Suspension Talks: Understeer & Oversteer

[Freeman]

Originally Posted by sowise

I think there would be improvement with a rear sway bar which is why I bought one. It would be greatly improved with a change to the front but I would think a stable @ss end would be beneficial. I think our stock is too small as it is.

See, those were my thoughts. I'd like to drive or ride in one to feel the difference for myself..

[SilverSpear]

The only way to see the benefit of a bar is through AutoX. Reading more and more about suspension setups, I learned and as Trev said, we need to focus on a better front anti-roll bar.

On the other hand, Nevin's bar is not to be missed. And since it is a 22mm, and since our noses are heavy, I guess a 23mm bar in the front would be the goal.

Again, I would love to have a 0% understeer, 25% oversteer SVX

[Trevor]

Originally Posted by SilverSpear

The only way to see the benefit of a bar is through AutoX. Reading more and more about suspension setups, I learned and as Trev said, we need to focus on a better front anti-roll bar.

On the other hand, Nevin's bar is not to be missed. And since it is a 22mm, and since our noses are heavy, I guess a 23mm bar in the front would be the goal.

Again, I would love to have a 0% understeer, 25% oversteer SVX

Kia ora Danny,

The diameter of the bar very much depends on the length of the bar, in particular the side arms and the position of attachment in relation to suspension movement, i.e. all of that which effects the leverage imposed on the twisting of the bar. If the bar is shaped to clear obstructions this will also have a marked effect.

On a cut and trial basis, it is best to start with the maximum anticipated, as it is possible to adjust later with a grinder. A blacksmith is the man for the job. However time spent at wreckers yards can often turn up something and a lot can be learned by observing different set ups. Even if modification is involved, a lot of work cam be saved. I have always been successful taking this route.

I presume you guys run front tyres say 5 PSI or more above the rear.

[SilverSpear]

Originally Posted by Trevor

Kia ora Danny,

The diameter of the bar very much depends on the length of the bar, in particular the side arms and the position of attachment in relation to suspension movement, i.e. all of that which effects the leverage imposed on the twisting of the bar. If the bar is shaped to clear obstructions this will also have a marked effect.

On a cut and trial basis, it is best to start with the maximum anticipated, as it is possible to adjust later with a grinder. A blacksmith is the man for the job. However time spent at wreckers yards can often turn up something and a lot can be learned by observing different set ups. Even if modification is involved, a lot of work cam be saved. I have always been successful taking this route.

I presume you guys run front tyres say 5 PSI or more above the rear.

Good thing there are people like you around here who push things into better knowledge Trev

I guess you are right, yes it is all related to the shape of the bar and the hands, but if we are to fab the exact same shape of OEM, how would we evaluate what thickness we need?

And definitely a blacksmith is required for the SVX bar, this is what I had in mind initially. And thank God we have lots of them around here

[thickasxthieves]

Originally Posted by Trevor

Changing the rear roll resistance is a downgrade. It is the front which must be stiffened.

In all of this, the SVX is no different from any car which is front heavy.

but in a front drive svx wouldnt a thicker/stiffer rear barwork wonders to fight understeer?

[shotgunslade]

Driver's experiences with the new rear sway bar very much depend upon how near the limit they are driving. If they are far from the limit of adhesion, they will experience the bar as beneficial. limiting lean in turns. If they are near the limits of adhesion at higher tire slip angles front or rear, they may experience the behaviors Trevor was describing.

With the nose heavy SVX, good handling behavior really depends upon having more roll stiffness in the front compared with the rear. I believe that adding the aluminum top mounts in front really enhanced my front roll stiffness, because my old rubber top mounts were really quite loose (front hood dimple from pothole testifies to that). I thought I could therefore get away with some additional rear roll stiffness. My spring rates are 345 lbs/in front and 285 lbs/in rear, not as stiff as some, but much stiffer than stock.

Having said all this, driving strategy is really important with the SVX. Trail braking is a good strategy to increase front bite and turn in. Avoiding full power with significant wheel turning angles is also a good strategy. Best approach to cornering is to do most of it under light braking and put the power down while letting the car track out.

Most of my off track excursions have occurred during full power with strong lateral acceleration (cornering). These incidents are testimony to the validity of the friction circle. With high lateral acceleration loads and full power, the tires can't handle all of these loads through friction with the surface, so they slip. Full acceleration with high lateral acceleration means you are certainly drifting. In my car, in some circumstances, with front and rear drifting, the radius of my front tire drift tends to be slightly shorter than that of my rears. So, I experience oversteer under full power at high lateral acceleration. It isn't like power-on oversteer in a rear wheel drive car, quick and easily correctable with countersteer and accelerator modulation, rather, the rear wheels slowly drift out. Unfortunately, it's much harder to correct. Counter steer works , but slowly, and I'm liable to run out of track before I can get it straightened out. The best way to correct this is to avoid this driving technique completely.


I look forward to seeing if this behavior goes away with the new suspension mods.

[Trevor]

Originally Posted by thickasxthieves

but in a front drive svx wouldnt a thicker/stiffer rear barwork wonders to fight understeer?

No, with front only drive front stiffness is even more important. Theorists may tell you otherwise. I am advising on the basis of driving experience.

[oab_au]

The problem with trying to arrive at an universal fix, is we have three different drive systems. When you lift the foot in a corner, the 4EAT looses rear drive, the manual retains 50% rear drive and the VTD retains 64% rear drive. So it is a bit hard to compare the handling with three different rear drives.

Harvey.

[Trevor]

Originally Posted by shotgunslade

Driver's experiences with the new rear sway bar very much depend upon how near the limit they are driving. If they are far from the limit of adhesion, they will experience the bar as beneficial. limiting lean in turns. If they are near the limits of adhesion at higher tire slip angles front or rear, they may experience the behaviors Trevor was describing.

With the nose heavy SVX, good handling behavior really depends upon having more roll stiffness in the front compared with the rear. I believe that adding the aluminum top mounts in front really enhanced my front roll stiffness, because my old rubber top mounts were really quite loose (front hood dimple from pothole testifies to that). I thought I could therefore get away with some additional rear roll stiffness. My spring rates are 345 lbs/in front and 285 lbs/in rear, not as stiff as some, but much stiffer than stock.

Having said all this, driving strategy is really important with the SVX. Trail braking is a good strategy to increase front bite and turn in. Avoiding full power with significant wheel turning angles is also a good strategy. Best approach to cornering is to do most of it under light braking and put the power down while letting the car track out.

Most of my off track excursions have occurred during full power with strong lateral acceleration (cornering). These incidents are testimony to the validity of the friction circle. With high lateral acceleration loads and full power, the tires can't handle all of these loads through friction with the surface, so they slip. Full acceleration with high lateral acceleration means you are certainly drifting. In my car, in some circumstances, with front and rear drifting, the radius of my front tire drift tends to be slightly shorter than that of my rears. So, I experience oversteer under full power at high lateral acceleration. It isn't like power-on oversteer in a rear wheel drive car, quick and easily correctable with countersteer and accelerator modulation, rather, the rear wheels slowly drift out. Unfortunately, it's much harder to correct. Counter steer works , but slowly, and I'm liable to run out of track before I can get it straightened out. The best way to correct this is to avoid this driving technique completely.


I look forward to seeing if this behavior goes away with the new suspension mods.

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

In order to overtake, before entry the car is placed inside of the opposition, who is the out braked to the point where the driver is ahead of front the other car, at which point he has the right of way and title to the corner. The car is then crossed up at scrambled round, tidiness being of no concern, with the opposition astern.

On entering a fast corner a drift is set up under a trailing throttle, with power then applied so that sideways inertia through the corner is offset by forward traction. Any car being driven around the corner and not drifting, can be overtaken on the outside.

Currently, when sticky racing tyres are in use, it is apparent that the quality of tyres dictate the cornering speed, and the result is an expensive slot car competition.

[sowise]

Will our cars drift much? I know it is apples and oranges but I remember seeing a video clip I think it was car and driver road test. The guy was driving a 350Z and an Audi TT. He was drifting through the corners in the 350Z smiling and all happy and when he did the Audi it seemed way more controlled but he didn't care for that. He said he had a hard time breaking it free due to the AWD (I am sure he had traction control off) so I would figure it would be fairly similar with our cars with the exception of dirt and gravel of course.

[Trevor]

Originally Posted by sowise

Will our cars drift much? I know it is apples and oranges but I remember seeing a video clip I think it was car and driver road test. The guy was driving a 350Z and an Audi TT. He was drifting through the corners in the 350Z smiling and all happy and when he did the Audi it seemed way more controlled but he didn't care for that. He said he had a hard time breaking it free due to the AWD (I am sure he had traction control off) so I would figure it would be fairly similar with our cars with the exception of dirt and gravel of course.

The techniques I have mentioned apply equally with a front wheel drive car. I see no reason why the SVX should present any problem.

Please do not confuse what I have described with boy racer stuff involving simple rear wheel power burn out nonsense, or the "sport" of drifting. I am referring to a drift which takes place at in excess of say 80 MPH minimum in forward speed.

[Nevin]

If I may: an excerpt from "Chassis Engineering" by Herb Adams.

Take from page 16 under the heading "Roll Force Distribution."

By varying the size and efectiveness of the front stabilizer bar vs. the size and effetivensss of the rear stabilizer bar, it is possible to change the understeer/oversteer characteristics of a car. Since the forces resisting the roll of the car are fed into the outside tires, it is possible to decide whether the front outside tire or the rear outside tire will absorb most of these forces. If a car has understeer, too much load is on the front outside tire. By increasing the effectiveness of the rear stabilizer bar, some of this load can be transferred during cornering to the outisde rear tire. Doing this will eliminate the understeer, because the front and rear outside tires will be more equally loaded.

As soon as I read that, a lightbulb went off in my head. "I wonder if I can get rid of some of my svx's understeer," is the paraphrazed thought that went through my head. This was one of the main reasons that I decided to try a rear bar first.

Basically, what the above is saying is that when the load is shared more equally between the tires, there will be more available grip for cornering. By adding stiffness to the rear, it keeps the car from rolling side to side which in turn takes some of the load off of the outside front tire. The rear outside tire is now holding more weight of the car and shares the cornering force more equally which means the car does more of what you want it to.

Now, I didn't just blindly go "lets take advantage of people and make a part with no research or testing." Do I have an engineering degree? No. Did I test the product before I sold it, and do as much research as I could? Of course I did! I used it for months on my own car and after I had good results I decided to ask my friend Tom (yt) if he would be willing to try one out on his car as well. He gladly accepted, and after excellent feedback I decided that this may be a part that others would be interested in as well. I thought it would be a bit selfish of me to have an inexpensive part that dramatically improves the handling of the car and not let anyone else know about it.

I never set out to make a profit or take advantage of anyone or trying to convince them that they "needed" a certain part. My only goal was to share the enjoyment that I had in driving my car, with other enthusiasts like myself.

Is the rear bar the "end-all" of suspension parts? Heavens no. But it is a part of the equation that should certainly not be overlooked. It is my belief through testing and development that it DOES provide a huge "bang for the buck" though. Everyone who has installed one has commented positively about it, and for that I am very glad. I could honestly care less if I never sold another one (because that would mean less work for me to do! ) but I want to provide a quality part to people who want one. No one else had yet stepped up, so I decided to make a go of it.

If you don't want a bar, I'm certainly not going to force anyone to buy one, but I know that if I had a strip every mod off my car but one, the bar would be the thing to stay.

Do I have plans for a front bar? I have not crossed it off my list yet, but will not get to it unless time permits. There are gains there to be had though, but I want to take one thing at a time. I'm a busy enough man as it is.

For all of the people on this board who have given me advice and help, I am thankful. And the knowledge they have shared with me has been irreplaceable. The SVX bunch is TRULY a unique car community, and I am simply doing what I can to help out my friends and fellow enthusiasts.

[Trevor]

An excerpt from "Chassis Engineering" by Herb Adams.

Take from page 16 under the heading "Roll Force Distribution."

"By varying the size and effectiveness of the front stabilizer bar vs. the size and effetivensss of the rear stabilizer bar, it is possible to change the understeer/oversteer characteristics of a car. Since the forces resisting the roll of the car are fed into the outside tires, it is possible to decide whether the front outside tire or the rear outside tire will absorb most of these forces. If a car has understeer, too much load is on the front outside tire. By increasing the effectiveness of the rear stabilizer bar, some of this load can be transferred during cornering to the outisde rear tire. Doing this will eliminate the understeer, because the front and rear outside tires will be more equally loaded."

When advising here, in anticipation of the above argument, for very good reason, I have referred to the application of practical driver experience, as opposed to that involving only engineering theory.

The above takes no account whatsoever, in respect of the huge amount of weight transfer which occurs, when in particular a front heavy car, is braked for a corner. The theory relies completely on there being an even and constant transfer of weight, under a mild cornering situation, where in point of fact understeer does not usually present a real problem, e.g. that experienced by the Sunday driver.

Would someeone please explain exactly how, “By increasing the effectiveness of the rear stabilizer bar, some of this load can be transferred during cornering to the outisde rear tire.” i.e. an effective amount, if and when most of the weight has transferred forwards, and the car rolls on an axis from corner to corner, and not the centre line?

I have read this type of engineer’s theory in several publications and I have discussed it with many drivers. The engineers concerned should leave their drawing boards and experiment at speed behind a driving wheel. That is provided they have the balls and skill, to take a corner on the limit.

[Nevin]

Yes, I understand fully your position and that weight transfer from the front to the rear axle is definitely something that happens. Static weight distribution and "live" weight distribution are two different things.

However, saying that changing the stiffness of the rear would do nothing is not accurate either. How about when you're accelerating out of a corner? As you state, weight transfer happens and more weight would transfer to the rear which would make it all the more important. Do you always drive a constant speed when you corner? Are you always slowing down when you corner? I've found that as I accelerate with my new bar, it creates even more grip, and as you state when I'm braking it's not as noticeable, but even with weight transferred off of it, it's still decreasing the cars tendency to roll.

Also, you say the following:

No, with front only drive front stiffness is even more important. Theorists may tell you otherwise. I am advising on the basis of driving experience.

So you have driven an SVX with a larger rear sway bar then? You can tell me from your own experience that ON AN SVX it does nothing? I myself also thought it would do nothing, but I can guarantee you that if you drove one, there would be no "placebo effect," you would surely feel the difference yourself. What about all the others that noticed similar effects to what I experienced?

And am I in no way tyring to say that the front is not important, because I do think that it is. I was just putting into practice something that had been theorized, and it worked. It just so happens to also be cheaper to make a rear bar than a front one not to mention much easier to change. Things that I thought that people other than myself might also appreciate.

Like I said, I'm not trying to force this on ANYONE. I'm just saying that regardless of how you theorize, it produces results. Theories are purely hypothetical... until you put them into practice. I have done this, and it has produced results.

[Freeman]

And that is exactly what I wanted to hear..