understeer how do I minimize it?

[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.

[DSP74]

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

[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... :)

[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.

[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.

[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.

[Hallen]

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.

Yep, but the front is also much heavier than the rear. The front spring rate as a function of how much weight the spring is carrying is still probably somewhat less than the rear rate.

[DSP74]

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.

Body roll doesn't transfer weight.


All cars regardless of independant suspension or not lose camber on body roll.....A car that didn't would have roll center movements all over the place and braking would suffer. Probably alot.

[DSP74]

Yep, but the front is also much heavier than the rear. The front spring rate as a function of how much weight the spring is carrying is still probably somewhat less than the rear rate.

Factor in that the front is a little heavier not alot, and the swaybar rate then the front is still stiffer. If the car weren't stiffer in front it would be literally undriveable.

[hendrik]

Wow!! Thanks to all for the comments. I will be a little more specific on what I have in my setup.. I mentioned that I have a H&R Cup kit, so that suspension. The car is an 89 325is. It has stock sways and I have changed the tires and wheels. I am currently running 15" team dynamics race 1.2s. They are wrapped in toyo R888 tires ( 195/50r15). I primarily run the car on road coarses, I haven't run an autox yet and don't plan on doing that to much. I would like to change the suspension out to a coilover setup, and from the chatter here maybe just add adjustable end links to my stock sways. Along with playing with the tire pressure. Thanks again for all of the input. Oh ya.. brake more before turning, accelerate out of the turn...

[Emre]

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

You can't simply compare the front and rear spring rates directly. The rear rates are effectively much lower due to their location on the trailing arm. Once you factor in the difference, you end up with a front that's effectively much stiffer than the rear.

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

Exactly.

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.

Whether the stiffness comes from springs are sways is a different matter to be debated in a different thread. The point is that if you want to eliminate understeer, you need all the roll stiffness you can get at the front of the car. Whether that roll stiffness comes from springs or sways is another issue.

[Fidhle007]

Wow!! Thanks to all for the comments. I will be a little more specific on what I have in my setup.. I mentioned that I have a H&R Cup kit, so that suspension. The car is an 89 325is. It has stock sways and I have changed the tires and wheels. I am currently running 15" team dynamics race 1.2s. They are wrapped in toyo R888 tires ( 195/50r15). I primarily run the car on road coarses, I haven't run an autox yet and don't plan on doing that to much. I would like to change the suspension out to a coilover setup, and from the chatter here maybe just add adjustable end links to my stock sways. Along with playing with the tire pressure. Thanks again for all of the input. Oh ya.. brake more before turning, accelerate out of the turn...

The cup kit is pretty low and soft, I'd go with an H&R Race (or IE III)/Blistein Sport combo and see where your at.

[z31maniac]

The cup kit is pretty low and soft, I'd go with an H&R Race (or IE III)/Blistein Sport combo and see where your at.

Terrible advice! lol

If you're going to buy another spring/shock setup, just man up and go with a ser of coilovers.

[DSP74]

Terrible advice! lol

If you're going to buy another spring/shock setup, just man up and go with a ser of coilovers.

Agree. BTW the Cosmo kit comes with rates I've seen similar to HnR race.... And I read today on another forum that the springs are 2.5" ID springs not some stupid 3.5" or whatever it was spring people were saying they came with......Probably OD 3.5"

Then you can change to any rate you want in the future too.....All for CHEAP.

[Fidhle007]

You realize that about 17% of r3v member will actually take the time to set up their coilovered cars, right? Coilovers that have not been set up properly (Yes, with scales and all that other shit) are completely pointless and a waste of money. For the everyday driver, and most other folks too, it's best to go with a setup where most of the hard work has been done for you. Spec E30 wouldn't use H&R Race springs if they sucked...