tonyj89117

Hi guys,

I am confused what certain suspension changes do in regards to reducing understeer and oversteer. I spoke with a buddy who is a suspension tech and the things he told me were totally opposite to what I thought was conventional wisdome. However, maybe 911's are different since the engine is in the rear with a 70% rear weight bias.

Anyways, how do the following changes affect the S2000's handling chacteristics?

How to reduce understeer?

Stiffer or softer front springs/shocks?
Higher or lower front tire pressure?
Higher or lower front ride height bias?
Stiffer or softer front sway bar?


How to reduce oversteer?

Stiffer or softer rear springs/shocks?
Higher or lower rear tire pressure?
Higher or lower rear ride height bias?
Stiffer or softer rear sway bar?


Thanks in advance guys.
Tony

Fongu

You can find the basics with a internet search. Here is a typical summary.
http://www.wtrscca.org/tech.htm

Here is something that describes suspension in general.
http://www.chris-longhurst.com/carbibles/s...sion_bible.html

All cars behave the same way, doesn't matter if it is a 911 or Yugo. Understeer or oversteer is determined from whether the front tires or rear tires have more grip.

Springs and swaybars control the roll stiffness. The stiffer end has less total tire grip. So stiffer front springs or swaybar, more understeer. Stiffer rear springs/swaybar more oversteer. The stiffer side transfers more weight to the outside tire. Tires with more weight on them are less "efficient" at generating grip making the stiffer side have less total grip.

Tire pressures are a little more complicated. The optimum tire pressure makes the biggest and most stable tire contact patch for maximum grip. If you graph the grip vs. air pressure of a typical tire it looks like a triangular doorstop. Grip slowly increases with increased tire pressure up to a peak. This is mainly from stabalizing the tire so it doen't distort the tire patch when it is under load. This is different from tire to tire and for different applications (like drag racing vs. road racing). Once the peak grip is exceeded tire grip decreases very fast with increasing pressure. This due to having too much pressure "balloning" the tire which makes the tire contact patch smaller.

After your basic questions, other factors that effect understeer and oversteer is alignment settings and damper (shock) settings. But probably the most important ways to control oversteer and understeer is driver inputs, i.e. weight transfer from steering, braking, throttle and wheel spin control with the throttle.

tonyj89117

Hi guys,

My car is already lowered approximately 30mm all around, but I want to lower it more in front to give it more of a rake.

I want to further reduce the front ride height an additional 10mm lower and leave the rear?

How will that affect my handling balance? A friend said it will make the front grip a little more. Does that mean I will have more oversteer?

Thanks.

tonyj89117

Thanks for the feedback.

What do you think is a good place to start on air pressure for road courses for an AP2 with stock wheels and tires?

Thanks.

Race Miata

Remember the general rule of thumb is "stiffer side slide".

To reduce understeer, softer front springs, shocks and/or sway.

By the same token, to reduce oversteer, softer rear springs, shocks and/or sway.

Theroetically, the taller the rear the more oversteer. However, there're many more factors involved in different ride height so there's no definite answer to that.

On most cars with not enough -ve camber, the higher the tire pressure the more grip. Same cannot be said for an S2000 with pretty optimized suspension from the factory, let alone a lowered one. It's easy to understand that if both front and rear tire pressures are at optimum, changing front tire pressure either way will reduce front grip.

EDIT: Oops, Fongu pretty much go it.

Race Miata

Not as simple as that. First, have you optimized your alignment settings after the lowering? Like Fongu says, in most cases the most important factors easily missed are wheel alignment and driver inputs.

Assuming you got optimized alignment and driver inputs before and after, then lowering the front more generally helps front grip. But lowering that much may sits the car (or close to doing so) on bumpstops. When the fronts sits on bumpstops, it's like adding tons of front springs and you know the effect.

IIGQ4U

Is there something that your car is doing or not doing that makes you want to run stinkbug style?

Fongu

My real answer is I don't know. Don't have experience with that configuration. The typical driving school response is take your manufacturer recommended pressure (I think 32 psi) and add 5-10 psi. So say try 38-40 psi. That should be OK since a RE050 has a max tire pressure is 50 psi. This "driving school" answer is due to that typically most street tires have softer sidewalls, so require more air pressure to prevent the sidewalls "folding" over and screwing up the tire patch. Also note that this is cold tire pressure. Tires get hotter when run hard, heating up the air in the tire, increasing the pressure. So, depending how "good" you are, tire pressures can vary quite a bit on the track.

I'm going to assume that you're a novice driver, so don't be offended if you're not. Don't worry about all this suspension tuning stuff for now. The most important thing for a novice is to have a safe car and worry about learning car control. The driver is the most important thing as far as controlling oversteer and understeer, it doesn't matter what the suspension settings are.

After getting control of the driving basics and you can feel what the car is doing, you can try out changing tire pressures. That's free so no big deal playing with it. Next alignment settings. Next swaybars if necessary. Lastly, shock/spring/ride height combo. This is the most complicated tuning method and is so easy to screw up the stock car handling if you as a driver can't read if the car is working well.

tonyj89117

I had the car corner balanced and aligned after the original 30mm lowering. I have the Tein coilovers, but don't know how much suspension travel I have left.

Is it obvious to determine if I am close to hitting the bumpstops?

Thanks.

tonyj89117

Actually I just reduced the front ride height another 15mm and the rear 5mm this evening. It looks better, but it is not that noticeable that the front is lower than the rear. Overall, my car is almost 2" lower in the front and 1.5' lower in the rear compared to the stock height. Do you think this is too low for optimum performance?

I only did this additional ride height change for aesthetic reasons. Do you think this change negatively affected the handling from optimum?

Thanks guys.