The long version......
This is not the ultimate handling guide because I'm going to tell you what bits you need to fit. Its because I hope it will de-mystify some of the "black magic" that kicks around. I've ben doing a lot of research recently into roll centers/weight transfer and like everyone else on the internet was getting tied up in debates over IC, CG, RC, SVIC blah blah. It is a contentious issue as the calculations and assumptions get really in depth and I made a few excel spreadsheets to test theories. On one of the engineering forums, an experienced chassis engineer wrote a short post in the middle of a long discussion that made me realise most of the internet debates have missed the point on roll centres and chassis "tuning" comes down to the first post. The rest is contact pacth, centre of gravity and application.
If you can understand what each is doing and at which point in a roll/pitch/bump they are doing it then you can decide yourself what bits you need to stiffen or soften to give the desired response.
I'll break it up into smaller chunks but in a nutshell, the first post says it all
1. We'll start with tyres as its something simple we can all understand. If you pump extra air in the front tyres, they go stiffer, the steering feels sharper 8), you then find it doesn't have as much grip and understeers more
. For drag racers, response isn't important, so they take the air out make the tyres soft and get more grip.
Yeh and...
Well if you ignore the affect of tyre temps, you can reverse the equation and stiffer = less grip whilst softer = less response.
The difficulty is finding a compromise between grip and response as you can't have both.
Here's a quick experiment for you to embaress youselves with.
Stand side on next to a wall and with your arm out at shoulder height, lean against it . If your hand doesn't move up then chances are you are transfering enough weight onto your hand to make it grip the wall. If you slowly slide your hand up the wall, you'll find it continues to grip as you are naturally trasnfering more weight on to the hand (contact patch) and control the slide. If you go back to the start, lean on your hand and then quickly (response) move it up the wall. You'll now find it more difficult to transfer enough weight onto your hand to maintain grip and if you move to fast you'll lose balance.
This experimient wont win any prizes and I'm sure some smart alec will say its easy but if you consider your hand to be a tyre, your arm suspension and your body the car you can see where I'm going.
The main learning point is you need weight transfer to make you hand grip. If you could transfer weight fast enough you could respond more quickly and maintain grip. But if you transfer weight too much weight and I ask you stand up staright again you'll find you can't respond very quickly as you're leaning so hard on the wall.
A more practical experiment is when you brake too sharply(response) the wheels lock up but if you apply the same force more slowly the tyres grip.
The best compromise is dependant on the application, whether you need more grip or response and which direction you need it in.
The same affect is happening in your springs, dampers, roll bars, bushes and chassis. Each of these elements will take differing times to react, the chassis is near instantaineous whilst the springs need time to compress before they can do anything. Car manufactureres try to set the mechanical stiffness of each so they overlap and provide the desired response and grip through out a turn/pitch/bump
To be continued.....
