posted on July 28, 2014 12:01
Project Ford Fiesta ST - Improving the Handling With ST Suspension
If you love performance compact cars, then you should really be paying close attention and focusing your next purchase intent on The Ford Fiesta ST. The Fiesta ST is basically the same joint Ford, Mazda 2 platform that we loved so much as a B Spec racer. We felt the chassis handled well but was lacking power in gobs. Well Ford fixed the problem in a big way with the Fiesta ST by dropping in a turbocharged direct injection Ecoboost 1.6 liter engine with a six speed manual transaxle that delivers 197 hp and good mileage together in a package that leaves you grinning from ear to ear.
When driving the ST for the first time, mental images come to mind of driving a turbo Honda or Sentra SE-R in the late 90's but with some big differences. The Fiesta ST is much tighter and more refined than any compact of that era and it is drop dead bulletproof and reliable, not like the SE-R with its glass transmission or the fragile ring lands and gasket blowing open deck of the Honda.
You drive around all day kicking booty with a silly grin on your face and you remember that it is all stock! The car is so good from the factory that you might be jaded and hesitate to modify it! However, this is MotoIQ and we are always up to a challenge, even ones like seeing if we can beat Ford's engineers in making a fun car more fun.
As usual one of the first things we work on is the suspension. We feel that if you are going to upgrade the engine like what we will do later, you first have to upgrade the chassis to make having additional power no problem to the car's overall balance. It just so happens that ST Suspension has recently come out with a set of coilovers for the car and we get to be one of the first ones to give them a test.
ST Suspension, previously a manufacturer of good quality but price point oriented suspension has upped the ante lately by upgrading to adjustable damping and adding camber plates on some models of their coilover suspension kits and the Fiesta ST is one of the first cars to benefit from the new hardware. Check out what we did to get it in the car.
The ST Suspension front strut is pretty decent quality for the price point. The steel body is first zinc plated then treated with yellow chromate for corrosion resistance. The lower spring seat is steel reinforced plastic. The plastic spring seat and the treated coilover body will resist sticking even after a salty east coast winter. It is single adjustable in damping with the adjustment affecting mostly the rebound damping.
The upper mount is adjustable for camber and has sealed bearing which is great for corrosion resistance. You can see the rubber bellows seal in this picture, a great feature for long term durability. The ST Suspension coilovers also have a tender spring with a plastic separator to reduce noise.
The upper mount also includes a camber plate. Camber is also adjustable via slots in the bottom mounting flange where the spindles bolt on. The stock Fiesta ST lacks any camber adjustability and the ability to add a lot of front negative camber is important for track driving and autocross. The strut is a twin tube in design pressurized with nitrogen gas for consistent damping.
The rear suspension uses an adjustable rear shock with a separate spring. Like the front strut, the rear shock is a gas pressurized twin tube. The damping adjuster, like the front affects mostly the rebound damping.
Tuesday, July 29, 2014 5:24 AM
I'm pretty sure drilling out my strut towers on a new vehicle would have made me freak the heck out. :-D
Tuesday, July 29, 2014 5:58 AM
Sweet! The FiST is one of my favorite new cars. Cobb seems to have some really nice parts for the powertrain that they are slowly releasing, maybe Mr. Hsu can hook you up? You'll probably want a Quaife diff if you increase the power though, those are hard to get. I've heard from the serious FiST autocrossers that they have a hard time getting the car to rotate in stock class form, but it sounds like 4 degrees of front camber is the ticket.
Tuesday, July 29, 2014 7:59 AM
I really think Ford got the package really right with the Fiesta. Great performance at a reasonable price point, and fun to drive. I spoke with a couple Ford engineers at SEMA last year and they all prefered the Fiesta over the Focus in fun-to-drive factor.
Tuesday, July 29, 2014 9:07 AM
Hmmmmm, no pictures of the car before, after or of any sort!? I'm excited to see what the car looks like and how this project heads :-)
Tuesday, July 29, 2014 10:03 AM
Nice to see you guys picked up a FiST!
I'd be curious to know your thoughts after driving the car around for awhile. I already like the way the car feels from Ford.
Tuesday, July 29, 2014 10:08 AM
It is one of those cars that you have to pick the mods carefully or you will mess it up! I was skeptical but one drive and I was like wow! I haven't been this excited about a car since the EVO/STI/GT-R. It is head and shoulders above anything else in the FWD sport compact world. Honda, Nissan and Toyota need to take notice.
Tuesday, July 29, 2014 7:03 PM
Cool trick for cutting an accurate hole in the strut tower!
You mention in your previous articles that the camber plates also adjust SAI, and can mess things up. Does the Fiesta have a lot of caster or some factor that makes it not matter as much? Or does the slot in the strut completely/almost-completely compensate for the camber plate?
Wednesday, July 30, 2014 2:33 AM
Guys, just a question on how the FiST handles; it kinda likes to tripod around tight turns (lifts inner rear wheel) due to the torsion beam design (just based on video reviews I watched)
Is this a good thing? Does this suspension address it? Should I even be bothered about it at all? :D
Wednesday, July 30, 2014 7:25 AM
Adrian, pretty much any FWD car setup for handling will do that regardless of the rear suspension design. Just on FWD cars with shorter wheelbases, it's a bit more pronounced, like on the old old VW Golfs from the 80s. But check out any road racing/touring cars that are FWD, and you'll often see the rear inner tire stop spinning if the driver is trail braking as the tire was lifted off the ground; a super stiff rear sway bar kinda becomes a beam now that I think about it... Also, FWD cars tend to have about a 65%/35%, but equal width tires front/rear. So to get the rear to rotate as much as the front, you have to reduce rear grip and picking one tire off the ground will do that. So the that's my general observation at least which may be flawed :)
Wednesday, July 30, 2014 10:13 AM
A FWD car that is set up well, which is usually a race car with race car like spring rates will not 3 wheel. It will be close but all 4 wheels will be on the ground.
Wednesday, July 30, 2014 1:24 PM
Something that was brought up on another forum about tripoding from a very quick autocrosser and I'm curious about your thoughts.
To make sense of this, the car has to be thought of as five masses; the sprung mass of the chassis and four unsprung masses of the wheel/suspension assemblies. Once you pick up a wheel, the wheel in the air basically becomes part of the sprung mass. While the net CoG is the same for the entire system, it shifts the CoG of the sprung mass towards the wheel that is in the air. This forces more weight on the other tire on the same end of the car and the same side of the car and pulls weight off the tire across from it. Basically the car titter-totters the weight of the wheel/suspension assembly in the air diagonally across the car.
Lift the rear inside tire and it puts more weight on the outside rear and inside front while removing weight from the outside front. The net effect suggested is that it evens out the weight slightly and actually getting the wheel off the ground (just a fraction of an inch) is needed to make this possible. Otherwise, if the tire is on the ground at all, it is providing very little grip anyway as the only weight on the tire is the unsprung mass of that corner but it is not helping pull weight off the front outside tire (the most heavily overloaded tire) at all because the unsprung mass is supported by the ground at that corner. Effects of the sway bars come into this too, but say you didn’t have a swaybar on that end of the car at all to make the wheels completely independent of each other on one end of the car.
Wednesday, July 30, 2014 1:47 PM
Wish there was an edit button. To add, very excited to see how the Project Fiesta goes. Wish they would put the 2.0L ecoboost in it though. My wifes Escape with the 2.0L ecoboost does great at moving it around and it's 1000 pounds heaiver then the fiesta. Even with the 1.6L though, it was more impressive then any of the other small SUVs on the market with similar power ratings. The ecoboost motors are torque monsters.
Wednesday, July 30, 2014 2:03 PM
"Lift the rear inside tire and it puts more weight on the outside rear and inside front while removing weight from the outside front."
Makes sense just thinking of Newton's 3rd law, every action has an equal and opposite reaction. No load on the inside rear, no equal and opposite reaction on the opposite corner.
If Ford put the 2.0L in the Fiesta, it'd kill Focus ST sales ;) I've been pestering a few people to see if they can fit up the twin-scroll turbo off the 2015 WRX and put it on the Fiesta; Fiesta still has the standard 4 exhaust port head whereas the 2.0L in the Focus has the integrated exhaust mani in the head and a single port exiting. Bump up the 1.6L to 300crank hp, it'd be a lot of fun!
Wednesday, July 30, 2014 8:38 PM
Lifting the inside rear does not remove weight from the outside front
Wednesday, July 30, 2014 11:12 PM
Hmm... Mike and Mike (ha!), I've never really thought about this situation before, so it's certainly interesting. So, I guess the question becomes, what has to occur for the inside rear to lift? The opposite corner front has to compress. For that front opposite corner to compress, a force has to be applied to compress the spring. A car turning means it is undergoing centripetal acceleration, F=ma, so a force has to be applied to get the car to turn. The force to turn is generated by the tires and that's a function of the normal force on the tire and the coefficient of friction. No friction, no force, no turning, no eventual lifting. So one key part is having a high enough coefficient of friction, so sticky tires and high-grip surface. The increased normal force on the right front must be due to weight transfer. The force coming off the inside rear has to be transferred to the other three tires in some distribution. So what’s going to cause the opposite front to compress more and not have the opposite rear compress as much? Part of that has to do with weight distribution, so the front heavy FWD cars. Weight transfer from braking would also be a main contributor. So all that said having thought about it a little more, yeah, lifting the inside rear isn’t going to take load off the opposite front. Granted, I haven’t thought about kinematics in a looooong time and I’m sleepy, so second opinions welcome. Why am I awake again?
This just got me to thinking about the drift cars which are almost lifting the inside front in a drift because the outside rear is generating so much force it’s causing that corner of the car to compress. As many of those cars have a more even weight distribution, it should be a forward acceleration force causing the weight transfer to the rear along with the turning force putting more force normal on the outside rear causing that corner to compress and the inside front to get light. I remember seeing pics of Dai’s old car looking like the inside front was about to lift, but never really thought about. Sleepy time.
Wednesday, July 30, 2014 11:40 PM
it's a combination of too much rear roll stiffness and not enough overall roll stiffness. Sometimes exaggerated by roll center location issues.
Thursday, July 31, 2014 10:23 AM
Thanks for your thoughts.
That was kind of what I was thinking too but it's hard to argue with somebody that has a lot more experience (and wins) on a particular platform that we were discussing. It makes a solid arguement based on statics too. But we are talking dynamic motion so the force distribution I am picturing that would make it true likely doesn't represent reality.
From experience though, I have seen what aligns with what you are saying. I'm currently lifting the inside rear on a RWD car. Putting a larger front sway bar on helped considerably although it is still doing it. Plan forward is more FSB, lower rear ride height and softer rear springs and shock valving. The spring rates I am at make it hard to beleive it is a lack of roll stiffness though as I'm at a wheel rate of around 500lb/in and I'm on street tires. Could be roll center issues but the car isn't all that low. Mcstrut front, the arms are roughly parallel with the ground and it's around 15* SAI.
Thanks for your time and any input you might have.
Thursday, July 31, 2014 10:47 AM
I initially was only thinking in a static domain when I mentioned Newton's 3rd law. Like a table that wobbles back and forth and you have to put something under the leg that's up in the air. So I went down the other thought path.
What car are you driving? S2000s used in stock class auto-x typically run very stiff FSB to keep the inside rear down. With the stock Torsen diff, when the inside rear lifts, you lose drive. So S2k guys add the super stiff FSB to try to keep the inside rear down on the ground. Are you limited in modifications by rules?
Per Kojima's speak of too much rear roll stiffness, have you considered removing the rear bar (assuming your car is equipped with one) to reduce the roll stiffness at the rear? Or add overall roll stiffness which I think would be accomplished with higher front spring rates and/or FSB?
On my S2k, I removed the rear bar as one in a number of suspension changes (front and rear spring rates, FSB, tire sizing). By having the rears independent of each other as they are no longer connected by the RSB, it allows the inside rear to droop.
Thursday, July 31, 2014 11:26 AM
It's an E36 318ti...essentially an E30 suspension wise. Terrible droop travel in the rear due to the semi-trailing arm suspension design once you go to a linear spring. Rear swaybar has been removed. I run in street mod, but it's nothing I take too serious anyway.
I don't think any more front spring is really an option on street tires. It's already terrible on grip when the roads get wet. It's around 2.8Hz up front and the back is softer at 2.4Hz. Despite the softer rear, it always goes towards oversteer. I feel like I need more bar and less spring up front, it's a 2350 pound car with 680lb/in springs up front...
Sorry for getting way off topic at this point though.
Thursday, July 31, 2014 7:07 PM
Argh... I had a spreadsheet I made a long time ago calculating ride frequency for my S2k. Can't find it now though. FWIW, I'm running about 680lb/in springs on the front with a motion ratio of ~0.7 using 235/40/17 Nitto NT01s. Car is ~2800lbs.
Thursday, July 31, 2014 9:24 PM
Mike, Josh Jaquot and Scott Oldham both ended up writing for Edmunds? I was just reading a Tesla long term review and their names popped up.
Friday, August 01, 2014 1:09 AM
Our reducing overall roll or figuring out the root cause of whats causing the roll. Removing the rear sway bar is usually a mistake no matter what experts might tell you that that is "better"
Thursday, August 07, 2014 4:24 AM
Amazed how a simple question spawned such a detailed discussion :D
Thursday, August 07, 2014 4:33 AM
Just for knowledge sake, I currently drive a EG6, with no rear sway bar (which is bad as you explained).
What I disliked with the stock sway bar on was that the car was too "snappy", a common problem with short wheelbase cars. After I removed the rear sway bar, I could control the rotation much better (via throttle inputs) and could correct slides in time.
What can I do to the car, so that I can run the rear sway bar and keep the cars rotation controllable?
Friday, August 22, 2014 8:04 PM
I just picked one of these up. Best thing since the B13 SE-R, truly.
Wednesday, October 29, 2014 7:40 AM
Cracked open the mystery suspension box:
Wednesday, October 29, 2014 7:43 AM
What would be the mistake in removing the rear sway bar, Mike?
It's mostly there as an additional spring, that will also limit droop. If you can get the rear dialed in without a sway, why would that be bad?
Asking this, as I've been racing a Civic hatch without the rear bar with no perceived ill effects.