walterheard

iTrader: (31)

Can anyone explain to me what more or less shock rebound does for the vehicle?

mtpocketsracing

iTrader: (2)

Rebound is the shock returning from being compressed. So if someone says it needs more rebound assume they want it to have less damping making the shock easier (softer)for the spring to push it back down.
And if they say it needs less they want it harder to push back down.

Off-road is typically softer for rebound and compression because you want the tires to follow the ground fast because they will be bouncing around a lot. Onroad harder. Less movement of the suspension so it can be stiffer.

spookie

iTrader: (25)

What MT said, the springs play into this as well, as where on the A-Arm the shock is mounted. I have came to the conclusion, the more inboard the shock is mounted, the less it travels and the thicker the oil has to be, to get the same dampening. The closer to the tire, the more it moves with the tire, ie more shock travel. I can spend hours and hours turning on the shocks on one truck, oils and spring rates and location to get them just so, for my driving.

walterheard

iTrader: (31)

So off road I would want the shocks to rebound more?

ThePanda

iTrader: (68)

Make the difference between rebound due to internal pressure, and rebound due to springs pulling out the shaft.

Rebound from pressure will to some extent make the shock feel more progressive.

walterheard

iTrader: (31)

So what would be the general rule for rebound? More rebound for bumpy conditions? Less rebound for smooth conditions?

ThePanda

iTrader: (68)

You usually want as little pressure rebound as possible. Spring rebound you need to tune it in conjunction with the oil rates.

spookie

iTrader: (25)

Some people use the drop test, drop the truck to the floor level, from about two or three feet up. Truck should firmly plant without bottoming out to badly. If it almost wants to "hop" back up and almost pops the tires off the floor, the oil is too light. If it hits, and "sticks" down almost bottomed out, the oil is too thick. You want the truck to almost just plant itself, when dropped.

If the frt pops way up, it needs thicker oil, if the rear does the hop, it needs thicker oil. When dropped, there should be no "hop" or very little, and the A arms should be level or slightly higher near the chassis (inboard) after it settles, not topped out or bottomed out. I'm sure I'll get heat for this post, but I set each one of my trucks up differently for what they will each be driven over. I have a sct with long travel, set up a little stiff for bashing and jumps, another sct set up for street with shorter travel and a little lighter action, since the road is smoother and I don't need the heavy dampening.

mtpocketsracing

iTrader: (2)

Yes but only to a degree. Way more than an onroad car for sure. But not so much that it makes the car handle badly. Suspension tuning is a constant battle finding that perfect balance. It's not as important when just basing but if you're trying to keep up in a track it's going to be necessary.
If you leave it hard it will make the car bounce around instead of the suspension absorbing the terrain. Anytime the tires are leaving the ground they're not doing anything. You'll have no steering, acceleration, or braking.
It gets more complex, you also have to pick the right spring rates and oil combo to handle the jumps. Yeah now it's starting to sink in it can be black magic huh lol. Just keep in mind it's always going to be a compromise. The car might work very well in one section on the track but land hard on some bigger jumps etc. You have to figure out what works best for you and your driving abilities.
There are several free downloads floating around that is about suspension tuning for rc cars.

Dave H

I'm with Panda on very little to no rebound, even for offroad. Better and more consistent to let the spring do it's thing alone.

Also agree with Spookie's drop test comments, especially watching the front and rear reaction. Normally they should react similarly, not pitch the car forward or backward. I have the best luck with a slight rebound up after landing for a offroad racer, but not a bounce as mentioned.

If you can try watching experienced racers drop theirs to get a feel. Also use the drop before measuring ride height front and rear, a deceptively important adjustment.

walterheard

iTrader: (31)

I went to the track today, i used no rebound truck bounced all over the place...I will try a little rebound next time i go to the track

ThePanda

iTrader: (68)

rebound should not have that much of an effect on the suspension rates. try posting up a spec sheet of your car... with how it was setup (spring rates, oils, car wt, etc) It will probably help us to get a better idea of how your car might need to be setup.

F. Mendoza

iTrader: (79)

In the Xray onroad manual it states that in onroad, high bite tracks should have 25% or less rebound in the shocks while low traction tracks should have upto 100% rebound in the shocks. I just use a ride height gauge and extend shocks 4 mm before capping them. Rebound and roll center adjustments drive me cuckoo.

mtpocketsracing

iTrader: (2)

That's a different setting were (or I was ) talking about.
When I'm talking about rebound settings is how fast or slow the shock extends with the spring installed. Changing this can only be done via oil viscosity or holes in the piston.

Btw spring rates are not supposed to be used for compression and rebound settings. The motorcycle suspension seminar I went to said the spring should only be changed to get the proper sag. Sag is the ride height with the rider on it. All suspensions are the same way.
That's why you'll rarely see the pros who truly understand this use springs to tune their car. Now obviously you may be forced to have to stop problems with some jumps. For instance if the back of the car slaps the top of the ramp causing the car to roll forward in the air. Or fast high grip flat corner tracks that have higher g loads to compress the suspension too much.

blis

+1 Spookie.

I doubt no rebound is the cause, when a car bounces it can be for a few reasons and often due to a lack of downward travel in suspension (droop), managed with springs. Then tune the dampers to absorb the knocks and accept at a certain height, you will bottom out. Trying to prevent this would mean stiffer springs, less travel and more bounce, so it's a matter of finding a compromise in how high you can jump and how fast you can get around on the ground.