C5 Corvette Sway Bar Sizes & Leaf + Coilover Spring Rate Research Notes

While researching coilovers and then subsequently researching why the QA1 coilovers understeered for me, I took a lot of notes on all of the various sway bar diameters along with various coilover spring rates. A lot of information I took from other folks and from various forum posts as many manufacturers don't list their specs for some reason, making it hard to compare just what you're getting. Below is my collated information from researching these things, make what you will of it!

Swaybars

Leaf Spring & Coilover Springs Rates

General Notes On My Findings

• General ballpark balanced handling values to shoot for that I have seen.
  • 350/450 for a street going car that is as aggresive as you should.
  • 450/550 for an aggressive street and sporadically track going car.
  • 550/650 for a primarily track. Still bearable enough on the street.
  • To setup a car that prefers to understeer (safest on the street) or incase you have larger than average rear sway bars, reduce rear spring rate 50lbs.
• Article from grassroots motorsporst researching and testing coil vs leaf effective spring rates. (TLDR: Not a direct comparison between the two)
• Ultra informative post on measured rate vs stated rate of leaf springs versus coilover springs (TLDR: Extreme leafsprings about Match 500lb coilover springs)
• Differentiation in spring rates on front versus rear is due to leverage ratios. If you look at the rear control arms with a coilover in them versus the front, the front is more vertical, the rear is less vertical. Thus the rear of a C5 corvette will compress the rear coilovers more for the same amount of wheel travel requiring a higher spring rate to result in a similar effective rate and consequently better balance the car. With the near 50/50 weight distribution of these cars, you want similar effective rates.
• Spec Corvette runs balanced / square spring rates and compenste for it with huge rear sway bars run as stiff as possible supposedly. Reviewing sway bar sizing, that very much appears to be the case!
  • Per conversation with a fellow who ran spec corvette for two years, he too wanted to run higher rear spring rates but instead was able to get the handling he wanted stiffening the spec corvette rear sway bars, which are already pretty thick per my findings above.
• I spoke with the gentleman who helped develop QA1's coilovers, and he ran 550/650 spring rates per his testing, and is what he recommended QA1 runs, Not sure why QA1 didn't follow that and instead went with 550 squared.
  • QA1 does have a 700lb spring available they can send. Eibach of course makes 600lb and 650lb springs with a 2.25" ID. I recommend the Eibach 650 rear springs.
• Penske communicated to me with email, they recommended the rates above, but mostly vendors seem to sell their stuff and pick the rates based on the user need.