Adjusting Shocks

[CaptainSquirts]

So with the click settings, how do you tell if you have them set correctly with the click adjustments? Also would that settings be good at autocross or would you have to adjust it just for autocross and then back for regular Daily driving?

[Loren]

This question was asked in the Mirage project thread. I thought it warranted its own topic.

So, with adjustable shocks, whether you have "clicks" or just free adjustment (like a Koni), how do you adjust them? First of all, clicks just give you easy and repeatable reference points. If you're using a Koni with no clicks, you'd have to think in 1/4 turns or even 1/8 turns to have a reference. (and with a Koni Sport, you always adjust from full soft because they "officially" have 2 turns of adjustment, but will go beyond that... beyond 2 turns is "no mans land", not calibrated, not where you want to be)

Anyway...

In a perfect world, you have selected your spring rates based on some good math. (using available shock travel, bump stop choice, swaybar choice, weight and weight distribution, and intended use as variables) Your spring rates are "correct". From there, proper damping should be "just enough" to control the oscillation of the spring. Stiffer spring = stiffer dampers. You can set that by driving over a healthy bump... does the car bounce-bounce-recover, or bounce-bounce-bounce? What you WANT it to do is smoothly go over the bump and finish with one smoothly controlled bounce and recovery. No additional bouncing, and no harshness. Too little damping and the spring takes over and bounces. Too much damping and it's harsh and unsettled. Just right and it just feels "right". That's what shocks should do. Control the motion of the suspension and just make everything feel "right".

But, we don't live in a perfect world. So, you may find yourself using your adjustable shocks to tweak the performance of the car. I'm NOT an expert at this, as I've never had truly good shocks. If you have shocks with separately adjustable compression AND rebound damping, this can get pretty complicated. But, most shocks have a single adjustment that either adjusts rebound-only (like a Koni Sport), or adjusts both rebound and compression together (like a lot of others).

In general, you can think of your basic oversteer/understeer stiffen/soften either end of the car rules. Your spring rates are what they are, you've got the bars set where you want them, tire pressure and alignment are optimized. You're using the shocks to fine-tune the balance of the car. Is it oversteering? Particularly in transitions? Soften the rear shocks. Is the steering response not sharp enough in transitions? Stiffen the front shocks. Once you've set a baseline of "critical damping" (see paragraph above), you have to figure out how much of an adjustment on either end makes a difference in the behavior of the car. Every car is different. Every suspension is different. There are broad "rules" and concepts to understant. But, you just have to experiement to figure out what's going to work with your setup and your driving style.

That's my take, anyway. I'm sure others can chime in with their experiences.

[Loren]

Specific to the Mirage, which spurred this question:

With stock front suspension, stock rear springs, and fancy adjustable rear shocks, a really soft shock setting seemed logical. But, what I was overlooking is that anytime you're not hitting a bump EXACTLY the same with both rear wheels, the swaybar is in play. And I've added a really big rear swaybar. So, effectively (unless I'm going perfectly straight and hit a bump perfectly straight), I've added a lot of rear spring rate, and thus need more rear damping.

In addition to that, I'm in the weird situation where the suspension is designed with 8" of travel, and my shock only has 5" of travel. So, I set the shock up with 1" of rebound travel (it can extend one inch before it "tops out" and the wheel begins to lift) and 4" of compression travel. (I'd have gone for a little closer to center, maybe 2 up and 3 down, but the shock body won't go any longer than that! I cheated it to about 1.5", but that's it!) And when the shock reaches full extension, it makes a noticable "thunk". So... we're using shock damping a little bit to try to control that. Stiffer shock (assuming the adjustment does both compression and rebound... which I have no documentation of, and didn't think to test when the shock was not on the car... but, I'm pretty sure it does) setting will slow the movement of the shock on extension, and maybe eliminate that harsh "topping out" effect. I tried it, it seems to have worked.

BUT... I'm still 100% in "band-aid" mode. I'm just playing by stock class rules. I can't change the spring rates, but I CAN change the shocks and the rear swaybar. So, I'm working with what I have. It's nowhere near ideal, and I don't expect it to be. I'm just trying to come up with something that will work "well enough" to be fun to drive and not eat tires.

So, I've still got the front suspension to put together. And with added front roll control (the front struts are going to be WAY stiffer than stock, even adjusted to full soft), maybe that will affect how much damping I need in the rear, as well. I'll have to tweak around with both ends to find the happy place.

AND THEN... (to answer your sub-question)... If the "autocross handling" compromise shock settings are uncomfortable on the street, yes, I can dial them softer for street use, and reset them to their autocross settings at each event. I've found that if I need to do that, it's usually just making the front stiffer for autocross if it's a RWD car, or making the rear stiffer for autocross if it's FWD. But, I'm lazy... I'll always try to find a good "compromise" setting for at least one end of the car so that I don't have to do as much at the events. A fully OPTIMIZED setup would probably have both ends being adjusted for autocross/street... and even different settings for asphalt/concrete, or "smooth/rough", etc. I usually aim for the middle ground because I don't like messing with the car once I've got it set up.

[jmdoc66]

From experience, I agree with Lauren. I adjust the Koni single adjustable struts on the Shelby to 2 turns to run an autocross, and back down to 1turn to drive home. My car doesn't ride like a Lincoln, but I prefer a firmer ride on the decent roads of Florida. I blame the 35 aspect ratio tires for any roughness during the ride.
The rear konis stay at 1/4 turn depending on the grip of autox site.

Though the adjust-ability adds complexity, it does allow you to run your tires at their 'correct' pressure to get optimum performance.

I have learned to test, find the set up, start there and stay there. I only adjust the rear 1/8 either way depending on the temperature of the day and that has been minimized by paying attention to my tire pressure between runs. I'm lucky my car is very consistent, but the driver isn't.

[Tim_M]

Both on my Corvette (Koni) and the Subaru (Ohlins replacements), I run full soft on the street and full stiff during competition (road course/autocross).

The Subaru lean is significant...going up on the dampening I find it much more nimble and tire roll is less especially on the maxed out camber fronts.

I figure I'm getting 85% of the correct setup...my driving has much more to improve on-so my focus.

[Native]

I'll add in that, and this varies by car, of course, the faster you go, the looser you get. So, if your car is set to stick well on a slower, more technical course, you may find you need to adjust your settings if you end up on a course that is less technical and allows faster turn speeds. And vice-versa. Skid-pad testing can help here to give you an idea of what your car does. For example, I set my car to be fairly neutral on a 100' skidpad. But if I try to drive it on a 75' skidpad with the same shock settings, it understeers.

[mymomswagon]

on my car, I'm thinking it needs less understeer and I'm wondering if I should reduce it either via my rear konis set firm vs thicker sway. Is that a tradeoff to consider? If yes, I'm thinking of putting the emphasis on the sway bar in order to preserve daily ride quality and set the shocks at "critical". The konis have to come off to adjust so I'd prefer to set once. On the other hand does emphasizing shock firmness allow the rear to behave more independently than with a sway? Or provide any lift / dive benefit? Sorry if I'm murdering terminology here

[Loren]

on my car, I'm thinking it needs less understeer and I'm wondering if I should reduce it either via my rear konis set firm vs thicker sway. Is that a tradeoff to consider?

When you're "band-aiding" a FWD car's tendency to understeer, you do whatever you can. Adding rear roll stiffness, either by spring rate, bar rate, firmer damping, or higher tire pressure will all yield similar results. The damper adjustment won't add any spring rate, it will just slow the movement of the suspension... but, if you slow it enough, you get more weight transfer to the front (most obvious when you actually lift a rear tire... all of the weight that was on that corner is now transferred diagonally to the front, and shared between the front tires). All of the other things I mentioned will, one way or another, actually increase spring rate.

Spring rates and bars are generally the "correct" way to fix a handling bias problem. In stock, you can't do springs, so that leaves the rear swaybar. But, as I recently confirmed with the Mirage, adding "effective rear spring rate" with a big swaybar DOES require more damping to control it.

There's never a simple answer to a suspension question.

If yes, I'm thinking of putting the emphasis on the sway bar in order to preserve daily ride quality and set the shocks at "critical".

Makes sense. But, if you're adding a large percentage of your spring rate via the swaybar, then the "bump test" won't really work. You have to tune those rear shock adjustments by feeling how the rear suspension handles an aggressive transition. Not as easy to test, a little more subjective. Basically, run the shocks as soft as you can get away with. Stiffen them until things "feel right".

The konis have to come off to adjust so I'd prefer to set once.

That's a pain. Are they at least separate shocks, so you don't have to deal with the springs? On the Mirage, I can change the rear shocks without even jacking up the car. Two plastic covers, top nuts and lower eye bolts.

On the other hand does emphasizing shock firmness allow the rear to behave more independently than with a sway?

Yeah. If you kept the rear swaybar / twist beam situation as stock... you could just add stiffer shocks to aid with the weight transfer, and it WOULD retain its independence. (in as much as a twist beam is "independent"... but, the suckers DO twist!)

Or provide any lift / dive benefit? Sorry if I'm murdering terminology here

Yet another compromise to consider, eh? Yes, firmer REBOUND damping on the rear is going to resist rear lift under braking. Since Koni Sports do adjust rebound, that would be something you'd surely feel.

[mymomswagon]

thanks! yes shocks are separate from springs, a blessing. still a bit of a pain including removing wheel liners and a charcoal canister on one side. oh well wife's away, time to play with shocks this weekend.