[royce]

you are smarter than me, go work out out how many degrees of change you get from teh height change caused by the shackle cycling, the end of the spring would change what 80mm from full compression to full droop?

[SuziBlu]

[Hybrid]

Extended shackles and redrilled spring hangers for RUF throws the castor off. Especially since there seems to be hardly any castor in the stock sierra anyway. I'm back to stock shackles after running extended ones with RUF and I left the castor wedges in. I reckon they are the easiest way to get the sierra to track well. On the freeway especially. Good return to centre and trucks/wind don't cause wandering like they used to. Either way I don't see caster causing death wobbles. I'm sure lack of it would make them a lot more noticeable though.

On topic, another thing to check for the wobbles is flogged out shackle bolts. Allows the shackle to move laterally. Everything else sounds like it's been covered.

[JrZook]

royce wrote:

you are smarter than me, go work out out how many degrees of change you get from teh height change caused by the shackle cycling, the end of the spring would change what 80mm from full compression to full droop?

4.82 degrees using a 950mm spring and central axle location

[royce]

why would the axle location come into it, the angle change is going to be the same all the way along the spring wont it?

[Fatzook]

royce wrote:

why would the axle location come into it, the angle change is going to be the same all the way along the spring wont it?

What if the spring is 'S' shaped during flex?

[JrZook]

royce wrote:

why would the axle location come into it, the angle change is going to be the same all the way along the spring wont it?

Correct! Its just the way i drew it up

[JrZook]

Fatzook wrote:

royce wrote:

why would the axle location come into it, the angle change is going to be the same all the way along the spring wont it?

What if the spring is 'S' shaped during flex?

lol if you can make an S shape at speed on the front end other than crawling your gonna have more issues than castor change

[Fatzook]

JrZook wrote:

Fatzook wrote:

royce wrote:

why would the axle location come into it, the angle change is going to be the same all the way along the spring wont it?

What if the spring is 'S' shaped during flex?

lol if you can make an S shape at speed on the front end other than crawling your gonna have more issues than castor change

Yeah I know this....

[royce]

ok go a bit further, whats the height change from a normal shackle angle on a stock shackle to the worst possible, IE vertical?

[alien]

my guess would be about 20-30mm.

[SuziBlu]

[JrZook]

royce wrote:

ok go a bit further, whats the height change from a normal shackle angle on a stock shackle to the worst possible, IE vertical?

If we assume that the angle of stock is say 45degrees then the effective shackle height is 56mm thus the difference in heights here is 24mm.
Therefore angular change at diff = 1.6degrees.

So if stock castor is say 2.5degrees then your only left with 0.9deg

[SuziBlu]

What is the "normal" shackle length.

[alien]

80mm pin to pin from memory?

[royce]

stock isnt 45 degrees is it, otherwise rather than carby threads every 3 days we would have a omg my shackle jsut fell over and it jammed under the bumper threads

[Fatzook]

SuziBlu wrote:

What is the "normal" shackle length.

70mm pin to pin

[Fatzook]

royce wrote:

stock isnt 45 degrees is it, otherwise rather than carby threads every 3 days we would have a omg my shackle jsut fell over and it jammed under the bumper threads

Its about 30 degrees from horizonal. It looks to be about 45 degrees from the chassis, which at the front is on about a 15 degree downward slope.

[JrZook]

royce wrote:

stock isnt 45 degrees is it, otherwise rather than carby threads every 3 days we would have a omg my shackle jsut fell over and it jammed under the bumper threads

Well give me a number to work with then

[SuziBlu]

[alien]

Don't forget of course the "ideal" shackle angle is dependant on the arch of the leaf its attached to... if the leaf is dead flat then the shackle angle can only decrease, but if the leaf is really arched then its got no droop and can only compress - so in the case of very lifted leaves a more vertical shackle angle would be more desirable to allow for the spring to compress.

[royce]

JrZook wrote:

royce wrote:

stock isnt 45 degrees is it, otherwise rather than carby threads every 3 days we would have a omg my shackle jsut fell over and it jammed under the bumper threads

Well give me a number to work with then

Fateveryoneremembercamothefallenzook says 30 from horizontal

[SuziBlu]

alien wrote:

Don't forget of course the "ideal" shackle angle is dependant on the arch of the leaf its attached to... if the leaf is dead flat then the shackle angle can only decrease, but if the leaf is really arched then its got no droop and can only compress - so in the case of very lifted leaves a more vertical shackle angle would be more desirable to allow for the spring to compress.

Yes, and also length has to be considered. I very long leaf will need a longer shackle to allow full movement, and a shorter leaf will not need this.

[Fatzook]

royce wrote:

JrZook wrote:

royce wrote:

stock isnt 45 degrees is it, otherwise rather than carby threads every 3 days we would have a omg my shackle jsut fell over and it jammed under the bumper threads

Well give me a number to work with then

Fateveryoneremembercamothefallenzook says 30 from horizontal

Sorry I meant verticle. Didn't read what I Typed. And cammo doesn't have leaves

[SuziBlu]

royce wrote:

JrZook wrote:

royce wrote:

stock isnt 45 degrees is it, otherwise rather than carby threads every 3 days we would have a omg my shackle jsut fell over and it jammed under the bumper threads

Well give me a number to work with then

Fateveryoneremembercamothefallenzook says 30 from horizontal

In regard to this, shouldn't you have a flat (sort of) shackle angle, protected from going too far by bump stops, this would allow maximum droop wouldn't it ?

[alien]

i think the problem with shackle droop is its like a drop shackle - its unsprung, so before the spring gets a chance to work the shackle has to drop to the point it picks up the spring tension. Thats my dumb logic on it anyway?

[SuziBlu]

[royce]

yeah but we are tlaking about castor change due to lifted springs in turn causing wobbles, not bloody suspension travel

[SuziBlu]

crikey, did we get off course, that must be a first.

I don't understand why, its beyond me, but everything I have read says if you lift over 2" you need to address caster or you will get the wobbles.

[Fatzook]

SuziBlu wrote:

crikey, did we get off course, that must be a first.

I don't understand why, its beyond me, but everything I have read says if you lift over 2" you need to address caster or you will get the wobbles.

I've never read that Many peeps say that extended shackles will alter castor though. I've never heard of castor being the CAUSE of wobbles. Increased lateral movement in the bushes due to longer shackles maybe......