Is Ackerman really that important?

I was under my '67 Chevelle and noticed the tie rods are in front. That imaginary line thats suspost to intersect with the middle of the rearend ain't even close. Really it doesn't look any different than the cars on here with the tie rod in front of the axle. My Chevelle drives great, just like my other newer cars and trucks. What gives?

 

you need it to keep the front tire from fighting each other in a turn. the wider or farther apart the tires, the more ackerman angle you need....outside tires having less of a steering angle, as apposed to the inside tire on a turn

 

Yes!

 

Ackerman schmackerman. It ain't important. Just some nonsense some know nothin' engineers came up with

 

Yes like groucho said it is important if you want to drive it.

You have some other things going on that isn't exactly the same as a beam axle. But you still need to have it right, it is based on the same principle. If you haven't changed anything then I suspect you are just wrong on your calculation.

 

If it wasn't important, we'd all still be driving our go-carts with the rope steering.... Just sayin'........

 

This is confusing me. Most old 4wd trucks with solid axles have the links in front of the axle and they drive fine. In very sharp turns the wheels/tires lean a lot and tend to be pushed through a turn. I guess I need to do some more research on this whole ackerman issue. Come to think of it my old coyote go-cart chassis had the links in front as well.

 

Ok here it is Boys and Girls!!
If it is rear steer the imaginary line goes from the King pin through the tie rod to the center of the rear end yolk. If it is front steer you measure From the center of the Axel to the center of the yolk and write that distance down. Now measure off that distance from the center of the front Axel to and imaginary point in front of the car. Now run the string from the kingpin through the tie rod to the imaginary point in front of the car. This is how front steer and rear steer cars get a fairly accurate Ackerman.

 

On race cars we use or have used anything from classic ackerman to much more or less even to anti-ackerman. None of them have a huge effect on the car on track. Of course we don't turn all that sharply either. I like to run pro-ackerman on low downforce cars and less on ones that make lots of aero.
It's not a huge tuning tool but common sense says it is useful on street cars. The links can be in front or behind the axle centerline and you can still achieve whatever you want.

 

now i'm confused......i can't visulize it

 

Just draw a line from the kingpin to the centre of the rear axle the tie rod end should intersect this line - project this line forward for front steer- that is Ackerman. It was later found that the best setup is a point just ahead of the center of the rear axle.

 

This drawing does not show Ackerman but it shows why it is important and it shows how it works so thanks for that.

 

ask any t-bucket guy that put his tie rod in front of the axle how it steers without modification. I never worried about it on a stock independent front end. On an early axle
you better get it close or settle for the bad steering as OK.

 

If I draw a line from the tie rod thru the lower ball joint, the line will never, ever intersect. In fact they are moving away from each other.

 

For a streeter normally when you run the tie rod in front of a rear steer you end up bending the steering arms (is that the correct term?) outwards. If you leave them alone it has a tendency to boat steer aside from scrubbing the tire when you turn.

You will notice that most fad Ts with the tie rod out front run narrow tires that is not just for looks it gives you more room to bend the steering arm.

 

Factory front steer vehicles have that designed in from the get go as fuzzy Knight mentioned.

The problem for us when we start mixing and matching comes when we drastically change the wheelbase of a vehicle. If you were to watch some of these extreme wheelbase rigs that guys build you would see that a lot of them don't want to track right on corners and the rear wheels aren't following through the same arc in the corners as the fronts.
You could easily check your own rig by going to an empty parking lot after a rain storm and drive through a puddle to get the tires wet and the make a 90 degree intersection style turn while the tires are wet and get out and check the tracks.
If the all follow the same arch you are good. If they don't it's off but may not be a huge issue unless the rig doesn't handle good in the corner.
The big problem is that the car/truck is trying to drag the tires sideways to correct it's self instead of making a smooth turn.

 

In Short - the Ackerman principal is so the when turning the inside tire turns at a different arc then the out side tire. The set up I describe is to insure your Ackerman is in the correct phase!!

 

Think top view

 

I totally got it now with the rear end as the reference point. Thanks!!!

 

The Tie Rods are not inline, with each other.
The Drag Link is behind the outer Tie Rod Ends.

This influences the degree of Ackerman.
Same idea as moving a Rack and Pinion forwards or backwards.
The angle on the Tie Rods, is part of the geometry.

To work correctly, the inside tire needs to turn sharper than the outside.
Exactly how you make this happen, doesn't matter.

 

I've often wondered....

The wheelbase of a pickup can be 2 or 3 feet different based on whether it is a standard cab shortbed, or a crew cab longbed.

Is the front suspension different in order to compensate for the ackerman?

Rich

 

A tire on a car that is going through a corner has a slip angle.

The slip angle is ( amongst other things ) affected by the weight on that tire .

So on racecars you take some Ackerman out to compensate for the weight transfer that happens while cornering.
( sometimes going to zero, or even anti Ackermann)

Some racecars get very light on the inside front wheel, or even lift it, so then the ackermann doesn't matter at all.

And sometimes other things are more important like aerodynamics ( Lotus, for example, had zero Ackermann for a while in the '60s to clean up airflow around the suspension parts of their Formula Racers )

I dont think anybody changes the amount of Ackermann on stretched Limo's or shortened Dune Buggy's, but it is affected by the wheelbase change.


So its probably more a range than a set number.

I doubt if any car with good suspension has 100% Ackermann, but the actual number varies for the application of the car.

 

Exactly.

I once tangled with another car and broke a tie rod adjust sleeve on the race track. I was able to run another three or four laps without that left front tire doing a thing (flopping around), because the dirt cars I raced transfer almost all the weight off that tire when at speed. When the caution came out and I slowed down the weight shifted back onto it and the car started having trouble pointing. I wasn't able to get back up to speed and had to retire, but so long as I kept the body rolled over and the rear up on the bars, it was fine.

We've found that on racing cars, anything from zero ackerman to 100% ackerman will work, more or less without a lot of handling change. The less ackerman you have, the more the chassis tends to understeer, but it is a very slight change, as in, you don't feel it, but the tire temps tell the story.

On a street car, zero ackerman at high steering angles (like in a parking lot say) will wear on the tires or make little ripples in the gravel, but that's about the extent of the irritation. The car will still steer and point just fine.

At highway speeds and steering angles, I doubt you'd ever feel the difference between a car with zero ackerman and 100% ackerman. The effect is just too small to be noticed at those steering angles.

Reverse ackerman is a problem, but still not a real harsh one. It makes the car tend toward understeer, and it wears on the tires, even at highway speeds. Unless the reverse ackerman is very severe, the car will still point and steer fairly well, but the tires will not last as long, and the car will shove the nose in gravel parking lots.

Also, the steering geometry of solid axles with solid tie rods cannot be compared to IFS with tie rods and drag links. The geometry involved is drastically different, so the ways you go about analyzing them is drastically different.

The two tie rod and drag link setup's ackerman is more or less exclusively set via the fore/aft drag link/rack location. Just about any steering arm configuration can be made to work if you can relocate the the rack/center link fore/aft in the car.

It's all geometry. Dispose of the dogma, think critically about the problem, effect a solution, and then test to verify that your solution really is.

 

I understand now. To expand on your statement, I modified the drawing to show how an increase in wheelbase, about 1.5' would screw up the Ackerman (see below)
How would this be fixed?

 

____________________________________________________
Ahh...thanks for reading my post... So, I was mistaken when I thought I had reverse ackerman. It seems ackerman is very simple for a straight axle (probably invented for horse drawn wagons) but very complex for IFS suspensions. Thanks for your explanation.

 

If you have ever driven a car with incorrect ackerman you will know how important it is to get right.

 

Sooo... if I understand correctly, this is really only something to worry about if the wheelbase has been significantly altered? Or can other changes (suspension?) cause a problem as well?

 

Opposite effect on a short w/b

 

As long as it is within a certain range it should be fine.

And 100% Ackermann is nice, if you have to push the thing around the shop a lot.

For acctual driving conditions you'll need a different number.