Thread: New to the site - Questions about my '31 Model A

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Originally Posted by jerry clayton

Been studing the build pics of the frame and finding that it doesn't have any bracing or triangulation for torsional flex was baffling me-then I discovered the site of the frame builder and that explained it-He really is a builder of v8 chopper bikes-also of course with a single front wheel there aren't any steering geometry issues as in a four wheel vehicle ( caster, camber, toe in, bump steer)

No steering issues? Motorcycle and bicycle steering geometry is fairly complicated. You do have caster (called rake by motorcycle builders and head tube angle by bicycle frame builders). In addition, you have fork offset on both bicycles and motorcycles. Motorcycles can also have raked trees, to increase offset and reduce excessive trail from a large rake. In the end, the builder is striving for a particular TRAIL. Trail is the horizontal distance between a line through the steering axis, intersecting the ground and the actual contact point of the tire, with the ground. Unless the caster angle is zero, there is always some amount of trail. Cars have a trail value, and it's simple to calculate. All it involves is caster and tire diameter. Trail = tire radius/tanC, where C is 90 minus the caster angle. A lot of car builders only think of caster and not the affect of tire diameter on the trail. The larger the tire, the more trail and the more caster angle, the larger the trail (for a given tire diameter). A google search on rake and trail will bring up a lot of articles.

rake and trail

Looks like there is no track bar on the front axle.....if not you need to add one, especially with the cross steer setup and hairpins. The axle will sway back and forth on the spring shackles causing the death wobble. Also I'd make sure the wheels have a proper balance. It's really a nice looking car, sounds like you just need to work a few bugs out. Also 2x on the anti-squeal spray for the back of the brake pads all the auto part stores sell it.