How do Caster Corrected Front Radius Arms Help? - Defender Source
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  #1  
Old May 4th, 2010, 02:29 AM
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How do Caster Corrected Front Radius Arms Help?

As I understand it these help with lifted vehicles, is that correct? If so what exactly are they doing?

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  #2  
Old May 4th, 2010, 03:28 AM
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This could be a bit confusing - but here goes.........
Say you lift your truck 2inches using longer springs, the axle is the located 2 inches further away from the chassis than standard, but the hockey stick mounts (radius arms) on the chassis, stay in the same place, so effectively the axle has rotated slightly causing the castor angle of the swivel bearings, in relation to an imaginary vertical line through the centre of the swivel, to have altered. This can affect the self centring ability and cause vaguness in the steering. So fitting castor corrected radius arms returns the angle of the swivels to a closer to standard castor angle, returning the correct geometry to the steering (happy days). Lots of folk seem to get away with a 2inch lift without any problems, so if I were considering a lift, I would budget for castor corrected front arms, but fit the springs first and try it, then buy the arms if considered necessary...........

Over here it is possible to buy castor corrected bushes for the standard arms, where the holes in the bushes are off centre, which is a cheaper option........... theres a link below, but IRRC Old Man Emu do em too

http://www.terrafirma4x4.com/product...p?cat=1&grp=23

Hope this helps

Paul
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  #3  
Old May 4th, 2010, 09:59 AM
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Quote:
Originally Posted by paulnb57 View Post
Over here it is possible to buy castor corrected bushes for the standard arms, where the holes in the bushes are off centre, which is a cheaper option........... theres a link below, but IRRC Old Man Emu do em too

http://www.terrafirma4x4.com/product...p?cat=1&grp=23

Hope this helps

Paul
If you go this route, be advised that they (Castor correction bushings) can have a tenancy to limit articulation off road, since there is less material between the bolt hole and the radius arm to 'flex', which allows the mounting points to 'bind' even sooner than they typically do..
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  #4  
Old May 4th, 2010, 10:03 AM
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Actually that helps tons, Your explanation makes total sense when I think about it. How is the Terra Firma stuff as a product line?


Quote:
Originally Posted by LRNAD90 View Post
If you go this route, be advised that they (Castor correction bushings) can have a tenancy to limit articulation off road, since there is less material between the bolt hole and the radius arm to 'flex', which allows the mounting points to 'bind' even sooner than they typically do..

So the actual arm is the better way to go then?

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  #5  
Old May 4th, 2010, 10:26 AM
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Quote:
Originally Posted by LRNAD90 View Post
If you go this route, be advised that they (Castor correction bushings) can have a tenancy to limit articulation off road, since there is less material between the bolt hole and the radius arm to 'flex', which allows the mounting points to 'bind' even sooner than they typically do..
That is not true... The amount of material is the same. The holes are just offset. The maximum amount of movement combined between both sides is the same.

------ Follow up post added May 4th, 2010 08:28 AM ------

Quote:
Originally Posted by IPSC_GUY View Post
So the actual arm is the better way to go then?
The "best" solution is to rotate the swivels. This allows both the pinion angle and the castor to be correct.

How much lift do you have?
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  #6  
Old May 4th, 2010, 10:49 AM
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Originally Posted by Red90 View Post
That is not true... The amount of material is the same. The holes are just offset. The maximum amount of movement combined between both sides is the same.
Well, we'll have to agree to disagree with that. I've seen it documented many times, not only in the Land Rover community, that it can. It may be technically correct that there is the same mount of material overall, but there certainly is not the same amount of material all the way around the bolt, so if the bushing needs to flex where the material has been reduced, it will bind sooner..

Quote:
Originally Posted by IPSC_GUY View Post
So the actual arm is the better way to go then?

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Well, you know what they say about opinions, but yes, in my opinion they are a better way to go than Castor correcting bushings, however..

Quote:
Originally Posted by Red90 View Post
The "best" solution is to rotate the swivels. This allows both the pinion angle and the Castor to be correct.

How much lift do you have?
Agreed, but its not the easiest, or least expensive way to go. For most guys that like to wrench in the garage, the corrected radius arms are often the best choice when considering cost/ease of installation, etc. And if there is ever any chance of wanting to return the truck to stock, then you will need new stock swivel balls to replace the modified balls..

RoverTym Service to Castor
Correct with the Swivel Ball modifications
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  #7  
Old May 4th, 2010, 11:07 AM
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The main issue is the "wander" caused by a lifted truck. I know this sounds like "ron good" advice, but if you put in a front trutrac the wander goes away and it tracks like stock.
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Old May 4th, 2010, 11:17 AM
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Quote:
Originally Posted by LRNAD90 View Post
Well, we'll have to agree to disagree with that. I've seen it documented many times, not only in the Land Rover community, that it can. It may be technically correct that there is the same mount of material overall, but there certainly is not the same amount of material all the way around the bolt, so if the bushing needs to flex where the material has been reduced, it will bind sooner..
One side flexes less, the other flexes more. In articulation, the combined movement is the same. I have personally owned and tested the articulation of castor corrected (offset) radius arm bushings versus normal ones and the articulation is the same. I am not basing my comments on stuff I read on the internet.

Are swivel balls any more expensive than radius arms? I do not see them much harder to change.
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Old May 4th, 2010, 11:35 PM
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You don't need to buy new swivels, you can just weld up and re-drill the ones you have.
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  #10  
Old May 5th, 2010, 01:01 AM
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Here's a picture to demonstrate caster angle. The "pivot" line is the line that goes through the top and bottom bearing on the swivel ball. It is angled so that it intersects the ground in FRONT of the tire. This is "positive" caster. This is a similar scenario to the shopping cart wheel where the pivot is in front of the wheel. When you push the cart the wheel "follows". If you try to drive that same cart backwards the wheels is harder to keep in front of the pivot point and just wants to turn around.

When the truck is lifted this caster angle is pulled closer to "0" or even "negative" which then makes the steering "light" and difficult to track straight.
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Old May 5th, 2010, 09:33 AM
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If you ride at all the easiest way to envision it is the angle at which your forks are tilted (rake/trail), on a race bike they're almost vertical which makes them steer quickly and behave twitchy (I ride a CBR900RR so I know this one ) on an easy rider they're at a shallow angle way out in front which causes steering to be slow and relaxed and unresponsive.


Adjusting castor causes similar effects, the reason you lose self centering is because the 'quicker' response is faster than the system is designed for, more or less. This is not 100% correlative but it is a good way to explain the behavior.
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Old May 5th, 2010, 11:04 AM
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You guys are only looking at part of the picture though. Without the arms, yes, your castor goes down and that can affect return to center and handling. How much? Probably not much considering how these trucks handle in the first place.

But, the closer you get to 0 the easier it is to turn your tires, by a significant amount. So with a lift probably comes bigger tires. I would rather run less castor. Also to consider is pinion angle. SB will fix this but the radius arms will point the pinion back down which you don't want if you have a CV shaft, which a lot of you do who lift your rigs. Just food for thought.
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Old May 5th, 2010, 12:11 PM
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Actually it makes a big difference. How much do you really drive near stock Rovers on the road?? The steering force is more affected by scrub radius and tire size. Scrub radius is changed more by changes in offset.
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Old May 5th, 2010, 08:56 PM
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On my current build the 40mm lift-springs (OME) seem to have the pinion pointing up a fair bit compared to the front TC output but this could be due to using a D1 front housing (they LOOK the same) so in this case fitting corrected arms would likely reduce vibration, for now I'm just putting on a D2 front shaft until it is finished and aligned and the castor can be properly measured and then decide what action to take.
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Old May 5th, 2010, 11:06 PM
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Quote:
Originally Posted by Red90 View Post
Actually it makes a big difference. How much do you really drive near stock Rovers on the road?? The steering force is more affected by scrub radius and tire size. Scrub radius is changed more by changes in offset.
Yes, tire size and scrub radius affect it more. But castor affects it as well. My point was that if you can get away with less castor, it's better offroad for stress and other reasons. You will be giving away handling on road but on a 2 in lift, I doubt its that much of an issue.
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