Jeff Young
GT40s Supporter
Ok, Ron suggested I post here as it appears there is a whole lot of track car knowledge. This particular area of inquiry revolves around that wonderful suspension design known as the "live rear axle."
I've got one on the ITS TR8 I race here with the SCCA in the US. Right now, it has basically a stock rear suspension, basically. It has lower parallel trailing arms with spherical bearings, a stock spring location (which I have to keep) about 2/3 of the down the arms towards the axle, triangulated uppers that angle inward towards the pumpkin of the differential (no sphericals there), a panhard rod, and some DA Konis revalved for my spring rate (300 lbs, fronts are 600).
I presently have a Quaife LSD and we run Hoosier's DOT road race radial, which is basically a racing slick.
Rules say bushings are free (meaning I can run sphericals, urethane, rubber, or air if I want), stock suspension mounting points must remain, but ANY traction bar can be used with traction bar basically defined as anything used to locate or stablize the rear axle.
Car handles decent, corners flat. It is really good in fast sweepers (think uphill esses of VIR). In slower stuff, and quick transitions, car will turn in nicely (no push/understeer), but has serious oversteer issues powering off.
After some discussions elsewhere I've come to the conclusion that I think the upper links are binding badly under roll, causing infinite spring rate, loss of traction and nasty wheelspin.
Under our rules, I can add a third link to the top of the diff and running to the chassis, and then use foam bushings on the triangulated upper links so that effectively they do nothing.
Some here in the states prefer that approach -- the "trilink" -- with a panhard or, better yet, a watts linkage to locate the axle laterally. Others say use the four link w/o a panhard.
Thoughts? Suggestions? Hypothecation? Speechification?
I've got one on the ITS TR8 I race here with the SCCA in the US. Right now, it has basically a stock rear suspension, basically. It has lower parallel trailing arms with spherical bearings, a stock spring location (which I have to keep) about 2/3 of the down the arms towards the axle, triangulated uppers that angle inward towards the pumpkin of the differential (no sphericals there), a panhard rod, and some DA Konis revalved for my spring rate (300 lbs, fronts are 600).
I presently have a Quaife LSD and we run Hoosier's DOT road race radial, which is basically a racing slick.
Rules say bushings are free (meaning I can run sphericals, urethane, rubber, or air if I want), stock suspension mounting points must remain, but ANY traction bar can be used with traction bar basically defined as anything used to locate or stablize the rear axle.
Car handles decent, corners flat. It is really good in fast sweepers (think uphill esses of VIR). In slower stuff, and quick transitions, car will turn in nicely (no push/understeer), but has serious oversteer issues powering off.
After some discussions elsewhere I've come to the conclusion that I think the upper links are binding badly under roll, causing infinite spring rate, loss of traction and nasty wheelspin.
Under our rules, I can add a third link to the top of the diff and running to the chassis, and then use foam bushings on the triangulated upper links so that effectively they do nothing.
Some here in the states prefer that approach -- the "trilink" -- with a panhard or, better yet, a watts linkage to locate the axle laterally. Others say use the four link w/o a panhard.
Thoughts? Suggestions? Hypothecation? Speechification?