Understanding Vehicle Dynamics pt. 2

[Unity112]

Basic Rules (again adapted from material from elsewhere - edited for content)
Here are some general basic rules if you want to improve your cars handling:

If you race in sanctioned competition, read your rule book before performing any modifications at all to your vehicle. It would be a pity to buy a fortune in trick parts only to have them declared illegal by an official. Beware of SCCA

[GTS LAID]

more more more

[CloNeGTS]

Just a few comments.....

No one currently makes an adjustable set of anti-roll bars for our cars

If you are talking about matched sets only, Eibach has a set coming out. Of course there are individual front and rears already available from Addco, ST.....

16, 17 and 18 inch wheels which look radical, really slow the car down because they are heavy and the bigger diameter screws up the gear ratio

MOST larger wheels are heavier, but not always. My RH Z5ks are 18s but only weight 3 lbs more than the stock 18s. Of course forged wheels are much lighter. And unless you are running 50 series tires on 18s, your rolling diameter should not be changing or change very little. Going from 205/50/17s to 215/35/18s, I'm losing .5% diameter.

The widest tire that you should run unless you have a turbo or some other ungodly power is a 205. Wider tires will result in more drag that our relatively low power engines can accelerate

I beg to differ here. It depends wholey on what kind or racing you are doing. In many Solo II events, since acceleration isn't as key as maintaining velocity, you will see many low power cars on insane width racing tires. A good friend of mine runs his 94 Celica on 225 racing tires and is consistently a podium finisher.

And while it isn't so much that the wider tires will make more drag, larger tires (which implies wider wheels in most cases)usually mean increasing unsprung weight which has a negative effect on suspension tuning. The negative effects of friction associated with wider tires would only outweigh the benefits in a car that requires great economy....not usually a great concern to racers. Top speed racing and solar car racing are examples that come to mind.

I'm open to discussion...........let's all learn.

[Celica RZ]

Do not lower your car too much! This perhaps is the number one no no. It is a symbol of a truly ignorant person with regards to suspension dynamics. Lowering looks really cool and can make a significant improvement to a cars cornering capability but going too low is detrimental to both handling and even safety. Going too low can cause bumpsteer, where the tie rods and control arms are traveling different arcs resulting in the wheels steering themselves with no steering wheel input. When a car is so low that the suspension bottoms under cornering loads, the end of the car that bottoms first will violently slide out. Super low guys are convinced that they are driving super touring cars but if you take them out on the track they will suck incredibly. Our [Celicas] have a short travel suspension as it is and cannot take being lowered more than 1.5-2 inches at the most. So install some good springs such as Eibach, H&R or Ground Control and DO NOT CUT THEM MORE TO MAKE YOUR CAR LOWER. If you have the Ground Control springs do not adjust them to lower your car more than two inches except if you are going to compete in car shows where the car will be a stationary display. You want to maintain at least 1-3/4" of travel.


how do you know that our car can only handle 1.5"- 2" drop? I'm curious cause I was looking to get custom Koni's and I wasn't sure what height I wanted it at 1.5" or 2" or 2.5"....

[CloNeGTS]

I don't know that anyone can say exactly how long you can go, but if you get any car too far away from its designed ride height, the suspension geometry will be all kinds of messed up, like bump steer as he said.

Something to notice, when you see the SCCA cars on Speedvision running at Mid Ohio and the like, they aren't slammed to the ground. They are lowered slightly, but they know that you want to remain in the "sweet spot" of the suspension to keep the car handling at it's best.