[Ron Sutton]

Ron

Starting with the first statement about looking at the car in two halves. Correct me if I am wrong but I'm assuming you are speaking about the need to tune each end of the cars roll resistance based on each ends independent RC and not that the effect at one end is independent of the other end of the car.

Rob,

Most of that statement is correct. Parts are not. One of my friends said, “Ron is a race car designer that did not go to engineering school, so he speaks car guy". Because I like to make complex things simple to understand, I’m going to explain this in layers, using car guy terms we all can relate to.

1. Each end of the car has a “mind of its own” about roll angle, due to differences front to rear … in track widths, CG heights, roll center heights, spring rates, shock valving & sway bar rates.

2. The ends of the car do “want to” roll differently … and each end would roll to its own desired roll angle … if there was a pivot in the middle of the car.

3. But there is not a pivot in the middle of the car … exactly. Chassis rigidity … specifically torsional rigidity … plays a role in how tied together the front & rear of the car are.

If the car with a 50/50 weight balance & had 100% chassis rigidity (it does not) … then the car would roll to an angle that averaged the roll angles of the two ends. In other words … if the front end “wants to” roll 1.5 degrees & the rear end “wants to” roll 2.5 degrees … if the car was 100% rigid & had a 50/50 weight balance, it would achieve an averaged roll angle of 2.0 degrees unilaterally.

But all car chassis flex or twist when the forces are different front & rear … including race car chassis. Stock production cars flex & twist a lot when high powered engines, grippy tires & performance suspensions are added … and drivers push them to their limits. Well designed race cars flex & twist very little … but they do flex & twist to a degree. Chassis designs differ …therefore so does the torsional rigidity differ between chassis brands & designs.

Without complicating the discussion by trying to quantify numbers … we could easily envision this example as a race car with a relatively stiff chassis achieving a 1.9 degree roll angle in the front & a 2.1 degree roll angle in the rear. This is just an example so everyone understands the concept. A more flexible car could & does achieve a higher degree of roll angle difference.

But … we still see the rear of this example car with a higher demand for roll angle … is “pulling” the front end with it. If we’re trying to get the car to run flatter … the solution is in tuning the rear suspension, not the front. So yes, we need to tune each end of the car independently … but so as to work together in harmony … because each end can & does affect the other end.

Did that make sense? Please feel free to ask about anything I didn’t state clearly enough.


.