Originally Posted by JamesL_71

By tension, they are simply referring to spring preload. The center spring preload affects the center-main chassis ride height, or "chassis sag". Preloading the spring more will raise the center of the chassis... you generally measure this right in front of the rear pod.

Droop is measured at the back of the rear pod. It is adjusted by changing the overall length of the center shock. Lengthen the shock by unscrewing the ball cup from the shock end, and this will increase rear pod droop.

I use a set of 1/10 Sedan droop blocks/gauge. While a gauge with finer resolution is ideal, the Hudy gauge w/ the .2mm increments only goes down to +2mm or so. You will need a gauge that goes down to -2mm or below... The gauge I use goes to -3mm. So you basically have to eyeball the intermediate increments. For example, if you want to set the rear pod droop to -1.5mm, change the center shock length until you end up right at -1mm on the gauge... then carefully unscrew the ball cup a little further, in 1/4 turn increments, until you get the rear pod roughly half way between the -2 and -1mm steps on the droop gauge.

That is how I measure droop at least. It would be great if someone came out with a 12th scale specific droop gauge that had .2mm resolution, but went down to -3-4mm.

Edit: In regards to the center spring, it is important to note that for a given amount of preload, a stiffer spring will result in a higher center chassis ride height.

Also... preloading the side springs has a slightly different effect than the center spring, since the side springs are a progressive rate design. With a linear rate spring, preload has little to no effect on the overall rate of the spring. But with a progressive spring that is not true. This is why preloading the side springs is often used as a tuning tool, not just for adjusting chassis tweak.