Flaw in F5 front suspension.

[mr bruce]

The upper spindle bracket puts the upper ball joint boss "in front" of the lower ball joint boss, when looking at the spindle from the spindle pin side.(try to run a straight steel rod thu both bosses, you'll see what I mean) Do to this you have to dial in mucho caster which thows the bump steer into progressive mode when you turn the wheel,do to the steering arm being on such an angle .This may explain the twichy steering felt in some of these cars, could also contribute to qwik loss of controll some have been experiencing.A fast fix may be the Mustang 11 spindle, and dropping the inner pivot of the upper control arm to get the roll centre back where it should be.

[Satanpez]

I would imagine that someone put some thought into the design of that suspension. Could there be a reason they designed it like that?

Could there be a fix to the current design?

I've got a set of those spindle brackets sitting right here, as I was planning on using fox mustang spindles on my Seven project. I ass-u-me-d that the ball joints would be in parallel. *sigh*

-steve in nj-

[mikiec]

Don't know if this is a problem not sure. I figured it was designed this way. I have a F5 and have experienced no problems with this setup.

Can you please explain why this is a problem.

Mike

[Satanpez]

I would think if anything it's built in anti-dive? It seems it's built-in castor, which may not be wanted if it's purely for racing.

-steve in nj-

[Excaliber]

Ideally the upper and lower ball joints would be near zero in alignment up and down (top and lower) when first installed with ALL adjustment potential positions in the "middle" of their range of adjustment.

From there you can reposition the upper ball to "lead" the lower ball. Like the "castor wheels" on a chair. When you push the chair, the wheel kind of spins around to follow the leading edge of it's mounting point. This is positive castor. Thats what makes your steering wheel tend to "straighten out" by itself after you turn a corner. It's the "castor" effect of the upper and lower ball joint relationship.

Camber is the top of the tire leaning in toward the car, or away from the car, or "zero", straight up and down in relation to the side of the car.

Toe-in is where the front edge of the front tires (or rear in IRS) are either "pigeon toed" in, or out, or zero, straight ahead.

Again, with ALL possible postioning nuts, screws, shims and other "alignment" items in the "mid position" these THREE critical alignments (camber, castor and toe) would be near zero. Now you can adjust all three TOGETHER at the same time to "dial in" your alignnment.

Alignment is done with the car sitting on a level surface, normal ride height, wheels straight ahead and all that. As soon as you "hit the road" and take a corner, the car leans, one coil spring is compressed and the other is lifted. The suspension "moves" up and down. As it does the relationship between camber, castor and toe start to "change". This is called "bump steer".

In an ideal and perfect world the relationship of the THREE alignments will always stay in perfect relationship to each other as the wheel moves up or down on either side. In the "real" world and unless you have some "exoctic" suspension the relationship WILL change, you WILL have some bump steer.

Some cars have less, some more. Sounds like FFR may inherently have a condition where to much "bump steer" is a fundemental design flaw. The "three" can still be adjusted, but the MORE adjustment you have to do to overcome the basic design flaw, the worse you will make the "bump steer" issues!

Solution? JBL of course, zero bump steer!

Ernie

Edit: Unless your a "racer" who is really in "tune" with the handling of YOUR car, you would probably not notice a "bump steer" condition. But exiting a corner at high speed under great "load" with "bump steer" could mean the difference between a "crash" and "making it" through the turn!

[mr0077]

??? Are you sure you're not trying to put the left upper (or lower), or both arms on the right side and vice-versa? The upper ball joint should be behind the lower (with a line from upper to lower ball joints leaning back at the top) for proper caster, otherwise the suspension is unstable, somewhat like backing up on a regular car, let the wheel go and watch it go all theway to full lock in one direction or the other; it's trying to flip around to a stable condition, like Ernie's example of castor wheels on a chair. Tell us more...sumpin's not right.

[mr bruce]

Smitty, you're following me. The upper ball joint is in front of the lower. Exactly backwards of what is correct. Then to dial in enough caster, it puts the steering arm on a hellatious angle. The tie rods go thu all sorts of girations when you turn rite or left.I've looked at every suspension book I have and have never seen a spindle designed in this way.As far as anti dive, that is supposed to be built into the mounts of the upper control arm, the M11 has this at around 3 degrees(?) You could shim the upper mount in the front bolt hole to put in more anti dive. But all this is moot, untill sumbuddy can tell me why the ball joint adapter is assbackwards.Every spindle I looked at has the ball joints rotating around the same axis.

[Satanpez]

I'm an idiot, didn't have my coffee at all before my last post. Anti-dive is set with the angle the upper arm is angled at.

Mr. Bruce: Do you think the spindle mount could be cut/modified/rewelded to get geometry that's wanted? I'd like to use mustang spindles on my Seven project.

-steve in nj-

[Excaliber]

Putting the upper ball joint ahead of the rear would nullify or make worse the "anti dive" characteristics. That setup is just "all wrong" man.

Ernie

[mr bruce]

Steve, www.billmitchellsvd.com has an a-arm conversion for the fox cars that has the brackets in the correct position. I don't know if he will sell just the brackets. Some of the F5 guys are just using the M11 spindles.With all the brake kits avaliable for those spindles ,that might be the cheap and easy way to go.but you will have to adjust the upper mounts to take into account the M11's lower overall spindle height.

[Satanpez]

Thanks.

I was going to go with the Fox spindles as they're cheap and easy to find parts for them. It's for a Seven, so I'm interested in cheap and light. No need for 13 inch rotors in a 1300 lb car.

I haven't bolted my spindle adapters to spindles yet. It's one of those "Take some measurements, then design the rest of the system around it" type things. Planning on doing my own upper and lower arms.

Thanks for the link. I'm gonna ask if they'll sell the brackets individually and how much.

-steve in nj-

[Jim@FactoryFive]

The upper ball joint on our car does fall behind the lower, otherwise we would have negative caster. The direction that the bracket points is not critical, only the relationship between three points, the upper and lower ball joints and the tie rod outer end. If the two ball joints are in the correct orientaion, the only thing left to worry about is the tie rod end and it relationship with the rack. If the spindle is tilted back raising the tie rod and the rack was left in its original location you could have severe bump steer, however our chassis does not leave the rack in the stock location. With SN95 spindles the bump steer on our car is very close to zero, with older spindles there is some however not enough for most people to notice on a street car. Our race cars come with an adjustable set-up. Using different spindles may work, but the geometry should be checked first for bump steer, camber gain, and roll center height.

Jim Schenck

[Excaliber]

Roll center height. What is that excatly and how is it measured?

Near zero bump steer from using the "correct" parts and just bolting them in is very impressive engineering. Better than many of the regular manufactuers (GM, Ford, Mercedes, etc.) on the market can claim.

Ernie

[Jim@FactoryFive]

Roll center is the imaginary point about which the car rolls when cornering. It is found by sketching the upper and lower control arms and extending there length to the point where they intersect. Then from this point sketch a line back through the center of the tire at ground level. Where the two lines (from either side of the car) intersect is the roll center. (Not a great description but should be easy to find a sample sketch somewhere on the net)

Near zero bumpsteer in this case is not nearly as impressive as in a regular production car with probably two or three times the travel. (It also is not to hard to do with production pieces if their relative relations aren't fixed.)

Jim

[mr bruce]

still, with the F5 bracket, the steel rod test won't work. The ball joints aren't rotating on the same axis. The Mitchel pieces do.Another advantage of the M11 spindles would put the spindle deeper into the wheel, helping scrub radius with extreemly wide wheels(12")

[Excaliber]

Oh I see what you mean about production cars. Double the suspension travel and double the possible bump steer problems. Tall ride height equals more suspension travel and a softer ride, but in general suspension angles will be more difficult to maintain.

Solution: "Slam it", put that baby on the ground, LOL.

,,,now that roll center thing I will have to research some more. I'm guessing you want a low roll center but it may be difficult to achieve without major mods.

Ernie

[Jim@FactoryFive]

The great thing about ball joints is they are spherical bearings and the shaft direction does not affect the axis about which they pivot. I agree that having the shafts point toward each other is good practice as it allows for a wider range of motion, however as long as the ball joint is not the limiting factor in steering, compression, or droop, the shaft angle doesn't hurt.

I am not against using Mustang II spindles to reach a different compromise, but I don't consider our original design as being flawed, it has worked very well in the spec racers running in the main NASA race groups.

Jim

[Highland Daytona Racing]

Gentlemen,

Pure and simple. If the upper control arm is ahead of the lower, it is a design flaw, its not right, its not ok, and its by no means normal.

Since the system is using Ford parts with Ford geometry, we can assume that the Ford engineers actually knew what they were doing. My guess would be that the frame builders have placed the mounting point of said control arms in the wrong place on their frame, i.e. to far foreward.

My experience with these cars has been that thier owners have had to dial in upwards of 9 degrees caster in order to get them to track at speed, Ouch!

My question would be; if something so basic as control arm relationships is that tweaked, what do the more complicated geometry equations look like?

Just my two cents, as if I know anything about chassis and suspension geometry...

Rick Rllis
HDR

[Jim@FactoryFive]

What are you refering to by the upper control arm being ahead of the lower? The upper ball joint is behind the lower (it has to be to have positive caster). The upper inner pivots are between the two lower pivots although that shouldn't make any difference. The spindle adapter comes forward for clearance of the castle nut, meaning the ball joint may angle forward slightly, but as long as the ball joints are in the right place and free to move the shape of the spindle is not important.

The Ford parts did not have an upper control arm in the first place so there is no relationship to draw from.

We normaly end up with 2-3 degrees of caster in although some people prefer as much as 5, above that the steering becomes very heavy and I don't know anyone running above 6, I don't even think there is enough adjustment to get it that far.

Jim

[klayfish]

OK,
I'm going to bring a copy of this thread to my builder/mechanic, because it does get a little over my head. But it is great timing, since we have been talking about this exact problem with my car.

Jim, maybe you can offer some advice.

My car has that "twitchy" feel in it, especially if the road is less than pooltable smooth. We have the caster around 3, about -1/2 camber, and the toe is about dead straight. I have the Flaming River 18:1 rack (which for the record, I am very unhappy with, far too slow steering for autox use).

The problem is worst on a highway with rough pavement. The car can be a handful at times. Part of it is probably the aggressive tire tread I have, but we wonder if there is something more.

Could there be something ever so slightly bent, or is there a fix for the FFR that you can recommend?

Steve Klayman