Ackermann Principle

[fabr]

One would think so at first glance but few things glanced at are as they seem.

[Entropy]

[fabr]

So,you say you like strict ackermann being used offroad ? 

[Entropy]

So,you say you like strict ackermann being used offroad ? 

Is that all you got?

[fabr]

Hell I agree with you! How can I have any more?

[LiveWire]

I often see comments about the inside tire being off the ground in a turn used as a reason for not needing Ackermann. I also often see comments about reverse Ackermann being needed for sliding. Those two things contradict each other. If the tire is off the ground and it does not matter what the inside tire is doing, then you would not need reverse Ackermann. I started with a theory/opinion which I applied to multiple cars that did not have 100% Ackermann and I made them much closer to it. The cars steered much better with it it, so I stuck with it. Without Ackermann, the cars tended to push going into the corner. A series of steps could be performed to pitch the car into a slide. When approaching a corner, I brake hard, putting a significant amount of down force on the front tires. When I added Ackermann, there was a dramatic reduction in push at that point. The car went where I pointed it. If I put the car into a slide, that is also the same time it lifts the inside front wheel. So I noticed little change for about 1/4-7/8 of a 180 turn. Although not as dramatic, there is less correction needed on the exit of the corner so I agree with those who say the tires should be pointed in the correct direction when they touch back down.

In summary, I have tried it both ways for myself. I prefer having Ackermann.

[fabr]

I have always had a hard time seeing the logic against ackermann but there's always room for discussion.

[VLADD]

I'm with Fabr and Entropy, on this and I think livewire worded it really well

[xcalibur]

okay i skipped to the end, but what about most buggy's that have the steering rack and tie rods mounted in front of the tires, and hackermann is almost impossible here as you would ram the steering pivot into the wheel to get the angle to the rear end, and what about BUMPSTEER here, that sucks bad, i'd rather just hit the gas harder and make my turn in the sand just fine. IMO

[SPEC]

okay i skipped to the end, but what about most buggy's that have the steering rack and tie rods mounted in front of the tires, and hackermann is almost impossible here as you would ram the steering pivot into the wheel to get the angle to the rear end, and what about BUMPSTEER here, that sucks bad, i'd rather just hit the gas harder and make my turn in the sand just fine. IMO

You should prolly read the whole thread
I'd like to hear more of your philosophy on ackerman and bumpsteer

[Rick S.]

You're right about proper ackerman being tough to achieve with the rack mounted in front. Especially if you have front brakes. I've never heard anyone mention this point before, but I do agree.
The best I've been able to do is both wheels turning the same angle. With a deeper offset on the wheel it could be better. Still probably shy of proper though. 

[Rick S.]

Bump steer is easily eliminated with the rack in front or back. Makes no difference.

[fabr]

okay i skipped to the end, but what about most buggy's that have the steering rack and tie rods mounted in front of the tires, and hackermann is almost impossible here as you would ram the steering pivot into the wheel to get the angle to the rear end, and what about BUMPSTEER here, that sucks bad, i'd rather just hit the gas harder and make my turn in the sand just fine. IMO

Yeah ,read the thread before posting is a good rule of thumb to live by.

[trojan]

The Edge sidewinder and piranha run reverse ackerman.

[Engineer]

You're right about proper ackerman being tough to achieve with the rack mounted in front. Especially if you have front brakes. I've never heard anyone mention this point before, but I do agree.
The best I've been able to do is both wheels turning the same angle. With a deeper offset on the wheel it could be better. Still probably shy of proper though. 

I have been working through the front suspension design for my car, and here is what I have found.  In order to get true ackerman with my wheelbase and track width, the tie rod end needs to be mounted 1.1" outside of the spindle / A-arm pivot.  This does make it difficult when you are mounting the spindle pivot as close as possible to the brake rotor.  However if you are using KPI (King Pin Inclination) then your top spindle pivot will be further away from the brake rotor than the bottom pivot.  In my case with 10" between spindle mounts, the top mount is 2.4" further away than the bottom with 14deg KPI.  So if I put the tie rod mount half way up the spindle, it will be further away from the brake rotor / wheel than the bottom spindle mount with full ackerman.  If you need more clearance it can be mounted even higher.

okay i skipped to the end, but what about most buggy's that have the steering rack and tie rods mounted in front of the tires, and hackermann is almost impossible here as you would ram the steering pivot into the wheel to get the angle to the rear end, and what about BUMPSTEER here, that sucks bad, i'd rather just hit the gas harder and make my turn in the sand just fine. IMO

As far as bumpsteer, it is easily eliminated if your drawing your design in any form of CAD.  draw the suspension in full compression, full bump, and in the midpoint, Then draw a circle based on the three tie rod locations on the spindle, and the center of that circle is where your inner tie rod mount should be.

Another note:  If your a-arm mounts are not parallel, (The rear mount is wider than the front), like I think Xcalibur's will be by seeing his frame, then choosing the non-bumpsteer location for the inside tie rod gets a bit trickier.  You will need to account for the A-arm mounting angle.