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Russellmn

Russellmn

Well-known member
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East Central MN
I'm getting ready to put Super Duty outers on a 14 bolt next week. Curious what opinions are on caster angles. Use will be trail riding on granite, iron mining overburden, etc... Not sure if people like zero caster or negative? Even positive caster??? Opinions solicited, reasoning for the opinion greatly appreciated.


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Run Zero caster for the rear.
With a closed center control valve the caster will not do a thing to self center. Only the valve will correct the steering angle.
I do not see a benefit to traction by adding caster and rolling the tire on its side. Maybe it throws the rear end around and helps shift weight and grabs new traction.
Caster might help with clearing lower links if it rolls the tire around the link instead of into it. But it might not add anymore steering degrees than Zero caster offers.
You didn’t ask, but Ackerman should be zero with parallel steering arms for max steering angle left and right at the same time.
 
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Russellmn said:
Yes, rear is becoming a steer axle. Front will be around 6* caster.
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I guess what I’m trying to get to is that why wouldn’t you want your rear steer axle to have the same castor as the front?

They are both steering axles, and castor angle is important on steering axles.
 
Mr Stubs said:
I guess what I’m trying to get to is that why wouldn’t you want your rear steer axle to have the same castor as the front?

They are both steering axles, and castor angle is important on steering axles.
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Well, I've heard people run all sorts of different castor settings, was hoping someone could articulate a reason for one over another and help me decide if that's a good reason for me to do the same...
 
HYDRODYNAMIC said:
I do not see a benefit to traction by adding caster and rolling the tire on its side. Maybe it throws the rear end around and helps shift weight and grabs new traction.
Caster might help with clearing lower links if it rolls the tire around the link instead of into it. But it might not add anymore steering degrees than Zero caster offers.
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So to me, these are all pro’s.
 
are you going to be steering the axle at any sort of speed?

how solid are you going to be able to make your connections?

are you running an external lock for high speed driving?
 
Provience said:
are you going to be steering the axle at any sort of speed?

how solid are you going to be able to make your connections?

are you running an external lock for high speed driving?
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I'll be awfully surprised if this thing comes outta low range...
connections will be tight, JHF steering arms, new heims, new PSC DE ram.
 
Russellmn said:
I'll be awfully surprised if this thing comes outta low range...
connections will be tight, JHF steering arms, new heims, new PSC DE ram.
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anything but postive, for the same reason you don't want negative caster on the front, would get my vote.

it seems like packaging would become an issue if you go "too far" negative with the links and DE ram

it seems like a few degrees would help when climbing, but it probably won't even matter then
 
So far I'm thinking a couple degrees negative giving me some cushion if I need more pinion up. I don't know that it will really matter, but figured if I'm building it, might as well find out if there's a better way than others...
 
So when talking negative/positive in the rear is it opposite? Ie: positive on both ends being / \ or both being / / ?

At first I was thinking the 2nd would be best, but I almost wonder if opposite would help a little when the front is climbing and the rear is still on flat, since it would be closer to perpendicular to the ground.

I feel like you could come up with equal list for benefits and downsides to both set ups, probably why zero is common.
 
YotaAtieToo said:
So when talking negative/positive in the rear is it opposite? Ie: positive on both ends being / \ or both being / / ?

At first I was thinking the 2nd would be best, but I almost wonder if opposite would help a little when the front is climbing and the rear is still on flat, since it would be closer to perpendicular to the ground.

I feel like you could come up with equal list for benefits and downsides to both set ups, probably why zero is common.
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What I learned in alignment class was "Positively out back" Positive camber/caster is always out and back as far as I know, so / /
 
YotaAtieToo said:
So when talking negative/positive in the rear is it opposite? Ie: positive on both ends being / \ or both being / / ?

At first I was thinking the 2nd would be best, but I almost wonder if opposite would help a little when the front is climbing and the rear is still on flat, since it would be closer to perpendicular to the ground.

I feel like you could come up with equal list for benefits and downsides to both set ups, probably why zero is common.
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positive angled toward front of car, negative angled toward rear of car. at least, that is how i'm using it :laughing:

think of bicycle front and rear

on the front, the weight of the car is pushing the tire forward, on the back, the weight of the car is pulling the tire along
 
I've run rear caster at zero and at similar direction to the front // style. Run it at zero. Rocking it back does no good for climbing or centering or whatever, but it does take some of your steering angle and turn it into up/down movement instead.
 
Provience said:
positive angled toward front of car, negative angled toward rear of car. at least, that is how i'm using it :laughing:
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That's what I thought, just wasn't sure if it was opposite when talking rear steer.

Quick Google shows about equal amount saying 0* and similar positive to the front. I'm sure there are downsides to both.
 
The whole purpose of caster is self centering. Any other benefit probably has a down fall too. If your not running a load reactive orbital on the rear, I don't see the reason to have anything but zero.
 
WaterH said:
The whole purpose of caster is self centering. Any other benefit probably has a down fall too. If your not running a load reactive orbital on the rear, I don't see the reason to have anything but zero.
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The reason it self centers is because it’s “biting” for traction. Why wouldn’t you want that on a steering axle, even a rear one?
 
Mr Stubs said:
The reason it self centers is because it’s “biting” for traction. Why wouldn’t you want that on a steering axle, even a rear one?
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I would say the reason it self centers is gravity. When you turn with caster, the vehicle rises ever so slightly. Of course it wants to go back down when you release the wheel.
 
WaterH said:
I would say the reason it self centers is gravity. When you turn with caster, the vehicle rises ever so slightly. Of course it wants to go back down when you release the wheel.
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None of that matters with full hydro steering though.

By that logic, the castor makes no difference in any full Hydro application.
 
Mr Stubs said:
None of that matters with full hydro steering though.

By that logic, the castor makes no difference in any full Hydro application.
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In a non-reactive full hydro application, at low speeds, with everything tight and good with zero play, it doesn't.
In a reactive full hydro application, it matters, reactive full hydro is basically a different kind of steering box with a fluid drag link instead of a metal rod.
If everything isn't tight and good and zero play, you'll have wobble. Right-way caster will tend to settle it. Wrong-way caster will magnify it. Speeds and harmonics can start or magnify it.
If you are driving on rear steer at speed, it will either be tight and good, or at least occasionally terrifying. The settling effects of caster at speed relative to the wobble that you'll get from things being out of whack, won't de-terrify it, because of how violent weight shifts from rear steering changes at speed are. I've had a single worn-out rod end (~1/8" of play at the rod end, translates to a wobbling inch or so of toe change at the tire) be noticeable on rear steer before, driving along, good good good shimmy good good good good wtf was that good good good good bump shimmy good good good....
If you are only ever up to trail speeds, rear caster really won't matter anyway.

Somebody has to have a service book for a GM Quadrasteer that calls out rear caster spec, I can't find it googling, but I'm thinking it was zero or very close to.
 
I don't want to pretend I know anything about rear steer. I'm just using my warped common sense. So I need to ask a question. Does anybody or everybody use a load reactive steering on rear steer? I don't know how that would work on a joy stick. Everybody does use a joy stick on the rear, don't they? I've seen elaborate electronic devices that will return to center. That leads me to believe that it's just regular hydro steering. (Like my tractor)
 
ScottRS said:
In a non-reactive full hydro application, at low speeds, with everything tight and good with zero play, it doesn't.
In a reactive full hydro application, it matters, reactive full hydro is basically a different kind of steering box with a fluid drag link instead of a metal rod.
If everything isn't tight and good and zero play, you'll have wobble. Right-way caster will tend to settle it. Wrong-way caster will magnify it. Speeds and harmonics can start or magnify it.
If you are driving on rear steer at speed, it will either be tight and good, or at least occasionally terrifying. The settling effects of caster at speed relative to the wobble that you'll get from things being out of whack, won't de-terrify it, because of how violent weight shifts from rear steering changes at speed are. I've had a single worn-out rod end (~1/8" of play at the rod end, translates to a wobbling inch or so of toe change at the tire) be noticeable on rear steer before, driving along, good good good shimmy good good good good wtf was that good good good good bump shimmy good good good....
If you are only ever up to trail speeds, rear caster really won't matter anyway.

Somebody has to have a service book for a GM Quadrasteer that calls out rear caster spec, I can't find it googling, but I'm thinking it was zero or very close to.
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This 100%.

Caster does affect front steering full hydro systems using load reactive orbital valves but rear steer valves are a fundamentally different type of valve. They are simple double acting directional control valves, open center with work ports closed to tank. That means that then the rear steer valve is actuated, it lets fluid into the rear ram (and the opposite port lets fluid return from the ram) but once you let go of the joystick, work ports are blocked completely. At that point it doesn't matter what the axle forces (caster) are doing, the steering angle will stay where it is. There is no such thing as a load reactive directional control valve.

What you see for "return to center" rear steer setups are electric solenoid coils that drive the rear steer directional valve. By setting up a series of sensors/switches on the axle, you can make the solenoid valve automatically actuate whichever direction is necessary until the steering is centered.
 
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