Q: “I‘ve got a conundrum of a sort. First, some background. I’ve been doing track days for the last 2 years and worked my way up to HPDE 4. Now for the odd issue I’ve encountered. My car in general has always been skittish at the limit, I’ve adjusted the settings (sway bars, coilovers, etc.), and thought the available range pushing for more oversteer at the edge/ limit so the car did not feel as if it would spin at the edge. Well, my last track event went pretty normal until the second day when the car just came together and started pushing at the limit like it never has before. I was comfortable and able to put down a new personal best time, and could have continued to chew time off with the way the car felt. The car was finally understeering at the limit and was very predictable. Fast forward to tear down and prep for the next track day. The front sway bar had become disconnected (the lower bolt had fallen off and I was running no front sway bar.) This should mean the car would have developed far more oversteer. Somehow the car was understeering perfectly at the edge of traction. I’m deeply confused as this is contrary to all the knowledge I’ve read as well as experienced myself.”
A: Very interesting! Why would a car begin to understeer more when the front anti-roll bar becomes disconnected? Normally, a softer, or disconnected front bar generates more front grip, so I understand why you’re confused.
Obviously, I don’t know for sure, but here’s what I suspect is going on. It’s possible to have understeer caused by too much roll, which is what may have happened when the bar was disconnected. There are cars that when the chassis rolls enough, the geometry changes the camber so much that the outside tire (which is doing most of the work) is not generating the grip it should be because it’s leaned over so far. It’s even possible that the roll changes toe and caster enough to take some grip away — or at least its responsiveness. This kind of understeer is called “roll understeer.”
You don’t mention where in the corner the understeer began. A stiff front bar does make the car responsive at turn-in. If the understeer started early, like just as you were turning into the corner, it may be that the car now felt lazy. Sometimes that can start the understeer, and it never really recovers, even through mid-corner.
If the understeer didn’t start until further into the corner, I’d guess that it’s roll understeer.
Sounds to me that when you connect the bar again, you should make it so that it’s softer overall, even if that means installing a smaller diameter bar.
FYI, I have an eBook available under the Freebies menu at SpeedSecrets.com that’s all about tuning your car’s handling. I just might have written something about this, there. You can download the eBook for free.