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Discussion Starter #1
In the past I’ve been a very strong proponent of “correct” ackermann angle for a vehicles specific wheelbase. This has always been tough to get, since the only way to achieve it, on a short wheelbase rig, has been to run a behind the axle tierod.

I’ve been playing around with my setup, and checking out how others perform on the trail, and I’ve come to the conclusion that “correct” ackermann is actually DETRIMENTAL to rockcrawling performance.

To illustrate this I’m going to use two fairly high profile rigs, that we’ve all seen before, and I don’t want anyone to think that I’m picking on anyone of the rigs as being better or worse.



In the first pic, Ant is climbing a ledge in the Sluice and is obviously trying to turn as sharply as possible to his left. But he is limited, since the outer tire (right side) is doing all the turning, but at full lock, his “correct” ackermann limits the outside tires turning angle. His left tire is at full lock, and if the rig would follow it’s track, it would turn tighter. So in this situation, “correct” ackermann is actually hurting the performance, much more than helping.



In the second pic, Lance is spankin’ the soupbowl. His rig has virtually no Ackermann engineered into the steering arms. He is cutting to his right, to avoid the second step. If his rig had the “correct” ackermann, his left tire would be attempting to climb the second step at full lock, which would be more difficult to do (but well within the rigs capabilities) since the left front and the right rear would be climbing at the same time. He is turning tighter because his “incorrect” ackermann is helping him make a tighter turn.

So here is a case, where the technically incorrect engineering (by SAE standards) works better! PERIOD.

What do you guys say? Personally I feel that the “incorrect” ackermann is less detrimental to onroad performance, then the “correct” ackermann is to slow speed (slower than 70 mph) offroad performance.
 

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It's the drivers ability to do with or without the ackerman crap.
You should have shown the wheely pivot move that lance pulled in the box.

Yep that was all ackerman if you ask me <IMG SRC="smilies/rolleyes.gif" border="0"> <IMG SRC="smilies/rolleyes.gif" border="0">
 

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Discussion Starter #4
Originally posted by Rocktoad:
<STRONG>It's the drivers ability to do with or without the ackerman crap.
You should have shown the wheely pivot move that lance pulled in the box.

Yep that was all ackerman if you ask me <IMG SRC="smilies/rolleyes.gif" border="0"> <IMG SRC="smilies/rolleyes.gif" border="0"></STRONG>
Yeah Yeah Yeah, I know Lance could take a bone stock Samurai with two broken axles and a blown headgasket and sweep the ARCA series!!! <IMG SRC="smilies/rolleyes.gif" border="0"> <IMG SRC="smilies/rolleyes.gif" border="0"> (where's the damn :webdaddybuttkiss: smiley when you need it!?) But this wasn't meant to be a discussion about driver ability!! <IMG SRC="smilies/biggrin.gif" border="0"> <IMG SRC="smilies/biggrin.gif" border="0">
 

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thanks for the info pat. So how can you calculate how to get the correct angle so that you can make the sharpest turns? I think this explains why my 96 ram makes a better u turn than my 98 4 runner.. worse engineering means better turning...
 

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Discussion Starter #6
Originally posted by PW:
<STRONG>thanks for the info pat. So how can you calculate how to get the correct angle so that you can make the sharpest turns? I think this explains why my 96 ram makes a better u turn than my 98 4 runner.. worse engineering means better turning...</STRONG>
Totally miss the point PW. Your Mommy's 4runner, makes a worse u turn because the IFS allows for much more alignment change as the suspension cycles. But since this has nothing to do with Rockcrawling, who cares!!? <IMG SRC="smilies/biggrin.gif" border="0"> <IMG SRC="smilies/biggrin.gif" border="0">

As for calculating the ideal offroad ackermann angle.... No ackermann at all would probably be the best compromise, since it will cause the outside tire in the turn to be at the greatest angle.
 

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Very interesting, that is a very good point but.... You are only taking one situation. What about the slabs?? What if the rig was leaned on the inner tire?
 

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Ok here is why you are WRONG!! <IMG SRC="smilies/tongue.gif" border="0">

D60's have knuckle stops on only the front of the knuckle. In the pic of me, my passenger tire is possibly on the steering stop. The driverside tire is actually turned further than that because there is not stop on the back of the knuckle. So effectively my outer tire is turning as sharp as BOTH of Lance's tires but my inner tire is actually turning FARTHER!

<IMG SRC="smilies/wink.gif" border="0"> <IMG SRC="smilies/massey.gif" border="0"> <IMG SRC="smilies/wink.gif" border="0">
 

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Worried about scrubbing speed in the corners???? Ackerman angle is a moot point with a front locker rig. I say set it up for max turning ability, and let the ackerman angle fall where it may.

Ackerman angle diagram.
 

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Originally posted by LAME:
<STRONG>Worried about scrubbing speed in the corners???? Ackerman angle is a moot point with a front locker rig. I say set it up for max turning ability, and let the ackerman angle fall where it may.

Ackerman angle diagram.
</STRONG>
The grey line is the angle of the drivers tire, right?? So ideal ackerman is to have that angle difference between the front tires be less??
 

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Discussion Starter #12
Originally posted by Ant:
<STRONG>Ok here is why you are WRONG!! <IMG SRC="smilies/tongue.gif" border="0">

D60's have knuckle stops on only the front of the knuckle. In the pic of me, my passenger tire is possibly on the steering stop. The driverside tire is actually turned further than that because there is not stop on the back of the knuckle. So effectively my outer tire is turning as sharp as BOTH of Lance's tires but my inner tire is actually turning FARTHER!

<IMG SRC="smilies/wink.gif" border="0"> <IMG SRC="smilies/massey.gif" border="0"> <IMG SRC="smilies/wink.gif" border="0"></STRONG>
Ok Sure yeah whatever buddy! <IMG SRC="smilies/rolleyes.gif" border="0">

If your right tire is on the stop, than you should adjust your stops so that you can get more steering out of that tire, but since your left is already at the maximum angle allowed by the knuckle design, how ya gonna do that? <IMG SRC="smilies/thefinger.gif" border="0">

My point is, that if you (and I don't mean just you personally Anty) had no ackermann, then both tires would be able to go to the max angle allowed by the knuckle design at the same time. Which would allow you to make tighter turns in almost all offroad situations.

Now as far as the slab thing? Unless your hubs are unlocked to negate the scrub caused by your detroit, and your Boggy's are aired up to street pressures, the "correct" ackermann is again no help, and if your hubs are unlocked, your most likely not in a situation where it's gonna make a difference anyways.
 

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Laars, you are thinking too much again - quit sucking down those cans of Red Bull!

I am not an automotive engineer (although I have played one on TV <IMG SRC="smilies/biggrin.gif" border="0"> ), so what I have to opine is purely "out of my ass" on this topic. However, the ackerman angle has more to do with on-road handling and tire wear characteristics than off-road. There are probably circumstances where the correct ackerman helps and, then again, circumstances where it does not help. Your steering should not turn beyond the angular capabilities of your front U-joints, beyond that, I doubt it matters too much about ackerman. Bad Ackerman Andy
 

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Originally posted by Convertiyota:
<STRONG>The grey line is the angle of the drivers tire, right?? So ideal ackerman is to have that angle difference between the front tires be less??</STRONG>
The tires turn around the same point, but have different radii to travel around. If the inside is at the same angle as the out side, the inside tire will have to slip. The slipping tire is an inefficent way to turn, you want each tire to turn smoothly, but perfect ackerman angle is almost impossible to get.

I think it doesn't matter with a wheelin' rig, because if it is locked up front, it is going to turn bad anyway, and we aren't trying to maintain speed around a corner.
 

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Discussion Starter #15
Originally posted by KrustyKruiser:
<STRONG>Laars, you are thinking too much again - quit sucking down those cans of Red Bull!

</STRONG>
Hey I resemble that remark!!! <IMG SRC="smilies/eyemouth.gif" border="0">

Only one a in my name though LIMEY!!!!!!! Get it straight!! <IMG SRC="smilies/biggrin.gif" border="0">

[ 11-01-2001: Message edited by: Patman ]
 

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Originally posted by KrustyKruiser:
<STRONG>There are probably circumstances where the correct ackerman helps and, then again, circumstances where it does not help.</STRONG>
We can go back and forth on this topic all day, and both sides have good arguements but Andy said it best..... you can't predict all obstacles and what setup would be best.
 

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Originally posted by Patman:
<STRONG>Personally I feel that the “incorrect” ackermann is less detrimental to onroad performance, then the “correct” ackermann is to slow speed (slower than 70 mph) offroad performance.</STRONG>
I'll agree.

If both tires/knuckles/u-joints are turned as far as they can possibly go (which doesn't happen w/ "proper" Ackerman), then obviously the turn will be tighter. Even on-road. Probably even with a locker.
Off road you never know which tire might be getting the most bite so it seems logical to have them both turn as far as possible to try to get the tightest turn possible. <IMG SRC="smilies/smile.gif" border="0">

I'm curious how the on-road performance is affected (for my daily driver rig). I'd guess on the highway not much at all, but in the city and in parking lots where the turns are tighter, there would just be more tire scrub/wear.


As far as the IFS 4runner turning radis goes, since the CV joint sees compound angles (steering in addition to suspension movement), I'd bet that the steering stops are set up to limit the knuckle angles more than on the Dodge. Especially if the Dodge is 2wd.
 

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There is no such thing as "correct" ackerman. There is 100% ackerman by at least 3 different definitions that all are slightly different(SAE, NSAI and the comon racer definition). 100% ackerman is almost never the fastest way around a racetrack. The only time I have ever recomended anyone run 100% ackerman was for a colegiate super mileage vehicle competition. I have set up racecars with overackerman under ackerman and reverse ackerman and in each case there were reasons why those were the best settings for the application. My bronco has reverse ackerman because that is the way ford made the knuckles. If I was going to set it where I wanted it with no concern for clearance I would go with parallel steering, which is what a bunch of people here are also recomending. If I had to errror one side or the other for clearance issues I would error on the side of adding a bit of ackerman, instead of reverse ackerman. But really it doesn't make a lot of difference.
 

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they ackerman isnt limiting anything in the first photo. the stops are limiting the outside tire and the ackerman is giving the inside a sharper bite then would be possible on a no ackerman set-up, as was stated by the owner of the ride.
is that truly full lock? why are the stops out so far?
 

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Originally posted by Gordon:
<STRONG> My bronco has reverse ackerman because that is the way ford made the knuckles. </STRONG>
So Gordon, that means that the outer tire is turning at a smaller radius than the inner tire? Does this produce excessive tire scrub and unusual wear patterns? Just curious. Thanxs Andy
 
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