having *equivalent* traction,
the only thing that will help stop the spin is better traction, i.e. stickier
tires or a better road surface. LSD will have no effect in such a case."
think about it like this.... all the power goes to one wheel and it starts to spin.... with a limited slip the power is mechanically transferred to the other tire effectively doubling your contact patch (the amount of tire on the ground) In off road trucks there is something called locking which forces both wheels in the rear to spin at the same rate at the same time. this is great for traction and propulsion but terrible for turning... remember that when you turn the outside wheel must spin faster than the inside wheel. SO an lsd allows both tires to be used for propulsion and also allows them to move at different rates.
Traction control is braking one tire causing the other tire to gain power by default (it may or may not actually get power). What ends up happening.. and you can see it in the video.. the traction control causes the car to sort of shuffle left right left right as it moves forward. SO to answer your question... yes, sticker tires, wider tires, better road surface reduce wheel spin.
Either an LSD or traction control dont really prevent wheel spin... they answer the question of... if there is wheel spin, what will I do with it..... shift power to the other side... or brake the wheel.
10-12-2011, 06:09 PM
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2006 E55 BEAST
I didn't buy this car to race it or be the fastest, I bought it because it's completely insane. IMO the LSD would restrict the insanity a bit.
But of course to each their own and everyone likes a different driving experience.
But of course to each their own and everyone likes a different driving experience.
