Suspension Binding... No More!
There are many things "wrong" with the SW20 suspension. It seems unrefined from factory and companies like Wilhelm Raceworks have developed kits to fix a multitude of the issues, such as suspension geometry. One of the other issues is suspension binding due to stock bushings or aftermarket polyurethane bushings. If anyone has swapped over to polyurethane bushings, you have found how incredible difficult it is to install the parts back in and articulate the suspension. That is because the movement of those control arms and other linkages is now twisting the polyurethane bushing and acting like its own spring.
This is NOT ideal. Back in 2014 I made a set of FK spherical inserts for the rear trailing arm because of this suspension binding issue. To this day, I still use the original FK bearing. I also purchased Wilhelm's front strut rod to eliminate the front suspension bind (and add some caster adjustment). I have been fine with this for awhile, but still, there are issues with the lower control arms.
The LCA's will physically rotate/twist when articulated (and in the rear its a lot more pronounced). This rotation compresses the polyurethane bushing and adds a level of binding into the mix.
The fix for these is to replace all the polyurethane bushings with spherical bearings. It is not as easy as it sounds. The MR2 SW20 suspension arms are locked and linked together in a way that make a very interesting movement from full droop to full compression. But with all the development from Alex Wilhelm and these new spherical bearing inserts, you can have a boundless, geometry corrected suspension.
Engineer Freely will be offering the following:
- Front LCA Spherical Inserts
- Rear LCA Spherical Inserts
- Rear Trailing Arm Spherical Inserts
- Trailing Arm to Rear LCA solid bushings
I refer to twist in bushings by the movement of the inserts in relation to the outer diameter of the bushing.
1) Front LCA Spherical Insert
This insert can be used with the Wilhelm Adjustable Strut rods and with the stock strut arm. Due to the way the strut arm bolts to the LCA, there is limited adjustability with Wilhelm's Arm (meaning you get about a 1" range of adjustability from the stock position). The reason is when you adjust the strut arm, the angle between the strut arm and the LCA will start to increase or decrease. This angle is proportional to the slop in the connection point of the double studs of the strut arm to the LCA. The slop in the bolted connect equates to about a 1" range which should be fine for anyone. However, if more range is desired, the bolt holes on the LCA can be bored open with a 0.5mm larger drill bit without issues.
So why is this only an issue with a double spherical setup? Well with spherical bearings, there is no give or take like the bushings will have. Once you exceed the limit of angle, it stops. On the rubber and polyurethane bushings, when you adjust the strut arm and exceed past the 1" range as described above, the LCA bushing will then start to compress and twist to adjust farther. You may not notice this issue at all, but it is happening. You are adding binding and a preloaded bushing into the mix of the suspension articulation. This is the issue we want to avoid.
The front LCA spherical insert uses FK bearings and when paired with Wilhelm's Strut rod, there appears to be no real limitation of articulation. During my tests I was able to compress the front suspension to 11.5" from wheel center to the fender with the limitation being my bump stop. There as no articulation binding from the spherical (remember, the spherical are not only moving with the suspension in the articulated direction, but also twisting in the opposite direction due to the design of the MR2 suspension, which would ultimately end up to be the real limit of how much it would be able to move). During full droop, 15.5" from the wheel center to the fender was achieved, but that is shock max. I disconnected the shock and was able to drop it all the way until my brake line maxed out. This means, there is no issue with spherical bearings being used in this design.
2) Rear LCA Spherical Insert
Much like the front suspension described above, the rear acts in a similar way. On the rear, the twist due to articulation is a lot more obvious since the location of the all the rest of the arms are in a different location compared to the front. The rear is more likely to be limited but the twist of the LCA bushing/bearing insert. When the aluminum housing makes contact with the spherical bearing inserts, that is the limit of twist.
During my testing I was able to test without and with the Wilhelm Geometry Kit (really what we are testing is the 1.25" spacer that spaces the LCA from the ball joint since this changes the location of the max articulation twist). I'll spill the beans, the rear LCA spherical bearings works without and with the Geometry Kit, so don't worry.
In stock form, without the kit, I was able to compress the shock to have the wheel center 10.5" from the fender (so with a 255/40/17, 24.5" tire, you would be tucking 1.75" into the fender) before I was sitting on the bump stops and visibly looking like the the spherical bearing was maxed out (fully twisted and mechanically locked). So keep in mind, at this point we may have found the mechanical limit of the spherical bushing design, however we are riding on the bump stops with a bunch of wheel tuck. You would hopefully never be in this situation on a road course!
On max droop, my coilovers were limited to 14" from the wheel center (I started to realize this was an issue with my coilover design because I actually don't have enough droop but that is a separate issue). I disconnected the shocks and was able to lower it 5-6 more. No issue with droop articulation twist.
With the Wilhelm Geometry kit, the spacer actually gives us some more breathing room. Basically the stock suspension puts us in the middle to upper range of the twist of the spherical bearing. The spacer pushes the LCA lower in the articulation sequence and puts the bearing into the range of the low-middle to upper-middle range. I was able to achieve the exact same results (10.5 compressed and 14" droop) but with the spherical bushing still having room to twist in both directions. So with a longer stroke shock, there is room all around.
3) Rear Trailing Arm Spherical Insert
This happened to be the one I created many years ago since I discovered how difficult it was to installed the suspension arms after the polyurethane bushings were installed. No issues with upper and lower articulation. Since this bushing is physically larger, there is more room for the bearing to move without mechanical lock. This would be the first one I would replace in the rear due to how much it will unbind the suspension.
4) Trailing Arm to Rear LCA solid bushings
This last bushing is one I saw Megan Racing's trailing arm get so wrong. They introduced a spherical bearing here and I can understand why they may have thought it was a good idea, but its not. You do not want flexibility here. This acts exactly like the front arms where it needs to be mechanically locked from arm to arm. Hux racing's arm's did it right with 1 degree of freedom to assist with the variable lengths of the trailing arm and the LCA. With factory arm's you have this interesting situation where "stockish location is sort of OK".
During testing I measured installed my whole spherical bushing setup of arms plus this solid bushing in the exact location where my last alignment was and everything just bolted together easily. I was able to add a little bit of adjustability to adjust rear caster (but since rear caster is almost irrelevant here, it really does not matter). So basically if you center up the wheel in the wheel well, the factory location of the trailing arm to the rear LCA is ideal, then there is no issue with the solid bushing. If for some reason you are trying to push the wheel way out of factory specs, then you may run into an issue, but this does not seem to be a case that most would ever fall into.
In summary, there are trade offs. You loose compliance and the ability to "fake" the extra adjustment since you won't be able to twist and compress the factory bushings or polyurethane bushings anymore. But you gain a freely articulated suspension geometry. There will be no added spring rate based on bound bushings.
What are my final parts I chose to use?
- Engineer Freely Full Spherical Bearing Kit (that was a given)
- Wilhelm Geometry Kit
- Wilhelm Adjustable Strut Rod