Rebound is effectively how much the shock piston returns out of the body, after being fully compressed. To try it, remove your springs, push the pistion in the whole way, then let go. If the piston returns to it's full length, then you have full rebound... simple. Now the confusing bit is how people mark it on setup sheets, sometimes a % and some times as mm. Either way, what is critical is that you matching shocks left and right at both ends of the car.... the setting can obvioulsy be different front and rear if required, but must be the same left and right. Thankfully the TRF shocks are pretty easy to get right (see later)
Ok, so what does it do? To quote TRF USA team memeber Corey Whiteman...
Its an adjustment not too many people play with. I have tried alot of different shock adjustments at many different tracks. The effect of rebound directly impacts the way the car handles bumps and negotiates quick switchbacks(aka shicanes). I have found the more rebound i use, makes the car more responsive/aggresive but can handle bumpy tracks much better, less rebound the opposite is true. The reason why rebound works best for bumps is rebound keeps the tire in contact with the track after you hit a bump, the longer you car stays in contact with the track the more stable it is. As for shicanes your car needs to change directions quickly, so with alot of rebound your car will be able to transfer the weight L/R quicker with assitance from the rebound. For me i almost always run full rebound just because i like a responsive car and if there is any inperfections in the track my car will keeps its composure. Hope this was not to confusing!
OK, so we have that out the way... how do you set it? From me... (:p)
You can vary it by setting the piston to a certain position in the shock when you build the shocks.
Firstly, you need to make sure your pushing the shafts up equal amounts for each pair of shocks. To do this, I build up the shocks unfilled (rubber bladder, and top mount included), placing a red o-ring on the shaft between the body and the ball joint (I use this later to help set the rebound, if you look at Viktor Wilcks car, he does this too... it's where the idea came from :p). Then I'll pull the shaft down full, and measure with calipers the length between teh bottom of the shock body, and the top of the ball joint. It doesn't really matter what this length is, as long as it's equal on the pair. You should set it so you get your shock lengh required for correct droop (I think for a shock 61.5mm long, 12.5mm is this length... or in that ball park).
With that done, dissamble the top of the shocks, and pore the oil you want to use on top. Remove all the air by gently pushing the piston up and down, then leave stand for a while (or make it even better and use a shock pump). When you can't see any air bubbles in the oil, Hold the shock body, and push the shaft in too your required rebound level. This is where the red O-ring on the shaft comes in handy. (I use this as my setting for rebound, but you can use more o-rings/spacers if you want more rebound). Then place the diaphram on top, taking care not to a) adjust the piston position (if your using spacers, this is easy, as just hold the shaft up against them) b) introduce air into the shock. Carry on building the shock, and when you push the piston in, you should have your desired level of rebound.
If you've used a lot of spacers, you can remove them by undoing the ball joint, just make sure you screw back up to the same length as before
Hopefully that helps, any Q's post away!
Regards
Ed
