Off-road damping?

I'm sure some of you are aware of Paco Motorsports' Offroadster.

I'm building a set of shocks for it, and I have two choices for starting valving. One is fairly heavy on the rebound, allowing the spring to take care of compression. The other is more evenly balanced between compression and rebound, more typical for a sports car.

Which would be a better choice for high speed dirt and possibly some sweet jumps?

For high speed off road the shock needs to be able to compress fully without bottoming out and then “Tuning the rebound stroke is much more difficult. Rebound controls the rate of shock extension and is dependent upon spring force. The rebound damping needs to be stiff enough to slowly release the built-up spring force after compression. The rebound damping also needs to be soft enough to keep the tire on the ground and prevent the suspension from packing up over repetitious bumps."

most off road high speed shocks are remote reservoir full adjustable and usually 2inch to 4.5inch bodys.

Reading between the lines on that cut and paste, it looks like little compression damping and lots of rebound.

The big bodies are for increased oil capacity and physical strength. The remote reservoirs are either for bypasses, increased oil capacity or to add separate compression and rebound adjustments on a monotube. As much fun as it would be to spec a full Dakar setup, I am working within the limitations of what will fit in this vehicle and the off-the-shelf parts I have to work with.

Keith Tanner wrote: I'm sure some of you are aware of Paco Motorsports' Offroadster. I'm building a set of shocks for it... Which would be a better choice for high speed dirt and possibly some sweet jumps?

A life insurance policy for the driver???

Most of the high end off road shocks have anywhere from 15" to 24" of travel as well and most desert racers run air/hydro bump stops as well so they can run softer compression without blowing the shocks out.

I would say have it as soft as it can be without fully bottoming out on compression and heavier on the rebound side.

I have suggested air bumps to him. This car has 12" of wheel travel in the front and 14" in the rear, we'll be able to maintain that. Luckily, it doesn't weigh as much as an Ultra4 or a Class 1.

I know of a rally guy who builds and revalves suspension for a bunch of rally junk out in washington who loves to spend hours on the phone talking, if youd like his number i can give it to you or search jvab imports and his cell is on the front page of his site. Id say a rally minded suspension is exactly what lifted miata owners are looking for, cause ive been in enough 4x4 offroad vehicles to know thats NOT what you want unless its some sand dune type thing

It's gonna be a little trial and error, but for high speed off-road stuff, you ideally want enough compression to keep it from blowing through travel too fast, but not enough that the suspension isn't responsive to small bumps. Bumpstops matter a lot too.

For rebound, it needs to be enough to keep it from being bouncy, but not so much that the suspension packs down over repeated bumps or that a tire won't follow a dip in the road.

I'd try the more balanced setup first and tweak from there as needed. It's unfortunately tough to get it perfect on the first shot, especially with a platform where there isn't tons of prior experience with that usage style.

In reply to rslifkin:

So it seems more about increasing the low-speed damping for both bump & rebound, correct?

petegossett wrote: In reply to rslifkin: So it seems more about increasing the low-speed damping for both bump & rebound, correct?

Too much low speed bump is bad, as it makes the tires squish before the suspension does (and it feels like your suspension is made of bricks on small bumps). It's the high speed bump that keeps you from slamming it to the stops too fast on the bigger hits.

I would err on the side of less compression damping. My shocks when revalved apparently got more compression damping and are very harsh on sharp high speed bumps which unsettles the car. It was better when the shocks were blown (aside from what happened after compression).

In reply to chiodos:

He'll also tell you to sell all the miatas and also tell you to specialize in Merkurs and rwd volvos and saabs or else your business will fail.

In reply to captdownshift:

ah ha! Glad someone else here has talked to john. Hes a wealth of knowledge but he does have his quirks. I can usually just get a bunch of uh huhs and yeahs out while he talks so be sure to ask all your questions first

In reply to chiodos:

It took me a while to warm up to him, but he's most definitely a wealth of knowledge and is right about 99% of what he speaks and offers amazing perspective that most don't want to hear or acknowledge. I'd love to hear his opinion on the offroad exocet.

Keith Tanner wrote: I have suggested air bumps to him. This car has 12" of wheel travel in the front and 14" in the rear, we'll be able to maintain that. Luckily, it doesn't weigh as much as an Ultra4 or a Class 1.

12-14" of travel? That is seriously impressive out of a Miata. How much wider are the control arms?

Fupdiggity wrote:

Keith Tanner wrote: I have suggested air bumps to him. This car has 12" of wheel travel in the front and 14" in the rear, we'll be able to maintain that. Luckily, it doesn't weigh as much as an Ultra4 or a Class 1.

12-14" of travel? That is seriously impressive out of a Miata. How much wider are the control arms?

There will be a full feature on the car in the next issue of Grassroots Motorsports.

I can't believe that I forgot to mention reaching out to Tim O'Neil last night. They're the US distributor for 50mm bilsteins and use then as the basis for all sorts of one off rally spec coil overs. Corner weight the car and call him with the info and he should be able to provide insight on dampening, rebound and spring rates.