Originally Posted by
stelio279
b3master, I thought I had a good handle on roll center but you just confused me again
I had understood the effect on roll center, particularly rear RC, as opposite as to what you just posted. I.e. lower rear roll center= more roll and that is BETTER in low traction conditions.
My understanding and reasoning is as follows:
During a curve, you maintain the best traction by maintaining pressure on both inside and outside tires as long as possible. When all weight gets suddenly transferred to the outside tire, you have less overall traction than if both rear tires were gripping). By slowing down weight transfer from inside to outside you get to smooth out this transfer and maintain pressure on both rear tires for longer.
On high traction tracks, we are not as concerned with maximizing traction since there is plenty of it, and we can raise RC to have less chassis roll and take advantage of a more responsive car.
Does this make sense to anyone else or do I really have it all wrong???
Note that I had come to this understanding based on reading-up a lot on this issue, including different books on (full scale) auto racing, several articles and websites such as this one:
http://www.thecartech.com/subjects/a...oll_Center.htm which states:
"Effects of Front Roll Center Adjustment
Front roll center has most effect on on-throttle steering during mid-corner and corner exit.
LOWER front roll center
* More on-throttle steering
* Car is less responsive
* Better on smooth, high grip tracks with long fast corners
HIGHER front roll center
* Less on-throttle steering
* Car is more responsive
* Use in high grip conditions to avoid traction rolling
* Use on tracks with quick direction changes (chicanes)"
You still have a great understanding on front and rear RC. Its all relative.
Methods described in this thread, once read entirely, cause racers to think independently to what they have heard or seen.
I didnt want other racers to blindly follow a statement such as "Raising the outer link (on the hub) will raise the roll center and will generally add more rear traction" simply because it isnt 100% true, not 100% of the time. It totally depends on what type of surface we are running on, and relative to setup starting point.
For sandy, loamy, flaky, natural and not packed surfaces its true. because you want enough pressure to dig into the surface, and having weight spread on to both tires doesnt cause enough pressure. hence its preferred to raise the RC and cause the outer tire to have more of the weight transferred to it so it can have higher pressure and bite in better to respond to directional change.
Not to mention sandy and loamy surfaces are usually bumpy and one would prefer a soft plush suspension and then counteract the excessive body roll caused by the softer suspension with a higher RC.
ON dry dusty low traction surface (still depends on other variables as well*) there usually isnt enough pressure from the tires to the surface to cause the ideal body roll and weight transfer, its preferred to soften up the suspension (keeping balance) and
then deal with RC depending on the result of the softer suspension. This doesnt take into account ruts, bumps, track imperfection. Once again like mentioned several times previously in the thread you want to set up the car to 80% of the track and deal with the remaining 20%.
I believe that each car and its unique weight distribution has an ideal body roll angle. Depending on the traction you will want to adjust RC to cause that maximum roll angle, not more, not less. Generally, dry hard low traction surfaces you will usually break lose before reaching the ideal angle. on high traction you most probably would exceed the idea body roll and cause traction rolls and instability.
If RC is too low
(generally lets say wrt stock setup*) it will cause excessive body roll, hence traction rolls on high track surfaces.
It will cause not enough tire pressure on low traction surfaces causing car to skid sideways excessively losing precious time at every corner. If front and rear RC are not equal it will cause push or spin out on low traction surfaces.
Conclusion dont change your understanding on RC, but also dont follow straight blind rules like "lower rc more traction" cause it isnt true.
There is balance to everything. In-to-corner, mid-corner, and out-of-corner traction are some to think of.
* Statements are greatly dependent on which car is being discussed and what is the starting setup point. This is why Fred's way to finding complete balance is ideal, You find the balance and THEN go from there. spring balance, piston and shock oil balance, Plush and pack balance, front to rear RC balance, in-to mid and out-of corner steering balance. Once balance is achieved THEN we can properly discuss and say lower or higher RC, it will be relative and based on your ideal balanced setup.
Let me summarize it in a different way:
**its all relative, to one car and its starting setup a higher RC might add traction to another car and its starting setup a higher RC might decrease traction.
***On one surface a lower RC will increase traction on another surface it will decrease traction.
Dont follow direct rules blindly. Im not trying to purposely confuse the some of you. I just want yall to think for yourselves for your particular track and surface and your setup's starting point. In the end I hope I made you understand clearer how its all relative.