LS suspension design: show me/explain why it is great

[Kumba]

Caliper location on the knuckle has more to do with cooling then anything else. Certain positions will tool better but pick up more trash/water/etc. Having the caliper slightly to the front of the center line of the knuckle on top will get it some airflow and help keep trash out. Having it trailing the centerline (to the back) of the knuckle will give more cooling but pick up more trash. No one puts them on the bottom of the knuckle since it's impractical (there's a ball joint down there and all) and you'd never get trash out of them. Another consideration on really big brakes, like 6 piston calipers, is where you can physically put them without hitting other suspension components.

Other then that I don't think you get anything from location on the spindle. Unsprung weight is unsprung weight. They don't weigh enough to cause any deflection in the suspension geometry.

 

[LS4me]

What I read a few years ago is that the caliper position is totally dependent on where if fits, nothing else. The rotor doesn't care where the pads grip it.

 

[Robot]

Caliper location on the knuckle has more to do with cooling then anything else. Certain positions will tool better but pick up more trash/water/etc. Having the caliper slightly to the front of the center line of the knuckle on top will get it some airflow and help keep trash out. Having it trailing the centerline (to the back) of the knuckle will give more cooling but pick up more trash. No one puts them on the bottom of the knuckle since it's impractical (there's a ball joint down there and all) and you'd never get trash out of them. Another consideration on really big brakes, like 6 piston calipers, is where you can physically put them without hitting other suspension components.

Other then that I don't think you get anything from location on the spindle. Unsprung weight is unsprung weight. They don't weigh enough to cause any deflection in the suspension geometry.

The caliper and bracket is connected to the steering knuckle assembly which is connected to the upper A arm and the lower control arm. When the brakes are applied, the rotor tries to move the caliper up and forward which puts enough tension on the steering knuckle to counter the compression of those components which is why the steering gets a little stiffer. Also, notice the shape of the lower control arm and the offset. Then think about what will happen when the steering knuckle assembly tries to rotate. Once you've thought of that go out and roll your car to a stop from a slow speed and just use the E brake and observe the front end rise up a bit.

 

[Robot]

I'm no suspension expert, but my observations on the passive 4 wheel steering is I don't like it. It makes the rear feel like it's swinging out a bit more than I want it to, and I'm glad that Bigrig said that the Deeza links is supposed to eliminate that because I've got a set of them out in the garage ready to go in as soon as I find a spare minute.

Aside from that, it's pretty much just an independent rear suspension. Nothing special about it from what I've seen, beyond that Ford seems to have not used quality materials seeing as the parts tend to wear out pretty quickly.

This is what could happen if you don't have the passive steering.

Antonio Pizzonia Crash Jaguar roadcar: http://youtu.be/Jc8uZGDAdQE.

 

[stugots]

This is what could happen if you don't have the passive steering.

No that's what happens when you take a turn at F1 speeds.

 

[FDR]

The caliper and bracket is connected to the steering knuckle assembly which is connected to the upper A arm and the lower control arm. When the brakes are applied, the rotor tries to move the caliper up and forward which puts enough tension on the steering knuckle to counter the compression of those components which is why the steering gets a little stiffer. Also, notice the shape of the lower control arm and the offset. Then think about what will happen when the steering knuckle assembly tries to rotate. Once you've thought of that go out and roll your car to a stop from a slow speed and just use the E brake and observe the front end rise up a bit.

The steering gets stiffer because of the caster effect. When driving normally, the car is pushing forward and the wheel's contact point is behind the pivot. The contact point gets pulled backwards, which, in this case, straightens the wheel. When you apply the brakes, the force exerted from the road to the wheel pulling the contact point backwards is much greater. To steer, you have to fight an additional force from the road trying to keep the wheels straight. The LS has heavy steering that makes this resistance much more pronounced

The caliper bracket is still fixed to a solid suspension member. There is a negligible amount of flex in the piece. If caliper locationade a performance difference, why don't all performance cars have the same location? The only consistency seems to be that they all put the calipers towards either the inside (both closest to the driver like the LS) or outside (front caliper to the front, rear to the rear)

 

[Kumba]

The mounting point of the caliper has an effect in terms of leverage on the knuckle. This is why they try to mount them low on the spindle so more of the load is put on the lower control arm. The upper arm is more for maintaining suspension geometry then supporting the weight/load of the car. You will get some deflection which will cause subtle changes to caster, camber, and toe but it won't be major like bump steer. You will get bigger changes from suspension traveling over uneven road then the twisting of the suspension components from braking.

A bigger effect will be the load transferring into the chassis which will want to lift up the rear of the car. That gets combined with all the weight of the car shifting forward and give you the classic nose dive under hard breaking.

 

[joegr]

Be aware as well that the LS (like many cars) has the steering boost controlled electronically, based on vehicle speed, braking, and the way the steering wheel is being turned.

 

[Robot]

The steering gets stiffer because of the caster effect. When driving normally, the car is pushing forward and the wheel's contact point is behind the pivot. The contact point gets pulled backwards, which, in this case, straightens the wheel. When you apply the brakes, the force exerted from the road to the wheel pulling the contact point backwards is much greater. To steer, you have to fight an additional force from the road trying to keep the wheels straight. The LS has heavy steering that makes this resistance much more pronounced

The caliper bracket is still fixed to a solid suspension member. There is a negligible amount of flex in the piece. If caliper locationade a performance difference, why don't all performance cars have the same location? The only consistency seems to be that they all put the calipers towards either the inside (both closest to the driver like the LS) or outside (front

The steering gets stiffer because of the caster effect. When driving normally, the car is pushing forward and the wheel's contact point is behind the pivot. The contact point gets pulled backwards, which, in this case, straightens the wheel. When you apply the brakes, the force exerted from the road to the wheel pulling the contact point backwards is much greater. To steer, you have to fight an additional force from the road trying to keep the wheels straight. The LS has heavy steering that makes this resistance much more pronounced

The caliper bracket is still fixed to a solid suspension member. There is a negligible amount of flex in the piece. If caliper locationade a performance difference, why don't all performance cars have the same location? The only consistency seems to be that they all put the calipers towards either the inside (both closest to the driver like the LS) or outside (front caliper to the front, rear to the rear)

caliper to the front, rear to the rear)

My LS brackets are fixed to the steering knuckle assembly which in turn is attached to the upper a arm at the top and the lower control arm at the bottom. Both of those units are have rubber bushings that flex. When the brakes are applied, the rotor exerts a force forward and up which tries to rotate the steering knuckle assembly. As it tries to move, it pushes up on the upper a arm and down on the lower control arm. If you notice the steering knuckle assembly is slanted backward to some degree. This action counteracts the tendency to dive. Now this is only one of many solutions to prevent dive under braking. BTW my LS has extremely light steering but that may be because I've dialed in some toe out for sharper turn in.

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One more thing, that Jag lost it in the corner because the Brits in their infinite wisdom thought the Ford suspension was too stiff and not plush enough for their pampered arses so they softened up the dampers which basically made it like a normal non Sporting version. I drove one once and it felt like a Towncar with a Cobra engine.

 

[HMBarger]

What I read a few years ago is that the caliper position is totally dependent on where if fits, nothing else. The rotor doesn't care where the pads grip it.

I looked into caliper location not too long ago after painting mine just wondering why they were where they were. Found the same info.

I just figure it's a good thing that they fit there (behind front rotor; in front of rear) because that's where you see them on nearly every high end sports car.

 

[Turboguy]

Thanks to all who contributed info, learning about this complex car is like peeling an onion. And working on it brings tears to our eyes too

 

[Robot]

Hey, and I realize I could be way wrong on my assessment of how this works but I gather my info from my cousin that was a tech at the Wixom plant and his ex wife who was on the development team in engineering at the same plant. That along with some casual observations of cars with anti dive technology that have the calipers toward the driver and looking at motorcycle brake setups with the same leads me to the conclusion that it could be the major factor. Like I said, I could be wrong but if I am I still love how I can hit the brakes and not look stupid.

 

[Kumba]

The only force the caliper exerts is a twisting force on the knuckle in the same direction the wheel spins. It is not capable of generating an up or down force. It's mounting position on the knuckle does not matter beyond changing the fulcrum of where that twisting force is generated.

Now how the control arms, their squishy bushing, and the suspension geometry react to this twisting motion may create some other things. But the brake caliper itself has nothing to do with pushing the knuckle up or down. It is merely creating a rotational force.

 

[Robot]

The only force the caliper exerts is a twisting force on the knuckle in the same direction the wheel spins. It is not capable of generating an up or down force. It's mounting position on the knuckle does not matter beyond changing the fulcrum of where that twisting force is generated.

Now how the control arms, their squishy bushing, and the suspension geometry react to this twisting motion may create some other things. But the brake caliper itself has nothing to do with pushing the knuckle up or down. It is merely creating a rotational force.

Thats my point. When that caliper exerts that twisting force it tries to stand the knuckle assembly uup straight. The top of the assembly tries to rotate forward and pushes up on the a arm and the bottom tries to rotate backward and pushes down on the control arm basically trying to spread them apart. If you could stand the knuckle assembly straight up it would raise the suspension of the car.

 

[stugots]

One more thing, that Jag lost it in the corner because the Brits in their infinite wisdom thought the Ford suspension was too stiff and not plush enough for their pampered arses so they softened up the dampers which basically made it like a normal non Sporting version. I drove one once and it felt like a Towncar with a Cobra engine.

No that's an S-type R. Pretty stiff. The only reason that crash happened is because the idiot driver used his F1 car's braking point. Any LS, or car for that matter, would've had a similar result.

 

[stugots]

I also wouldn't get caught up in the passive 4 wheel steer. Many many cars use this to a certain extent and it is nothing new or groundbreaking. Active 4 wheel steer is another story.

Wikipedia:
Many modern vehicles have passive rear steering. On many vehicles, when cornering, the rear wheels tend to steer slightly to the outside of a turn, which can reduce stability. The passive steering system uses the lateral forces generated in a turn (through suspension geometry) and the bushings to correct this tendency and steer the wheels slightly to the inside of the corner. This improves the stability of the car, through the turn. This effect is called compliance understeer and it, or its opposite, is present on all suspensions.

 

[Robot]

No that's an S-type R. Pretty stiff. The only reason that crash happened is because the idiot driver used his F1 car's braking point. Any LS, or car for that matter, would've had a similar result.

Did you see that brake dive in the front? An LS wouldn't have done that and would have drifted around the corner. One of the reviews I read had issues with them softening the suspension the way they did. There is much more weight up front and if anything they should have done like Ford did and reduce the spring rate and stiffen the dampers. It rode like a Towncar to me and was nowhere near as stiff as my car and it has all original stuff on it.

 

[LS4me]

I also wouldn't get caught up in the passive 4 wheel steer. Many many cars use this to a certain extent and it is nothing new or groundbreaking. Active 4 wheel steer is another story.

Wikipedia:
Many modern vehicles have passive rear steering. On many vehicles, when cornering, the rear wheels tend to steer slightly to the outside of a turn, which can reduce stability. The passive steering system uses the lateral forces generated in a turn (through suspension geometry) and the bushings to correct this tendency and steer the wheels slightly to the inside of the corner. This improves the stability of the car, through the turn. This effect is called compliance understeer and it, or its opposite, is present on all suspensions.

I don't think I would quote Wikipedia as a authoritative source. I may just go in and edit that information........

 

[joegr]

.... This effect is called compliance understeer and it, or its opposite, is present on all suspensions.

I suspect that this quote could be correct, considering that it is saying that either understeer or oversteer is present on all suspensions. It is not saying that all suspensions have rear passive steering. Certainly, I've had cars with solid rear axles that did not.

 

[stugots]

I suspect that this quote could be correct, considering that it is saying that either understeer or oversteer is present on all suspensions. It is not saying that all suspensions have rear passive steering. Certainly, I've had cars with solid rear axles that did not.

My mistake it was 2 am when I read that. The main point I'm trying to make is pretty much all modern cars use some level of passive steer.





Talking with an engineer about it he gave me the impression that

 

[stugots]

I don't think I would quote Wikipedia as a authoritative source. I may just go in and edit that information........

I'm sure you could find other sources. I was talking with my engineer cousin about it. He blew me off when I said my car had it. I guess it's not too much of a big deal, almost every car uses bushings to some extent to allow the wheel to steer.

 

[tijoe]

No one has mentioned that the LS uses Ford's DEW98 platform. You can find more information about the suspension design if you search on DEW98.
The platform was/is an excellent design for mid-size sedans, but in Ford's eyes, was too expensive to propagate to other cars. Jaguar still uses variants of the design in its new cars.

I should add that the design is very optimized for its application and is very difficult to change or modify; Wheels have large negative offset, and you can only put on wider rims if you add the spacing to the outside. This leads to having to flare the fender wells. If you go too far outboard, then you start affecting the suspension geometry and there is no adjustability to change the caster and camber. About all you can adjust is toe in and toe out.

 

[stugots]

I don't think I would quote Wikipedia as a authoritative source. I may just go in and edit that information........

I'm sure you could find other sources. I was talking with my engineer cousin about it. He blew me off when I said my car had it. I guess it's not too much of a big deal, almost every car uses bushings to some extent to allow the wheel to steer.

 

[LS4me]

I'm sure you could find other sources. I was talking with my engineer cousin about it. He blew me off when I said my car had it. I guess it's not too much of a big deal, almost every car uses bushings to some extent to allow the wheel to steer.

Disconnect the rear tie rods and see how much play there is in the knuckle (it's like an inch!). I have yet to see a rear tie rod that is other than a solid piece; I'm NOT talking about the (required) mounting bushing. That bushing may be flexible, but it isn't supposed to be. ALL cars have over or under steer built in. In fact, understeer is the preferable choice for "driver protection".

Passive rear steering may be widely used now, but it sure wasn't in 1999!!!!!!

 

[stugots]

Disconnect the rear tie rods and see how much play there is in the knuckle (it's like an inch!). I have yet to see a rear tie rod that is other than a solid piece; I'm NOT talking about the (required) mounting bushing. That bushing may be flexible, but it isn't supposed to be. ALL cars have over or under steer built in. In fact, understeer is the preferable choice for "driver protection".

Passive rear steering may be widely used now, but it sure wasn't in 1999!!!!!!

I mean the Rx7 had it in 1986. I think it's a cool feature to talk about but I wouldn't go too much into it, in regards to turbos article. I think there are other more important things to bring up about the cars suspension design.