From: Barry Lenoble [lenobleb@symbol.com]
Sent: Friday, December 08, 2000 10:27 AM
To: 928
Subject: [928] Springs and Racing

Hello,

I love reading the race stuff. That's why I'm into Porsches.

There seems to be some confusion about the effect of spring 
rate on lap times.

Spring rate, by itself, has very little to do with lap times. In fact, 
for most cars, increasing spring rate alone with have just about 
zero effect on lap times.

If you want to decrease your lap times without increasing power, 
you need to increase the amount of grip your car has. It's really 
very simple, more grip = faster speeds on the track.

How can you increase grip? The easiest way it to get either stickier 
tires, and or wider wheels and wider tires. Assuming you already have 
the best wheels and tires you can afford, you must look to other ways. 

Grip is decreased when you have weight transfer. So, in order to 
MINIMIZE the lose of grip (you can't INCREASE grip w/o changing 
wheels and or tires) you must minimize the amount of weight transfer 
that occurs when the car is braking, accelerating, or cornering. Unless 
you totally re-engineer you suspension, the ONLY way you can change 
the amount of weight transfer is to lower the center of gravity. Changing 
springs, shocks, or swaybars does NOT change the amount of weight
transfer. That can only be done by physically moving weight around in 
the car, or, more commonly, by lowering the car. If you lower the car, you 
increase the risk of running out of suspension travel, or bottoming out the 
suspension. So, you typically  increase the spring rate so that you don't 
bottom the suspension.

That's the main reason why race cars have stiffer springs than street cars. 

Another important reason is to decrease the amount of chamber change 
that occurs when a car leans. Increasing the spring rate will help with that. 
However, the effects of body lean on tire chamber change is very much 
dependant on the suspension design.

So, in conclusion, if you want to go fast:

1. Put on the widest wheels with the stickiest rubber you can afford. 
2. Remove as much weight from the car as possible. 
3. Lower the car as much as possible (but make sure you still have
   suficient suspension travel)
4. Select a spring rate that maintains the proper ride height.
5. Select shocks and swaybars to tune handling characteristics of
    understeer and oversteer.

If you just increase spring rate, but don't change anything else, don't
expect any real changes in lap times.

For more information on this and other racing subjects, I suggest the
"--- to Win" series of books (like "Engineer to Win, Tune to Win, 
Race to Win) by Carrol Smith.

Comments welcome,
Barry Lenoble
e-motion-racing@juno.com
http://members.rennlist.com/drive944/

>  ....................."I only gained .3 seconds
> going from an october race time of 1:54.4 to my
> New race suspension with double the spring rates as before time of 1:54.1.
> the bottomline was that the car was much more manuverable than before, and
> a heck of a lot more fun to drive.  I wasnt feeling like I was tipping over
> in the long off cambered sweepers and not diving the nose under hard
> braking.  much more control!!!!   But, contrary to most of the so called
> suspension set up "experts" it didnt make me a whole lot faster."