Gettin' to be about that time to outline objectives for suspension design, so I have a roadmap of what to target. Figured I'd write this up while my shrimp dethaw (for a delicious stir fry in a bit!).
I had a discussion with a coworker the other day, as we were discussing racecar stability issues. Among other things, I believe his comment was to the effect that the race engineers were going to set up the car for maximum possible grip, and then let the (very well paid) driver deal with it and get the car around the track, even if the car drives poorly.
I respectfully disagree (SB!), or at least that will not be my MO. Maybe that would work for a qualifying setup, but the race is what matters and it's not like you're going to be changing your kinematic package between Saturday and Sunday.
Drivers are human. I don't care if it's Kyle Busch or Felipe Massa or Joe Blow. Eventually they deviate from perfection, and when grip limited if it's bad enough that means you're ending the race one way or another, flying into the wall, another car, a gravel trap, or what have you. Chance of screwing up royally will generally increase with:
- Long duration races (a matter of probability)
- Pushing your or the machine's limit closer to 10-tenths (decreases margin for error or deviation)
- Having someone fighting you for position (have to mentally process more things)
- Having an unpredictable, twitchy, inconsistent race car (increases inherent deviation and variation from the perfect lap)
Realistically you're not going to be putting down 10-tenths all-out qualifying laps every minute of the race. Too great a chance of wadding the car up, as you would be constantly at the absolute limit with zero margin for error. Realistically, a driver is going to want to drive around the edge of his comfort level and be able to "dig deep" when required to make a pass for position or the lead, when strategy dictates. That's
why there is a "race pace" and "qualifying pace." Obviously more talented and experienced drivers have a broader comfort zone than rookies, but there's still a limit!
Edit - Now that I think of it, Dale Jr. may have proven this point a few times in the 2008 NSCS season. I seem to remember a few times he drove the hell out of the car, right up near the wall, at the limit... moved forward in position... but inevitably something went awry from pushing too hard and it cost him. The other HMS drivers seem to be able to back off ultimate pace a bit and conserve their equipment until the end and/or when they really need it.If your car isn't predictable and drives like absolute shit, there's no way you're going to feel comfortable driving as hard as if it were smooth. Your race pace might only be 8-tenths instead of 9. Plus, every fraction of a second you're spending correcting a poorly handling car, is time off your perfect lap.
The point being, it makes sense to me that you want to make the car as pleasant and easy to drive as possible. Even if it isn't the absolute maximum theoretically possible level of grip, and might have a longer "perfect" lap time, over the course of a race the lower probability of the driver blowing a braking zone or corner... and the smaller sum of small errors over a long race, would probably make up for it.
As such, suspension goals (kinematic and kinetic) will include:
- High grip levels in cornering, trail-brake entry, and on-throttle exit
- Predictable, smooth transitions between corner phases
- Predictable, smooth reaction to bumps and load transfer
- Appropriate range of adjustment
- Quick method of changing chassis parameters
Worthy of note, generally I think maximum cornering grip is what most people focus in on, or at least look at first. It is hard however to make a pass mid-corner. You're already near the limit of adhesion with the cornering power of the tires saturating, and don't really have that much maneuvering potential. It is
much easier to out-brake someone or pass them on the next straight by getting the power down early. I will probably be willing to sacrifice
some cornering grip for being able to brake deeper and get the power down sooner.
How to achieve those goals with kinematics (linkage movement) and kinetics (springs, bars, dampers)... will come up next. Now it's time to prepare my shrimp.
To be perfectly honest I'm amazed this worked. I'll likely be using the upper control arm mount bracket to adjust static camber by means of shims. As such, no shims will be the most camber you can throw at the thing, and I have to design accordingly. Previously I had been doing all my design at 0 inclination. Went in, changed my mates around to set the RF wheel and tire at -4 camber, and bam! All the a-arms automatically regenerated and no mates fell apart. No parts flew off into infinity! Now I can go change my track width, max static camber, upright geometry, or chassis geometry, and everything should automatically regenerate to fit. Beaut!
What's next? Tried getting some of the rudimentary geometry into the OptimumK demo, but had some issues. Cool software but to be honest it doesn't seem very robust. Don't think I'll be 
shelling out $1700 for it just yet! I'll have to think of a better way. Now that I think of it, for simple stuff where I don't have any anti-___ geometry I could probably make a simple front-view sketch in CAD and do some simple analysis that way. That might be perfect! Nice!
