Reducing understeer?

[VinnAY]

I have a PP rear sway bar if any one needs it, free to a good home, take off from my 15 GT/PP. I had upgraded to the Steeda rear drag bar...what an improvement!

Sponsored

 

[BmacIL]

One last thing I got to inform you on. When you stiffen your suspension with stiffer sway bars you will make the car react quicker. You may think you are a racer just because you have it set up as stiff as possible and it goes around curves as flat as a pancake but the trade of is snap oversteer. This w I'll get you into trouble very fast, much faster then understeer ever will. Be careful and dont over set up your car. Make the car work for you and learn the limits before you reset them.

Yep, absolutely. This is true of not just stiff bars, but stiff suspension in general. It's quite possible to reduce overall grip by going too stiff because of the load rate of the tires during weight transfer. Tires are not only normal load sensitive, but also load rate sensitive. One should only go as stiff as required to 1) increase responsiveness necessary for going faster and/or 2) control suspension geometry adequately by roll reduction. Anything beyond that will just make the car harder to drive.

 

[BmacIL]

Stiffening the rear sway bar reduces rear grip essentially. It can reduce the understeer in a way by increasing the oversteer tendency (making it more likely to unsettle the rear). With your PP springs though you don't have to worry as much about that unless you went to a very stiff rear bar I guess.

Stiffening the front sway bar seems counterintuitive but it actually works because of the dynamic camber of the MacPherson strut suspension. It sucks.

I love it when the counterintuitive (but sound physics) theory works in practice. My car has less understeer than it's ever had with the BMR front bar set on medium, OE PP1 rear bar. It is just a hair away from neutral at the limit of grip. Changing only that from the OEM front bar sharpened the handling significantly and reduced understeer significantly. Keeping the front flat really makes it work.

 

[Norm Peterson]

It's crossed my mind from discussions like this one that the more you lower a strut suspension, the greater the need for more negative camber if you don't care to go toward "stupid-stiff" with the suspension.


Norm

 

[Bluemustang]

I love it when the counterintuitive (but sound physics) theory works in practice. My car has less understeer than it's ever had with the BMR front bar set on medium, OE PP1 rear bar. It is just a hair away from neutral at the limit of grip. Changing only that from the OEM front bar sharpened the handling significantly and reduced understeer significantly. Keeping the front flat really makes it work.

Amen to that brother. Theory =》reality is the best part. It also gives you confirmation that what you're doing is good and is making a real difference.

When I stopped thinking of the handling balance using simply the conventional norms it started to make sense. Stiffening the front IS good because of what happens to the MacPherson during roll. The rear is less critical IMO because the IRS operates differently. Sometimes conventional wisdom does not apply, especially when you learn distinct differences exist. Now, of course with anything you CAN over stiffen it, but I think that threshold is much higher than what is typically seen on strut/spring combos for street applications.

 

[BmacIL]

Amen to that brother. Theory =》reality is the best part. It also gives you confirmation that what you're doing is good and is making a real difference.

When I stopped thinking of the handling balance using simply the conventional norms it started to make sense. Stiffening the front IS good because of what happens to the MacPherson during roll. The rear is less critical IMO because the IRS operates differently. Sometimes conventional wisdom does not apply, especially when you learn distinct differences exist. Now, of course with anything you CAN over stiffen it, but I think that threshold is much higher than what is typically seen on strut/spring combos for street applications.

Yeah with the car being a heavy 54% front.

 

[Norm Peterson]

Sometimes conventional wisdom does not apply, especially when you learn distinct differences exist. Now, of course with anything you CAN over stiffen it, but I think that threshold is much higher than what is typically seen on strut/spring combos for street applications.

The problem with "conventional wisdom" in this case is that it what it is based on is far from a complete look at what is going on.

You kind of have to ask yourself when the conventional answer seems so simple is "what is being overlooked here?".


Norm

 

[Bluemustang]

The problem with "conventional wisdom" in this case is that it what it is based on is far from a complete look at what is going on.

You kind of have to ask yourself when the conventional answer seems so simple is "what is being overlooked here?".


Norm

Right, this a very good point, Norm. What I am trying to think about more, is how do the suspensions work? Only when understanding how they function (and where the weaknesses exist) can we begin to see more of that complete look. After that I think it's about the car starting to tell you what it needs.

And like you said, its important to question yourself to see if make sense in the end. Fortunately i have some smarter individuals around me to help lol

Edit: I meant to say smarter individuals than me lol. Was not sure if it came across that way or not.

 

[BmacIL]

The problem with "conventional wisdom" in this case is that it what it is based on is far from a complete look at what is going on.

You kind of have to ask yourself when the conventional answer seems so simple is "what is being overlooked here?".


Norm

Norm,
What we're on about is that the conventional roll stiffness distribution relative to weight distribution is also typically assuming a SLA type suspension front and rear. McPherson strut really throws a curveball to that because of the dynamic camber it has (lacks). Of course you know all this, but it takes a bit to reckon with if you're used to more conventional study of an SLA type front and rear.

 

[Norm Peterson]

Norm,
What we're on about is that the conventional roll stiffness distribution relative to weight distribution is also typically assuming a SLA type suspension front and rear. McPherson strut really throws a curveball to that because of the dynamic camber it has (lacks). Of course you know all this, but it takes a bit to reckon with if you're used to more conventional study of an SLA type front and rear.

What I'm getting at is that tire grip effects due to lateral load transfer distribution shouldn't ever be looked at in total isolation from other effects (camber consequences being but one). The MacStrut is probably the poster-boy example for why, but no reasonable suspension design is totally exempt. Just not as severely affected/compromised.

I guess that means that "conventional wisdom" needs to get enough wiser to at least recognize that other effects are present . . . and unfortunately none of those "changes to make to reduce understeer or oversteer" tables seem to be getting the job done, at least not in their present form.


Norm

 

[BmacIL]

What I'm getting at is that tire grip effects due to lateral load transfer distribution shouldn't ever be looked at in total isolation from other effects (camber consequences being but one)

Of course. There's almost nothing that can be done that doesn't have a tradeoff.

Sponsored