Fiesta ST braking like garbage!

I think this might be an alignment issue but I wanted to check out some opinions first.

I ran out of brake pads for my Camaro over the weekend at Gingerman and the new ones didn't arrive in time for yesterday's event, so I took the Fiesta ST to Road America yesterday. Handling-wise, it was adequate on street tires. Speed-wise, it was adequate with 196hp. Braking-wise, ABSOLUTE GARBAGE.

A bunch of the internet insisted that stock pads with good fluid are acceptable for track use. I'm not sure how slow you need to be going to make that be true but it was certainly not the case for me. I have the summer-only black wheels/tires package, which is said to include the "D" spec brake pads, which are higher performance than the "E" spec pads that come with the all-season tire package. I did a complete flush and fill with Castrol SRF.

The brakes are totally lifeless. Not much feeling in the pedal at all. It varied in firmness/softness, sometimes during the same braking action! The brakes are tiny on this car, but it isn't a very fast car so that's probably fine. This thread isn't about that.

What it is about is the way the car swayed and wagged and wiggled under hard braking. Seriously, between the numb pedal and the back end of the car feeling like it was going to swing my car around into the wall, I didn't feel comfortable doing the whole day. I stopped after two sessions. Even at the relatively slow speeds of this car (compared to my other cars, not a value judgment on anything anyone else is driving or what might be "enough" at Road America), the braking was terrifying! At 5 and at Canada Corner, I seriously thought I wasn't going to be able to slow enough not to hit the walls with the back of the car waggling all around like that. I started braking earlier and earlier, and even braking at 5 before the hill, and it still swung all over the place.

I don't see this car becoming my primary track car - the 1LE is simply amazing at going fast and staying cool. But it could be really nice to only spend, say, $190 for front brakes instead of three times that! Ditto for tires! And I bought this car with the intention of it being a backup track car, so it would be nice to be able to drive it.

What can be done about taming that waggle? I want the car to brake straight and not shimmy itself around whenever I go nose-down under hard braking. It was seriously unsettling, both to the car and to me! It turned the day into absolutely no fun. Is this an alignment problem? Too much rear brake bias that I might fix with actual track pads in the front and maybe these stock pads in the back?

That sounds really frustrating. I have no real input, but I was there in the light blue M3. I'm sorry you missed out on a really beautiful day to be at the track. 

This sounds to me like to much rear brake, or not enough front.  

My RS waggles under heavy braking as well, its a bit unnerving and I need to verify the alignment because the factory spec range isn't good enough for the high speeds you run at on a track.

Get a real alignment done by someone who works on race cars and will not settle for "within specs" for the alignment.

Follow up with tire pressure settings and/or brake pad compound changes.

The dead pedal feel indicates the brake pads may be glazed.

I can't help with your wagging and shaking issues, but I do know that my friends that are a bit more serious with their trackwork (and you obviously are based on your other toys) end up running a full race pad on the FiSTs and FoSTs.  They've found that because the "e-diff" is continually applying brakes they never adequately cool and often quickly glaze or just melt and destroy rotors if they go with even an aggressive street/track compound like a carbotech XP8.   They were talking of keeping a matched set of rotors and XP10 or 12s, even for track days.

One of my buddies nuked a front set of HP+ pads and rotors at a TNiA event!  We're talking deep scoring into the rotors and the pads were almost down to the baking plates.

Brake coolers are a big bonus here.

I'll start with a disclaimer.

My only experience with these is a short ride as a passenger on an autocross course, so very limited knowledge.

Is this problem unique to your Fiesta compared to what other people have experienced on a road course?

I believe that these cars use the front brakes as a substitute for a limited-slip and to help with turn in. In such cases, you may be using those front brakes a lot more than you think, thus overheating and/or glazing the pads.

Did you get a lap, or at least a few turns that were okay?

I have noticed this squirminess of the my FiST on the street even under moderate braking (I have never tracked my personal car) but I never noticed that on the cars at ST Octane Academy.  Like Stefan said I suspect the alignment has a lot to do with with the unbalance, I also think better fluid and pads would help a lot.  The torque vectoring does not help with these problems either.

Road America is also a big track for the little brakes on the FiST.

Floating Doc said:

Is this problem unique to your Fiesta compared to what other people have experienced on a road course?

I believe that these cars use the front brakes as a substitute for a limited-slip and to help with turn in. In such cases, you may be using those front brakes a lot more than you think, thus overheating and/or glazing the pads.

Did you get a lap, or at least a few turns that were okay?

This is correct. They control slip and torque vector with the brakes. The glazing theory checks out. Like I said up top, that's not the concerning part. I can put hotter pads in and take care of most of that. I'm more concerned with how out of sorts the car got under hard braking. I need to fix that quick.

I got a couple laps in, but not many. It was a disappointing day.

Ram50Ron said:

I also think better fluid and pads would help a lot.

What's better fluid than Castrol SRF? If there's something goes even hotter than that, I'll take it!

In reply to Lugnut :

I wonder how much of the squirreliness under braking is suspension tuning so that casual drivers don't whine about all the understeer.

https://grassrootsmotorsports.com/forum/build-projects-and-project-cars/2014-ford-fiesta-st-g-street-autocrosser/85752/page3/

Scroll most of the way down. Looks like your problem might be more complicated than you might think.

I had to do a couple hard brakings, 80 to 40 the other day with my stock ST with no problems while changing lanes.

What tires are on it?

I can feel a huge difference in mine with different tires on it... especially if they’re a taller side wall than was fitted stock.

can stability control be defeated in these cars? I also wonder if a true LSD would help by mechanically vectoring the torque rather than letting the brakes do it for you

In reply to mad_machine :

You can turn off everything except the brake-operated fake LSD.

Yikes, That does sound nerve racking.

Brake Engineer by trade here, and to me it sounds like there could be a few  things going on here.

First and foremost, since this sounds like you are de-loading the rear tires so the traction control is desperately trying to make sense of what happening and sort it out.

Super short wheelbase cars like the FiST have a LOT of longitudinal weight transfer when braking, meaning most of the weight is shifted to the front tires when you hit the brakes. Combine that with the fact that most of your weight is up front and you have sticky summer tires and what happens is the weight crushes the front suspension and nearly completely lifts the rear tires of the ground like a cantilever, giving away all their grip. This can be super unstable as you enter a corner. The front tires use brake vectoring to pull you through and the rears nearly come around on you until the stability control starts to mess with things mid corner and throws it all out of wack.

Think of the car like a skateboard, if you step on the nose the rear wheels will come up and you end up balancing precariously on the fronts.

There are a few remedies for this kind of thing; The first is to lower the car and run stiffer springs and possibly even sway bars up front. Although it can possibly making you slightly more prone to understeer, it will greatly reduce the amount of weight that is transferred to the front tires when braking into a corner. Then it's just a matter of hitting a late apex and nailing the throttle on your way out.

A rear spoiler might help a tiny bit with really high speed corners (yes wings still do something for FWD cars, but that's a whole different thread) but I will ALWAYS recommend sorting out the suspension before wasting time on aero.

Other possibilities are that your pads are actually overheating and fading due to the torque vectoring system and when it come time to hit them hard, either the left or right pads have done a lot more work, and are over heated. This means the pads on the other side are going to bite harder and the ABS has to sort out which corner needs the most pressure. This too could lead to a squirrelly braking feel.

Try getting a thermometer or vulcanometer and check your rotor temps on all 4 corners as soon as you come off track to check itf this really is the problem, you should see big temp differentials more than 100 degrees if that is the case.

The solution to that would be to get pads that have a wider temperature range that will give a more neutral bite and friction even if there is a temp difference, brake cooler ducting can help here to.

Hope this helps you get back to the track. Good luck.

Matthew Kennedy said:

In reply to mad_machine :

You can turn off everything except the brake-operated fake LSD.

And that is a good thing IMO.  A powerful engine in a light front driver with an open diff is just screaming to break the diff pin after excessive single wheel spinnage.

SAAB and Volvo's traction control only kicked in if the front wheels were spinning at different rates.  You could spin the tires until the fuel tank ran dry as long as both tires were spinning the same speed.

In reply to SpartaEvolution :

FiST is super short wheelbase?  It's slightly longer than the A2/A3 chassis Golfs, and about the same as the A4, none of which were known for squirrelly handling, despite them BEING known for cornering on three wheels with any effort.  (Well, not the A4s...)

FWIW, it's also roughly 3" longer than all three generations of RX-7, the Mk1 and Mk2 Ford Escort (95" sweet spot!), and... well, there have been acres of cars made in the 90-95" wheelbase region for a long time.  Maybe the Fiesta is super short compared the the F350 SuperCrew longbed vapebro truck sitting next to it at the Ford dealership...

Knurled. said:

In reply to SpartaEvolution :

FiST is super short wheelbase?  It's slightly longer than the A2/A3 chassis Golfs, and about the same as the A4, none of which were known for squirrelly handling, despite them BEING known for cornering on three wheels with any effort.  (Well, not the A4s...)

 

FWIW, it's also roughly 3" longer than all three generations of RX-7, the Mk1 and Mk2 Ford Escort (95" sweet spot!), and... well, there have been acres of cars made in the 90-95" wheelbase region for a long time.  Maybe the Fiesta is super short compared the the F350 SuperCrew longbed vapebro truck sitting next to it at the Ford dealership...

But looking at the proportions of the FiST, I wouldn't be surprised if its center of gravity is higher relative to wheelbase length than any of those other examples. 

I don't have anything to add, but I'm very interested in following along to see what's up. My Mazda2 was inherently very unstable under braking on dirt which made it an excellent rallycross car. I only ever drove one FiST on dirt and it was pretty much the same, just with more power and super weird behaviour under power due to the Elsd losing it's mind. 

In reply to Knurled. :

You're absolutely correct that the FiST isn't setting any records for shortest ever wheelbase, but it's no land yacht.

And as rslifkin mentioned its CG isn't exactly below the axle either.

It's not possible to diagnose exactly what is causing the OPs instability over an internet thread but de-loading of the rear tires due to weight transfer is a legitimate possibility.

For example a few years back FCA was having this rather disturbing problem with the Jeep renegade despite  that car having a wheelbase 3.5 inches longer than even the FiST, more weight, and less grippy all-season tires.

https://www.youtube.com/watch?v=b_phpt10QH4

(warning I did not pick the music)

I'm not making the claim that this is definitely the problem, but it is totally possible for a brand new car with certain options do some "less-than-stable" things in the right conditions.

 

The Fiesta is certainly not the primary track car, so it's not really an emergency to get all of this sorted out. I'll plan on some track pads and an alignment and we'll see how that feels. It just sucks to pay for a whole day and not enjoy driving for it!

My shiny new Pagid RSL2s for the Camaro have arrived, so I'll be doing Blackhawk on Wednesday with those. I'm excited - they're like the RS14s I like so much but they are supposed to last for a good long time.

Could some of the problem be that the track is narrow compared to the wheelbase? The Focus ST has a 4” longer WB with about a 3.5” wider track. 

In reply to Knurled. :

I completely agree.  My FoST is great on track until the brakes get cooked.  To Ford's credit the e-diff stuff does do the job, it just cooks the brakes in the process.

The OP is obviously delusional. I've seen three STs in the last week that were all decked out with aftermarket boy-racer stuff, clearing identifying them as serious racers. Obviously there is nothing wrong with the car!

Kidding aside, nearly all "sports cars" aren't. If you're going to seriously track the car, invest in some real brake pads. The mfgs put in what works best for the street (avoiding lawsuits if track pads were used). That said, is there anything in the manual about traction or stability control (I know nothing about the cars)? Maybe it's a software thing? Probably the best thing is to troll various "race" sites and see what other drivers of this car are doing - or seeing if there's actually something wrong with yours.