Ackerman Angle and AWB Mopars

[Stoga]

I am curious, on AWB Mopars, was the stock Ackerman angle of the spindles ever changed. My understanding of Ackerman angle was that your steering arms would point to the center of the rear axle. If they pointed to a place behind the rear axle, according to this page, the steering input will be:
Less Ackerman
1. Initial steering response will be more direct.
2. Your vehicle will react faster to any steering input.
This link is for RC vehicles, but the same principles still hold.
http://www.rc-truckncar-tuning.com/ackerman.html
Now I've pondered just for the fun of it to make a shortened wheel base vehicle, maybe chop the middle out of a minivan like they used to do with shorty vans in the 70s.
Will I have to bend or adjust my steering arms to keep my vehicle from being over sensitive to steering input? People are driving AWB Mopars and I'm just curious if they had to deal with this or was it not enough problem to be of concern? Thanks in advance for any input!

[DartGT66]

They didnät change. Sll they did was move the existing parts forward. Since hte rear axle was moved forward too, the overall change was so small, that it propably didn't have much effect.

[Dart 360]

The reason for the angle is so that the steering wheels can turn or steer different arc's when going around a corner to stop scrubbing of the tyre. The inner tyre needs to turn more.

[Ray Bell]

Like so many things in production cars, there is a lot of compromise in steering geometry...

You will probably find that the steering arms are made to be correct for the most common wheelbase that the component is used on. If the steering arms bolt on, then you have a chance that they may change them between different models.

Where you are talking about wheelbase changes of up to 12" or so, it really won't make much difference. But if you're slicing three or four feet out of a wheelbase, you'll get a lot of change. Tyres will tend to squeal while turning tight corners, parking and so on, and there'll be undue wear.

This issue comes into the same category as bump steer... usually the engineers try to get it right, but production variations might well muck it all up.

The Australian-assembled Mopars had a real dilemma. The usual style of steering box would never fit beside the right side of the engine, so steering boxes of the older style were bolted up to the frame rail just ahead of the floor, with the Pitman arm pointing forward.

Get the picture? Pitman arms in the original design of these suspensions pointed toward the back of the car and turned in a parallel arc to the steering arms.

But not here, no sir! We get our Ackerman and our bump steer out as soon as we start to turn the steering.

[John Kunkel]

Trucks are a good place to illustrate the effects of wheelbase on Ackerman, the outfit I used to work for bought a bunch of late eighties long-wheelbase Chevy crew cab pickups.

If you locked the wheels in one direction as you came to a stop on pavement, the truck wouldn't move when you went to take off unless you gave it enough throttle to spin the tires. Straightening the wheel a few degrees would get you moving but you could feel the chatter of the tires scrubbing. The same suspension/steering on a short wheelbase drove normally.

[Ray Bell]

That was the sort of thing I was guessing took place, John...

Cars and trucks are, no matter what we think about them, built to a price. Some manufacturers will place enough importance on this aspect to get it right, to make a different steering arm for different wheelbases using the same suspensions. Most won't.

As the bits are going down the line, each function costs money. The easiest way to give variation to the Ackerman angle is to have a bolt-on steering arm, which is going to involve different tooling and a separate piece to be made for each wheelbase.

Then the spindle/upright must have at least two holes drilled and two threads cut into it, and a flat machined on it, or some other perfunctionary attachment method. It all costs money.

My feeling is, however, that a part of your 'can't get it moving' problem with the long wheelbase Chevy might have been an extreme turning angle of the wheel necessary to get the turning circle down to useful proportions.

[quietdad]

Neat little "how to" at http://public.fotki.com/VincePutt/dr...awb-factory-a/

[Stoga]

Thanks, guys, thats the kind of info I was looking for! I figure if I get into it, if the tires don't squeal and it'll go down the road, I can call it good...
If not, grab a flame wrench!