which to do first? front or back

[MeisterR]

The thing with "Vehicle Dynamic" is a complete package all working together.
The basis of these are the tyres, you can only generate as much traction your tyres will generate no matter what suspension you are using.

On FWD race car, we do have suspension that have minimal "droop" travel in the rear.
The reason for that is when you corner hard into a turn, the rear damper "tops out".
This help the turn in of the car as well as traction, because turning motion are on the front wheels.

You have only as much traction to use as your tyres can generate, so suspension don't help you "pick up" any traction.
What it will allow you to do is direct what available traction to more useful task, or take away what you don't need.

The only time you can pick up traction is if the suspension you are using isn't using the available grip from the tyres.
So for example, stick a set of racing slick tyres on the OEM suspension and there will be more to gain from the suspension.
On the other hand, stick a set of racing suspension on a car with the OEM road tyres, and chances are it will do worst because the suspension are design for tyres that can generate more traction than what the OEM tyres can provide.

Jerrick

 

[Ryephile]

Really good post and nice to see someone who knows what they are talking about w/r/t suspension and handling. Haven't seen much useful info on these forums and so I just haven't bothered with suspension mods to this point. Rather not spend money on something if I don't know what it's doing.

One point I just wanted to clarify is that when you say "The rear torsion bar will increase rear suspension roll couple and thus cornering wheel rate, which will reduce understeer by making the rear end "looser" at the limit," isn't the reduction in understeer technically sacrificing overall traction? If I understand correctly, with a stiffer torsion bar, the body roll of the car when cornering (though possibly reduced) exerts more of an upward force on the inside rear tire so that it has less traction and therefore the rear is more likely to step out. But it's not like you are picking that up with increased traction up front, so you may be losing traction overall. In the end, you may not be picking up any actual time. Is that right?

I like the concept of your thought experiment. Consider for a moment a WRC race car. How often do you see them not in a 4-wheel drift? They're doing that because it's the quickest way around the corner on that surface. On pavement, the slip angles need to be much less to achieve peak lateral-g, but nevertheless the concept is similar. If you're not using all 4 tires to make the car turn, then you're leaving lap time on the table. This is where you get terms like feeling the car "rotate" or "pivot", which are much quicker terms than "push" or "hook", terms that indicate markedly unbalanced setups.

A more scientific approach would be to take tire pyrometer readings for a given suspension setup. Change one component, go out and do hot laps, measure the lap time and also measure the tire temps. You'll notice that lap times will lower as all 4 tires are within optimal temperature range for that particular tire. If the fronts are overcooked and the rears are cold, then you're wasting time because your rear end is not rotating to help turn the car. In the end, if a car is understeering, it's going to be slower around the track than the same car that's has its suspension tuned to better maximize the grip all 4 tires.

 

[D-resonant]

Balanced handling is not what the FiST has. It still understeers at the limit during steady-state cornering. You can Scandinavian-flick it into a corner to get it to oversteer but it is not its normal state. Also, using terms like "upset" and "throw out of balance" is quite sensationalized and quite subjective. If I gave you a back-to-back with a stock FiST and one with 5% more rear wheel rate almost nobody would be able to tell the difference on an imperfect public road.


The OP is mentioning "improved" handling, but we still don't know what that definition is for them. Is "improved" decreased understeer, increased positive caster for a stronger centering effect, increased low speed damping to improve weight transition quickness, or what?


The rear torsion bar will increase rear suspension roll couple and thus cornering wheel rate, which will reduce understeer by making the rear end "looser" at the limit. The front chassis brace does not change wheel rate but it might improve geometry fidelity and give a more precise sensation but it won't change the inherent handling balance.

The whole chassis brace thing is going to be either placebo or minor sensation, because no matter what the spring rates are much softer than any chassis flex or bending. Spring rates versus typical chassis bending force is way over an order of magnitude. You'll bottom out the suspension, bend a control arm, snap a wheel before bending the chassis a whole degree. That's just the physics of it.

Very eloquently stated. Geometry fidelity. Thanks.

 

[DaveG99]

Man after reading these replies I feel like I'll just leave it stock. Lol. I guess you can't just want your car to handle "better". You have to know what specific part you want to adjust. There are certain cars that are known for handling awesome. Like a Porsche for example. I don't know specifically what I want my fiesta to do better but I would like it to perform more like a Porsche I guess. Anything that helps it get around a corner faster is what I consider better.

 

[MeisterR]

Man after reading these replies I feel like I'll just leave it stock. Lol. I guess you can't just want your car to handle "better". You have to know what specific part you want to adjust. There are certain cars that are known for handling awesome. Like a Porsche for example. I don't know specifically what I want my fiesta to do better but I would like it to perform more like a Porsche I guess. Anything that helps it get around a corner faster is what I consider better.

I don't think that, mind you there are limits.
You won't get a FWD corner like a specialise RWD, it is 2 completely different chassis setup.
However, there are certainly a lot of improvement you can make over the OEM setup.
If OEM factory all comes out with perfect suspension, we aftermarket suspension specialist will be out of a job.

The thing with OEM is that they have a long list of compromise that they have to deal with.
Most of the time, adjustments is not an option so they have to find a point that will appeal to the masses.

When it comes to suspension, it is vehicle dynamic engineer that should work out what goes into the car (Or you hope someone did the math and the numbers wasn't pick out of thin air).
All the technical mumble jumbo (Wheel Frequency, cracking pressure, etc) aren't something the consumer should be concern with.
What is important is a suspension system that will do what it say out of the box.

That is one reason I decide to stay within the "coilovers" industry because you can design a system that are engineered to work out of the box.
You don't make a spring and hope what ever damper the customer put on will work with it, or vice versa.
It allows the user to get a setup that is already tuned, and they will just do the last fine setting to their personal preference.

You can have a setup with stiffer springs rate, and the driver can set the damping softer for daily usage, and stiffer for track use.
You end up with the best of both world provided that the math was done correctly in the first place, something we have been very good at.

That is the reason I don't suggest getting brace or sway bar while using the OEM springs / strut.
Because if you are looking for performance gain, it is best to switch out the parts that actually control the vehicle dynamics to a performance unit.
Than to add parts to a compromise, and hope the end result is something that you like.

Jerrick

 

[Joker328]

The thing with "Vehicle Dynamic" is a complete package all working together.
The basis of these are the tyres, you can only generate as much traction your tyres will generate no matter what suspension you are using.

On FWD race car, we do have suspension that have minimal "droop" travel in the rear.
The reason for that is when you corner hard into a turn, the rear damper "tops out".
This help the turn in of the car as well as traction, because turning motion are on the front wheels.

You have only as much traction to use as your tyres can generate, so suspension don't help you "pick up" any traction.
What it will allow you to do is direct what available traction to more useful task, or take away what you don't need.

The only time you can pick up traction is if the suspension you are using isn't using the available grip from the tyres.
So for example, stick a set of racing slick tyres on the OEM suspension and there will be more to gain from the suspension.
On the other hand, stick a set of racing suspension on a car with the OEM road tyres, and chances are it will do worst because the suspension are design for tyres that can generate more traction than what the OEM tyres can provide.

Jerrick

I wasn't saying suspension can "pick up" traction per se, but that the traction you are losing in the rear/inside is not fully transferred to the front/outside, so you are losing overall traction if the rear is slipping. I'm not a physicist or an engineer, but there must be some benefit to having the forces more evenly distributed across the tires so that they are not slipping. If the tail is sliding out because the rear inside tire has little/no weight on it, it would seem you are generating less total force toward the inside of the turn (don't know the technical term for this) than if no tires were slipping. This is why you don't see race car drivers over/under steering; it is slower. So with a torsion bar or anti-roll bar, there would seem to be a balance between really soft which would allow too much body roll and too stiff which would reduce the independence of the suspension and cause the inside tire to lift more easily, especially if there is a bump or some kind of upset. Even stock, I notice that whenever I hit a slight bump in a turn, the rear tends to kick out as both wheels are affected. All that would seem to be exaggerated with a stiffer torsion bar.

Overall, we are still back to the question of based on someone's individual car setup and driving style, what is the car doing, what do you want it to be doing, and what is the best or most cost-effective way to do that. As [MENTION=4567]Ryephile[/MENTION] pointed out, there isn't much good data out there on how these braces and torsion bars impact handling in different conditions. But I think we are in agreement that most folks are likely to see a much more noticeable improvement with perhaps fewer unintended consequences by going with coilovers (and ideally adjustable ones if you want to have ideal handing on track and daily driving).

 

[Plainrt]

I'd be interested to see real world test. Stock fiesta vs the oh so great coilover setup with same driver.Lots of talk how so great but no real data. I have had coilovers on other cars and koni setups on same cars. Konis always got my vote in the end.

 

[DaveG99]

Some really good information in this thread. I've learned a few things.

 

[Ryephile]

I'd be interested to see real world test. Stock fiesta vs the oh so great coilover setup with same driver.Lots of talk how so great but no real data. I have had coilovers on other cars and koni setups on same cars. Konis always got my vote in the end.

The only reasonably reputable one I've found is a write-up from MotoIQ: http://www.motoiq.com/MagazineArtic...mproving-the-Handling-With-ST-Suspension.aspx

They claimed 2 seconds improvement over stock with the ST XTA coilovers at Willow Springs.


Koni makes everything from junk to excellent dampers, so just throwing the name out there isn't very specific. e.g. I used to have a set of Koni 8041's on my Miata until I upgraded to Penske 7500's.

Also, hardly all coilovers are made equal. There are low-cost setups like Megan, K-Sport, and BC, and then there are bespoke high-end solutions from ANZE, and then everything in the middle for all budgets and applications. Generally you get what you pay for, but there are some high value setups like Bilstein B14 and Ohlins DFV and KW V3 that usually perform very well for their price.

 

[MeisterR]

I'd be interested to see real world test. Stock fiesta vs the oh so great coilover setup with same driver.Lots of talk how so great but no real data. I have had coilovers on other cars and koni setups on same cars. Konis always got my vote in the end.

I don't have one for Fiesta, but we did do something similar as a fun project with a MK1 Miata call The Ring Banana.
The idea was to make this 90hp Miata go around the ring in the 8 minute mark as cheap as possible.
You can see all their crazy project here: https://www.facebook.com/TheRingBanana/

Here is the base lap, a completely stock, used up, 90hp miata doing it's base lap (Nurburgring BTG 9:21.8)
https://www.youtube.com/watch?v=GHx6tSvjC94

Here is same car, same driver, only change from the base lap was from the 10 years old Kumho street tyres to Kumho V70A (Nurburgring BTG 8:59.9)
We didn't expect to hit the target on the first try, and didn't expect the tyres alone to knock 21 seconds off.
https://www.youtube.com/watch?v=mZCIXpODnxE

So after that, we decide to put the 10 years old road tyres back on, just install the suspension and re-do the alignment, and see what it will do.
We expected maybe about a 5 to 10 seconds difference, as after all it was still using the same 10 years old tyres as the base lap

Here is same car, same driver, only change was from base lap was MeisterR Zeta-R Coilovers and alignment (Nurburgring BTG 8:54.3)
The car knock 27 seconds off with suspension and alignment alone, and that was a surprise to everyone actually.

https://www.youtube.com/watch?v=UpFi0dfRnUM

Then finally, we put the V70A back on and do a final lap before the snow kicks in and the Nurburgring close.

Here is same car, same driver, only change was from base lap was MeisterR Zeta-R Coilovers, alignment, and Kumho V70A tyres (Nurburgring BTG 8:39.5)
The final lap knock over 40 seconds off he base lap, in a fully unprepared 90hp little Miata, and that was where we ended this fun little project.

https://www.youtube.com/watch?v=EvToQblt29Y

Now this was a bit of fun, nothing scientific.
There are different traffic at different time, and even with the same driver who is a professional race driver and the official driver for the Nissan GTR Ring Taxi, there are lots of variable.
But you can't deny that uprated suspension made a difference, the result will vary of course.

Jerrick

 

[Ryephile]

[MENTION=4680]MeisterR[/MENTION] That's pretty cool, thanks for sharing.

 

[BRGT350]

Personally, looking at what you are trying to achieve, I say a set of adjustable coilovers will probably be a better way forward.
I am not saying all the added parts does not work, but changing out the core of the suspension with something better will yield better result.

With adjustable coilovers, you get linear rate springs that are a bit more predictable.
You can adjustable front top mount so you can tune your front camber.
And you get adjustable damping that you can adjust ride quality, as well as suspension bias.

The adjustable damper is the main thing, because if you feel the rear isn't loose enough, you can stiffen the damping to get the rear to step out more.
If the front isn't griping well, you can soften the damper to let the front get more traction.
This adjustable damping allows you to dial in a setting that is right for the driver, help you to tune out understeer if it is something you do not want.

In the end, you get a different and much better car to drive than OEM springs / strut with added brace.

Jerrick

Yes, this is exactly correct. As an ex-suspension engineer, this is 100% the direction to go to change the handling of the car. Adding a rear bar just increases oversteer on a car that is already tail happy. I am not convinced the additional bracing does anything for the ST, besides add weight to the car and less weight to your wallet. You just can't create enough traction with street tires to deform the chassis enough to where a dinky brace is going to do anything. The Fiesta chassis is remarkably stiff. When you get into R-compound tires and are fighting .010 seconds off your lap time, then bracing starts to play a part. I would bet 95% of ST drivers are limited by 2 things, tires and skill. The tires aren't sticky enough to generate enough force to deflect the steel components and the driver doesn't have the skillset to drive a car at the limit in which those forces are created. The deformation of the bushings is way more than anything you will get in the steel parts. Adding a brace with rubber bushings and street tires isn't going to do anything. Unless somebody can provide data, I am not buying it.

Shocks, struts, springs, and tires are the biggest players in handling. Next up is tuning the suspension. Front toe can make significant changes in the corner entry behavior. If you lower the car, be sure to check bump steer as any toe change in bump will upset the balance of the car as the suspension articulates in a corner. Adjust tire pressures after that. Adding braces and torsion bars aren't going to do much. Get to the core of the suspension and go from there. Also, be sure you aren't changing parts on the car to make up for poor driver habits. I have been there before. It wasn't the car that was the problem, it was me not knowing enough about driving a car.

 

[RAAMaudio]

A few of us are in agreement

This car is very stiff and with all the mods below I still do not feel the need for adding braces, parts that do not make the car faster make it slower is how I look at it.

I do have a two point $2 DIY front brace as it seemed the only place the car needed one but also it is the rear mount for my diffuser and a bit of an inverted Gurney flap as well as part of ducting to bring in air near the DP to help pull more air from the engine bay, advised to me by a real race shop manager. He also agreed with my thought no other braces needed and my car was on 225 slicks on 9" wide wheels around, he drove the car and manages the shop that maintains the Octane cars and dozens of other race cars and they build customer cars there as well.

I have urethane front stock sway bar bushings and recently dropped the subframe to install aluminum steering rack bushings and still did not decide to do a larger front bar though was temped to try the none ST one.

I installed urethane bushings in all areas, some race, some street as not all the race ones were made yet when I ordered and was sent a mixture but so far very happy with them.

I do have a 5-way rear bar I modded off a BMW to do some testing with but have never felt a need to run it but did just go from 6/5k BC springs to 8/7K Swift springs so likely still not going to test the rear bar for some time yet. I cut the axle flanges loose and changed the rear camber and toe, -1.9, 0 degrees toe as did not like the stock setup from prior FWD experience.

My car is very fast and very neutral on track but could be a bit stiffer and the ride on 15's was so good I wanted to stiffen up the springs.

All these mods were done with the car had 293 miles on it, just 5 miles by me.

I have modded many cars and rarely used chassis bracing unless a full caged car on wide slicks, I plan to test a DIY STB at some point as well but the towers tie into the firewall really well as it is. If I do this it will be a simple bar at the front of the towers or two tubes that come together in the middle of the firewall if there is clearance for that setup.

----------------

At some point I will be considering different coilovers up front, if I go to coilovers in the rear I will then stiffen up the shock mounts and possibly build some bracing as needed since they are not engineered for that kind of load.