Steering and alignment settings (part 1 of ?)

Getting late and this may get involved... but we'll put on some Wes Montgomery and start at taking a crack at it. Steering (Ackermann) and alignment (toe) settings are an important design and tuning point, but for us at least seemed to be last on the list of things to adjust. More often than not I think we never really did much of it!

Even if you wanted to tune it on the skidpad or a simple 'squared off' course you've got plenty of combinations to run through if you take the brute force approach:

• Front axle: Toe in? Parallel? Toe out?
• Rear axle: Toe in? Parallel? Toe out?
• 'Static' Ackermann: Generally positive? Parallel? negative?
• Ackermann 'progression': No change? Transition toward more negative at high steer angle? Transition to more positive at high steer angle?

Bearing in mind that in theory, those above parameters can change based on changing static camber settings or bolting on a different set of tires, or even just by adding or removing roll stiffness (changing dynamic camber).

That's a bitch. Good luck track testing all of that and getting any sort of consistent read on subtle changes.. when the track is evolving (rubbering in, changing temp).. while ambient air temp is changing (slightly changing downforce, drag, and engine power).. and as you're wearing down tire sets. Really I think the only good way to do it is by using tire data, which hopefully (but not always) is sufficiently accurate.

Even then, you have to know what you're designing for. In my opinion a good part of it is getting the left and right slip angles "matched" so the tires saturate at the same time. Wish I had a good graphic to describe this. Maybe tomorrow. But let's say at a given limit cornering loading your outside tire peaks at 6° slip angle and your inside tire peaks at 8° slip angle. The left and right wheels really aren't that independent, so the only way you're going to get the tires to both peak at the same time is to run some pro-Ackermann steering and/or toe out. Otherwise if you had been completely parallel and steering both tires to 7° you'd be overdriving and abusing the outside tire while underutilizing the inside tire. I'm not sure of a great way to determine this using telemetry without using wheel force transducers.

That's my limit steering strategy. On-center (near 0°) is a bit more difficult for me to grasp. Intuitively I'd think you wouldn't want to run dramatic amounts of toe in any event as it will slow you down on the straights (tire is generating lateral force but starting to point backwards).

The thing that I'm not convinced of are the "conventional wisdom" that toe-out on the front "helps turn-in," toe-in on the rear "helps rear stability," and that any amount of toe-out rear is going to make the car a bitch to drive. The reasons why are not obvious to me at the moment. I'll have to think about that. With the rear tires anyway, if they don't peak at the same point (and chances are with your luck they won't) you're invariably leaving grip on the table unless you can split the slip angles a bit!

Long story short: "Limit" steer settings are a hell of a lot more obvious to me than on-center ones.