Technical Ackerman, Shmackerman.

I have just learned about an interesting front end angle of geometry. I have heard of it and about it before but never really paid attention to the details. The sad part is that I have probably done a million alignments. But the machine really does it all for you. Caster sweep, set camber, then toe. If it's in the green, let it go. Don't forget the print out.
My point is that I have been setting up the steering on my 1927 Model T coupe and the Ackerman angle for the front axle I am using is set up for a 101.4 inch wheelbase. The wheel base on my T is 109 & 3/8th inches.
So the rear axle is 8 inches beyond the Ackerman angle for the front axle.
What's that going to change or do as far as the cars turning, or handling?
Sorry if this is a dumb question. Thanks for any help.

 

There is a huge thread here with a ton of good info. I'm sure someone will post it up.

 

https://www.jalopyjournal.com/forum/threads/cowl-steering-just-stop.1101046/

 

With that little difference I doubt you will see any difference or problem.

 

You'll be fine ! You're a hell of a lot closer than most , especially the tie rod in front bunch ! Seriously you're good to go !

As an aside , I had to chuckle at your comment about frt end alignment , " as long as the lights green etc. " I did front end alignments from 1965- 1975 , no green lights , no lights at all , specs were printed in the motor manual , you drove the car to feel. for problems , felt the front tires to check for problems & set the front end to track & not wear tires , the printout was when you wrote the bill !

 

As an example... Chevy trucks use the same front end set up in all different wheelbase trucks. Apparently the GM engineers don't think it is too critical.

 

I’d get the car off the ground so you have some working room. Use a plumb bob to establish points on the ground for the center lines of your king pins, tie rod end eyes on the steering arms and the center of your rear axle.
Lines extended between the three points should meet in the center of the rear end.
I’d give you a sketch but cannot do that at this time

 

It will give you a little bit of front tire scrub when you turn, and the sharper the turn, the more it will give.

As they said, it's not enough to worry about.

 

Fuggadaboudit

 

One of the first suspension geometry threads I followed in the infancy of the HAMB was called Ackerman and Roll Center, it really pointed out how much I didn't know. I wonder if it shows up in the archives, it was a pre-crash thread.

 

I doubt that small amount will be any issue. Theoretically should be at the rearend center, but practically you are close enough.

 

Thanks for the help guys!

 

So what front axle and spindles do you have?

 

A friend and I both had Studebaker M series trucks . Both had GM frame clips . The Ackerman was way off . On mine, after about 5000 miles my front tires would start cupping. About the same with my buddies. He kept taking it for realignment and I kept telling him you can keep getting alignments til your broke cause it won't fix your ackerman. Bill

 

I wonder what the Ackerman on my bus is.

 

Guys bend their steering arms to raise or lower the tie rod to clear engine/frame obstacles. I would guess they could be bent outward to compensate for the longer wheelbase, which would require the tie rod to be lengthened.
Unless you plan to drive the car more than several thousand miles per year, you probably won't notice any difference.

 

A lot like my hair cuts.
Short on the sides and LOOONNG ON TOP to cover my bald spot.

 

It's a jeep axle.

 

When I did heavy truck alignments every now and then you would find wrong Ackerman, particularly when manufacturers started stretching wheelbase on trucks that saw a lot of city and regional use. You would think that their engineers would have noticed it. It required a steering arm change on the spindle through warranty.
If it bugs you, you can lay out centers with a plumb bob on the floor and heat and bend the arms to correct. That difference wouldn't take much. You can compensate for the scrub by fudging the toe setting, or extending the steering stops, but at another cost. Or just let it go

 

I think I would have to toe it in a bunch to overcome that? Probably to the point of wearing tires anyway.
I think I will just let it go and just watch the tire wear and decide from there.
I think that it would take a torch and some serious heft to bend the arms in.
And real world, I would be guessing when to stop bending.

 

Only when it’s backwards you’ll know how important it is. Ask a lot of old drag racers.

 

On race cars and high performance road cars ,the designers dial out [less] Ackermann .

This is to allow for the increased slip angles on the outside tyre requiring more steering input. Ackermann would cause the inside wheel to drag.

Some designers use "bump steer Toe-in" into the geometry to reduce this effect
So even altering Toe settings will alter ackermann

Only an issue at low speeds on a car park queen!

The word "Ackermann" should be blocked on the search feature of every automotive forum.
As soon as somebody learns this "black art", they tend overthink it.

 

Please elaborate, if you don't mind Sir?
What do you mean by backwards?

 

I'm certain that I am over thinking it.
I have never studied this principle before and it has caused me to learn a new perspective on suspension geometry.

 

by backwards, he means the crossover point for the steering arm/kingpin lines is in front of the car, instead of near the back of the car.

this happens if you use a front tie rod with rear tie rod type steering arms.

 

Picture this:
If your ride is a rear steer (tie rods behind the axle) your steering arms then to face towards the center of the vehicle, going towards the rear axle for the correct (or near correct) Ackermann.
If your ride is a front steer, (tie rods in front of the axle) your steering arms tend to point outward, away from the center of the vehicle for a correct (or near correct) Ackermann.

Now, lets say you took rear steer axle complete with steering arms, and installed it in a vehicle designed for front steer. You simply swap the steering arms side to side, and shorten the tie rods so the steering works, but the Ackermann will be backwards. Instead of those steering arms pointing out like they are suppose to, they are pointing in.

Many front steer setups have problems. Often times, there isn't enough space between the axle and the wheel for the tie rod ends to fit (the shorter the wheel base, the farther outward the tie rod ends have to be), so the guy bends the steering arms towards the center of the car so the tie rods don't interfere with wheels or the axle. When they bent the front steer steering arms towards the center of the vehicle, they made the Ackermann backwards. Might work OK out on the highway, but those slow, sharper turns in the parking lot can really tear up the tires. Gene

 

You are overthinking it.
In the ideal situation, ackermann keeps the wheels on their true path, during sharp turns.
In the real world this only happens when pulling into a driveway / carpark.
In 99% of driving, the steering wheel wouldn't even move 30 deg [which is approx 2 degs of the front wheels turning with a 16:1 steering box]

Radial tyres changed everything.........they perform better with a bit of sidewall "pre-load" [which is why they handle better neg camber ]
In the ideal situation they would have positive camber for the road curvature.

Road racing cars have minimal to zero ackerman. [With racing tyres]

 

That’s some smart stuff.
So we know what it is.
Anybody got examples (hopefully pictures) of correcting bad Ackerman.
fir example. You changed front suspension or have a wheelbase change ot it was bad from the factory.

 

Yep. When I went to S10 spindles/steering arms my Ackerman was all wrong (wheels toed in at full lock instead of out). Not noticeable going down the road but I couldn't do U-turns without a fight. Had to change the steering arms to outboard of the ball joints to correct it, turns on a dime now.