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Time to read 7 min
When converting a fully driven street car to a track car upgrading suspension components is a must. When we started our journey of driving my 15 STi to and from the track we upgraded the suspension with some small changes such as going from rubber OEM bushings to polyurethane bushings , and if you've done this before you probably instantly realized how much vibration and road noise the rubber bushings have been absorbing almost instantly (unless your car is already pretty loud). You also probably notice how much tighter the car feels around turns due to the movement being more restricted in comparison to the rubber bushings. Well, we now took it a step further and upgraded our bushings to SPL's FK spherical bearings among other full race car mode goodies.
The first upgrade we installed on the STI was SPL's Rear Traction Arms. These were super easy to install and due to being made out of Billet 6061 -T6 Aluminum they were also light weight, which as an added bonus makes them easier to install over your head. So what's the benefit of these rear traction arms you might ask? If you've had your car on track, you probably experienced wheel hop at one point. This is not ideal for your times on the track nor does it make your drivetrain happy with the repeated torsional unloading and loading. To clarify what wheel hop is - it's when bushing deflection ( movement) causes oscillation ( the repetitive torsional unloading and loading) in the rear suspension under hard acceleration and braking.
Example of wheel hop is when one is at the start of a race in a standing start or a turn with a slow exit where one will be in a lower gear and fighting to get back to throttle as quickly as possible , in either of these scenarios the driver can experience a harsh jolt or thump feel in the steering wheel or seat. This is jolt feeling is due to the bushing deflection which is causing the tires to lose contact traction and gain it, then lose it and gain it again a few times in a row (oscillation) . So with the goal being to have the car a full purpose track car, we've upgraded to SPL's Rear Traction Arms which, elimate the bushing deflection due to their use of their 3 piece FK spherical bearings which offer increased stability and response when getting back on the throttle aggressively.
Photo Credit: Danny Phantom
To easily tune out rear bump steer and anti-squat, SPL Parts has made their rear traction arms length adjustable. Bumpsteer is a measure of wheel steer angle change with vertical suspension travel or when your wheels turn in and out as your car is moving up and down basically steering without you turning the wheel. Since we don’t want this happening on a race track we try to get as close to zero or near zero bump steer as we can. To do so we need to have the tie rods on either side of the car to be pointing toward a point called the instant center. The instant center is a point where the inner tie rod pivot is in line with the lower control arm inner pivot point as shown in the picture below. The tie rods also need to be a specific length and SPL makes adjusting the length easy while installed on the car so we can tune out the bump steer quickly.
As mentioned the adjustable length on the rear traction arms also helps with anti squat. Anti squat is how the rear in will move vertically and compress under acceleration and braking. When you adjust the length of the traction arm it allows the weight transfer to the rear to be reduced, anti squat increased and forces from acceleration to be passed through the suspension and control arms rather than the struts/coilovers. Achieving an optimal percentage of anti squat can also help the car maintain a level ride height and allow for the tires to have a better contact patch under acceleration. The ability to adjust this length allows for quick adjustments to reach the desired percentage of anti squat for your specific application.
Photo Credit: Danny Phantom
Continue with more upgrades in the rear SPL's Rear Toe Arms with the eccentric lock out kit, helps eliminate bushing deflection as well as enables optimal tire wear and handling in high speed turns. SPL's toe arms are made from 2024 Aluminum and have the 3 piece Teflon linked FK Hiem joints, which is ideal to handle the tough demands on the race track. To explain toe, imagine viewing a car from above and observing the angle of the wheels from the center. When the front of the wheels are pointing towards the center of the car then that would be positive toe or toe in- if the front of the wheels are pointed away from the center of the car then that would be tow out or negative toe. SPL's Rear Toe Arms make it easy to adjust toe to the settings to your desired specification. What's great about this set from SPL is it also comes with the eccentric lockout kit , which replaces the OEM eccentric bolts that tend to slip when you're racing. When the OEM eccentric bolt slip, they can change rear alignment specs and cause uneven tire wear and issues with handling in corners which essentially can make you slower and not use the full tire - you're paying for the whole might as well use the whole tire.
After tapping a tirewall at Lime Rock and mashing the one gator you're not supposed to hit at the WeatherTech Raceway Laguna (Turn 6), I can confirm that this eccentric lockout kit holds up to the claims. Despite the impacts nothing in regard to the toe arms moved and I think the team, SPL themselves and I were all impressed to see the kind of load these things could handle and remain perfectly intact. The other plus side to the lockout kit is that you can uninstall and reinstall the toe arms and keep the prior alignment settings, so no having to redo everything if you take them out.
Photo Credit: Danny Phantom
Continuing on to the upgrades in the rear, next is SPL's adjustable Rear Lower Camber Arms. These also help eliminate bushing deflection due to their spherical bearings and allow for easy camber adjustments. When viewing a car from the front, camber is the inward or outward angle of the wheel. The angle of the camber is what allows proper tire wear, better handling and speed when aligned correctly. Since our goal is road racing and we have the car lowered, unwanted negative camber can occur and SPL's camber arms will allow us to adjust how much negative or positive camber we want for our application.
The last upgrade we did in the rear are SPL's PRO Rear Sway bar end links. Swaybars work to keep the tires in contact with the track by decreasing weight transfer. To achieve bettering handling, corner balancing and better aerodynamics the car will need to be lowered sometimes, which causes the suspension geometry to change. It's important to be sure the angle of the sway bar is correct when doing so and thankfully SPL's adjustable rear sway bar end links can be shortened or extended easily to ensure a proper angle of attack and eliminate unwanted preload. These endlinks are made with a 2- piece Teflon lined FK 1/2" bearings to ensure they can handle the load from stiffer sway bars.
Photo Credit: Rob Wilkinson
Moving on to the front, we kept the upgrades simple and replaced our weaker outer front tie rod with SPL's Front Tie Rod Ends that are Bumpsteer Adjustable. We chose SPL to upgrade to because their tie rod ends are beefed up and able to take on our track abuse since they are machined heat treated nickel plated 4140 chromoly steel shanks with 304 stainless steel bump steer spacers, 2024-T351 aluminum turnbuckles paired with the low-friction PTFE-lined FK rod ends. Having these built to handle the demand on track is crucial especially given that these will directly affect ability to steer the car. The steering assembly is made up of a rack, knuckle and inner and outer tie rod and the outer tie rod is what is connecting to the steering knuckle which is what turns the front wheels. SPL's front tie rod ends being adjustable allow us to modify the length of the tie rod which will adjust toe. Increasing the tie rod length pushes the back of the wheel away from the center of the car , which then pushes the frontside of the wheel towards the center and creates toe in. Very similar to the rear traction arm we touched on, the front tie rods have adjustments that allow us to tune out unwanted bumpsteer in the front.
After we installed these upgrades, we took the car to the track to see how it would hold up and compare to what we had prior. I wanted to test these out with the least amount of variables changed as possible to really have a fair assessment, so we picked Lime Rock as our track to test at with a set of sticker Yokohama A052's again. However, we did have to detune the car from the 660whp we had last year to midgait some engine issues. Previously with the old suspension set up and the full power, I was only able to manage a 1.01.4 but this time with slower powered car I was able to do a 0.58.4! We were smoothly able to adjust the toe as needed at the track and the car felt way easier to handle which like I mentioned, might have led to some over confidence and a quick meeting with the tire wall. At least we know the car is there, the driver just needs to catch up! Last thing I'd like to point out about why SPL's products are so great in my opinion - they’re made in the USA which I feel is rare to find anymore. Great quality, great customer service and great craftsmanship that help get great track side results.
Photo Credit: Danny Phantom
Note: Keep in mind these products are chosen for a full race car application and not a daily driver. When choosing products always keep in mind the purpose of your build.
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