AD70

"I'm saying "stiffer springs need more bump damping"
No, you dont need more bump , maybe a softer anti roll bar , but you sure need more rebound.

rbluemx6

iTrader: (2)

Just curious as to why most would rather revalve an NA HD to match NB specs vs as you put it, use more spring to keep rebound in check? Seems like it's more money spent and pointless too just to use the stock springs.

wannafbody

iTrader: (1)

And I've read claims that twin tubes can react faster to smaller road inmperfections than a monotube. Anyone can make any claim about any product. It's a lot harder to separate fact from hype.

hustler

iTrader: (6)

Bernie,
I'm mentally challenged from huffing agent orange while in the bush. Can you tell me the difference between these two comparing the middle setting on both?


Yes, it's true, I can't read a shock-dyno. It's obvious the 949 has more low speed compression damping, more high-rebound damping, and less low-speed, but what is more desirable and what are people ultimately looking for on a shock dyno to say "this is a good damper" or "I'm afraid, hold me!"?

wannafbody

iTrader: (1)

Looks to me as if the Afco has more compression. The rebound comes up faster on the Afco's as well. Based on the differences between monotube and twin tube construction it's possible that both might feel pretty similar. IMO, to know for sure, real world, back to back testing would be needed.

hustler

iTrader: (6)

You're right...again let me emphasize my ignorance, which is extreme.

JasonC SBB

My reasoning was in the scenario I described in one of my first posts. In that post I was talking about low speed damping.
https://www.miataturbo.net/showpost....8&postcount=60

True if talking about high speed damping, not if talking about low speed damping. Hitting the bump you describe exercises high speed damping.

JasonC SBB

That may be because Afcos were developed for bumpier roads (Keith was tuning the Targa miata) than the Xida. Thus a greater knee point in the bump damping, because the larger bumps on real world roads (as opposed to track and autox), "excites" the springs more - see my first post with the scenario of the ground dropping away.

JasonC SBB

What does "react faster" mean - less stiction during small movements (probably true for twintubes), or less deadband during small movements (true for monotubes)? Either one can be interpreted as "react faster".

JasonC SBB

Not enough info. Is the objective to get the truck to pass some kind of ground clearance test at tech, then lower itself from aero forces at speed? Was it a non adjustable shock? Was it a kludge and there was no time to change out the shock? Note that NASCAR ovals are way smoother than normal roads.

I'm just calling baloney to the myth "bump damping is for unsprung weight" - bump and rebound both play a role in both sprung and unsprung weight control. The system is symmetric in bump and rebound; the only assymetry is when considering (a) tire catches air and (b) bumpstops are contacted.

wannafbody

iTrader: (1)

OK, here's my real world experience. I recently replaced a set of rear Illuminas with FM 233# springs for the "dreaded' NA HD's paired with 300 pound springs. The HD's don't feel noticably worse dropping into potholes than the Illuminas with higher compression. I'm kind of shocked that the HD's feel as good as they do.

I know a multi national AX champion who took Koni DA's off his car and won on Koni SA's because in his opinion compression adjustment is not needed.

JasonC SBB

A pothole exercises high speed, not low speed damping.

As for #2, who knows. There could be other factors. Are Koni DA's twin or monotube?
I know of another AX champ whose car improved with increased low speed bump damping in the rear - it helped trail braking turn-in.
In my car, the increased rear bump low and mid speed bump damping noticeably improved traction on bumpy back roads.

Bernie S.

No, that was what we were doing to get the spoiler IN the air. This also helped when the truck was in yaw. It opened the bed up to act as a wing. Stiff spring, not compression.

I wouldn't say that we were in a pinch, we started it about 3 races into the season. Ended up winning the championship. (2004, if you want to check stats)

And yes, the shock was adjustable. We ran a rebound adjustable jet.

You comment on the oval tracks, false. If half of them were I40, they would be repaved. Ever watch a Bristol race before the repave? Ever seen the tunnel turn "jump" in Texas? Not to count all of the rough tracks in the NE I have experience with working with Bush North (before it was Bush East).

Thompson, Waterford..... anyone in those areas want to chime in? Maybe even Salem, IN.

What I said was there is a proper tune for the compression. Not that there is a cookie cutter one for every where. You have to take into account the velocity along with the unsprung weight. If a Miata is running on a smooth road, compression needs to be less than if he was running on a rough road. Not because the unsprung weight changed, but the velocity at which it is moving has. But changing it just becuase you changed a spring, that is wrong.

Bernie S.

A pothole would be rebound. The jolt the suspension sees is not from the hole, but from the tire dropping down and hitting the back side of the hole. Do you want to tune for this, or the other 99.999% of your driving.

Bernie S.

Shocks are all about timing. If you are transferring weight too fast to the front, rebound in the rear will slow the transfer. If you are transferring too fast to the rear, rebound in the front.

The only time you would need to do anything different is if you are limited by rules, or set-up.

Example:
Let's say the rules set a max rebound number and you have maxed that limit and still need to slow transfer to the front, then yes as a "band-aid" you would use low speed compression in the front.


But we are talking about a proper suspension, and trying to get people to understand that before we hit on manipulation.

Let's go back to your thought of increasing compression because we went up on spring rate. What is your logic behind that? Sounds like a double whammy to me. Like you are trying two things at once to fix a problem. Now, if you couldn't change the spring, or didn't want to, then I guess you may try the compression. That doesn't make it the right thing to do.

If you are trying to make the car feel quicker, such as a slalom course, try the sway bar.

This isn't a thread about how we can change one thing instead of another. This is a thread about shocks, the proper way to tune them, and the function of each part form real world experience. Experience that includes 100's of customers, 1000's of wins, and multiple championships.

Bernie S.

To me, it looks like the first set has more low speed. It appears they overbuilt the shock with preload, along with a small bleed. This will give you a wider range of adjustment because each adjustment is a percentage of the initial valving. This would be more of a general use shock, than the proper tuned Xida.

What people are looking for (or should be looking for) on a graph is totally up to what there intentions are, along with set-up.

wannafbody

iTrader: (1)

The AFCO was designed for pounding down backroads. The Xida was designed for pounding around a racetrack.

Bernie, do you feel that NA Bilsteins need more compression?

JasonC SBB

A pothole exercises both. The wheel goes down first - a lot of high speed rebound slows it down, but also sucks the car's body down. The wheel goes back up - a lot of high speed bump will push the car's body up. Because there's typically more high speed rebound than bump, once the wheel is past the pothole, the body has a downward vertical velocity, and more low-speed bump damping would reduce the downward overshoot, and thus the distance the body travels downward, before it bounces back up again. During the upward bounce, low speed rebound plays a role and reduces overshoot past the body's normal rest point.

If you hit a sharp bump instead of a pothole, the same things happen with bump and rebound reversed. See what I wrote above about symmetry, unless the wheel catches air or the bumpstops are contacted.

In both cases of a pothole or bump or other sharp ground "input" to the system, you want the dampers to offer no resistance. You need the dampers to resist the oscillations and body motions from the spring. These are opposite requirements. This is the logic behind the "skyhook" damping algorithms of Delphi's MR (magneto-rheologic aka "magnetic ride" aka "magnaride") systems. The Audi R8 has it, and the Ferrari 599, and now it's an option on some Caddies and 'Vettes.

So a non active damper will be too hard while the wheels are moving rapidly due to road imperfections, and may be too soft for body motions. This is the logic of digressive valving, because very rapid shaft motions from large road imperfections exercise high speed valving. Because one wants to err on the side of imparting too much downward velocity on the body (which bottoms the suspension) instead of imparting too much upward velocity (and the car may catch air), shocks are valved for softer high speed bump than high speed rebound. The exception may be off-road applications such as rally or Baja cars.

But this is far from "bump is for unsprung weight and rebound is for sprung weight".

JasonC SBB

You are talking about low speed rebound vs bump tuning front or rear in order to tune the transient handling response, and I don't disagree with the concepts.

The concept I disagree with is "bump damping is for unsprung weight, rebound damping is for sprung weight".

Bernie S.

A lot of low speed rebound keeps it from dropping out, not high speed. Solves the rest, so no need for further detail.

If you want to suck a car down you would use low speed, not high speed. You would work with offsetting the "0" point on the graph. Every time the shock moves, it has to pass through 0, so low speed is the more critical. If you can do your job right with low speed, the shock doesn't need a lot of high speed rebound. It will never see it.

I don't know what you are trying to do here, but you are wrong. If you want to keep confirming that, keep posting.