Autocross/daily driver questions

[kz]

Changing springs without changing dampers is a sure way to completely mess the handling up. It is a terrible idea.

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[kz]

Given stock setup is underdamped - yes. Of course Ford Performance will sell springs (note it's UK - in US they don't sell it) - why wouldn't they ? 99 % of people installing lowering springs do not that to improve handling. They want "lowered" look.

 

[shogun32]

you don't want the Ford cut-down bumpstops (crap) nor the 'adjustable' blue ones from Steeda. Eibach, and cut them down with a butter knife. Ok, hobby knife.

 

[TeeLew]

If my understanding is not erroneous the default sag of the FA coilover results in 90mm of the stroke taken up (75%) at rest which is absolutely insane. Not only does this mean the gas pressure is vastly higher than the base 150psi it leaves a mere inch before hitting the bottom bumper. Since up front the MR is ~1 I can only absorb a 1" bump before I'm into the bumper. That is flagrantly wrong. By cranking in preload and moving the ride height my goal is to change that to 35% of stroke used at rest. We'll see if I can get things adjusted to achieve that.

Where are you getting your initial spring perch height numbers? Are you just running the perch to contact? Is that even a rational ride height with the piston that far down in the shock body? I would expect several (10-15) turns of preload to get to some nominal ride height measurement.

 

[shogun32]

It's coming straight from FA. Their instructions VERY clearly state (and I've confirmed), set no more than 1/4" spring preload. Total stroke is 107mm. I had this set built to be 117mm.

I fully intend to put as much preload into the system as I can to put the resting height of the piston as close to 1/3 distance. But something is going to have to give - probably droop.

 

[TeeLew]

How are they defining 'spring preload'? Are they talking about having the spring preloaded at static ride height (in which case you'd have zero droop + 1/4" of spring preload)?

In that scenario, the front ride would be a mile high.

 

[shogun32]

No no. Shock on table Proload collar just touching spring to keep from rattling. Then add 6mm.

At 8kg/mm spring equilibrium is achieved with considerably less travel used up than with 5k. Ditto 10k

They predicted their dimensions and setup based on stupid high front spring tates. They looked at me like I was nuts for using 5k.

And yet their valving isn't sufficient for 5k let alone 10 or more.

 

[TeeLew]

That's just bizarre. I didn't understand earlier and I understand less now.

 

[TeeLew]

Were you meant to run 1500#/in springs?

 

[BlackPlague]

Keep a sharp eye on if the coilovers in the rear are coil over shock body in the shock's location or in the factory locations inboard on the control arm. The actual wheel spring rate is very different depending on if they're at the stock control arm and subframe mount locations or relocated to the shock position. The factory shock mount location isn't the strongest mount, so fatigue is a concern when you also relocate the springs to mount there.

Most coilovers(Bilsteins, unmodified Ohlins) are not optimized for autocross (sorry), although they may work well for your driving style as delivered., with the Ohlins you'd want to buy those from someone who can set them up differently (valving and spring rates) than how they come by default. IDK anyone who does that for the Bilsteins, but they may be out there.

FWIW, at least a couple of good coilover-base setups use coilovers in the front and the DR rear springs with divorced shocks in the rear. The rear DR rates seem to be high enough for nearly all uses, but the front rates, at 350 for the DRs are not as high as some autocrossers and road course people want to go.

With the stock perches you can't really go any higher than the DR rates without needing dedicated helper springs to keep them seated, which dictates a coilover. The DR "dual rate" is already like having a helper spring built in.

Based on this, and some further conversation, it sounds like c/o are for someone who really knows what they want, and I'm not that guy (yet).

you don't want the Ford cut-down bumpstops (crap) nor the 'adjustable' blue ones from Steeda. Eibach, and cut them down with a butter knife. Ok, hobby knife.

I didn't know the bumpstops were that big of a deal... I thought it was just protection from bottoming out and damaging the shock... Am I missing something? Or am I on the right track, and it's just more important than I thought?

The actual wheel spring rate is very different depending on if they're at the stock control arm and subframe mount locations or relocated to the shock position.

The Ohlins and the Bilstein seem to be separate shock/spring mount rear locations, so I would assume the spring rates would be a direct comparison to any replacement rear spring. I get that changing the location on the control arm would change the leverage, and therefore the spring rates wouldn't necessarily correlate to the same effective spring rate. It seems counterproductive to move the spring mount out to the weaker shock mount just to have "true" coilovers in the back.

If I'm missing something here, please enlighten me

 

[shogun32]

I thought it was just protection from bottoming out and damaging the shock.

unfortunately car guys have decided to use them as part of the spring. I am of the opinion that they should only be used as a last ditch means of decellerating the wheel assembly before hitting mechanical limit. That view is in the distinct minority however.

 

[BlackPlague]

unfortunately car guys have decided to use them as part of the spring. I am of the opinion that they should only be used as a last ditch means of decellerating the wheel assembly before hitting mechanical limit. That view is in the distinct minority however.

Yeah this is how I see them. If your springs are traveling so far as to bottom out during normal (race included) driving, that seems excessive. Plus I would expect a bumpstop to effectively act as a drastic change in spring rate, upsetting the car. I could see them hitting the stop when there's a big pothole or something, really causing drastic, uncontrolled movement of the control arm, but yeah, last ditch damage prevention

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