Project FR-S: More Rear Suspension with Cusco and Whiteline

by Mike Kojima

In our last segment we brought the front suspension of our FR-S up to the latest top standards with new parts developed for the car since we started developing our project.  Now it's time to bring the rear suspension up to snuff with some of the latest parts now out for the car.  Since we started out project, Cusco and Whiteline have come up with more parts for the rear suspension.

Our suspension had first gotten done well over a year ago and we used Suabaru STI parts in the initial stage.  We used Cusco adjustable lower arms and some Whiteline bushings and their first generation of rear swaybar.  As we are running tires much bigger than stock, (265 vs 215), the additional grip was causing a lot of body roll even with our KW coilovers and upsized swaybar.

With only the lower arm adjustable we could not reduce our negative camber as much as we wanted to and we still had a bunch of squishy rubber bushings in the back of the car.  Now that Cusco and Whiteline have come out with more parts it was time for us to get installing again.

Want more Project FR-S?  MotoIQ Project Scion FR-S

We already had the Cusco lower rear control arm but to eliminate some rubber and add some adjustability in the toe curve we added Cusco's traction link that replaces the stock part.  Making this link shorter gives more toe in under roll, making it longer reduces the toe in under roll.  We made the link slightly longer to reduce toe in under roll.
We also installed Cusco's toe links for toe adjustability.  With the use of these links we could lock out the stock toe adjusting eccentrics.  With spherical bearing replacing rubber the toe is controlled more accurately under hard side load.  You can really feel rear toe changes when driving hard.  Most drivers can feel 1/8" of an inch change so it's important to reduce deflection here.
Whiteline has come up with a larger adjustable X-Blade rear bar for the FR-S (part number BSR54XZ) than what we previously ran.  It is 18mm thick vs the 16mm thick part we had before.  This is much better than the stock 14mm part with is nearly useless.  The new bar is approximately 60% stiffer than the old part and a whopping 170% stiffer than stock.  This gain gives around a 30% overall increase in rear roll stiffness.  The X-Blade rear swaybar comes with Whiteline's new ball joint adjustable swaybar links, positioning collars and braces that secure the chassis mounts to the crossmember so they won't tear out.  Having adjustable end links is important to take the preload out of the bar when corner weighting.
Previously we had added Whiteline's subframe bushings (part number KDT921) that filled the gaps in the rubber mounts with urethane.  Although these helped reduce subframe movement greatly, there was still a bunch of soft rubber back there.  To get rid of the rubber we opted to completely replace the bushings with Whiteline's urethane parts to get rid of more compliance.
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Tuesday, March 25, 2014 3:34 AM
Lots of cool parts there!

Changing the bushing to an eccentric does however very very little to enhancing the geometry, you are only changing the distance between outer and inner pivot points, the inner pivot is still fixed to the subframe :)
Mike Kojima
Mike Kojimalink
Tuesday, March 25, 2014 8:31 AM
No it's moving the center of rotation of the link hence it is changing the geometry quite a bit, the whole half thickness of the bushing material in the vertical direction.
Tuesday, March 25, 2014 8:47 AM
I'm assuming if you just pull the fuse for the electric power steering that it would be way to heavy. But is it possible to tune the amount of assist and how quickly it reacts to changes? Is it possible to access the electric power steering through the ECM? Or does it have a completely separate control module?
Alan Davis
Alan Davislink
Tuesday, March 25, 2014 8:56 AM
I didn't see the driver in the driver's seat while the alignment was being done. I know you guys had him (or weight equivalent) in the driver's seat while the alignment was being performed...
Mike Kojima
Mike Kojimalink
Tuesday, March 25, 2014 9:11 AM
sethulrich- one one knows how to reprogram the electric power steering yet. I have never liked any electrical assist steering systems, they feel weird. So far the steering feel is the only thing our pro drivers have complained about as well.

AlanD- On street cars I usually don't bother. Street cars have chassis deflection and bushing compliance even with urethane bushings and it doesn't make a measurable difference unless you are corner weighting. I usually don't bother corner weighting street cars either unless they have really weird corner weights. A race car with bearings and a cage, you bet but on a street car no. Most modern cars come out pretty good when you scale them or good enough.
Tuesday, March 25, 2014 9:32 AM
Howard must be sick of dropping that subframe by now. It's really interesting that all of the bushing changes haven't changed the NHV yet. My Altezza wasn't bad till I installed a urethane diff nose bushing. Maybe the FRS has really good sound insulation.

Ill get one eventually.
Tuesday, March 25, 2014 11:54 AM
Why is toe measured in inches rather than degrees? If you get a larger diameter tire an 1/8" toe is less slip angle than on a smaller diameter, right? So why wouldn't you measure it as an angle?
Mike Kojima
Mike Kojimalink
Tuesday, March 25, 2014 12:57 PM
No better reason than its easy to set toe by inches in the field.
Tuesday, March 25, 2014 1:27 PM
Makes sense.
Thursday, April 03, 2014 2:47 PM
Using inches for toe over degrees by industry standard means it's referenced to a standard tire size. Either 26" or 28" diameter, don't remember which it is. In this case though, it's not, but the difference in any feasible tire diameter is likely within the realms of measurement accuracy and repeatability.

I mega-loath bushing installs.

It would be interesting to see how much of a change to roll-center, toe-curve and anti-squat this makes. Probably a pretty small amount, but every little bit counts.
Wednesday, May 28, 2014 7:22 PM
I looked into modifying the electric power steering in my 2013 Si and used this article with some success: http://www.autospeed.com/cms/article.html?&A=111532
In summary, you can intercept some of the signals sent by the car to the electric steering mechanism to induce less boost by using pots and resistors. In my case pulling the fuse worked but the effort was extremely high and it also disabled VSA and ABS. I wish we could incorporate an ECU type flash to fix this!
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