Under light-duty driving, the progressive rate springs soak up the small bumps as a softer spring would, but when the conditions get rough and the jumps get big, the progressive rate springs step up to the challenge by getting firmer as the suspension is compressed. This resists the chassis from bottoming out from jumps to keep the chassis under control.
Weights & Dimensions
Search JPerkins.com by matching specification
Search for matching products across the site or just by Traxxas or just in Accessories/Car/Springs
You can also find more similar products in the Traxxas brand store in Accessories/Springs.