Suspension Talks: Understeer & Oversteer

[Trevor]

Kia ora Nevin,

I agree with what you are saying, but I am confident that a rear bar is in no way going to satisfy the requirements raised within this thread. I have not stated that a rear bar is useless, only that it will not prove effective for the application involved here.

The opening paragraph reads. ---

Hey guys, I guess it is time to refresh the issue of the SVX's suspension, especially after all the recent mods that are now available.
In hopes that this thread will evolve to become a how-to-guide for racers, autoxers and engine modders. The subject definitely needs discussion.

[Nevin]

Originally Posted by Trevor

Kia ora Nevin,

I agree with what you are saying, but I am confident that a rear bar is in no way going to satisfy the requirements raised within this thread. I have not stated that a rear bar is useless, only that it will not prove effective for the application involved here.

The opening paragraph reads. ---

Hey guys, I guess it is time to refresh the issue of the SVX's suspension, especially after all the recent mods that are now available.
In hopes that this thread will evolve to become a how-to-guide for racers, autoxers and engine modders. The subject definitely needs discussion.

Thank you for clarifying, Trevor. I should also apologize for jumping the gun to assume that you were "attacking" what I had done, which you in no way ever did. I perhaps replied with too much hostility, and your remarks in no way deserved it.

I agree that within the confines of this topic, the rear bar has now been discussed at length, and that there are still many other areas to consider as well.

[shotgunslade]

All very true, however I am unable to understand modern descriptions of cornering technique, and in particular the invented reference to “trail braking.” .

Not invented, often used and even encouraged, by name, in the Skip Barber School. Trail braking is continuing the braking process, although at a much reduced rate, into and after turn-in for the corner. It is effective for understeering cars, because it transfers weight to the front, giving the tires more bite, and thus reducing slip angles.

There is only one fast way round a tight corner on a racing circuit, when driving a car which has, other than sticky tyres
Having approached the corner at maximum speed, braking is left to the very last possible moment, under braking the rear is set sliding at the turn in, power is applied in order to set up a drift and adhesion is controlled so that on exit maximum traction is available. During practice it is often necessary to exceed the limit and a spin out results, as is required to establish the limits.

Most of the above is just WRONG. There are many fast lines around a track. You can watch any race and see how driver's styles and lines differ. Front wheel, rear wheel and all wheel drive cars need different strategies to go fast

The rear-end hanging out style described above may be appropriate for rear-wheel drive cars, but it doesn't work for SVX's. We can't use the rear drive wheels to push the car through the turn. Applying extra power in a turn causes oversteer in a rear drive car, it usually causes understeer in our car. To get oversteer and thus rotation in an SVX you need to decelerate, to shift weight off the rear wheels, either with a throttle lift or with braking. The tail out strategy is really only achievable and useful in an SVX in very tight turns, where you turn in under heavier braking and the rear end comes around. By compacting the turning in a tight corner, you can stop turning sooner and accelerate sooner, with the wheels straighter which is much more effective at putting the power to the ground.

For higher speed corners, the strategy is similar, but not as dramatic. The basic strategy is to get the turning mostly done before you slam the accelerator, often using light braking to make those front tires stick and taking weight off the rear so it will rotate. If you don't follow this strategy, one of two things will happen. either you will understeer and have to turn more and possibly lift in order not to plow off the road, or you may, like I have done, spin, as both ends of the car reach the limits of adhesion at the same time and the rear slides quicker than the front.

As for the rear sway bar, I'll see this weekend how it does. A stiffer front sway bar would certainly be a welcome addition. Bill is the only person I know of with one of those.

[SilverSpear]

Okkkk now... since everybody agrees that we need a front swaybar, I think the right debate here would be related to its thickness and shape.

For the thickness... I leave it to the experts.

For the shape, it is currently an "L" + "I". I guess fabbing the same style would be costly as hell, I guess we need someone to fab it (Nev?) the same as the rear, a continuous "U". Yeah I know, it will be a PITA to install, but on the other hand it is a "one-time PITA" installation if memory serves right... Plus it would be cheaper to fab.

Who cares to start hammerin' me

[Trevor]

Originally Posted by shotgunslade

Not invented, often used and even encouraged, by name, in the Skip Barber School. Trail braking is continuing the braking process, although at a much reduced rate, into and after turn-in for the corner. It is effective for understeering cars, because it transfers weight to the front, giving the tires more bite, and thus reducing slip angles.


Most of the above is just WRONG. There are many fast lines around a track. You can watch any race and see how driver's styles and lines differ. Front wheel, rear wheel and all wheel drive cars need different strategies to go fast

The rear-end hanging out style described above may be appropriate for rear-wheel drive cars, but it doesn't work for SVX's. We can't use the rear drive wheels to push the car through the turn. Applying extra power in a turn causes oversteer in a rear drive car, it usually causes understeer in our car. To get oversteer and thus rotation in an SVX you need to decelerate, to shift weight off the rear wheels, either with a throttle lift or with braking. The tail out strategy is really only achievable and useful in an SVX in very tight turns, where you turn in under heavier braking and the rear end comes around. By compacting the turning in a tight corner, you can stop turning sooner and accelerate sooner, with the wheels straighter which is much more effective at putting the power to the ground.

For higher speed corners, the strategy is similar, but not as dramatic. The basic strategy is to get the turning mostly done before you slam the accelerator, often using light braking to make those front tires stick and taking weight off the rear so it will rotate. If you don't follow this strategy, one of two things will happen. either you will understeer and have to turn more and possibly lift in order not to plow off the road, or you may, like I have done, spin, as both ends of the car reach the limits of adhesion at the same time and the rear slides quicker than the front.

As for the rear sway bar, I'll see this weekend how it does. A stiffer front sway bar would certainly be a welcome addition. Bill is the only person I know of with one of those.

Forget racing schools, they are for playboys with a big cheque book. Your advice clearly indicates that you have never raced on the limit, whereby a mistake is likely to be fatal. I have been happy with, no roll cage, no harness, no run off areas at corners, plenty of fixed hard objects to stop one quickly. Nothing I have stated is wrong.

There is only two situations which apply during racing. The car is under maximum acceleration or maximum braking, i.e. the exception being very fast sweeping corners a situation not covered within your description. Otherwise the driver is simply pissing about.

“Front wheel, rear wheel and all wheel drive cars need different strategies to go fast.”

There is no strategy as such, there is but instinct and judgement. A driver has it, or he does not. It can be detected a mile off. The guy who sits up on the steering wheel and points the car, as against he who sits back and feels the car with his body and directs it accordingly, with hands and feet.

“To get oversteer and thus rotation in an SVX you need to decelerate, to shift weight off the rear wheels, either with a throttle lift or with braking. The tail out strategy is really only achievable and useful in an SVX in very tight turns, where you turn in under heavier braking and the rear end comes around.”

Exactly as I have decreed. But damn it in a motor race, who would lift the throttle if not braking or negotiating a very fast sweeping corner? There is confusion here as to what is a tight corner. A corner/turn is any section of the road which can not be negotiated, without substantial slow down using the brakes. Otherwise the term, "sweeper or sweeping turn" is more applicable.

“For higher speed corners, the strategy is similar, but not as dramatic. The basic strategy is to get the turning mostly done before you slam the accelerator, often using light braking to make those front tires stick and taking weight off the rear so it will rotate.”

Slam the accelerator? It is very clear that you have never negotiated a fast sweeper, nor have you driven in a real motor race and been any where near the limit. You are probably talking about a medium radius corner, but on entry why would you be wasting time under light braking? Furthermore slamming the accelerator on any sort of real racing car, will cause wheel spin and loss of control.

If you are seriously racing, braking before the corner will be at absolute maximum stopping power, maximum possible forward weight will have then occurred. If braking can be continued through the corner, the car is not on the limit and is not going as fast as it could be.

I have raced front and rear wheel cars and when I first ran a front drive car I read all the theory, but could make no sense of it. I simply got aboard and drove the thing with an open mind, relying on the seat of my pants for instruction, rather than some form of theory. I quickly found that it was easier to set the rear out under braking on entering a corner, than with rear drive. Traction from the front, was automatically catered for without special thought.

If the car spins out on a sweeping corner at high speed, after the car has rotated and as is going backwards, the brakes should be applied hard. The weight then transfers to the rear and the front slides with the car then moving inwards, back onto the circuit. With the brakes held on the spin continues to the outside and off at ever reducing momentum. It works believe me. I am describing a situation where you have lost it, and any thought of opposite lock correction is worthless. This advice transcends, --- “brakes are the last resort.”

[Trevor]

Originally Posted by SilverSpear

Okkkk now... since everybody agrees that we need a front swaybar, I think the right debate here would be related to its thickness and shape.

For the thickness... I leave it to the experts.

For the shape, it is currently an "L" + "I". I guess fabbing the same style would be costly as hell, I guess we need someone to fab it (Nev?) the same as the rear, a continuous "U". Yeah I know, it will be a PITA to install, but on the other hand it is a "one-time PITA" installation if memory serves right... Plus it would be cheaper to fab.

Who cares to start hammerin' me

You can not leave the stiffness entirely to "the experts." In all of this the expert is the driver and only he can decide on preference. Once the mechanics have been sorted there is no substitute for practical testing under the applicable conditions.

Where racing set ups are involved, it is usual to provide adjustment via a means of shifting the point at which leverage is applied. However this can be difficult within a confined space. As I previously suggested, it is an advantage if an existing OEM bar, from some popular vehicle can be used at least as a basis.

[icingdeath88]

Originally Posted by SilverSpear

Okkkk now... since everybody agrees that we need a front swaybar, I think the right debate here would be related to its thickness and shape.

For the thickness... I leave it to the experts.

For the shape, it is currently an "L" + "I". I guess fabbing the same style would be costly as hell, I guess we need someone to fab it (Nev?) the same as the rear, a continuous "U". Yeah I know, it will be a PITA to install, but on the other hand it is a "one-time PITA" installation if memory serves right... Plus it would be cheaper to fab.

Who cares to start hammerin' me

How would you get a U-type bar in there at all? Pain in the ass aside, is it even do-able?

[shotgunslade]

It is so difficult arguing with such a world famous racing driver. I guess my instructor at the Panoz School, Joe Foster (Google him), doesn't know what he is talking about. Thank God we all have Trevor to keep us on the right path.

[Trevor]

Originally Posted by oab_au

Dan when you go out on a real track, and race in a real race, like Trevor has, you will find out all about it.

Harvey.

Harvey as always your crappy posts are based on nothing but sarcasm. I have been their and done it. There is no shame in saying so when posting relative information. You by contrast claim engineering status without the required credentials.

[Freeman]

I would just take the sarcasm with a grain of salt.. We know that you are very knowledgeable when it comes to engineering and especially when it comes to unique cars like the SVX, as is Harvey and many others here but not everyone is happy or going to agree.. That's the internet..

Constant battles.. Fun isn't it?

[Trevor]

Originally Posted by shotgunslade

It is so difficult arguing with such a world famous racing driver. I guess my instructor at the Panoz School, Joe Foster (Google him), doesn't know what he is talking about. Thank God we all have Trevor to keep us on the right path.

Again sarcasm rather than fact. My guess is that you have not properly interpreted what you have been told, and your instructor thank god, has not been game to sit along side you when you drive close to the limit. I commiserate with him.

[SilverSpear]

Originally Posted by icingdeath88

How would you get a U-type bar in there at all? Pain in the ass aside, is it even do-able?

Well you have to dismantle the hell out of the front suspension to do that. But if I am not mistaken you do it only once in a lifetime.

AND GUYS CAN WE PLEASE KEEP IT CIVILIZED IN THIS THREAD?

[bwb3]

Gosh, I never knew I was a playboy with a big check book.
Gene

[shotgunslade]

I know I should keep it civilized, but some of the opinions expressed here are wrong and misleading. The hairy chested, devil take the hindmost attitude toward driving expressed here is obsolete, expensive and ultimately dangerous. I certainly wouldn't want to share the track with any harboring those ideas.

Racing drivers don't die behind the wheel very much anymore; certainly not like they used to. Many of the heroes of my youth, Wolfgang Von Trips, Jimmy Clark, Peter Revson, Bruce McLaren, Mark Donohue, and later, Ayrton Senna died in track accidents, but attitudes have changed, and things are much safer. You don't have to make off-track excursions to learn how to drive your car and to learn where the limits are.

Trevor is right that you feel what the car is doing and adjust to it. You explore the limits gingerly, feeling what's happening, then when you detect the limit, back off or correct. Having said all that, driving strategies are appropriate. The range of responses to any given situation is vast. Knowledge of your car, how it responds, and likely successful approaches to different types of corners, and different conditions narrow that range so that you can explore what works best.

As for always driving full throttle or full braking, that is hogwash. I have ridden with some very good drivers, and they are very smooth. They do utilize throttle lifts to loosen the rear end, and a touch of throttle to settle the car during transitions. They rarely coast, but they are often modulating, either throttle or brake. While braking before a turn may be full on braking, really good drivers, on the appropriate turns, will leave a little extra speed to shed during turn-in, so they can get some extra front end grip to tighten the turn-in. That braking is not full on, it is merely to get some additional front end weighting.

So, I really don't know what this argument is about. We have recognized that while the new rear sway bar may help street driving to feel more controlled, it could be detrimental driving at the limit, depending upon the balance between front and rear roll stiffness. Excessive rear roll stiffness in a front heavy, all wheel drive car results in increased understeer, sometimes unexpectedly acute. I related some strategies that I have found to be successful, trying to utilize braking or throttle lifting to increase front tire bite, and avoiding, to the extent possible, full throttle at high turning angles. These observations were greeted by a roar of senescent testosterone, spewing truths, half-truths, and errors indiscriminately. At least, that is my opinion. So, ban me. I'd rather be banned than have some member of this forum go out to the track and explore the limits of his car by cutting grass, only to discover that the SVX is not also good at cutting down trees.

[Trevor]

Originally Posted by shotgunslade

I know I should keep it civilized, but some of the opinions expressed here are wrong and misleading. The hairy chested, devil take the hindmost attitude toward driving expressed here is obsolete, expensive and ultimately dangerous. I certainly wouldn't want to share the track with any harboring those ideas. ----------


---------As for always driving full throttle or full braking, that is hogwash. I have ridden with some very good drivers, and they are very smooth. They do utilize throttle lifts to loosen the rear end, and a touch of throttle to settle the car during transitions. They rarely coast, but they are often modulating, either throttle or brake. While braking before a turn may be full on braking, really good drivers, on the appropriate turns, will leave a little extra speed to shed during turn-in, so they can get some extra front end grip to tighten the turn-in. That braking is not full on, it is merely to get some additional front end weighting.--------

------- So, I really don't know what this argument is about. .

Nothing I have posted is "wrong and misleading."

There has been a lack of understanding, because my description covering relatively tight cornering, as is most affected by a front roll bar, has been taken to apply to sweeping bends, where that described in the above paragraph applies. Reference to my posts will make this clear.

As for the hairy chested rough untidy driver, they do not go very fast.

A factor of risk has always been part of many sports. Without it such sports lose their appeal. I am no longer interested in motor racing, but have great appreciation of rally drivers and their navigators.

It has been stated that I do not know what I am about. I anticipate being accused of showing off, but bugger it, I am going to defend myself. ---

The photo at the head of this post, appeared in the largest of N.Z. newspapers, heading an article covering a national series of motor races. The caption was, "A Wet Day at Pukekohe" and was/is considered quite spectacular, to the point of being again published in the current issue of the magazine, Classic Driver, captioned "That's Car Control."

The photographer had no problem in catching the action, as I had been setting up the same drift lap after lap. The car has just topped a notorious rising sweeper and is progressing at around 90 MPH, after having bounced over a much feared undulation at the top of the rise. The surface is very slippery because it is raining, and the car is fitted with standard cross ply road tyres. Knowledge of the circuit is required in order to fully appreciate the circumstances involved.

Using the technique described here, I have just overtaken an MG midget on the inside. Believe it or not, the MG, due to money spent, had the legs on my SP250 Daimler on the main straight, and it was necessary for me to get the better of him on the more demanding parts of the circuit. Setting up the same attitude when the circuit was dry, did not require opposite lock.

Having drawn attention to the photo, I point out that careful scrutiny will disclose immediately inside the front right wheel, the bottom of a link connecting a specially fitted roll bar. The bar was taken from a wrecked GM Holden.

At this point the sarcastic can let fly, I do not give a damn.