The Stovebolt Site Forums The Shop Area Driveline Tie rod location and turning radius

I am rebuilding the front steering,suspension and brakes on an old hotrod truck. It has a 6" drop tube axle. I will have to fabricate the tie rod arms that mount to the spindle. How is turning radius affected by location of tie rod pivot to spindle centerline? Another question - is 1/8" toe out pretty standard setting on kingpin axles? Thanks in advance.

It's more common to run 1/8" toe in, not out on most systems. Is the tie rod ahead of the axle or behind it? Toe is intended to compensate for slight flexing of the tie rods to provide straight-ahead wheel position while driving, so the design of the tie rods and steering arms will determine where the static settings need to be.

The shorter the radius from the tie rod end to the kingpin, the faster the turning rate will be- - - -IF- - - -the steering arm at the drag link is also short. The length of the Pitman arm and the steering arm the drag link attaches to is what's going to determine the quickness of the steering. TO AVOID BUMP STEER, THE DRAG LINK MUST BE PARALLEL TO THE GROUND! Lowered suspension systems are notorious for having bump steer unless the steering gear is also repositioned vertically to match the axle drop. The angle of the steering arms in relation to the spindle affects "Ackerman" which is also described as "toe-out in turns". That is absolutely critical for good handling, as the toe does not remain the same when the wheels are turned away from center. The wheel on the inside of a turn must turn a tighter circle, pivoting around an imaginary point established by drawing a line through both rear wheels, and intersecting lines from the front wheels, turned away from center to negotiate a normal turn. If you are deviating from factory-engineered steering geometry, be absolutely sure you have the equivalent of a mechanical engineering degree. Mistakes in that area can be deadly dangerous to you and everyone who shares the road with you.

I'm expressing the above opinions after 30-something years of teaching wheel alignment and suspension system repair, and designing several very successful round track race car steering systems. If it doesn't work properly on paper and in the fabrication shop, don't even think about putting it on the street!
Jerry

Thanks Jerry. The tie rod is behind the axle, and drag link is parallel. I will be making tie rod arms that attach to back of spindle (as opposed to inside of spindle), and that moves the hole for tie rod bolt 15/16" to inside of spindle centerline. I can put the hole back to spindle centerline (have not started making them yet). Just curious what a shorter tie rod (about 2") would do to steering - if anything.

I think you're confusing your terms, or at least confusing ME. The tie rod connects the steering arms with each other, right and left. Are you considering making shorter steering arms, the parts that bolt onto the spindles? That could possibly result in too straight an angle between the tie rod and the steering arm at full turn right or left, resulting in a locked-up situation. Be sure to set the steering stops to prevent getting the angle too close to straight when you reach full travel of the spindles. It's possible you'll lose some of the angularity possible at full travel if you shorten the steering arms that much. What's the necessity for using a shorter steering arm?
Jerry

Sorry for the confusion - the steering arms will not be shorter. The tie rod bar that connects the steering arms will be shorter because the hole that tie rod end fits into will be moved toward center of frame about an inch.

Do some extensive testing of the toe change as the steering moves from center to full travel in both directions. Changing the distance from the tie rod end pivot point to the brake backing plate will have a major effect on the Ackerman angle. If you get it wrong, the vehicle will have very unpredictable handling in turns.
Jerry

Edit: After doing some research in some old training material I used to use while teaching steering fundamentals, I found a diagram showing a method for finding bent steering arms. It might apply in your situation. Stretch a string from the kingpin pivot point to the center of the rear axle on both sides. With the wheels pointed exactly straight ahead, the steering arm tie rod end hole should intersect the line from front to rear on both sides. On an independent suspension system, the lower ball joint will be the front pivot point you're looking for. Good luck!
Jerry