This very interesting, but I'm moving it to Suspension. I have a question about this topic.

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To reach me by email please use this address wrcfan@teamfocaljet.com

 

This is very interesting. I have a question for someone with more suspension engineering knowledge then I (P-51?).

I have noticed the same thing and thought I was going nuts. It can almost feel like a "deflection" at the rear when going over surface irregularities, especially when the angle of attach is asymmetrical (sort of akin to bumpsteer).

I was just about to check all the suspension point bushings and fasteners to see if something was loose.

My question is this, would having low profile (i.e. stiff sidewall) tires and stiff springs/dampers (H&R coilovers) amplify either the effect of the rear steer, or at the very least make the driver "more aware" that it was happening?

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To reach me by email please use this address wrcfan@teamfocaljet.com

 

Yes, interesting at least because now I feel sorta validated on what I thought I felt when taking my car on the fast twisties. Yes, and like wrcfan states, I thought that certain bumps cause some slight directional changes; It throws others off guard when they drive a focus for the first time. My Contour SVT buddy was a little scared by it when I let him drive mine.

But like everyone else, I'm no suspension guru, I'm a computer guru, and perhaps those more knowledgeable can share some insight

[This message has been edited by covert1 (edited 10-18-2001).]

 

hmm, interesting. I only started noticing this since installing the KW Sport Kit.

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by wrcfan:
My question is this, would having low profile (i.e. stiff sidewall) tires and stiff springs/dampers (H&R coilovers) amplify either the effect of the rear steer, or at the very least make the driver "more aware" that it was happening?<HR></BLOCKQUOTE>

This is pretty much what I was thinking...that the stiffer springs were enhancing the effect a bit. I too would like to hear what Rob has to say about this. Or any of the other suspension gurus around here.

focalBlur - thanks for the post...really interesting info.

 

In the original post, on the topic of Traction-Control, unless it is European and somehow different from "Advance-Trac", it is WRONG. "Advance-Trac" uses the ABS for Traction Control. EXACTLY why your lap times were slower, the engine was bogging, and I chose to save the $$1000 and someday get the Quaife Limited-Slip Differential for "Traction-Control".

$$$.$$
It supposedly detects the slipping wheel, and applies localized ABS.
Sure wish Non "Advance-Trac" ABS = 4WheelDiscs.

If you have "Advance-Trac" it may accentuate the condition you are describing??...

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Focus On FASTER!!

[This message has been edited by michaelxi (edited 10-18-2001).]

 

I would need a better description of what you asking to figure it out. But in general, stiffer sidewalls will always let you feel more of what the suspension is doing.

Basically, the suspension does all this moving around, but if it doesn't have anything to "push against" it won't have any effect. What I mean is, for say bumpsteer, if the sidewalls are really mushy, the sidewalls absorb the deflection. So the suspension can't push against the ground, so the bumpsteer forces don't affect the body.

I have long hypothesised that there are some VERY funky things going on in the rear end of the Focus. There is one too many suspension links. I can't figure out if whoever designed it is a genius or a fool.

Either, they didn't know what they are doing, and screwed it up but are lucky it works out ok. Or they're geniuses and tuned the whole think to work perfectly with calculated bushing stiffnesses.

Basically, there are those two lower links, when you should only have 1. As the suspension travels up and down, they move in different arcs. This means the lateral movement between them is different. I think the trailing arm actually gets *bent* slightly and this is how they control toe.

 

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by P-51:
I would need a better description of what you asking to figure it out. But in general, stiffer sidewalls will always let you feel more of what the suspension is doing.

Basically, the suspension does all this moving around, but if it doesn't have anything to "push against" it won't have any effect. What I mean is, for say bumpsteer, if the sidewalls are really mushy, the sidewalls absorb the deflection. So the suspension can't push against the ground, so the bumpsteer forces don't affect the body.

I have long hypothesised that there are some VERY funky things going on in the rear end of the Focus. There is one too many suspension links. I can't figure out if whoever designed it is a genius or a fool.

Either, they didn't know what they are doing, and screwed it up but are lucky it works out ok. Or they're geniuses and tuned the whole think to work perfectly with calculated bushing stiffnesses.

Basically, there are those two lower links, when you should only have 1. As the suspension travels up and down, they move in different arcs. This means the lateral movement between them is different. I think the trailing arm actually gets *bent* slightly and this is how they control toe.<HR></BLOCKQUOTE>

you are right there are alot of funky things going on back there.

The two lower links allow the wheels to toe out out under braking \--/.

all suspentions are compromises the focus handles very well even though the Suspention is soft.

The trailing plate is flexibile it's primary job is to locate the wheel fore and aft. it can twist in the other direction. (up,down left, right)

the links are only used in tension. this allow the links to control the location the wheel and let the springs and shocks control the up and down movement.

The suspention is very good and cheap[/]

Ford will be using it in more cars in the future. I wouldn't be suprized if it would be used on the next mustang.

The purpose of passive rear wheel steering is stability in high speed manuvers. it keeps the tire rolling instead of skiding.



[This message has been edited by biker16 (edited 10-18-2001).]

 

That is what I was thinking. Why is that trailing arm so thin? Some think because it's cheap. I think it's because it's flexible, and the front and rear lower links bend that arm to toe the wheels in or out depending if it's up or down. If so, it's an ingenious solution because it's cheap, and effective.

I've talked about this with some people around here, one of them a guy who did an internship at SVE and still has connection. He doesn't think that arm bends. But I think there are too many links for it to not bend...

Now, assuming that it does bend, and you say it toes out under braking (when the rear end lifts) then it would DEFINITELY have rear wheel steering.

As the car rolls, the inside suspension extends, this would make it toe out, or turn into the turn. The outside suspension compresses, and thus toes in. This aims the outside rear wheel into the corner as well.

Voila, passive rear steering.

Again, this is just a hypothesis. Eventually, I'd like to get a stock focus into my garage and take some measurements.

 

Let me try to explain it a little better and see if a). Others that are experiencing it agree and b). If it helps to communicate more to our experts.

While driving down a flat smooth road, you drive over a manhole cover that is recessed, let's say an inch or so. Not a "pothole" but a chamfered hole that causes suspension movement but not abruptly (like an actual pot hole would).

It's right in the middle of the right side track of the car so both right side tires go over it.

The front suspension acts as you would expect. The right wheel drops and returns. It only moves in one plane, vertically.

A millisecond later the rear wheel goes over the exact same surface irregularity. The wheel makes the same dropping motion... But, and I have yet to determine if this happens on the wheel down or wheel up motion, there seems to be a slight movement of the wheel in another plane (side to side).

I can only describe it as "kicking out". Mind you it is a very slight effect but something I notice. Some people may be more sensitive to it then others and it may make some people feel like the car is unstable, as mentioned by the Contour driver reference above.

I guess my point was, as you pointed out Rob, that the stiffer tires/suspension accentuate this effect to the driver. On a stock vehicle the effect is probably buffered quite a bit by the "slop" in a combination of sidewall flex and deflection of the softer springs/dampers.

[This message has been edited by wrcfan (edited 10-18-2001).]

 

Yes, it would make sense that that would happen. As the suspension moves up or down, the arm swings and moves the wheel in or out.

Only... this happens on the front too. So I don't know why you could feel it in back but not front.

I've never noticed that... but I came from driving a Mustang, so the suspension feels so good in comparison to that nightmare...

 

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by wrcfan:
...there seems to be a slight movement of the wheel in another plane (side to side).

I can only describe it as "kicking out". Mind you it is a very slight effect but something I notice...<HR></BLOCKQUOTE>

This is exactly what I am experiencing. Very nice explanation.

Freaked me out the first time I felt it.

I'm assuming, for the time being, that this is normal for the Focus rear suspension and won't cause any long term problems...is this right? The effect does seem to be 'enhanced' by stiffer sprngs.

 

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by P-51:
Yes, it would make sense that that would happen. As the suspension moves up or down, the arm swings and moves the wheel in or out.<HR></BLOCKQUOTE>

When you say "moves the wheel in or out" do you mean without changing the direction that wheel is moving in the forward direction?

I understand the track getting wider as the suspension deflects and even approaching toe-in under extreme deflectons.

I guess what I'm saying is that the rear toes-in a bit, even under slight deflection of the suspension. It could also be that that front does the same but the rear does it more therefore gives this "rear steer" feeling.

 

Also, not to add more logs on the fire, but... for the people that are experiencing this:

Do you notice it even more on wet surfaces?

I know that sounds weird but I know to set up a car to go fast in the wet you soften it quite a bit. Therefore, for us with coilovers or similarly stiff set ups, rain adds an even larger amplification of the effect.

One more thought, could it be attributed to improper bump stop configuration?

 

This is an interesting topic, and I have some anecdotal evidence.

There was a turn I used to take that had a very bumpy surface -- in my ZX3 (stock suspension) it would feel as if the back-end was wanting to come around a bit, but it didn't feel uncontrolled. I was thinking there was wheel-hop, but wheel-hop feels like there was a loss of control, and this didn't really feel like it was out of control. Does this make sense or am I just an idiot and had wheel-hop on the uneven surface?

Second question: would anti-sway bars make this effect more pronounced, or less pronounced?

-Daniel.

 

The trailing link is flexible but since the focus is FWD not RWD the blade can be thin. it is only used in tension.

on the X-type the blade it wider and thicker than the focus it needs it because it is AWD. it is also lighter to use steel stampings over forged, or cast steel links.

I belive they will start to use composite links instead of steel or alumnium.

most of the movement of the trailing link is thru the "voided bushing" It is about 1.5 in in diameter it is rubber with cutouts in it to to allow movement. when you set your parking brake on a hill it is what moves back.

the \ / effect during braking is not related to dive. it it is due to the interaction of the bushings and the geometry of the suspention. in a good suspention all up and down movements are controled thru the springs and shocks.

The interaction of the geometry and the bushings allow for passive RWS.

 

dude i thought i was the only one. When taking a turn across an intersection with long iregularities in the road, like a line of a pothholes, the whole rear seems as it shifts about a foot in the direction of the force of the turn, you know? It feels really unstable. Ive driven many other cars through that turn and they feel normal, but in my car it just seems like it shifts over the bumps, kinda weird, kinda scary sometimes cause you think your slipping and are about to slide but you dont really.

 

So would you say this effect is beneficial for autocross? It seems, if I understand correctly, that this is sort of a way of having your rear wheels track straight when necessary, and having them toe out automatically(rear toe out being an autocross trick to aid in turn-in), under hard, fast turning conditions. Am I in left field, or is this really cool? Does anyone know if this only happens on irregular surfaces?

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Focus On FASTER!!

 

it happens under cornering forces so yes it would help in auto-x IMO

when you take a turn at high speed this happens, the g forces cause rear steer

 

Does anybody else notice that you seem to accelerate a bit faster in mild bends than when going straight ahead. It might be my mind playing tricks on me but it seems with the same throttle pressure, mph's seem to go up easier than when going straight ahead.

 

One thing to take into consideration is the fact that our weight distribution is also favoring the front, so the amount of energy needed to affect the front end(from the suspension) would have to be greater than the rear in order to get the same effect(for wrcfan's pothole explanation).
Also, this sounds pretty damn close to describing the "easilly accessible oversteer" that some reviews describe the car as having. Personally, I think the car's real stable and the only time I feel things get "outta line" is when I purpousfully induce oversteer with either braking(even in mid-turn) and throttle lift-off...sometimes, it seems that I can be turning the wheel at a greater angle of "attack" and throttle it to get oversteer also, but it's a very particular feeling. So, I guess I have no complaints.

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Mali-Blue ZX3

 

Two Things:
Tonight on my way home from work, i took a TIGHT, off-camber, concrete, OFF-ramp at pretty good speed, and noticed a sensation I remembered from the first time I ever tried to push the car quickly through a corner, when I was first "feeling it out". At the time, I thought I had over-steer happening. Tonight, I had the window down, stereo off, and had the same sensation. I noticed that while I felt the back end track oddly, I heard NO tire slippage at all, and if I was steady, the car was truly steady in that state, NOT trying to dance around on the edge of traction.
HMMMMMMM!!!!!

Second, I never saw an answer the question about sway bars.
Would a larger rear bar increase, decrease, or not affect this process?
CURIOUS?COOL. Eh?

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Focus On FASTER!!

[This message has been edited by michaelxi (edited 10-20-2001).]

 

i took a hairpin tonight at about 45mph (recommended speed was 15) in a 35mph zone... noticed that the tail of the car seemed to very slightly push to the outside of the corner. even in stock form this car sticks like glue compared to most other cars out there.

 

Yeah,
My point is that you notice the rear push out a tad....W/O SLIDING,While UNDER CONTROL.
NIFTY!!!

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Focus On FASTER!!

 

Anybody on the sway bar Q????

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Focus On FASTER!!

 

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by michaelxi:
Anybody on the sway bar Q????

<HR></BLOCKQUOTE>

I would say no. it wouldnt effect it jsut cause more oversteer.