EricJ Posted March 26 Report Share Posted March 26 20 minutes ago, Shadrach said: The axel of a bike never is as far as I know. It either aligns with the fork/fork slider or is ahead of it as pictured. That's a good example showing that it's really the relationship between the tire contact patch and the steering axis that matters. With a decent rake angle in the forks and a large tire radius the axle can be in front of the steering axis but the tire contact patch behind it. That's what creates the caster effect. As the tire contact patch approaches the steering axis stability is lost. 2 Quote Link to comment Share on other sites More sharing options...
PT20J Posted March 26 Report Share Posted March 26 Comparing autos (and airplanes) to bicycles and motorcycles may be confusing because each vehicle has it's own terminology for the same geometric parameters. Here's a picture from Wikipedia showing that a bicycle has, what in automobiles is called, positive caster. We're talking about caster (steering axis angle), bicycle manufacturers talk about trail. But the idea is the same: the tire contact point is behind the extended steering axis. 2 Quote Link to comment Share on other sites More sharing options...
Shadrach Posted March 26 Report Share Posted March 26 3 hours ago, PT20J said: Comparing autos (and airplanes) to bicycles and motorcycles may be confusing because each vehicle has it's own terminology for the same geometric parameters. Here's a picture from Wikipedia showing that a bicycle has, what in automobiles is called, positive caster. We're talking about caster (steering axis angle), bicycle manufacturers talk about trail. But the idea is the same: the tire contact point is behind the extended steering axis. The shipping cart comparison is more odd as the zero axis (axle and contact patch) and steering axis do not intersect. Quote Link to comment Share on other sites More sharing options...
PT20J Posted March 26 Report Share Posted March 26 4 hours ago, PT20J said: It's harder to visualize when the pivot point is at an angle. It's more obvious when the pivot point is vertical as on a shopping cart wheel. The force moving the wheel forward acts at the pivot point and the friction force on the wheel acts in the opposite direction at the ground contact point. When the wheel is moving straight ahead, the two forces are in alignment, but when the wheel is turned, the two forces are not aligned and thus create a restoring torque that turns the wheel back into alignment. Perhaps a picture is better to illustrate the idea: 1 Quote Link to comment Share on other sites More sharing options...
PT20J Posted March 26 Report Share Posted March 26 It's interesting to note that the restoring force is dependent upon the coefficient of friction between the surface and the tire. That's why there is little restoring force on icy surfaces or when hydroplaning. 1 Quote Link to comment Share on other sites More sharing options...
carusoam Posted March 27 Report Share Posted March 27 Awesome drawings Skip! those donuts in the stack of five… they are more than original… those are called Firestone donuts… look carefully at the work completed… the four stack donuts may have a different steel tube or other part associated with the change from five to four donuts…. if for some reason, the proper angles can’t be achieved by following the MM instructions… it could be, a part didn’t get swapped in as expected… check the center tube for its health… they have a high likelihood of suffering from thinning over the decades… Fuzzy PP memories only, not a mechanic… Best regards, -a- 1 Quote Link to comment Share on other sites More sharing options...
Shadrach Posted March 27 Report Share Posted March 27 3 hours ago, PT20J said: Perhaps a picture is better to illustrate the idea: Skip, What did you use to create these drawings? 1 Quote Link to comment Share on other sites More sharing options...
carusoam Posted March 27 Report Share Posted March 27 Drawing board pen stencils ooooold schoool! 2 Quote Link to comment Share on other sites More sharing options...
Hank Posted March 27 Report Share Posted March 27 4 hours ago, PT20J said: Perhaps a picture is better to illustrate the idea: 52 minutes ago, Shadrach said: Skip, What did you use to create these drawings? Looks like Pencil CAD to me! Definitely a straight edge (I uses to carryna small 30-60-90 triangle in my shirt pocket) and either a compass or circle template. But it looks much better than a completely freehand sketch. 1 Quote Link to comment Share on other sites More sharing options...
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