Suspension Talks: Understeer & Oversteer

[SilverSpear]

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.

To start with, a small explanation of Understeer & Oversteer:
- Understeer: It is the condition in which the vehicle does not follow the trajectory the driver is trying to impose while taking the corner because the effective slip angle at the front is larger than that at the rear, instead following a less curved trajectory.

- Oversteer: It is the condition in which the vehicle is said to oversteer when the rear wheels do not track behind the front wheels but instead slide out toward the outside of the turn. Oversteer can throw the car into a spin.

As a base rule, to have the less evil of the two (oversteer), the car needs to be softened from the front or stiffened from the back. But to what extent is this applicable on the "SVX"?

So far, we have/had the following suspension components available:

- Koni/GC;
- Bontrager rear bar/endlinks/bushings;
- PowerGrid front endlinks;
- Strong-Flex complete car suspension bushings;
- 15$ & 20$ mods from svxfiles.

Now the debatable question is: How to successfully manage all these mods in the SVX in order to have a "harmonic", stiff and acceptable suspension?

The specific requirements to know are:

- Koni/GC: Konis are fixed, GC are variable. What is the correct stiffness for GC?
- Bontrager rear bar/endlinks/bushings: Fixed
- PowerGrid front endlinks: Fixed
- Strong-Flex complete car suspension bushings: Variable in Normal and Strong.
- 15$ & 20$ mods from svxfiles: Fixed.

Choosing the ultimate of each will lead to instability and spins out of control. I know that through my own setup. With just stiffened struts (more than the Konis and the rear > front) and teflon bushings in the front, I can feel that my car will definitely spins out if I try a sudden right/left move at a moderate speed.

The SVX is not the WRX nor the EVO. It weighs a lot in the front, so we cannot really compare it to either one.
Furthermore taking into consideration the Automatics, 5 speeders, 6 speeders and the 6 speeders with DCCD control... We need to know what is the best for each setup.

Huge subject, YES. We need to get this sorted out, best input I see comes from people who researched and experienced them in the past. Let us make SVXi better

[LetItSnow]

I'm only aware of two people besides myself who have gone through the math to create a good combination of stiffness and balance (oversteer/understeer). You can throw conventional combinations of parts at a car and hope they come out OK, but that doesn't make sense!

My spring rates were selected for an autocross capable, yet comfortable ride, giving a tendency toward neutral balance with mild understeer for a shade of safety. The numbers worked out nicely!

To buy a set of GC springs based on a combo shown around is crazy; they're absolutely customizable.

[lhopp77]

Originally Posted by SilverSpear

So far, we have/had the following suspension components available:

- Koni/GC;
- Bontrager rear bar/endlinks/bushings;
- PowerGrid front endlinks;
- Strong-Flex complete car suspension bushings;
- 15$ & 20$ mods from svxfiles.

And where do the K-Mac adjustable front caster/camber plates fit into this equation for consideration? Or do they?

Lee

[Crazy_pilot]

Originally Posted by LetItSnow

My spring rates were selected for an autocross capable, yet comfortable ride, giving a tendency toward neutral balance with mild understeer for a shade of safety. The numbers worked out nicely!

What rates are you running Rob?

[LetItSnow]

They've been in for a while now! I think they're 385/315, but I'll take a look.

[Freeman]

Here is an example of the PERFECT suspension..

[SilverSpear]

A perfect suspension for me is a setup that can cause a maximum of 5% understeer and 25% oversteer.

Looks mean nothing really...

And yes forgot the K-Macs....

[sabin]

i'm running 380/340 on my gc

[sicksubie]

415lb /385lb. for me... It still pushes a bit through corners (I do not have the rear sway bar installed yet) but breathe on the throttle and I can get the back end to rotate quite nicely ...

I imagine with the rear bar it will be neutral/ slight oversteer through the corners with no throttle being applied...

[SilverSpear]

Now we need to know the effect of the bushes along with your setup Bobby...

[sicksubie]

unfortunately my time in the garage has been minimal and the time I have had has been used for other things

[Trevor]

Originally Posted by sicksubie

415lb /385lb. for me... It still pushes a bit through corners (I do not have the rear sway bar installed yet) but breathe on the throttle and I can get the back end to rotate quite nicely ...

I imagine with the rear bar it will be neutral/ slight oversteer through the corners with no throttle being applied...

When braking and entering a corner in serious anger, as a result of severe weight transfer, in particular a front heavy car rolls across an axis from corner to corner, rather than the centre line. In this situation the front requires roll stiffness rather than the rear. Load is applied to the outside front wheel and the inside rear lifts.

The theory of transferring load at the rear to the outside rear wheel, does not work properly in practice, due to the majority of weight having transferred towards the front. Those pushing this theory are basing argument on straight line bump steer and the inbuilt understeer provided by manufactures, so that idiots can sleep at the wheel.

Some negative camber at the front is also very effective, and provided not overdone can in fact actually improve tyre wear.

Getting rid of soft mountings and bushes sharpens up the handling like nothing else on a cost for result basis. This is particularly so in respect of the steering rack and associated components. The very keen, should fit a rack from a four wheel steer JDM, which has a higher ratio.

A resourceful driver will always prefer a touch of over steer and most certainly no under steering at the front end. The very serious go so far as fit a lightweight steering wheel, free of the inertia which normally kills feel.

As of late I am aware that it will be considered that --- “you come off as the most self righteous pompous a-hole on the planet.” as a result of me presenting specific advice, but I do not give a damn. There may be some who appreciate sincere information presented honestly and based on genuine practical experience.

[icingdeath88]

Originally Posted by Trevor

When braking and entering a corner in serious anger, as a result of severe weight transfer, in particular a front heavy car rolls across an axis from corner to corner, rather than the centre line. In this situation the front requires roll stiffness rather than the rear. Load is applied to the outside front wheel and the inside rear lifts.

The theory of transferring load at the rear to the outside rear wheel, does not work properly in practice, due to the majority of weight having transferred towards the front. Those pushing this theory are basing argument on straight line bump steer and the inbuilt understeer provided by manufactures, so that idiots can sleep at the wheel.

Some negative camber at the front is also very effective, and provided not overdone can in fact actually improve tyre wear.

Getting rid of soft mountings and bushes sharpens up the handling like nothing else on a cost for result basis. This is particularly so in respect of the steering rack and associated components. The very keen, should fit a rack from a four wheel steer JDM, which has a higher ratio.

A resourceful driver will always prefer a touch of over steer and most certainly no under steering at the front end. The very serious go so far as fit a lightweight steering wheel, free of the inertia which normally kills feel.

As of late I am aware that it will be considered that --- “you come off as the most self righteous pompous a-hole on the planet.” as a result of me presenting specific advice, but I do not give a damn. There may be some who appreciate sincere information presented honestly and based on genuine practical experience.

The corner to corner axis is hard to visualize, but thinking about it that is how it feels. On hard turns the front corner dips down.

Speaking of steering racks, how would one even get a 4WS steering rack? Any way to modify the regular steering rack to give it a better ratio, or would that fall into the "prohibitively expensive" category? Also, what about an sti steering rack? If sperry can retrofit sti knuckles on the svx, why not the steering rack? Any other ideas?

[SilverSpear]

Originally Posted by Trevor

When braking and entering a corner in serious anger, as a result of severe weight transfer, in particular a front heavy car rolls across an axis from corner to corner, rather than the centre line. In this situation the front requires roll stiffness rather than the rear. Load is applied to the outside front wheel and the inside rear lifts.

Hello Trev,

Wouldn't you want some softness in the front suspension to be able to "absorb" the tendency to slip? I mean if the front is also stiff, the car will slide, no?

Originally Posted by Trevor

The theory of transferring load at the rear to the outside rear wheel, does not work properly in practice, due to the majority of weight having transferred towards the front. Those pushing this theory are basing argument on straight line bump steer and the inbuilt understeer provided by manufactures, so that idiots can sleep at the wheel.

Some negative camber at the front is also very effective, and provided not overdone can in fact actually improve tyre wear.

That is logical...

Originally Posted by Trevor

A resourceful driver will always prefer a touch of over steer and most certainly no under steering at the front end.

Yup... this is the goal.

Originally Posted by Trevor

As of late I am aware that it will be considered that --- “you come off as the most self righteous pompous a-hole on the planet.” as a result of me presenting specific advice, but I do not give a damn. There may be some who appreciate sincere information presented honestly and based on genuine practical experience.

Well everybody starts with theories Trev, then later comes practice. What you said above are the basics for all cars, but that doesn't always apply on the car in question.

[Trevor]

Originally Posted by SilverSpear

Hello Trev,

Wouldn't you want some softness in the front suspension to be able to "absorb" the tendency to slip? I mean if the front is also stiff, the car will slide, no?

Kia ora,

I do not understand your reasoning. In no way did I suggest that the suspension should be stiffened. An anti roll device does not alter the verticle compliance of the suspension.

Well everybody starts with theories Trev, then later comes practice. What you said above are the basics for all cars, but that doesn't always apply on the car in question.

What I have suggested tends to go against standard theories in respect of the basics for all cars, and is based on what occurs in practice in respect of the car in question, i.e. one which is decidedly front heavy. Theory as practised by a driver.