bnight said:

Regarding shock settings they are timing devices Rebound control how fast the car transfer weight front-to-back and Compression how the car recover from hitting curbs and potholes (overall you want compression to be as soft as possible) while Rebound especially on Mustang is a bit more complicated: Stiffening the front (More rebound) makes it more responsive but it also leads to understeer in mid corner and corner exit since the rear been Softer has more grip.

Overall when you are setting your suspension you always have to start with the front: Start from full soft Rebound or some neutral settings like middle of the adjustment range go on track and notice how the car changes add 2 clicks or so to front rebound until the point the car starts to understeer on Entry (it will be doing it when full soft as well so hard to judge) then ones you start skipping under braking and car understeer into the entry dial 2 clicks back. Now you can focus on the rear ether same number of clicks or +-2 depending on what you like in a car (Understeer/Neutral/Oversteer) rule of thumb is that the car has to oversteer on entry and to be Neutral on corner exit so you overall want to keep the rear 2 clicks or so Softer than the front (this will result in better corner exit).

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Not agruing here...discussing. I'm curious how you run your dampers.

You say, "...you want the compression to be as soft as possible." While I will agree that is 'a' way to run the damping, it's not the only way. I guess I would add to your statement with, "..., but as stiff as necessary."

From a pure mathematical view of settling a mass/spring/damper system, it doesn't really care whether the mass is moving one way or the other. It's about how much energy is being dissipated. As we start to tie the car together end-to-end or side-to-side, now the compression/rebound difference gains importance.

Increasing compression damping is necessary any time you have a (generally big) compressive input where the chassis is moving relative to the road. You want to eliminate the damping on the bumps where the chassis is stay relatively level and the wheel is moving relative to the chassis.

You want enough front compression force to support the nose of the car without excessive head-bobbing while applying the brakes hard or in a combination of braking/steering (track dependent). If you have to slowly roll into the brake pedal to keep the nose from a big pitch motion, then you need to increase front (especially low-speed) compression forces. You'll reach a point of diminishing returns where increasing damping doesn't help you apply the brake at a faster rate. Somewhere on that 'brake application rate' vs. 'compression forces' curve, you'll find a minimum necessary compression setting. It'll be *at least* close to the 'diminishing returns' setting. Cars with significant front aero may run very high low-speed compression forces (>1000N @ 25mm/sec or 225# @ 1 in/sec). In many ways, that's why you spend the money on the dampers, so they do things like this. You can do whatever you want to the tuning of a street car damper, it will never be able to produce these types of forces. They stop damping and turn into oil-filled springs.

The rear compression is dictated by the throttle-induced squat in the car. When you come out of traction corners and go to throttle, you want the chassis to take this input as a single motion with as little rebound as possible. If the rear end of the car doesn't have enough damping, it can lead to a 'pumping' sensation on corner exit that puts the rear into a load/unload situation that hurts traction. So, there has to be enough compression damping in the rear to absorb the chassis motion due to throttle inputs in lower gears without a big overshoots.

It's common for both ends of the car to have some sort of steep, initial segment on the compression force curve to accomdate these driver input loads. At something like 50-100 mm/sec (2-4 in/sec) the compression force curve slope will have a reduction of slope (to make a digressive curve) and then the forces will continue linearly on for the remainder of the working shaft velocity range. It's very common for the front to have significantly more low-speed compression damping than the rear, not because of the weight, but because of the impulse pitch load due to braking combined with aerodynamic (as well as mechanical) front ride height sensitivity.

Junkyard Dog said:

Tires and track time with instruction are going to solve the issue of his car squirming around to the right under hard braking following a high speed straight? This is just an issue that can be instructed away?

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No, I dont' think it was that particular thing. You have to figure something like that out even for the street. It was more about which coil-overs to buy and those fun little bunny-holes.

Akel said:

This is my first time tuning shocks, after some research online people said to do a 2:1 or 3:1 compression ratio for rebound and compression.

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Remember, though, the adjusters are working on the valving that's built into the shocks with the shim stack. Typically, that 2:1 - 3:1 damping ratio is built into the baseline valving and you use the adjusters to tweak from there. That's something a shock dyno chart would show you.

Akel said:

The instability under braking comes from threshold braking, it is initially fine but when the car begins to slow down more that's when it starts to wiggle

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Okay, if it's relatively stable under straight-line braking and then gets squirrely at turn-in, you could try increasing front rebound and/or softening rear compression. In that transition mode, the inside front is extending and the outside rear is compressing; the other 2 corners aren't moving (in a prefect world). To increase rear-end stability, we want to increase the weight on the outside front / inside rear diagonal and reduce weight on the inside front / outside rear diagonal.

Akel said:

Went back home and redid the settings, everything matched and one side was still softer so i put one click of Compression down on one side and it seemed to even out more, so my suspicion is that the shock are not behaving the same and are off a tad.

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Low-volume shocks may have small differences between them, like one shim washer is thinner by half a human hair. Because of this, one shock may match another when 1-3 clicks different. The adjusters are used to match shocks to each other as much as to tune handling. Again, that's what shock dynos are for.

@TeeLew gave you some high-quality shock prices. At that end of the game, you're not paying for the adjustability alone, you're paying for the consistency and repeatability in adjustment. You may be paying for using a completely different machining process to hold a much tighter tolerance. And you're paying not only for the parts in the shocks you receive, but also the cost of the parts rejected in the QC process. The tighter the QC, the more parts rejected.

Big picture, I still think you'll be happier going back to your Ford Racing shocks and BMR springs, rather than trying to dial in the 2-ways.

@Akel I responded on your build thread, but those rear brake pad pictures you posted suggest a problem with one of your rear calipers. Which of course would cause all sorts of instability.

stevbd said:

@Akel I responded on your build thread, but those rear brake pad pictures you posted suggest a problem with one of your rear calipers. Which of course would cause all sorts of instability.

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Hmmm, it would make sense. And I actually might have 2 different calipers back there. One of my boots tore up a few years ago and I replaced one side. Now one side has a caliper with a black booth and the other side has an orange booth.
The driver side has a black booth(this one had one pad with more material) and the Passenger side has the orange one, I saw it got a tare in a the booth again. But my mechanic said as long as it is not leaking we should be ok.

Dave_W said:

Big picture, I still think you'll be happier going back to your Ford Racing shocks and BMR springs, rather than trying to dial in the 2-ways.

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I agree 100% I might try and fix the brakes first and then swap them out. I don't want to change to much all at once and not be able to tell what helped and what didn't.

Junkyard Dog said:

Tires and track time with instruction are going to solve the issue of his car squirming around to the right under hard braking following a high speed straight? This is just an issue that can be instructed away?

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If you think you can gain confidence with a parts gun, have at it. You could possibly be the first!

"Don't ride upgrades.
Ride up grades."

Eddie Merckx

TMSBOSS said:

If you think you can gain confidence with a parts gun, have at it. You could possibly be the first!

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I think there is a problem in communication.

If he has bad rear brakes, then this is an issue that needs to be fixed with new parts.

If the rear brakes have an issue then that needs addressed before anything else.

But I think someone new to HPDE trying to dial in adjustable dampers is an uphill battle, especially when they are a type without a large user base to provide good guidance.

The FP dampers and BMR springs work very well and you already have them. I have them and get the opposite experience you do, I feel my car is extremely planted everywhere and inspires confidence. It holds its own against cars that cost a hell of alot more.

thelostotter said:

If the rear brakes have an issue then that needs addressed before anything else.

But I think someone new to HPDE trying to dial in adjustable dampers is an uphill battle, especially when they are a type without a large user base to provide good guidance.

The FP dampers and BMR springs work very well and you already have them. I have them and get the opposite experience you do, I feel my car is extremely planted everywhere and inspires confidence. It holds its own against cars that cost a hell of alot more.

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Exactly. Getting an instructor which can assist with adjustments is likely the best way to go. Seat of the pants over trying to understand an issue from a few posts.

TeeLew said:

Not agruing here...discussing. I'm curious how you run your dampers.

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For starters the Ohlins are Rebound only though it does add a bit of Compression when you add rebound it's not major enough to matter very much. So I played on track with almost the whole range of adjustment and what Rebound does is just controlling the weight transfer in the car (as you put it controlling brake dive / body roll etc.) When the car is soft the only way I can describe it is that it's taking time for the car to take a set in a corner for a long time I was running (17/19) rebound from full stiff (Ohlins are inverted) and the car was very soft so was taking a lot of time to take a set. For example my current street setting is (14/14). One time I give the car to a friend on Serres and he didn't liked how soft it was so we dialed 4 clicks of rebound all around (13/15) and despite the track getting hotter our lap times stayed the same while everyone else dropped 1 second or so. So I continue this trend of adding rebound and settled on (6/6) which is my current setting though I don't really like it the car picked up 2 more seconds at the same track from 1:29.9 all the way down to 1:27.9 but there are a few issues that I have with this settings. Namely corner exit understeer in slow corners (T5 on Serres), Corner Entry understeer in fast corners the S entry in Dracon, and Mid corner oversteer in fast corners (T13 Serres, Parabolica long left on Dracon). Regarding compression I think you just need enough to control the car over bumps (aka curbs) because most tracks are usually smooth (I know in States that's not exactly the case aka Sebring) but overall the Compression adjustment is just that how the car react over bumps. I personally think it will be easier for the author to dial just Rebound first instead of trying to dial compression as well as it's really tricky. While I agree that switching back to FP and BMR might be beneficial to a HPDE driver that it's just starting out I think the drop in spring rates will be annoying. Which is why I tried to direct him in the right way to dial the Rebound on his shocks on most China made shocks you can't go wrong with going full stiff as usually they lack the range of adjustment needed for meaningful changes with just a few clicks.