iRacing.com has a very accurate recreation of Mazda Raceway and I know the track fairly well, so I decided to see if I could get myself some fast laps and improve the car mechanically.
The Mustang is a good choice for this exercise, I think. It has odd suspension design, it's heavy, and has temperamental handling.
I'm starting with the factory base-line setup for the car. This includes an already fairly aggressive stance on the car, with higher rear ride height, a decent amount of camber, low tire pressures and toe-in/toe-out already set on the car. These more aggressively tuned settings are offset somewhat by the lack of a rear anti-roll bar, slightly higher front tire pressures and soft damper settings. These settings should make the car a little slower to respond.
The first thing I will do is drive the car for 20 minutes at the base-line settings. This will do two things. For one, it will give me a basic lap time to work from so that I can ensure the settings I change are making the car faster, and for two, it will allow me to feel out what exactly this car needs improved for the track.
The first session was uneventful. I ran laps in the 1:37.7 to 1:38.4 range, and I found that while the base-line setup does handle fairly well at Mazda Raceway, it is sluggish during the corner entry and mid-corner phases, though it puts the power down fairly well on the exits of corners. The big problem is occasional chronic understeer. If you're not on top of your pedal inputs, you can easily find yourself sliding off the edge in turns 4, 5, and especially 10. I'd like to try and control that.
The first change I'm going to make is to add the rear anti-roll bar. Currently the front anti-roll bar is set to medium, so I will add the softest (thinnest) anti-roll bar in the rear to keep the rear of the car from rolling over in the corners. Normally a stiffer roll bar reduces overall grip, but I can't stand the idea of not having at least a soft one back there.
15 minutes later and I'm happy with my change. My lap time gaps got tighter, and my best time got improved by 0.060 seconds. The car responds much better at turn-in and in the mid corner, and the exit speeds weren't negatively affected - in fact, I gained a mile per hour on almost every straight. I probably won't do any more roll bar tweaking.
The tire temperatures indicate that the tire pressures and camber are set well. That may change once we start adjusting suspension components though.
The next change I'm going to make is to the toe settings of the car. Currently the rear has some toe-out, which will make things a little more "loose" feeling - the rear will want to step out a bit more. So I'm going to remove some of that looseness.
The change didn't really affect the times, but it felt better to drive anyway. That massive wash-out understeer problem is going away.
Now I want to play with the dampers. The track is very smooth, so the dampers are really only going to control the balance of the car, not really provide any bump relief. So I'll stiffen the bump (compression) settings of the dampers and leave the rebound (extension) setting be - I don't want to change the balance of the car.
5 laps later and I think I'm going to make them even more stiff. I'll put the fronts up to +30 clicks and the rears to +26 clicks.
2 laps later and I've broken my lap record by two tenths, with a 1:37.406. That time would put me 8th on the world record leaderboard.
The stiffened dampers made the car much more responsive, and more stable with my driving style - the understeer issue is almost nonexistent, and fixing it hasn't made the car devilish to drive either. Most of my laps landed in the mid to high 1:37s, and the tire wear became much more even, both across the surface temperature wise and over all four tires in terms of tread depth.
Tomorrow I'll play with the ride height, but I suspect I won't find much time.
These simulators sure are helpful in learning how to set up a car.