This works fine until you apply some torque and the diff tries to twist out of the frame (that’s bad).
We recently took out Locost out to Ocala Grand Prix for some shakedown laps, and basically to see if anything was going to fall off. After a thorough nut-and-bolt check, we hit the track and learned that even though our Locost has not been aligned with anything more accurate than the human eyeball, it’s a hoot to drive. At least until the front wheel starts to come off. A bent wheel that was not allowing the lug nuts to stay tight was the first problem we encountered, which is easily fixable with some cooler wheels.
The other problem we encountered will need a little more extensive solution. After a few laps, a horrible clunking noise began to be heard from the rear of the car under acceleration. What we originally thought was a diff failure turned out to be more of a design oversight. The Miata diff is usually connected to the engine and trans through an aluminum powertrain brace. With the shortened driveshaft and narrow center tunnel of the Locost, there is no way to install such a brace, and the Miata rear end simply hangs in the back of the Locost on two rather stout bolts. This works fine until you apply some torque and the diff tries to twist out of the frame (that’s bad).
A solution needed to be devised to better locate the rear end, so we visited out local Miata expert, Stu Brumer of BSI racing. After complimenting the overall design and sturdiness of the Locost chassis, he helped us brainstorm some ways to control the torque at the rear end. Our solution was to affix ears to the back of a stock Miata housing, then run a brace rearward to a new mount that will be affixed to the chassis. Using rod ends will allow us to preload and adjust the differential angle. BSI is currently in the experimental stages of their solution. We’ll shoot some pictures when fabrication begins. Hopefully by this time next week the brace will be in place and the Locost will be ready for some zero-60 sprints.
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