When setting up steering arms for correct ackerman (I've pulled a line from center of rear axle, over steering arm where tie rods drop in to the kingpin). My question is, do you use the centre of the kingpin at the top (looking from top down), bottom of the kingpin (looking from bottom up) or at the approximatoin of the mid point (looking from the side). I ask because the bottom of the kingpin is wider than at the top. Thanks in advance
It's very good to fix badly or real poor done ackerman. You get better control an braking in turns. Some things to know about ackerman; The center of kingpin{top to bottom/mid point is fine to use. The engineering of design is help the two front tires in a turn,to be rolling so they are not fighting each other=in side tire should turn more then out side tire. At normal speeds,it works very well an helps control an minizies tire ware. Some mistake is not a big deal,here is why;The real world fact of it,is being close is good too,with any error on the side of a bit less then full ackerman{ Speed and or braking in a turn makes scrub angle=tire is not going exactly as it is pointed{that is scrub angle and get more an more off ,as load gets bigger. Many race cars use zero ackerman ,do too higher scrub angle on out side tire,then in side.
If you get your Ackerman within the range of top to bottom of the king pin, you are probably closer than 90% of the cars here.
I like to use the lower ball joints as the reference points since the steering arms and tie rods are typically significantly closer to the plane of operation of the lowers then the upper ball joints. Spindle heights and suspension designs like strut type setups may vary but the steering arms are usually near the lower ball joints.
Since the ackerman rear point is the center of the rear axle, I think the front measuring point would be where the spindle centerline intersects the kingpin centerline, or upper and lower ball joint centerline.
I measured my old stock Blazer solid axle front steer 4x4 a few months ago. The tie rod is the same length as the lower ball joint distance. The uppers are a couple inches narrower.
I think close is good enough. Look at modern pickup trucks with short beds, long beds, and extended cabs. They all use the same spindles. Sent from my SM-T350 using The H.A.M.B. mobile app
Thanks...I'm gonna go with "that should be close enough"... Probably should have mentioned it's for a '38 Ford, with a dropped '36 axle, '38 spindles with steering arms heated and moved to clear the axle drop, split bones (about 10"s apart at centre crossmember), reverse eye spring etc.
This is the best approach...... And remember with engineering "It is F***ed when a welder can't fix it"
Yep, exactly. There are no different steering arms for late model rigs for different wheel bases. Unless you are doing something extreme like using a MII spindle on a 140 inch wheel base car you aren't going to know the difference any how. Where the issue lies with our cars is when for some reason someone decides that they need to bend the steering arms in or out possibly for clearance. That might be that set of 40 round back spindles you got at the swap meet for a bargain price that back in the 80's some guy decided that he needed to bend the arms towards the center of the car a half inch or so to clear those 8 inch rims and G 60 tires he had on it. Or that set of chrome round backs I have with the welded on hand made steering arms. My guess is that those aren't even close but the welded on pieces won't pass WSP inspection on a bet so all three welded on arms are coming off and will be replaced with bolt on arms. My guess is that half the guys on here who like to throw themselves into these Ackerman discussions don't have all that much of a clue as to how it works and just like to sound knowledgeable or think they do. I'd have to say make your line as close to the center of the spindle/kingpin as you can get and straight across the center of the tie rod end. A puddle in the parking lot test might tell you fairly well if it is right on or close enough. If the Ackerman is right you are going to have four real even tracks when you make a turn with the wheel held steady. It it is off the tracks are going to be uneven and may even cross each other. A good discussion on it here with some math at a lot higher level than can deal with. http://what-when-how.com/automobile/the-ackermann-principle-as-applied-to-steering-automobile/
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