Steering All Over the Place at 55mph+

Demonx2 said

My $0.02.....I know EXACTLY how you feel. You are describing my avatar car but mine gets bad at speeds above 70+ mph (partway to the 1/8 mile mark). Mine's not fixed yet but I know it is due to having NO positive caster. Lucky to get it to 0deg caster. Feels exactly as you describe - car wants to swerve and swap ends.

Before it goes back to the track, new SPA fully adjustable UCA's I got from Peter Bergman go in. You can bet it will have at least +2deg of caster to start with. I suspect your alignment likely does not have any or at least has insufficient positive caster. These guys on here made me a believer and my car's antics backed them up!! I encourage you to follow these guy's advice!

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You wont have any trouble getting +2° or a lot more with the SPC UCA’s, I have +6.5° with mine. A drag race set up is a bit different than what I run, but yeah, even a couple of degrees will make a big difference.

It’s hard to overstate that the original alignment specs were intended for bias ply tires and are completely backwards for radials. The tire construction totally changes how the tires act under loads, and radials need positive caster. With little positive caster, or even no or negative caster, radials will feel like driving a shopping cart.

Unfortunately, the stock parts weren’t really designed for a significant amount of positive caster. The offset bushings definitely can fix that if used to increase caster, typically that will get you a good +3.5° which is good for most drivers and tire set ups. As the front tires get wider, more positive caster helps keep the wide tires from tracking. Which is why I run so much, I’ve got 275/35/18’s up front. So a “pro-touring” or handling set up with wide front tires can use a lot more than what you can get with just offset bushings.