[shiv]

Good afternoon all.

Just a question about how much down force is on the drooping tyre during flex.

As im aware as the opposite side flexs up into the bumpstop it creates down force on the opposite tyre, flexing it down creating more stable droop?

I just want to know the rough amount of the force created on just a zook with 32" tyres no load in the rear.

what i want to do is link the 2 ends of a drop shackle with a coil sping so the the droop is created through down force.

Any ideas or thoughts?

[Gwagensteve]

This is an interesting idea. I think there are some practical problems though. Coil springs have a relatively small range of motion compared to their overall length. I think it's going to be tough to design something that fits in the space.

Maybe you could use a spring like the blue one the hinge bolt to try and keep the shackle open:



Any rate on the shackle is better than no rate. Increasing rate will improve things up until the point the car starts to "ride" on the shackle in normal use.

However, there's a lot more downwards pressure being exterted by the weight of the tyre and wheel, axle, and leverage than via the shackle. It might be a lot of fab for nothing.

Before you go down this path, set your bumpstops inboard, sort your shock length, and then make up some shackles the same length bolt to bolt as the drop shackles you have, and remove any spring clips. Take the car for a drive, then swap in the drop shackles and take it for another drive. I bet it doesn't really feel any better with the drop shackles in, and might feel worse.

My take is that it's all the mods that drop shackles require that add the capability, not the shackles themselves.

Steve.

[shiv]

Ah yes well i can get custom made springs design (mates rates) so thought id explore this path.

you raised some good points thou. ill check the flex i can achieve with inboard bumpstops (just got new shocks)

My first idea was to have the spring mounted on the leaf (closest to the shackle end) to an ankhor point. But 31zook mentioned going from shackle end to end.

not sure what would be best option.

[shiv]

Maybe park one side on the scales and jack up the opposite tyre till the shackle unloads and see what weigh it applies? ranging from just open to full open.

So having a sping try and hold the hinge open is better then having one try and keep it closed? i though having it hold the shackle shut till the down force is apply.

so you'd have your leaf flex and with more leverage you will open the shackle and get more flex?

[shiv]

I have a design to make this work but just got to get the spring right.

Any idea what the weights should be closed and opened?

Example: lets say it needs 100kg of weight to fully just shut the shackle. now should i have the spring try and hold as close to 100kg when full open aswell or have it curve off to a set amount.

Any ideas?

I think having the spring try and retain as much tension as possible would work best?

[SierraDan]

Can i ask why you want to use drop shackles and going to that effort to possibly make them work better?

[Joshyboy26]

i think what everyone hates about them is how they 'unload' and open up. so if thats they case you would obviously want the springs holding them closed until the 'required force' is achieved through actual flexing action.

but then if you have it held shut, when you flex the wieght is on the opposite wheel so this will in theory not want to open up and i am not really sure on the whole leverage from the other wheel thing.

[Zook_Fan]

What are you trying to achieve by adding a spring?
Are you trying to stop the momentum of body roll when the open shackle quickly closes when the weight shifts onto it?
Are you trying to stop the wheel dangling down with no weight on it?

By having a spring trying to hold the system open you will need a spring rate of half of the unsprung mass of that axle, (tyres, diff, housing, axles, brakes, etc) to get any benefit out of it. That should atleast push the shackle open when there is no force pushing from the bottom of the wheel. However if you do this it will technically alter the ride when the whole car lifts and compresses which could make for a harsh ride at high speeds.

If you try and hold it closed than only when the other side is pushing it down will the shackle be of any benefit. Not a bad idea and would get rid of the unloading of the shackle as the wheel would need a predetermined, by the spring rate, force already pushing down to allow the shackle to move.

Did you try that test of weighing the unloaded wheels? My thoughts is as soon as the shackle starts to open and the other side of the diff is not on a bumpstop the force on the wheel will be around half the unsprung mass.

[shiv]

Cheers Zook_fan.

Yeah not sure if i want to hold it shut till force opens it or have it si it wants to open as soon as you start to flex.

If they are lockable shackles have them spring open would be good as as you flex the shackle and spring are flexing keeping the tyre on the ground with weight. (lock them on road)

if not lockable. having a spring hold them shut till sufficent down force is applied would make them less unload, but i would think if its forced open and the weight shifts floppy or being pulled shut, its still going to snap back. were if it spring open it will less likely want to snap back as you need more and more weight to flex the leaf and also the shackle.

I was thinking to achieve the right spring i would:

(Total weight of car under tyre) - (unloaded weight of tyre and axle under tyre) divided by 2 (as its split between both spring hangers?)

Example (200kg)-(50kg)/2 = 75kg needed to close the shackle.

Make sense or am i taking crazy pills

[SierraDan]

Pinned with the spring holding them shut while unpinned would be best.

First time i saw drop shackles in a car i thought the diff fell out of the car it was that quick. i wouldnt call it flex. slowing that down and adding some rate to it would be best.

[Jackson]

Joshyboy26 wrote:

i think what everyone hates about them is how they 'unload' and open up. so if thats they case you would obviously want the springs holding them closed until the 'required force' is achieved through actual flexing action.

Is it because they unload or because they unload then if weight moves back onto that side there is no rate in the shackle until it closes up again? In this case you would want the shackle being forced open so that as weight starts to move onto that spring at least the shackle won't insta close.

Working out the actual minimum force required in the spring is a pretty mighty feat. If you get the springs cheap then best bet is going to be trial and error.

This is actually a pretty cool idea though, if you made it so that it does hold the shackle open it will allow that drooping tyre to exert more than just its weight into the ground (conventional drop shackles that wheel is just sitting on the ground) which means more friction.

I guess if the spring is holding the shackle open I guess you want the shackles to be closed on flat ground? So the exerted by the springs when closed is going to have to be less that 1/4 of the weight of a Sierra. However the centre of gravity is probably forward of centre so the front springs will have to be higher rate than the rear and might end up being higher than a quarter of the weight.

[Zook_Fan]

shiv wrote:

Cheers Zook_fan.

Yeah not sure if i want to hold it shut till force opens it or have it si it wants to open as soon as you start to flex.

If they are lockable shackles have them spring open would be good as as you flex the shackle and spring are flexing keeping the tyre on the ground with weight. (lock them on road)

if not lockable. having a spring hold them shut till sufficent down force is applied would make them less unload, but i would think if its forced open and the weight shifts floppy or being pulled shut, its still going to snap back. were if it spring open it will less likely want to snap back as you need more and more weight to flex the leaf and also the shackle.

I was thinking to achieve the right spring i would:

(Total weight of car under tyre) - (unloaded weight of tyre and axle under tyre) divided by 2 (as its split between both spring hangers?)

Example (200kg)-(50kg)/2 = 75kg needed to close the shackle.

Make sense or am i taking crazy pills

I'm pretty sure you'll want a different rate spring depending on which way you go. To hold the wheel up you only need the unsprung mass divided by 2. That will keep force on the shackle but it will still open as much as the leaf would normally flex. Effectively you are adding a helper spring to the system. I think this is the best option.

If you are trying to push the wheel down then I would go for your spring calcs however this will actually keep the car at full shackle extension at rest. You'll be sitting really high and you will have long shackles that handle badly but will allow more up travel. Not really an improvement on correct length normal shackles.

[Jackson]

If he uses springs that are 75kg they will not hold the shackles of a 900kg car open...

[Joshyboy26]

You wont want springs to hold them open, when your on a spooky side angle it might help push you over, sure youll probably be pretty close anyway but any little bit helps.

[Zook_Fan]

Jackson wrote:

If he uses springs that are 75kg they will not hold the shackles of a 900kg car open...

His "example" and his written formula are miles apart. He said:

shiv wrote:

(Total weight of car under tyre) - (unloaded weight of tyre and axle under tyre) divided by 2

Which pretty much means over the whole car he's got: total mass - unsprung mass divided by 2. That's half of the unsprung mass at each wheel in spring rate.

[Jackson]

Zook_Fan wrote:

shiv wrote:

(Total weight of car under tyre) - (unloaded weight of tyre and axle under tyre) divided by 2

Which pretty much means over the whole car he's got: total mass - unsprung mass divided by 2. That's half of the unsprung mass at each wheel in spring rate.

I think he was talking about one wheel?

So he is saying "((Total mass of car/4)-(Weight of diff and tyre/2))/2 (something to do with the spring hanger.)" Either way I think this is way to generalised and would only work if the centre of gravity was dead centre of the car. I also think considering that most of the time you will be moving you will have other forces due to acceleration etc that working out the actual rate required is going to be pretty difficult.

Joshyboy26 wrote:

You wont want springs to hold them open, when your on a spooky side angle it might help push you over, sure youll probably be pretty close anyway but any little bit helps.

I'm not sure about this. Would you rather have a wheel, which is on the low side of the car anyway, pushing up or have the body roll onto an unloaded shackle which can keep rolling until the shackle has closed up.

[JrZook]

Wonder if you could fab up some sort of X-link setup and use the flop shackles?

[Joshyboy26]

Jackson wrote:

Zook_Fan wrote:

shiv wrote:

(Total weight of car under tyre) - (unloaded weight of tyre and axle under tyre) divided by 2

Which pretty much means over the whole car he's got: total mass - unsprung mass divided by 2. That's half of the unsprung mass at each wheel in spring rate.

I think he was talking about one wheel?

So he is saying "((Total mass of car/4)-(Weight of diff and tyre/2))/2 (something to do with the spring hanger.)" Either way I think this is way to generalised and would only work if the centre of gravity was dead centre of the car. I also think considering that most of the time you will be moving you will have other forces due to acceleration etc that working out the actual rate required is going to be pretty difficult.

Joshyboy26 wrote:

You wont want springs to hold them open, when your on a spooky side angle it might help push you over, sure youll probably be pretty close anyway but any little bit helps.

I'm not sure about this. Would you rather have a wheel, which is on the low side of the car anyway, pushing up or have the body roll onto an unloaded shackle which can keep rolling until the shackle has closed up.

see this is two situations where its a shonky idea. while i applaud you shiv for thinking about it, its great to try new things, though im not really so sure it will work so well in practise.

[Zook_Fan]

JrZook wrote:

Wonder if you could fab up some sort of X-link setup and use the flop shackles?

I think this would be the way. If you still want to induce force a sway bar setup or torsion bar style setup may be better than coil springs

[SierraDan]

Zook_Fan wrote:

JrZook wrote:

Wonder if you could fab up some sort of X-link setup and use the flop shackles?

I think this would be the way. If you still want to induce force a sway bar setup or torsion bar style setup may be better than coil springs

Some longer leaf springs would be good too...

[shiv]

Thanks for the input.

[jdk81]

If you use springs to keep them closed, you will reduce the force the tyres put into the ground, they have to overcome this force, for them to get pushed into the ground.
I suspect you will pretty much be relying solely on leverage to generate the force required to open the shackle.
I popo this idea.

If you use spring force to keep them open (meaning they are closed under normal conditions due to vehicle weight etc), you will create a progressive rate which is what you want, but it would need lots of testing, to get the rate right.
You would need powerful springs to try to achieve what you want, packaged in a drop-shackle.

Spring loaded drop shackles is verging into 3/4 elliptical spring territory.

I popo this idea, as it is time and effort you can spend towards coils etc, proven with known results. Farmgineering isnt a good idea on the road.

[31zook]

The idea was that if he used a spring on the drop shackle it wouldn't unload (as much) on side angles. More of an aid as apossed to a brilliant solution.

[shiv]

I figured having a wheel off the grounds is no help so if i had drop shackles would increase droop but having a spring hold them together would help the unloading factor. i figure if the uptravel on the other side is good on the bumpstop it will have leverage to open the shackle. That force holding the shackle open should stop the free load up if the weight shifts to that side.

Even thou your not geting as much weight to the ground for traction it should help with stability? Correct me if im wrong cause this is the reason i asked the question

[SierraDan]

On that.. I'd rather have no flex than drop shackles. I've driven some big stuff with many wheels in the air. The biggest thing I lacked to hinder was wheelbase and tyre size.

It was a brick, but a stable and predictable brick. Rather than a slinky on a plate of jelly.


The work you seem keen to do to get the shackles to be a bit better would be about as much work as some longer springs which would be better.

That's my opinion, I'm sure someone will tell me I'm wrong and drop shackles are the sickest.

[shiv]

LOL no i believe you Dan, i seen the pics of you rocknrolling as a brick.

Just thoughts on the subject. As for the work involved, majority can be at work. cant really put longer leafs in at work may just be abit to suss.

[JrZook]

SierraDan wrote:

On that.. I'd rather have no flex than drop shackles.

*If* you had a complete a running zuk I would love you to do a comparison lets say with a 2inch sus lift one with welded shocks ie NO flex and one with the same 2inch sus lif, un-welded shocks and drop shackles. Then report back to as to which one is more stable and capable


On this I still reckon an X-link setup on leafs with slinky shackles would be pretty interesting

[SierraDan]

Sorry for exaggerating. "stock flex".
Better?