which commercial vehicle brands use More Ackerman setting and to what extent?

[cranknpiston]

Which commercial vehicle brands use More Ackerman setting and to what extent?
How do you estimate the percentage of More Ackerman that will suit your vehicle best?

 

[BrianPetersen]

What makes you think it is "brand-specific"?

What type of commercial vehicle are we talking about?

What's the application?

Just to put the thought in your mind ... In roadracing, there can be a benefit to "anti-ackermann", at least for the few degrees of steering on each side of centered, because the outside wheel when cornering has much more force on it and therefore has a much greater slip angle. "Anti-ackermann" can put the inside wheel in a more favorable (lower) slip angle when the outside wheel has a high slip angle due to the high side forces on it.

But in regular driving, with rather minimal cornering forces, the less the wheels have to slip sideways, the longer the tires will last, so the more accurate the Ackermann matches up with the vehicle's requirements (dependent on wheelbase and track width etc) the better off it will be ... in theory. But any "commercial vehicle" that has tandem axles (or more, on a trailer) is gonna have slip angles at the tandems that are fighting each other in sharp corners. On a trailer with many axles, you can see the side slippage.

Many cars have been built with Ackermann way out of whack. The old "box" GM full-size cars (1977-on) always squealed their tires when cornering, no matter how gently, because of how screwed up the front end geometry was. Lots of people still bought them.

FWIW lots of "commercial vehicle brands" buy their steering axles from the same set of suppliers, and I don't think they tailor the knuckles to the wheelbase ... they just set it to some nominal geometry that'll be okay for (almost) everyone and call it good enough. They are not building sports cars. It's better to just make all the axles the same.

 

[cranknpiston]

You got me a little wrong here. I merely want to know the examples of commercial vehicle brand (toyota, chevrolet...any type of passenger street car) models that have used More Ackerman Steering and not True Ackerman or Less Ackerman geometry, and by how much (the percentage like 150% 200%).
Since i'm only working on Pro-Ackerman (True,More,Less) at the moment, i'm trying to figure out when are each of these used and when they're used, to what extent and why to that particular extent.

 

[cranknpiston]

And for the second part, for an ATV of wheelbase almost the same as its track width (54") what percent of More Ackerman would you suggest, and why?

 

[GregLocock]

I doubt you'll find a non-proprietary list as virtually nobody could make use of it. So it is time to break out the stick with two pointers and go to a car yard.



Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

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[cranknpiston]

If I got that right, do you mean to say that nobody could make use of More Ackerman geometry? Why is that?

 

[GregLocock]

No, you don't get that right.

Why would you want more Ackerman? what would you have to do to the car to make it work? I know the answers, I'm just wondering what on earth you are getting at.



Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

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[cranknpiston]

I'd want more Ackerman because i'm thinking of going for an initial front Toe-in setting as I have known that rear wheel drive vehicles go good with a front Toe-in setting for straight line stability, and to compensate for the sluggishness that the toe-in provides during turning we could use a More Ackerman setting.

 

[GregLocock]

Well, you've got that bit right, toe-in is like fake anti-ackerman, near the centre. I think you are probably gilding the lily by modifying the ackerman, but fair enough. So, plot your steering angle for each of the front wheels vs steering wheel angle, the difference between the wheel angles is the ackerman, and then compare that with the theoretical ackerman characteristic for your car.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[cranknpiston]

That's alright, but lets get to the actual topic.
How do I estimate the extent of more ackerman that I should apply to the vehicle? I mean, if the vehicle isn't built yet, and I want to figure out the extent of more ackerman that I should have on it having the wheelbase, track width and the degrees of Toe-in known.

 

[GregLocock]

Well I'm afraid that is a bit beyond my experience. I change ackerman for turning circle, primarily, and we then cope with the on centre effects (which, frankly, are in the noise floor).

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[BrianPetersen]

Your wheelbase is out of range for production cars, anyhow. And the tires are different.

Go to a motorcycle dealer and take a look at any of the production ATVs that they build. If the Ackermann is considerably out of whack, it will be visible when driving in a tight circle.

Or just design it at "nominal" and make something adjustable a little bit.