F1Fan

Hi Blair,

The Roush front anti-roll bar is a hollow bar and as you correctly posted the rear is a solid bar.

The Roush guy you talked to probably did not know what the effective spring rate is for their springs because they are not usually given this sort of info and the fact that progressive spring designs are hader to characterize than a linear spring. Because of the dynamic spring rate it is pretty hard to arrive at a meaningful number for most folks. Having said that you can figure out the so called effective rate if you measure the compressed spring height at static ride height and and then put them on a load cell and measure the load at that height. But this can be deceiving as the rate will rise sharply once you get past the heel of the curve. You need to measure the full range of the spring and consider the overall curve within the length range the spring operates in. This information is much more useful and can give you much more insight into the springs traits.

Most progressive springs are basically lightswitches with a softer initial rate that is just enough to hold the car up off the next part of the spring rate curve. It is tricky to get a progressive spring to work just right unless you have tight control over the weight of the car they are going into. Too light and the car takes too long to get into the heel of the spring curve. By comparison if the car is just a little bit too heavy the spring is effectively always into the stiff part of the spring curve and behaves very differently when compared to a progressive design where the car is just on the edge of the heel of the rate curve.

The Roush springs might be as you say but if the front and rear springs were both raised only 35% the fronts would be 185lb. and the rears 190lb. which would be the softest sport springs I've ever heard of on an S197GT chassis not to mention rates that are inverted from the norm. Ford has designed the S197 to safely push instead of rotate when the car is working the tires hard.

Most of the major so called sport springs are in the range of about 200-225lb. in front and about 165-185lb. on the rear axle. I've measured and tested many of the popular springs on the market for the S197 chassis and seriously doubt the Roush springs are that soft based on how they feel on in a car and given the basic understeering nature the Roush suspension has.

You have been reading handling generalizations that apply to cars with fully independant front and rear control arm suspension. Go back and read the descriptions of the cars they are dealing with. In any case they are GENERALIZATIONS and obviously cannot and do not apply for all chassis and suspension designs.

Here is a key bit of info for you, the S197 chassis has a strut front suspension and a stick rear axle. The trick is that most conventional strut suspensions have very limited camber gain as the suspension is compressed. What this means is that the camber angle stays pretty much the same throughout the suspension's range of motion. A control arm suspension with unequal upper and lower length arms can be designed to have increasing camber as the suspension compresses. So what happens when your S197 chassis rolls is the inital static negative camber you dialed in gets used up, the tire goes positive camber and there goes your ideal contact patch. This is the single biggest weakness of the strut type suspension.

So now that you know about struts and unequal lenght control/A-arm suspension can you see the reason your car pushed worse with the smaller stock anti-roll bar was not for the reasons you thought? What happened with the smaller front bar is that your car was rolling more which causes your tire contact patches to shrink due to camber loss. The larger front bar helped reduce roll and helped to keep the front tires flatter which gives you more tire contact patch and more grip and less push. Of course you could crank in more negative camber but tire wear goes to hell and this gets expensive very quickly.

You should probably go back to the 35mm Roush front bar and relocate your front control arms with a Steeda kit. Or if you have 18" wheels install a Steeda X5 balljoint kit and inconjunction with the Roush 35mm bar get a flatter car on the cheap. These puppies raise your chassis roll center and reduce your chassis roll without increasing roll bar rates or spring rates using suspensoin geometry to your advantage.

Does this help?

Cheers!

Sleeper_08

I am curious on your thoughts on how the Porsche Boxster/Cayman/911 series, which all have strut front suspensions, but are known for their handling ability, overcome this inherent weakness?

Blair

Hi F1fan:

The Roush front bar is definitely solid. I confirmed this on the Roush webpage and the thing weights at least 2x as much as the stock one. I did put the Roush front back on and it did reduce the turn in understeer I was experiencing. Definitely had me scratching my head for a while, but the increased tire rollover makes sense.

Regarding the Steeda parts, I have been considering getting ball joints, but they have been pretty low on my to do list. If i remember correctly, they are used to restore the front control arms to parallel to the ground after lowering to coorect geometry and raise the front roll center if lowered too much. My car is only about 1.0" lower in front, it doesn't seem that this minimal lowering will lower the front roll center far enough to warrant adjustment. What do you think? Also, if I get the ball joints to restore the geometry of the front control arms. will this have any effect on reducing front end dive during braking?

Thanks

157dB

F1Fan, what about addressing the bump
steer issue with lowering the S197s front
end with springs instead of dropped spindles?

If I lower her I am going all out with the dropped
spindles and do it the ?right way?

JOHNNY

Blair, Fran has 20 inch roush wheels on his 427r and thing handels like it's on rails, I may have of set of camber plate I will check Sunday if I do your more than welcome to them? I also have a set of h@r springs if you want to try them out their new?

loots06

I will be upgrading my suspension very soon and was thinking about getting front and rear sway bars. I'm thinking about getting the eibach front and rear sway bars to match the prokt springs. I do have 20" wheels and the front end does seem to be a little loose in general. any recommendations would be great appreciated.

Thanks.

Norm Peterson

Keep in mind that the roll center for a strut suspension drops much faster than its ride height does. Without any numbers to work with, if you figure that the change in roll center height is about double the ride height change you won't be much off. Just for information, the rear RCH drops by only half of rear lowering assuming that you are still running a PHB.

Whether you'd notice a 2" drop in front RCH is partly a function of how sensitive you might be to this sort of thing - and on what ride height mods you've done to the rear suspension. Whether you might consider this condition something that needs correction depends somewhat on what you're comfortable with as you go from straight ahead through "turn-in" to steady-state cornering (this is not in any way a criticism; different people simply have different preferences in this).


Norm

timothyrw

money!

the bmw 1 and 3 series use struts as well.

check out these suspension walk-arounds:

135i
http://blogs.edmunds.com/roadtests/2...alkaround.html

m3
http://blogs.edmunds.com/roadtests/2...alkaround.html

"Econoboxes and budget-minded front-drive cars can't afford what it takes to maximize a strut layout. They usually have one-piece lower A- or L-arms, a relatively large positive scrub radius*, a propensity for torque steer and steering kickback, and lackluster steering feel.

*Scrub radius = the distance between the center of the tire's contact patch and the imaginary point where the steering pivot axis meets the road.

But the 135i has zero torque steer because it's rear-drive. And the high price they charge for BMWs means they can invest more to make the strut work better in the steering department.

You'll notice that there is no one-piece lower arm in sight. Instead, there are two aluminum lower links (yellow and blue) and two lower ball joints. When steering (green), you get an odd monkey-motion at the ball joints because steering pivot axis moves outboard to the imaginary point where the two lower links would intersect if they were extended out. This arrangement can result in a zero (or even negative) scrub radius if the engineer so desires.

All it takes is money."

F1Fan

Hi Blair,

I've never removed or installed a Roush anti-roll bar but I have seen them up close and personal while removing the Roush struts and installing D-Specs and Koni Sport struts and reaar dampers. IIRC Roush front anti-roll bars are hollow, look at the ends and you can see from the way they are finished the bars ends are formed from the bar material. The Roush front bars are not pounded flat like solid bars are made they are smoothly formed from the tube material.

As far as the Steeda X5 balljoints go it is easy to see if you need them. Put your car on level ground and look under the car. If your front lower control arm's inside pivot point is lower than your outside pivot point you will very likely benefit from the X5 ball joints. How much depends on your chassis setup and handling tastes. Your front end will not roll nearly as much with the X5 balljoints installed and your front-end grip will very likely go up.

On an S197 chassis to reduce brake dive you must increase spring rate. You could change geometry but you won't like what it does the your ride and handling much. Unfortunately the only way to increase your spring rates freely is to install coilovers which are not inexpensive and create a whole host of new things to play with to get your suspension setup the way you like it to work. A coilover suspension is more work and requires more effort to make right but they do work very well.

HTH!

F1Fan

Hi Sleeper_08,

The way Porsche's front strut suspensions work is quite a bit more sophisticated (more expensive) than the traditional and much simpler (cheaper) McPherson strut used on the S197 chassis. These Porsches use a complex geometry which is designed to dynamically enhance steering and handling response depending on what the chassis doing at the time. These ideas came from the now famous Porsche rear suspension and are now applied to the front strut design geometry. You should also know that these Porsche front suspensions are much more limited in wheel travel than the S197 Mustang chassis for exactly the same reasons I mentioned. Struts still have limitations no matter how fancy you get and limiting total suspension travel is still the best compromise to control the strut suspension's limits.

Combine the fact that the S197 is a front engine car with a front biased static weight balance is pretty much 180 degrees from the Porsche 911 chassis and almost 180 degress from the Boxster/Cayman chassis. Porsches are much easier on their front tires and the steering is always talking to you. Because of this people like the way Porsches feel at the steering wheel, I know I loved mine.

But the real reason the current Porsches handle so well is actually all at the rear of the car and their very sophisticated rear suspension concepts first seen in the 928 production cars. This is pretty ironic because Porsche is known largely for building legendary rear-engine and mid-engined cars. So waht happened is that Porsche after many years of struggling with the stong tendancy of the early conventional suspended chassis to oversteer when pushed to their limits found a way to control the behavior of the car's handling.

What Porsche discovered was that by controling the deflection of a set of specially made bushings they could control the way the rear suspension worked under different situations and tame the 911's legendary oversteer and make these care much better handling. The current generation Porsches all take advantage of this technology.

HTH!