Dancing around at highway speed and heavy braking

[Erbarry]

So my car has been moving around a lot while driving on the highway and gets pretty sketchy on heavy braking. Took it in to Les Schwab to get an alignment check and seems pretty off to me. They told me to take it back to Ford since its still under warranty and they wouldnt want to void anything if the messed with it. Here is the sheet they gave me. What do you guys think and what has been your experience with alignments straight out the dealer?

 

[LilPartyBox]

Well, under braking the rear gets lighter in proportion to the amount of braking. The heavier the braking the more weight shifts forward and the less grip in the rear. There also may be slight inputs at the steering wheel. The combination creates looseness at the rear that can amount to a bit of wiggle under braking. I get it too sometimes and i just had my alignment done. I'm training myself to be light on the steering wheel inputs when braking hard.

I was thinking of stiffening the rear a click or two to see it helps keep it planted but winter is coming, so no real point in tweaking my setup for at the limit braking if I'm going to be driving miss daisy all season. I think i still have my alignment sheet at home. If i do i'll post a pic of it.

But that moving around on the highway is not normal at all. Did the shop say you were way out of spec?

EDIT: As promised

 

[OffTheWall503]

I also noticed on the stock wheels/tires and suspension that it would "wallow" on the highway, making it hard to stay straight without occasionally making slight adjustments with the steering wheel. The rear end also felt like it might swing out under heavy braking at higher speeds. For me, lowering springs seemed to have solved these problems. It's also nice not having as much brake dip towards the front of the vehicle when braking.

 

[CanadianGuy]

One more point for highway speed. Check well balance. An off balanced wheel/ bent rim etc... can feel very floaty on the highway even if you do not fell it at low speed.

 

[Joker328]

What seems off about that alignment to you? Looks like it is all well within spec, which is what Ford will tell you as well. The looseness under braking is typical as others have noted. I think what CanadianGuy is trying to say is to check if your wheels/tires are balanced, which is a good idea. Do you still have the stock wheels/tires on it? You might also check your tire pressure and consider going with a little lower pressure in the rear if you don't have any weight back there and the rear is skittish at speed. Other than that, I'm not sure what it would be. Is there any pattern to when it feels loose?

 

[Erbarry]

I know its with in spec its just off from left to right and I'd like it more balanced. I'm still running stock wheels/tires. I'll check tire pressure in the morning when the wheels are cool. Just driving in a straight line above 60mph it wonders around and when there's cracks the car will chase them around. With the braking it's from high speed, heavy braking, I've tried seeing if it's me moving the steering wheel slightly but I've tried multiple times and I've been steady with the steering wheel. It doesn't seem like it's the rear moving around but I could be wrong. I might just be thinking it would drive like my Evo which is much heavier and wider tires but I can slam the brakes doing 120 and have the car stay straight/steady and feel safe which is not the case with the Fiesta at this moment.

 

[M-Sport fan]

Any low profile tire will 'tramline', or follow grooves, or heavy/overweight semi truck created 'double tracks' on the highway.

Usually it is the wider low profile rubber which does this, but our factory rubber bands are so low profile that it would not surprise me at all that this happens to them on badly grooved roads, even at a relatively thin 205 section width.

 

[D-resonant]

When I was running the factory suspension, this was normal, especially when the factory Bridgestones got worn down (from playing in the canyons).

The addition of front lower two-point brace helped calm this.

Later with more adjustability afforded by coil-overs, setting toe to zero helped. (From .15deg total to 0)

 

[Accel Junky]

I had the same feeling on the highway and under heavy braking. So far, the lowering springs seemed to have helped highway stability. Heavy braking seems a little better (haven't taken it back to the track yet) but I think the issue is the light rear end combined with your rear toe (maybe even your unequal front toe). You've got one toe'd out and the other is not equal to. Should be toe'd in equally for straight line stability. Unfortunately that can't be adjusted in the rear to my knowledge. Here's my alignment for reference:

 

[Sekred]

Increasing the track helps with the twitching rear end feeling under heavy braking and high speed lane changing. This seems to a be more common complaint on the Euro spec ST, maybe because it is a little lighter in the rear, not really sure. I change the rim off set from 42.5 to 35mm to clear my BBK and it has helped with the stability, its a noticeable improvement actually.

 

[Accel Junky]

^^ Good point that I forgot to add. Switching to the 17x8 +40 wheels definitely aided stability as well.

 

[Erbarry]

So I dropped the pressure all around to 35psi and that helped a bit with the highway driving, haven't tried the hard braking yet.

 

[Intuit]

Any low profile tire will 'tramline', or follow grooves, or heavy/overweight semi truck created 'double tracks' on the highway.

Usually it is the wider low profile rubber which does this, but our factory rubber bands are so low profile that it would not surprise me at all that this happens to them on badly grooved roads, even at a relatively thin 205 section width.

Experienced this a couple of rainy nights ago, accelerating in a middle lane. The harder you accelerate the greater the pull. The *worse* thing to do at highway speeds is to try too hard to correct; kind of have to let it guide you and at what point "too" much extra steering input is required, just have to ease off the accel/brake.

This affects pretty much any small vehicle with narrower tracks. I suspect the problem may worsen with a more aggressive camber and tighter swaybar linkage. Even my motorcycle would road-steer under those conditions. It has to do with the tire contact patch which is the very mechanism of turning.