TheSamba.com :: View topic - Flat towing beam vs A arm front suspension....

Tue Jun 14, 2016 12:14 pm

When I bought my bug I flat towed it home. It was a 1967 with ball joint.

Now the ball joint or king pin beam suspensions seem to have almost no positive caster from what I can tell. However the front axle is offset behind the joints. Does this have the same effect as positive caster and what makes the wheel center and flat towing possible?

The reason I'm asking is I'm thinking about installing A arm front suspension and I've noticed that the spindles they sell don't have the axle offset. It is directly inline with the upper and lower heims. So with the A arms is it critical to have positive caster designed into the setup?

I feel like if you had A arms with zero caster the car would not flat tow well.
To be honest I feel like if you didn't have the axle behind the heims a little it would still not flat tow well.

Can anyone shed any light on this.
Thanks,
Mike

Tue Jun 14, 2016 1:41 pm

Unless the A-arm is home built without design criteria it will have caster. This is what forces the car to return to straight after a lane change for instance. If a design had no positive caster it would be scary to drive. Too much and it's a fight to turn cause the wheels want to "flop" to center. All cars and suspension should have it. 7 degrees is about the norm in our sport.
You would not see caster in the spindle. It is either in the frame head, lower control arm mount or offset upper and lower a-arms.

Tue Jun 14, 2016 6:00 pm

Get a pair of $10 caster shims and put behindlower beam, it will improve handling and towing more the a $500 "A"arm front suspension...

Dale

Wed Jun 15, 2016 8:00 am

Hmmm,
I see, for some reason I didn't realize the caster could be achieved with the axle centered on the spindle.
I get it now.
If I do decide to stick with the beam I'll get some shims.

Thanks fellas.

Wed Jun 15, 2016 9:05 am

In torsion bar front ends caster is achieved by length of trailing arms from pivot point on torsion bar to intersecting line through spindle... Generally top arm is a tad bit longer if beam is perfectly vertical.... Also chassis angle/geometry to ground is also deciding factor...

If you raise rear of vehicle (huge tires) with out raising front you decrease caster... Big issue with shortened chassis like in FG dune buggies.... Usual fix to over come squirrely handling to "riding on rails" is caster shims under lower beams....

Dale

Tue Jun 21, 2016 5:28 pm

The angle of the king pin or the line through the middle of the ball joints is where the actual caster is at in automotive front suspensions.
In cars caster does not rely on where the axle is in relation to the cross member or the a-arm pivots or the trailing arms on a VW.

The beam in a link pin or a ball joint Bug is attached to the frame at about 6-8° positive caster (the top of the beam is farther back than the bottom of the beam). This is where VW created the caster angle. Occasionally we encounter a Baja or a dune buggy where someone has built it incorrectly so the beam is not at the correct angle.

With an a-arm front suspension, the caster is in the angle of the line through the middle of the upper and lower ball joints or heim joints. In this case it's just like any a-arm car. Like other cars with a-arms, the spindles for a-arm buggies are inclined to the rear so the upper ball joint or heim is to the rear of the lower ball joint or heim.

There is also "kingpin inclination", where the upper joint is inboard of the the lower joint. There are other factors in suspension design.

I recommend you get your a-arm suspension from a reputable vendor. The entire setup should be well designed and fabricated.

Tue Jun 21, 2016 10:43 pm

The a-arm kit has a 12 degree caster and will return to center. My kit #1 is pinkie steering at 80 mph (when the wheels are balanced). Flat towing has never been an issue.

Wed Jun 22, 2016 7:13 am

ellobo wrote: The a-arm kit has a 12 degree caster and will return to center. My kit #1 is pinkie steering at 80 mph (when the wheels are balanced). Flat towing has never been an issue.

Yeah and I have same handling with K&K front end and caster shims.... Saving costs of full "A" arm front suspension...

Dale

Wed Jun 22, 2016 7:39 am

dustymojave wrote: The angle of the king pin or the line through the middle of the ball joints is where the actual caster is at in automotive front suspensions.
In cars caster does not rely on where the axle is in relation to the cross member or the a-arm pivots or the trailing arms on a VW.

This is the part that was difficult for me to grasp. Still odd to me but I get it.

Thanks for all the info from everyone, very helpful. :D