View Single Post
      10-19-2012, 07:28 AM   #37

Drives: 2011 135i M-Sport :D
Join Date: Nov 2010
Location: NoVA

iTrader: (1)

Purp Derp...i think this is the nicest and most constructive post you've ever made on here haha...thanks mate!

Originally Posted by Purple Derple View Post
Alright, long read ahead. Get some snacks. Have an open mind, there actually is some collective wisdom in this thread,

Like Gary and Flinchy and others have said, increasing oversteer tendency does not necessarily reduce understeer. You can have a car that is both tight and loose. For example, a car that pushes on turn in and mid corner, and is loose on exit. My guess is this is how a 1 series would behave with a overly thick rear anti-roll bar. What a miserable handful that would be! If you've ever driven in the rain, a car does this exact thing pretty willingly.

Anti-roll bars primarily behave like springs on that end of the car. However, they cannot affect the total load that is transfered from side to side. In fact, there is NOTHING you can do to the suspension to affect how much load transfers besides lowering the ride height. So no, a stiffer rear or front for that matter bar wont more lead to a more balanced car necessarily in the sense of evenly distributing weight over all four contact patches. It would simply defy phsyics. So while the car may remain flatter, it still transfers just as much load in the corner.

Let me quote for you. I know it is poor form to use such a big block quote, but he demonstrates the concept better than I can. Carl Lopez writes in Going Faster!: Mastering the Art of Race Driving, "To Illustrate how spring rates affect the cornering balance of the car, let's go to an extreme and see what happens...the front springs and shocks [are] removed and replaced by solid bars, essentially making the front suspension solid...whe the car corners and the load transfers, all of the... load will be absorbed by the outside front tire (assuming an infitnitely rigid chassis), since the front end resists all the rolling motion of the car. The outside rear tire doesn't contribute to any of this and consequently retains 100% of its original grip. The outside front, because of all this extra load, suffesrs a loss in CF relative to the rear and as a result operates at a higher slip angle than the rear tire will. The car goes into understeer--in this case, probably pretty gross understeer--as the outside front is hopelessly overtaxed." He goes on to show a similar example for the rear, which to this thread is most relevant; "Now, lets put the shock/spring unit back on the front of the car and make the rear suspension solid. Under cornering...all the load transfer goes to the outside rear tire, causing the rear end to operate at higher slip angles--the definition of oversteer. What you're seeing here is the world's stiffest spring, one with a spring rate of a million pounds per inch, or so. Nobody would really do this to a poor car, but it helps to illustrate the principle. All other things equal, a stiffer spring will increas the resistance to roll and absorb more of the load transfer at the end of the car on which it is installed." So, "At the rear, a stiffer spring increases the tendency toward oversteer, while a softer one goes in the opposite direction, decreasing the oversteer tendency and increasing the tendency toward understeer."

Since we know anti-roll bars behave just like springs that resist lateral motion only, we can substitue the spring concept in that passage with the anti-roll bar concept to understand its behavior. Because of this behavior, anti roll bars are used to tune front to back handling balance, just like you thought. But of course there is much nuance and dark art to suspension tuning. Spring rates and damper rates are used primarily while anti-roll bars are used for more fine tuning. For some more thoughts about it, check out this thread started by the pro driver, racing coach and and author Ross Bentley, I also reccomend his books. They're totally mental and are applicable to more than just race driving. I was reallysurprised to see him post on the forum actually and encourage everyone to pick his brain--I know I will.

Likewise, given that you cannot change the total load transferred, a flatter car is not necessarily faster, depending on the circuit. Indeed, take a track that does not have transition corners like MR Laguna Seca for example. A relatively compliant suspension is faster at the track because compliance = grip at the cost of transitional weight management given that the car does not bottom out and that the suspension geometry doesn't overly roll into challenges. But managing transitional weight is not the priority when the track has 1 transitional corner and it is low speed and leads onto a downhill section like at Laguna Seca. So it is not rewarding to tune the car to a relatively unimportant corner.

Gary said more lively as in easier to spin as in less grip in the rear as in less ability to put power down and we can see why. That is definitely not faster. Nothing to do with driver confidence as a fast drive will driver as fast as the car can go no matter how stupid the car behaves.
Faster, faster, faster, until the thrill of speed overcomes the fear of death… – Hunter Thompson