Suspension Voodoo

[John Herman]

I'll try and give you a little more concrete info to help you "hack" the suspension. I raced a very nose heavy, strut FWD car. Lower the front until the lower control arms are level. Ideally you want as much travel as you can get, so after you lower it, look at how much space is between the top of the strut and the bottom of the strut mount. This will let you know how bad the situation is, and whether you need shorter struts. Lower the rear so the car is about level. Check to make sure your rear suspension also has some travel. The limiting factor on my car (not the same as yours) is the travel in the rear. This is a FWD car, so you need to pay attention/focus on the front end esspecially. Spring rate, I'd start with spring rates equal to the corner weight. So if you have 600 pounds on each front corner on average, use a 600 lb/in spring. Disconnect one of the sway bar end links, but keep it there to experiment with it easily. I raced with a front bar for many years, but eventually tuned the car to eliminate it. The first few times I tried this, I was actually slower! For the rear (unfortunately I don't know your suspension design), but I'd shoot for a wheel rate (not the same as spring rate) 1 to 2 times greater than the front. Use a BIG rear bar. Depending on bar diameter availability, this can be balanced with spring rate choices. Adjust the toe on the front to be 1/8" out. Adjust the rear to be straight ahead(that's where mine has always been). Yes, some people will toe the rear out to help the turn-in, but this ultimately makes the car a bit unstable, and at your point, there is no reason to make the car harder to drive. Put about -2 deg of negative camber on everything. Adjust tire pressures using a tire pyrometer/read the tire wear. Don't set it based on what everyone "thinks" is right. Get the best double adjustable struts/shocks you can afford which will work with these spring rates. You will use the struts/shock adjustments to fine tune the turn-in and other transcient manuvers. Use the springs/bars to tune the steady-state handling. Eliminate all the rubber parts you can, as things will easily deflect with the loads you are putting on them, and the shock/strut adjustments won't do much if rubber parts are flexing away. A cheap way to check suspension travel is to put a zip tie around the shaft of the strut and drive it hard. See how far the zip tie was pushed up the shaft. You DO NOT want the suspension to bottom out in corners. I think this should get you close, with a good steady platform from where you can start tuning things. To be REALLY fast, it will be about all the little tweeks that will be needed as you learn to drive and more importantly "feel" what the car is telling you. It will take time and don't be afraid of slowing down while you experiment. Note my comment above about front bar removal. Good luck.

[wepsbee]

I'll try and give you a little more concrete info to help you "hack" the suspension. I raced a very nose heavy, strut FWD car. Lower the front until the lower control arms are level. Ideally you want as much travel as you can get, so after you lower it, look at how much space is between the top of the strut and the bottom of the strut mount. This will let you know how bad the situation is, and whether you need shorter struts. Lower the rear so the car is about level. Check to make sure your rear suspension also has some travel. The limiting factor on my car (not the same as yours) is the travel in the rear. This is a FWD car, so you need to pay attention/focus on the front end esspecially. Spring rate, I'd start with spring rates equal to the corner weight. So if you have 600 pounds on each front corner on average, use a 600 lb/in spring. Disconnect one of the sway bar end links, but keep it there to experiment with it easily. I raced with a front bar for many years, but eventually tuned the car to eliminate it. The first few times I tried this, I was actually slower! For the rear (unfortunately I don't know your suspension design), but I'd shoot for a wheel rate (not the same as spring rate) 1 to 2 times greater than the front. Use a BIG rear bar. Depending on bar diameter availability, this can be balanced with spring rate choices. Adjust the toe on the front to be 1/8" out. Adjust the rear to be straight ahead(that's where mine has always been). Yes, some people will toe the rear out to help the turn-in, but this ultimately makes the car a bit unstable, and at your point, there is no reason to make the car harder to drive. Put about -2 deg of negative camber on everything. Adjust tire pressures using a tire pyrometer/read the tire wear. Don't set it based on what everyone "thinks" is right. Get the best double adjustable struts/shocks you can afford which will work with these spring rates. You will use the struts/shock adjustments to fine tune the turn-in and other transcient manuvers. Use the springs/bars to tune the steady-state handling. Eliminate all the rubber parts you can, as things will easily deflect with the loads you are putting on them, and the shock/strut adjustments won't do much if rubber parts are flexing away. A cheap way to check suspension travel is to put a zip tie around the shaft of the strut and drive it hard. See how far the zip tie was pushed up the shaft. You DO NOT want the suspension to bottom out in corners. I think this should get you close, with a good steady platform from where you can start tuning things. To be REALLY fast, it will be about all the little tweeks that will be needed as you learn to drive and more importantly "feel" what the car is telling you. It will take time and don't be afraid of slowing down while you experiment. Note my comment above about front bar removal. Good luck.

Great info, thanks, learning about the car and how it really works is half the fun

[Greg Amy]

Sorry for the quote/response format. I hate it, too, but it's the easiest to attack.

"any suspension can be made to work well once you stop it from moving." Most appropriate as relates to struts...

A damper only works when it's moving. If you are sprung as stiff as a go-kart then dampers really don't matter that much.

Not necessarily true. If you disagree, consider the ramifications of using 1100-in/lb springs and no dampers...unless the suspension is truly solid, there is movement that must be controlled via dampers.

..first, a strut car can be make as fast as an "a" arm car.

Only if you can move the pickup points of the suspension components. In Improved Touring we cannot do that. Ergo, by the design of a street-geometry MacStrut car, it will never be able to be as fast as a comparable street-geometry a-arm car.

Second, front drive cars like a lot more spring than a rear wheel drive...something esoteric about keeping the inside front wheel planted.

Well, no. It's something more esoteric about most of them using MacStruts and that that implies.

Third, shocks, shocks, shocks...talk with Lee at Koni...

Si, si, si!

I...purchased a set of 8600 series Double adjustable shocks put together by Koni USA.

Off-the-shelf valving? Those are good for ~500-700 in-lb springs; after that you'll need to revalve them for more rebound.

I have 500 6" Eibachs in the front and 400 7" Eibachs in the back.

Start by swapping the spring rates front-to-rear, and start looking for springs in 50-lb increments up to 700.

The set up will most absolutely be different on Hoosiers than the others.

You're tire-limited, now. You'll never be as fast as the others until you buy Hoosier or comparable.

Greg, at that point in time I was more than willing to pull the trigger on the "better" suspension package.

I know that, Dave, I'm just pulling your nuts.

And, your experience is not relevant, as you followed Greg's Step #1...

Someone else noted (was it in this thread?) about how rates and all that are irrelevant once a tire is in the air. It may work that way in computer simulations and in the book of theory, but in the Book of Reality it most decisively remains important. There are many other factors to consider, such as swaybars (which impart the lifted wheel's suspension forces to the other side) chassis flex (which imparts forces through suspension components), and wheel stiffness.

And in the end, never settle for "what the experts say" because your situation is always different. I can't count the number of times we've made things work that "the experts" say are wrong ("Kakashi, dude" is one of our favorite team sayings... http://www.kakashiracing.com/team.html)

Lots to consider, lots to test.

GA