understeer how do I minimize it?

[Hallen]

Converntional wisdom on a BMW is to run stiffer springs in the rear than the front (usually 150-200 pounds different).

I run a stock front sway and no rear bar on my E30 track car. Big sway bars are the American way to tune the suspension, springs and shocks with fine tuning from the sways is the European way to tune the suspension- not that one way is better than the other.

Yep, that is true from what I have seen. But, that is because the motion ratio of the rear suspension compared to the front suspension. Because the rear suspension has a longer "lever" to push on the spring from the wheel side, you need more spring there to get your wheel rate where you need it.

Off the top of my head, I can't remember the motion ratio numbers, but the front is close to 1, meaning the wheel moves approximately the same amount as the spring compresses, and the rear is something like 0.64, meaning the wheel moves farther than the spring compresses. (I think I have that straight, correct me if I'm wrong). This means you need stiffer springs in the rear to get the same effect as the springs in the front. Forgive me if this is already obvious to you...

I think the other comments here are interesting, if the car is well sorted already, thicker bars in the front will increase understeer. But if the body roll is causing the car to lose camber, then stiffer front bar can help decrease understeer. However, I am not exactly understanding how body roll is causing the loss of camber when we have independent suspensions.

I can see situations where the body roll transfers enough weight to the front outside wheel that it overcomes the mechanical grip that the tire produces therefore causing sliding and understeer. In that case, either stiffer springs or a stiffer roll bar should help decrease understeer by balancing the weight load a bit better.

My comment earlier about bars acting like springs was in reference to body roll only. Obviously, increasing the spring rate is going to have other effects, some not desirable, as well as controlling roll.

[DSP74]

Stiffer springs in the rear are only due to the motion ratio in the rear.

When comparing wheel rates INCLUDING THE SWAYBAR (which is difficult to accurately calculate) the front is much stiffer....even if you stick with a stock front bar and no rear.

[gobuffs]

Just look at what everyone is running the next time you go to a BMW CCA Club Race. Every single car in the field has an incredibly stiff front end (either springs or sways) and a relatively soft rear end. Many of the really fast guys in high-powered cars have no rear sways at all.

Converntional wisdom on a BMW is to run stiffer springs in the rear than the front (usually 150-200 pounds different).

I run a stock front sway and no rear bar on my E30 track car. Big sway bars are the American way to tune the suspension, springs and shocks with fine tuning from the sways is the European way to tune the suspension- not that one way is better than the other.

[Fidhle007]

That's because no one understands the science of weight transfer. I understand the concept but at the limit it's hard to be thinking about it effectively. This is why I'm slow still... :)

[DSP74]

The other thing that happens so much regardless of suspension setup is inducing understeer...

[Emre]

I don't think you got the point of my post. He may be correct in general but there is more than one way to get that soft rear and stiff front.

Sorry if I misunderstood your post. It sounded like you were politely trying to say that DSP74 was off the mark.

[moatilliatta]

maybe ill add my front sway bar again and see if mine will increase grip up front..

[joshh]

DSP74's experience is fully in line with what BMW racers have known since the 1960's. There is no controversy here. This is not a matter of subjective "personal experience." He is objectively correct.

Just look at what everyone is running the next time you go to a BMW CCA Club Race. Every single car in the field has an incredibly stiff front end (either springs or sways) and a relatively soft rear end. Many of the really fast guys in high-powered cars have no rear sways at all. Many guys in lower powered cars still favor relatively stiff rear ends. But one thing is common: the front ends are stiff as hell. Are these guys all idiots? Have they not read Carroll Smith? Do they want their cars to understeer?

The bottom line is that if you want good front-end grip on an E30 chassis, you should: (1) stiffen the front end through some combination of springs and swaybars; and (2) add more negative camber.

I don't think you got the point of my post. He may be correct in general but there is more than one way to get that soft rear and stiff front.

[DSP74]

. you aren't going to gain positive camber until you compress the suspension to the point in the geometry where the angle is more than 90 degrees - until then, you are still gaining camber

You aren't thinking about what the car does in a dynamic situation. Compressing the suspension will gain negative camber. However everytime the car roll you will gain POSITVE camber. No matter what. If we didn't, we wouldn't be running 3 or more degrees negative camber. We do that because we hope that after we lose the static camber we have adjusted in, we end up just about right during roll.

So you do gain camber in compression and lose alot more in roll

[Emre]

Keep in mind here DSP74 is giving his opinion on the matter from his experiance.

DSP74's experience is fully in line with what BMW racers have known since the 1960's. There is no controversy here. This is not a matter of subjective "personal experience." He is objectively correct.

Just look at what everyone is running the next time you go to a BMW CCA Club Race. Every single car in the field has an incredibly stiff front end (either springs or sways) and a relatively soft rear end. Many of the really fast guys in high-powered cars have no rear sways at all. Many guys in lower powered cars still favor relatively stiff rear ends. But one thing is common: the front ends are stiff as hell. Are these guys all idiots? Have they not read Carroll Smith? Do they want their cars to understeer?

The bottom line is that if you want good front-end grip on an E30 chassis, you should: (1) stiffen the front end through some combination of springs and swaybars; and (2) add more negative camber.

[Emre]

Typically understeer is corrected by reducing the front bar or increasing the rear bar.

That's the theory...but that assumes the suspension is already working optimally to begin with. Our cars have a pretty compromised suspension setup with insufficient camber gain in the front end during hard cornering. So, the conventional wisdom that increasing front rollbar thickness will worsen understeer does not apply in this case.

throwing a larger front sway bar on a car that already pushes isn't the answer.

If your car has a McPherson strut suspension and inadequate camber (i.e., is a BMW), then adding a larger front swaybar is absolutely the answer. Increasing front roll stiffness is critical.

To help with understeer, you can...soften the fronts

Not on an E30 you can't. Theory is fine. But real-life experience setting up and tracking cars is better. Just check your tire temps and you'll see what I'm talking about.

[atomic]

http://www.rogerkrausracing.com/TechSheets/overunder.shtml

[nando]

Camber control in a dynamic situation. Nothing to do with ride height (although I guess you could hurt the camber CURVE by being VERY, VERY low.....

If a car doesn't have enough negative camber a bigger bar will limit roll making the car gain less positive camber. Making the front end stick more.


Put the books away guys


edit: to clarify ALL cars lose camber during roll

it has everything to do with how low you are. you aren't going to gain positive camber until you compress the suspension to the point in the geometry where the angle is more than 90 degrees - until then, you are still gaining camber. if you are rolling so badly that you are compressing the suspension way past it's normal range, you probably have too soft of a spring rate and are probably bottoming out the struts anyway.

[joshh]

Keep in mind here DSP74 is giving his opinion on the matter from his experiance.
There are many ways to get the same effect. Some work better than others for each individual.
Just throwing that in there.:???:

[Fidhle007]

Let's start from the beginning, what do you want to do with the car?