Low Buck H3 SAS - touchdown!

[4speedfunk]

If anything you would want to go SHORTER, not longer, on the Pitman arm. A longer Pitman arm will increase steering speed/sensitivity and decrease assist.

Okay...that makes sense. However, going shorter would increase the ratio on the drag-link. I guess I was thinking that the ideal situation would be having the pitman and the steering arm identical c-to-c lengths. Making them the same would remove any leverage multiplication between the two, and thus guarantee that 10 degrees of swing at the pitman equals 10 degrees at the knuckles, AND "effort in" would equal "effort out". Not only that but, the drag-link itself would stay parallel to the axle, straight and true throughout the entire travel range.

Currently, my steering system does not do this because I have a 5.25" pitman and 7.0" steering arm (.75:1 ratio). In short...I have another reduction in the drag-link system (after the steering box) that is caused by the un-equal length arms. Making the pitman arm even shorter I'm sure would effect this problem. As it is now...as the pitman swings through its arc, the movement generated at the knuckles is decreased by .75 but the...but the assist is increased, right? If this is true then that ratio grows even further, the deeper you go into the pitman's arc. As my steering approaches full lock...it gets noticeably slower because of the difference in angles between the two arms. ALSO...the drag-link does not stay parallel to the axle like it would if both arms were the same. Instead there is some variance because each end of it is connected to a different length radius. I'm sure this last tid-bit adds some sort of multiplication factor to the whole thing.

This stuff makes my head hurt!

My thought on increasing the pitman arm length was to try to get a closer ratio between the pitman and the steering arm....and not really adjust the ratio between the pitman and the steering wheel. Seems like identical length arms would result in a more consistent "feel" throughout the steering's range, and also keep the drag link parallel at all times. Obviously there are volumes and volumes of things to learn about steering geometry. I really don't know what factory systems use for this ratio. So to by-pass all the theory and math:

Is there an ideal pitman-to-steering arm ratio that a typical steering system should have? A sweet-spot? A rule-of-thumb that I should be using?

 

[bebe]

Is there an ideal pitman-to-steering arm ratio that a typical steering system should have? A sweet-spot? A rule-of-thumb that I should be using?

There is no simple answer to that question....but there is BillaVista!!!!! :thumbsup

 

[MaxPF]

Is there an ideal pitman-to-steering arm ratio that a typical steering system should have? A sweet-spot? A rule-of-thumb that I should be using?

Not particularly. Mechanical advantage between the Pitman arm and steering arm are just another tool for accomplishing the desired goal. As long as the steering isn't ridiculously asymmetric and has the speed and level of assist you want, there isn't an issue. Steering "feel" will be more affected by the ratio of the box and whether or not it's variable ratio than it will by unequal length Pitman-steering arm. Parallelism between the drag link and the axle doesn't really affect anything, whereas parallelism between the imaginary Panhard rod and imaginary drag link IS important for minimizing bump steer*. Ackerman is also important, but it is built in to the knuckles in a low steer arrangement, and is usually adequate for vehicles with at least 108" of wheelbase. Many high steer arms have little, no, or reverse Ackerman, because they are badly designed.

* When I say "imaginary", I am referring to an imaginary line drawn between the two attachment points of a link, be it a drag link or Panhard rod. The reason I phrase it this way is because many builds use an "S" shaped drag link and/or a bent Panhard rod for oil pan or crossmember clearance, and the straight parts of the physical link are not indicative of the actual working angle of the link. Making, say, a straight Panhard rod parallel to straight parts of an S-shaped draglink would induce bump steer rather than eliminate it.