Projects My '23 Roadster project

I have to agree with plym49. The tie rod doesn't know if it is in the front or rear. As long as it is set up correct it is a parallel universe. My cj jeep has tie rod in front, it drives fine. Pitman arm too far behind radius rod will cause bump steer. Center of steering sector shaft should be at center of radius rod pivot or you will be all over the road. Harley

 

Hey, M58;

You got it right in post 41.

You also shouldn't have much, if any, problem(s) w/the Trac-Loc. Just make sure to use a limited-slip fluid (friction-modifier). They are not an aggressive limited-slip. Should work well for you.

Marcus...

 

There is nothing "Parallel" in Ackerman !!!!! JW

 

If the tie rod in front is parallel to where the rear tie rod would be in back it will work fine. If the offset of the steering arms is the same to the inside and the same offset rear to front what difference will it make? Harley

 

all the jeep cj steering I'm familiar with is a totally different animal. Plenty of IFS setups have tie rod in front..again totally different animal.

 

All use the correct Ackerman principal for that application. JW

 

agreed JW sooo many variables here in general I'm glad Mech58 has his sorted already lol

 

Harley its to do with arm ratios,say you turn left and with the arms and tie rod behind the axle the left arm shortens and right lengthens, this gives a differential in tie rod end travel and it is this that gives the ability to turn with each tire following it true path and not slipping/scuffing. With the tie rod in front these angle must reverse so that's why the arms must face out. JW

 

Plym49,re; post 55. Ackerman has nothing to do with the steering self-centring, caster is what does this. JW

 

I'm going to produce a diagram and post it on here for Plym49, won't take me long.

And you are correct 26 T about caster. Any of you guys ever drive a '71 or a '72 Volkswagen Super Beetle? They were set up with 0* caster from the factory. SCARY as hell to drive, especially at higher speeds. VW corrected the flaw in '73.

 

Here ya go folks:

 

And as far as 'not understanding how the tire knows where the tie rod is' goes...it doesn't 'know', it's a fact - a law of physics. If the front-mounted tie rod ends are not inline with the Ackerman angle - say they're inboard of the Ackerman, then when the wheels are turned one way or the other, the outboard wheel will be turned at a sharper radius than the inboard wheel - this will create a braking or dragging effect as you go around a turn and it will also wear the fuck out of a set of tires. The best way to truly understand it is to experiment with it in a hands-on setting. This is the best way I can describe it.

 

ALSO - on wheel back space - shallow backspacing on steering axle-mounted wheels causes problems with steering as well. Ideally, you want your pivot point to be in the center of the contact patch of the tire. In order for this to occur the wheel has to be backspaced accordingly so that it places the centerline perpendicular to the axis of the king pin or knuckle. Steering axles setup in this manner are the easiest to steer. The further off center you go with your pivot point, the more effort it takes to steer the wheel and the more wear and tear you will notice on your components over time.

 

Cheers M58,thats a cool diagram and I hope that this is put to rest and understood now. On with the build....... its getting exciting. JW

 

The above diagram is a great example of the misconception around how to put the tie rod in front of the axle.

We ant the steering arms to point to the front - at the same angle relative to the backing plate as if the arms were pointed backwards - but not along the same line!

At the same angle. Not as a continuation of the same line.

If the steering arms are 15 degrees away from the plane of the backing plate to set the Ackerman, they need to be at the same 15 degree angle but pointing to the front to have the tie rod in front.

That diagram has them at 165 degrees, because they are extending the same line from the rear end. That is why some of your guys are not picturing it correctly and saying the arms would hit the rims.

Here is another way to picture it: Extend the wheelbase to the front - 106" to the front in the case of OP's build. Run a tranverse line between those two points. That is the imaginary center of an imaginary rear axle if you transposed the setup of the car, and that is how you do it for the tie rod in the front.

Now, do you understand that doing it as I describe will get you front-facing steering arm that do not hit the rims and also have the correct Ackerman angle? The front-facing steering arms point inwards, not outwards.

IOW, in the diagram above, the steering arms will be roughly along the line of that red arrow. The rims would not get hit as the tie rod is that much shorter, and the tie rod would not know that it is in front and the Ackerman will be perfect.

It all goes back to geometry class in school and how parallel lines work.

I hope the above explanation is clear and if not, I will try to explain it again.

 

I think you are confused sir - go in your shop and do some experimenting as I have and you will see. You were the one asking the questions here just yesterday and now all of a sudden you're the expert? Now I'm confused too.

 

Umm, the entire idea of the Ackerman angle is to get the inside tire to turn at a sharper angle than the outside wheel because the inside wheel travels a shorter distance.

 

That is correct - not sure how you gleaned anything different than that from my explanation.

 

Here's another diagram that I didn't create that I found on the web...

 

Poor, poor Mr. Ackermann, even though he tried to steer all his friends properly, he was probably misunderstood most of his life! Gary

 

I'll add one last point here - if I were to reverse my current steering arrangement and place my tie rod out front - essentially creating the arrangement that you describe plym49, then I would have what is commonly referred to as a "Reverse Ackerman" setup. With that arrangement the OUTSIDE wheel would be turned sharper than the inside wheel while going around a turn. The tires would skid sideways. Reverse Ackerman is commonly applied on dirt track cars and even on some asphalt cars. The main advantage of a 'proper' Ackerman angle on your steering arrangement comes at lower speeds with tight maneuvering.

Anyway, I am just about sick of discussing this topic in this thread. I think we've just about beat it to death.

 

That is correct Ackerman,lets let the man build a t now!

 

Mechanic 58, you're exactly right......... if the lines shown don't intersect as shown it ain't gonna work......... period.

 

Mechanic 58, what are you planning for exhaust? I am using a 425 Olds and want
all options for exhaust. I would prefer using HiPo stockers if possible. I will be using
a Var pitch 400...should be fun.

 

Please reread post 76. The diagram in post 72 is incomplete. Do you see that red arrow labeled knuckle/kingpin? It happens to be in the right spot. A tie rod connected there behaves the same as the tie rod out back, or the imaginary line extended forward and interfering with the wheel. Complementary angles.

 

plym49, everyone should read post 76, because it demonstates clearly that you do not understand the basic principles of steering geometry. Mech58 has had a tough time getting to grips with it, which he now has. When yr in a hole, its best to stop diggin.

 

Oh my goodness, you seem to be having a problem with basic geometry: the interactions of angles and lines. My statements are correct. Take a step back, think it through, and it will click.

 

Plym 49.
I think you should start a new thread about Ackerman instead for dicuss it in this buildthread.
You are the only one that not not understand it here.

 

Let's take this step by step, my friend.

1 - We all agree that the diagram in post 72 illustrates the way to set Ackerman angle. Usually, the tie rod is behind the front axle.

2 - Extending the imaginary line from the center of the rear axle forward through the inner tie rod end location, one can find a spot to run the tie rod in front of the axle - where it can interfere with the wheel. Again, we all agree on this.

Now please read this next part carefully as this is where some will gain new insight. This is the part where some have not followed along:

3 - Do you agree that the front axle does not know where the rear end is? OK, try this: draw the same diagram as in post 72 but on a longer piece of paper. Draw another rear end the same wheelbase, but in front of the car. Draw your Ackerman line. Do you see what happens?

What happens is that you recreate the same angles and steering arm locations. Except flipped. The non-wheel-interfering tie rod ends up in front, and the wheel-interfering tie rod in back.

And the Ackerman is exactly the same in either case; perfect for the wheelbase in question.

This is a graphic example of what I have been attempting to explain - that there is a non-interfering tie rod placement in front of the axle that provides the exact same Ackerman as the wheel-interfering in front or non-interfering in back.

My original question was to ask why there should be a problem with a wheel-interfering tie rod in front, since there is a geometrically identical alternative that eliminates the problem.

Now you can either read and absorb this, draw it out on paper and see for yourself, or persist with insults. It doesn't matter since facts are facts and if you take the time to think this through you will come to understand that there is an alternative for situations where the tie rod needs to be in front that provides correct Ackerman.