Roll Center Correction & Bump Steer Correction
2013-2019 FRS – BRZ – GT86
Price is for one kit, both front wheels
We feel this kit is vital to obtain best handling and compliance in any lowered 86
What are Roll Center Adjusters?
All car suspensions are designed to have their RC (Roll Center) above ground. This is the virtual pivot point for each corner of suspension. The CG (Center of Gravity) is slightly above the RC. This allows the suspension to resist roll when the car experiences lateral G in a turn.
Lowering any car lowers RC. Strut cars can lose RC height 2-3X faster than ride height. Meaning, lowering the car 2″ might lower RC 5-7″. This means your lowered car will roll more at a given lateral G. This is one reason why much stiffer springs and sway bars are needed when cars are lowered. The problem with such stiff suspension is that it reduces compliance and grip. No purpose-built pro level race car skips roll center correction, but it is often ignored for amateur tuners who do not yet understand suspension geometry and all its implications.
The other issue with lowering RC too much is a change on Roll Center Axis. This is the virtual axis between front and rear roll centers. This is a key element to handling, and very finely tuned in the 86. Again, lowering an 86 say 1.5″ will change the angle or “rake” of the roll center axis and produce unwanted pitching moments and require band-aid fixes such as excessively stiff spring rates. This kit corrects front roll center so there is less need for heavy spring rates and huge sway bars to resist roll. This reduction in effective wheel rate incerases compliance, which is a go0d thing. Compliance equals grip.
What is Bump Steer Correction?
All cars have steering geometry optimized for OEM ride height. Toe angle changes with suspension movement. This is intentional and is part of the OEM suspension tuning. If a car is lowered, the steering geometry will be in a different part of its toe curve. Lowering too much almost always results in adverse bump steer characteristics. Notice how a stock 86 tracks nicely in a long fast curve as the suspension moves? If lowered too much without bumpsteer correction, the car begins to dart around in curves when it hits bumps. This is often due more to lack of bump steer correction than bad shocks. This kit corrects bumpsteer so the car can be lowered for best handling and response.