posted on March 09, 2014 10:31
Project FR-S: Getting More Out of Our Front Suspension With Whiteline and Turn In Concepts!
The suspension on our FR-S was originally done over a year ago when we were prepping the car for the 2012 SEMA show. At the time the car was pretty new on the market and our choices were limited to a few prime items plus stuff we made work from the Subaru STI that shares some parts with the FR-S/BRZ. Since the time when we first built the car, Whiteline has come out with a bunch of parts dedicated to the FR-S/BRZ chassis that we have been eagerly awaiting.
With its wide and sticky 265/35-18 Achilles 123S tires, our FR-S was producing a lot of grip. The stick was translating into a lot of body roll and sluggish transient response even though we had added KW's V3 coilovers and a Whiteline front anti sway bar. This was a case of tuning the car to our combo and at the time, there was little on the market available but now it's time to upgrade to Whiteline's full product line up and get serious.
To gain more front roll stiffness we obtained Whiteline's newest FR-S/BRZ front sway bar, the heavy duty X Blade Adjustable model. It is 22mm in diameter and features Whiteline's newest low maintenance rod end adjustable end links for low compliance and long quiet life. The endlinks are adjustable for end to end length which is important for removing preload after the car is corner weighted. The bar has two positions for adjustment, just the thing for at the track chassis tuning. The new bar is almost 50% stiffer than our old one which has more than a 30% influence on our front end's total amount of roll stiffness.
We also used Whiteline's roll center correction and bump steer reduction kit. The use of this kit is very important for a car that has been lowered as much as ours. By dropping the outer ball joint and tie rod ends with longer shanked parts, the roll center is raised without adding bump steer. This restores a close to stock roll center height on a lowered car. With a higher roll center, there is a lower roll moment to cause body roll in the first place. This is adding geometric anti roll. The suspension will resist roll independent of spring and bar rates. Putting the lower control arm in a more factory like position also helps a McPherson strut car by making the car less likely to gain positive camber under roll. This also helps front grip.
The FR-S/BRZ suffers from big squishy rubber bushings that support the steering rack. We got these solid delrin bushings from Turn In Concepts. The solid bushings will eliminate all play in our steering.
Whiteline has front forward lower control arm bushings (part number KCA434)
that do several things, first the obvious, they replace a big squishy rubber part with firm polyurethane. You can see that since this part must displace radially and axially due to its sideways mounting, that the bushing itself has engineered flex built into it in the right direction to prevent binding. Next the cool stuff. The bushing cants the front of the lower control arm inward pulling the wheel forward, increasing caster by over 0.5 degrees. This helps stability and turn in by giving negative camber when the wheel is turned. Lastly, it move the pivot point of the lower control arm up by around 0.3 inches which reduces anti dive. Reducing anti dive means that the front end will have more grip if you are trail braking or left foot braking. It also raises the roll center slightly and improves the camber curve slightly as well.
Monday, March 10, 2014 5:15 AM
Wow, that's a lot of static camber!
Monday, March 10, 2014 6:47 AM
In my experience poly bushings have a very short service life in a street car, once the grease dries out and dirt gets in the polyurethane wears away creating a lot of slop very quickly. Even if you are diligent about cleaning and regreasing, which is a major pain, they still deform pretty quickly. What makes these different?
Monday, March 10, 2014 7:40 AM
In our experience Whiteline bushings made within the last two years are made out of a more resilient urethane and last longer than others. It doesn't seem to take a compression set like others.
Monday, March 10, 2014 9:16 AM
Wow, those alignment numbers are beautiful compares to what I was able to get on my '08 WRX. Without camber plates I was on the order of -1.5deg camber, 6.5deg caster, and (iirc) 16deg kingpin or so.
Mike, can you speak to the toe setting here? I know your suspension guides mentioned toe out can be needed to compensate for large camber. Is 1/8" appropriate for 3.5deg? Or would you consider that to be additional toe out to sharpen turn in?
Clearly this varies tire to tire based in cornering stiffness but I've never heard a good rule of thumb.
Monday, March 10, 2014 10:16 AM
@ ED9Man: 2 years and about 40-50k miles on my Whiteline bushings on the Jetta TDI project and no problems here.
Monday, March 10, 2014 10:33 AM
So KPI leads caster by 3 degrees here. Is there a general rule of thumb for wanting one to exceed the other? If I'm remembering correctly, caster gains camber when the wheel turns, but loses it on suspension compression whereas KPI is the exact opposite. So the net product here is a wheel that loses a little camber to steering input, but gains it back and then some with compression and even more now with proper geometry from the roll center/bump steer kit.
Monday, March 10, 2014 10:50 AM
Good to know about the bushings. I bet part of it is that SoCal is a little easier on them than New England is!
Monday, March 10, 2014 11:01 AM
@Dusty, the static camber is appropriate for track cars. My old Evo with a strut setup, I ran -3.0. Even the S2000 with the multi-link front, -3.0 is common.
@ED9man, NE is pretty rough on all parts of the car as you well know :) My S2k is a Texas and SoCal car, and barely a hint of rust anywhere on the underside. I think the most rusty part I have delt with are the nuts on the cat.
Monday, March 10, 2014 11:21 AM
I usually run toe out with a cars that have a lot of camber to counteract the camber thrust when the car is going straight ahead. This results in less rolling resistance as well and improves turn-in.
Leading caster with KPI is one of my tricks on cars that allow this adjustment. Too much caster can result in jacking weight across the car causing understeer when the wheel is turned. KPI counteracts this as well as improves straight ahead stability and feel.
Monday, March 10, 2014 12:45 PM
Another great article!
Regarding the stuck bolts, I use Plus Gas at work which does exactly what it shows on the front of the tin! I work in a tyre factory so you get all kinds of seized bolts and fasteners from rust to chemical corrosion all the way to lime-scale and Plus gas does pretty well. This is the stuff for reference http://www.ebay.co.uk/itm/Plusgas-803-10-Plusgas-Tin-500ml-Lubricating-Sprays-Oils-/181295611715
It also works its way into un-cured (green) rubber pretty well if that's any use to you guys and girls!
Monday, March 10, 2014 8:33 PM
What is "transient response"? Wiki says "the response of a system to a change from equilibrium". To me, this could mean a few things...
Monday, March 10, 2014 11:35 PM
Basically what is meant in this context is that the car will more quickly and precisely react to driver inputs.
Rather than taking some time to 'set into the corner' and wallowing midcorner when the driver tries to adjust the line, these mods would hopefully make it drive 'crisper' and make it easier for the driver to best utilize the tires and take the line they intend.