As we look through our comments in the log book, one that stands out is rear wheel spin as we try to accelerate to the next corner. We’ve worked on the KW coil-over suspension to try and increase rear end grip, and even tried different tires, settling on the Hankook Ventus R-S3. And while this has helped, at most event sites we can still slide the rear exiting medium to high speed corners, resulting in sideways motion without forward progress. A look at the data stream from our onboard Race Technology data logger shows the OE Mazda diff still allows some single wheel spin, and we’re getting inside wheelspin and not just sliding both rears.
So we turned to the guys at OS Giken, makers of some tricky driveline parts and the OS Super Lock LSD. This tunable limited slip diff allows the rear end to lock smoothly with power application, and can be tuned to have different lock rates during acceleration and deceleration.
To simplify our installation and allow us the opportunity to try some back to back testing, we sourced a separate diff carrier to install the Giken unit in. This allowed us to simply swap out the pre-loaded diff housing in about 2.5 hours, with the help of a co-worker’s lift. Some things shouldn’t be done on the garage floor.
After a few break in miles, Project STR driver Chris Harvey joined the fun with the Windy City Miata Club to get an initial read on how the freshly installed OS Giken limited slip differential works. The competitors enjoyed great courses and lots of runs as they battled to reduce time throughout the day. Chris piloted the Project STR MX5 to the quickest time of the day for all Mazda's entered and 2nd overall for the event, just a few tenths behind a well prepped and driven BMW M3 running on ultra-grippy Hoosier autocross tires.
Next up for Project STR will be the SCCA Great Lakes Division Championship event held at Grissom AFB in Peru, IN, August 6th and 7th.