[Ron Sutton]

Originally Posted by FETorino

In a previous post on scrub and spindles you focused on maximizing track width. At some point on a really tight course such as some of the peanut autoxs maybe too much track is a bad thing?

What about that? Is there an optimal range based on a ratio of track vs wheelbase and I imagine this changes with the cars intended use. Specific to my problem I am somewhat limited on track and over indulging in wheelbase so what unique issues does that cause for my build?

Good question. Since we're only talking PT cars here, and not designing unique cars from scratch, we can keep the discussion to track widths in the 55-65" range. Wider provides stability, roll resistance & makes it easier to work all four tires more evenly. But width can add aero drag, depending on the package (aka car shape). There is no optimum Track to WB ratio. If there was a ratio, it would only give one more thing for car guys to debate.

For road courses, having the track wider helps in a big way. At cornering speeds of 60-100 mph these PT cars want to roll too much. Of course we select springs & sway bars to help reduce this roll, but widening the track width achieves the same goal as lowering the CG ... it reduces the leverage the CG has that produces roll angle in the first place.

Lowering the CG or widening the track width reduces roll angle at the source ... where springs, swaybars & roll centers are used to deal with the excessive roll angle after the fact. When the track width is wider, a specific "optimum" roll angle can be achieved with softer springs & smaller sway bars, which is a plus.

Wider track widths make the car WAY more drivable ... in a wide variety of lines ... providing the driver more confidence & options ... when a car is driven to its limits in high speed corners. A narrow track width is the opposite, making the car more knife edgy, often limiting the driver to a single narrow groove the car will run well in and does instills the opposite of confidence ... concern and/or fear ... in the driver.

For tight AutoX tracks, the primary drawback to wide track widths can be literally fitting through the cones. When I was at the Pleasanton GG AutoX in the spring, the chicane was literally 70" wide if you drew a straight line through it. Rob's red truck has a 71-72" overall width. Where everyone else ... talent permitting ... could thread the chicane, Rob had to turn left, right & left. Serious disadvantage there. Where on bigger AutoX tracks, his wider TW is an advantage.

The other issue ... "could" be ... getting the car to roll enough to help it turn well. This would only be an issue if the car is on a traditional low travel suspension set-up that needs the car to roll ... and the car couldn't achieve enough roll with their spring, sway bar & roll center package. Obviously, this could be remedied with softer springs. smaller sway bars or lower roll centers.