Double shocks. Any unintended concequences

[Apocalypse]

Shocks (more correctly dampers) - these simply convert energy that has been released by the vehicle's motion over bumps and that has been stored in the springs into heat to keep the vehicles stable.

like a spring it has a resistance to travel - but it's an increasing resistance that increases with speed of travel.

most modern ones operate by passing fluid through a restrictor - some have an additional set of external bypasses that varies resistance according the position of the piston, others have an additional set of valves in the piston that allow different resistance curves depending on the speed of travel


E=mv^2 - so, the more mass there is the more energy needs to be handled, AND velocity is squared - so if you double the speed of motion, you quadruple the energy that needs to be handled.

What happens is that as you compress the suspension (called bump or compression) the damper moves - the faster the damper moves the more resistance it has. high end shocks have separate high speed bump and rebound (suspension movement over the surface) and low speed bump / rebound (lean caused by cornering) - effectively increasing your spring rate until the motion slows down and stops, then changes direction. At very high speed - a big bump - the initial resistance on the shock can be well into the 1000kgf/cm range . hit it too hard and you'll just burst the can or tear the orifice wide open (you never ever want to hear the words ''your orifice has been torn wide open'. ever. )

so, if you hit a big bump, ideally your SHOCK HIGH SPEED BUMP RATE should be hard enough to prevent the vehicle from bottoming out. When you get to a corner it should be stiff enough to allow the vehicle to roll, but not roll excessively (Fortuner drivers take note... )

Then, once the suspension stops moving up, it will want to return to the 'static' load position - rebound. the energy stored in the spring will try and fling the body up wards. obviously this is bad as it will then bounce up and down as it goes down the road.

the rebound thus need to absorb that energy too - the valving needs to be hard enough to damp out the upward inertia of the vehicles mass, but if it's too hard it will make the vehicle return to ride height too slowly , which means the next bump might crash through etc.

The SIZE of the shock is important. The heat that is being absorbed has to be dissipated - as the oil and metals get hot the oils viscosity drops, the tolerance between bore and piston tightens up (creating more heat) and the orifices change size, wear increases and plastics start to melt. What that means is that a hot shock is ineffective, is likely to wear out and might even seize up and break.

The heat is dissipated via the tube exposure to air - obviously a 38mm tube has less area than a 50mm tube to dissipate heat. big offroad shocks can be 100mm and stacked up several deep.... Shocks being too hot isn't good. Many performance shocks have air ducted to them, and often have cooling fins to increase the surface area too.

[Apocalypse]

Where does that leave us with the OPs original question?

the complaint is that his shocks get too hot with the load he carries an the roads he travels....

basically there is too much energy being shunted into the shocks and he needs to reduce how much energy they are handling.

as noted...

reduce weight. no one wants to hear that negativity in their life.....

Change driving style. as noted the energy dispersed by the shock is exponential to the speed of suspension movement. you don't need to slow down an awful lot to reduce bumping (which reduces travel as well as speed of the shock shaft) to halve the energy that is being dealt with. dropping from 110km/h to 100km/h for instance, will HALVE the shock's work.

More cooling - bigger tube shocks, longer shocks with a lift all add to area. A defender wouldn't be having any problem with airflow around the shocks, but a common problem is them being encased in mud - the mud insulates and keeps heat in, and prevents dispersion of heat too. keep 'em clean.

More shock - yup, 2 shocks dispersing the same amount of energy are going to run cooler - BUT - you are messing with your damping rates. The pistons are still moving at the same rate, so your resistance is the same - so now you've doubled your damping, which might get messy, break off mountings , harsh ride etc, unstable over bumps etc, plus you will be too heavy on the rebound which means a slow return to ride height . It's not something you just do. Most shocks installed in multiples are very very soft to allow for total correct damping. be very careful.

Heavier duty Springs - a heavier spring takes load off the shock by decreasing work during bump phase - while the shock might momentarily be experiencing huge numbers due to momentary high speed , most of it's work is at quite low numbers - adding 20to 30kg/cm to it's resistance in a lot of the range will massively reduce it's work.

For my money - with what has been described here (and presuming they are decent shocks that have been fitted) I'd put in heavier springs before considering dual shocks.

[david bfreesani]

Alex is the only person who answered the actual question as to two shocks "sharing" the work. So you can do it, but with softer or crappier shocks.

If I may ask another question Alex, if I install a higher rated shock, but install the shock at an angle compared to its intended angle, would the additional leverage get me back to the damping rate I want. Could I play with the shock angle to achieve the desired damping?

Sent from my SM-G925F using Tapatalk

[Mad Manny]

Excellent posts Apoc...

[Apocalypse]

Alex is the only person who answered the actual question as to two shocks "sharing" the work. So you can do it, but with softer or crappier shocks.

If I may ask another question Alex, if I install a higher rated shock, but install the shock at an angle compared to its intended angle, would the additional leverage get me back to the damping rate I want. Could I play with the shock angle to achieve the desired damping?

Sent from my SM-G925F using Tapatalk

the maximum mechanical advantage is obviously directly up and down

as soon as you put it at an angle - like at the back of a bakkie - you have a decreasing mechanical advantage on the shock, as it swings through an arc. At 45 degrees (where they start) it's only moving half as much as the axle travel , and as it swings to horizontal it does less and less, until it's horizontal and just moving the end up and down - this while the spring is 'fully loaded' with stored energy,

Dumber than a dumb thing. no one has ever adequately explained why they are placed like that on a bakkie.

On a double wishbone set up you angle the spring/shock in such a fashion that there is INCREASING mechanical advantage on the spring/shock assy (i.e. as the suspension compresses the spring and shock effectively increase in rate as the angle between wishbone and shock opens up towards 90 degrees. You never ever want the suspension travel to reach a point where the angle between the wishbone and shock is greater than 90.

On a formula car where the shock would have to lay almost horizontally they use a pushrod via a bell crank which improves the mechanical advantage on the shock and spring. Again, the angles are set so that the mechanical advantage increases with suspension compression.

[grips]

Excellent posts Apoc...

As usual. Nice Alex.

[david bfreesani]

Alex is the only person who answered the actual question as to two shocks "sharing" the work. So you can do it, but with softer or crappier shocks.

If I may ask another question Alex, if I install a higher rated shock, but install the shock at an angle compared to its intended angle, would the additional leverage get me back to the damping rate I want. Could I play with the shock angle to achieve the desired damping?

Sent from my SM-G925F using Tapatalk

the maximum mechanical advantage is obviously directly up and down

as soon as you put it at an angle - like at the back of a bakkie - you have a decreasing mechanical advantage on the shock, as it swings through an arc. At 45 degrees (where they start) it's only moving half as much as the axle travel , and as it swings to horizontal it does less and less, until it's horizontal and just moving the end up and down - this while the spring is 'fully loaded' with stored energy,

Dumber than a dumb thing. no one has ever adequately explained why they are placed like that on a bakkie.

On a double wishbone set up you angle the spring/shock in such a fashion that there is INCREASING mechanical advantage on the spring/shock assy (i.e. as the suspension compresses the spring and shock effectively increase in rate as the angle between wishbone and shock opens up towards 90 degrees. You never ever want the suspension travel to reach a point where the angle between the wishbone and shock is greater than 90.

On a formula car where the shock would have to lay almost horizontally they use a pushrod via a bell crank which improves the mechanical advantage on the shock and spring. Again, the angles are set so that the mechanical advantage increases with suspension compression.

Thanks Alex. Something to consider in my setup. I wanted over counter type shocks, but with the best range possible. Turns out Gabriel has the longest range production shock at 375mm, but its for the L113 busses and trucks. Expecting the damping rate to be somewhat higher than that for a 2 ton vehicle, I was wondering if I could tilt it to get the damping within something that would work for me, and at the same time, use the angle to score some more travel. But your explanation (which makes perfect sense), is going to cause the exact problem you describe as the normal working height, and further compression, would push the shock into a sharper angle and diminish its capacity. But, I may still be able to find a compromise with a shock usually working on a 5 ton vehicle.

Thanks for the info. Expert advise as usual.

Sent from my SM-G925F using Tapatalk

[Apocalypse]

Alex is the only person who answered the actual question as to two shocks "sharing" the work. So you can do it, but with softer or crappier shocks.

If I may ask another question Alex, if I install a higher rated shock, but install the shock at an angle compared to its intended angle, would the additional leverage get me back to the damping rate I want. Could I play with the shock angle to achieve the desired damping?

Sent from my SM-G925F using Tapatalk

the maximum mechanical advantage is obviously directly up and down

as soon as you put it at an angle - like at the back of a bakkie - you have a decreasing mechanical advantage on the shock, as it swings through an arc. At 45 degrees (where they start) it's only moving half as much as the axle travel , and as it swings to horizontal it does less and less, until it's horizontal and just moving the end up and down - this while the spring is 'fully loaded' with stored energy,

Dumber than a dumb thing. no one has ever adequately explained why they are placed like that on a bakkie.

On a double wishbone set up you angle the spring/shock in such a fashion that there is INCREASING mechanical advantage on the spring/shock assy (i.e. as the suspension compresses the spring and shock effectively increase in rate as the angle between wishbone and shock opens up towards 90 degrees. You never ever want the suspension travel to reach a point where the angle between the wishbone and shock is greater than 90.

On a formula car where the shock would have to lay almost horizontally they use a pushrod via a bell crank which improves the mechanical advantage on the shock and spring. Again, the angles are set so that the mechanical advantage increases with suspension compression.

Thanks Alex. Something to consider in my setup. I wanted over counter type shocks, but with the best range possible. Turns out Gabriel has the longest range production shock at 375mm, but its for the L113 busses and trucks. Expecting the damping rate to be somewhat higher than that for a 2 ton vehicle, I was wondering if I could tilt it to get the damping within something that would work for me, and at the same time, use the angle to score some more travel. But your explanation (which makes perfect sense), is going to cause the exact problem you describe as the normal working height, and further compression, would push the shock into a sharper angle and diminish its capacity. But, I may still be able to find a compromise with a shock usually working on a 5 ton vehicle.

Thanks for the info. Expert advise as usual.

Sent from my SM-G925F using Tapatalk

run a stiff short throw shock via a 4 or 5 : 1 Bellcrank.....

Or take a look at the Trophy Trucks. They run their 16" stroke coil over dampers and bypass shocks halfway down the trailing arms, giving them 32" of travel at the wheels.... Obviously the trailing arms need to be meaty.

[david bfreesani]

Meety arms worries me. Not sure I want to get into the mechanics of the EvoLever setup like they do on the Jeeps. Thats why I thought of just straight stiff shock at a slight angle. But something that does not push the shock more than 25-30deg at full compression. Still gives me massive droop range.

I just need to figure what angle will be comfortable for that particular shock on a 2 ton vehicle. And then I have a space challange in the front to get any angle on the shock.

All ideas I am playing with. Just weighing up the possibilities.

Sent from my SM-G925F using Tapatalk

[wolley]

Thanks gents, and thank you for excellent posts. I though to wait a bit before responding, and work with more input, which I really appteciate

1. Load. I carry a custom build alucab canopy with the usual plus a few things (like 185 lt water etc.) My calc of the canopy's weight is 1.55T when loaded. The vehicle has additional mods to itself like build-in fuel tanks (90 lts) that adds up. I have taken it to a weightbridge and tge rear axle came in at 2.6T, with minor contents not loaded ( i.e. hald water and no food). Its is a lot of weight I know

2. Springs. It has the standard double spring setup the 130 comes with. I added air bags not so much for load but rather to lift the back side about 2 inches.

3. Shocks. Standard shocks works but damping is not great with too much up and down movement. I tried large bore shocks but they broke and did not last at all. My current shock is tough dogs with 9 settings. They work like magic but come at a steep price. At setting 7 under load it works well. They have worn a bit in the last 3 years and Now need to be at setting 9 for the same result.

The reason for my post is to validate. Do I continue with those or goto x2 cheaper shocks. The second reason is that I currently need to replace the lower rubbers a few times per year that tells me I am operating on the limits

I will follow through on the advice tabled above.

(To add. The double [standard] springs at the back already eats into my kidneys when it is empty. Can longer springs add to assist the shocks without making the ride less confortable?l

Sent from my SM-G955F using Tapatalk

[david bfreesani]

I must say, with the kind of weight you are expecting the suspension to carry, you can't expect to have the comfort you desire. Take an Ivico Daily unladen and see what it feels like. Its like the onroad/offroad capability debate. Whatever you score on one side of the table, and give up on the other.

Maybe someone can look at a helper spring setup that can take up the strain over a certain weight, but leave you comfort unladen with only one set of springs working when that light. But thats some modification right there.

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[grips]

Thanks gents, and thank you for excellent posts. I though to wait a bit before responding, and work with more input, which I really appteciate

1. Load. I carry a custom build alucab canopy with the usual plus a few things (like 185 lt water etc.) My calc of the canopy's weight is 1.55T when loaded. The vehicle has additional mods to itself like build-in fuel tanks (90 lts) that adds up. I have taken it to a weightbridge and tge rear axle came in at 2.6T, with minor contents not loaded ( i.e. hald water and no food). Its is a lot of weight I know

2. Springs. It has the standard double spring setup the 130 comes with. I added air bags not so much for load but rather to lift the back side about 2 inches.

3. Shocks. Standard shocks works but damping is not great with too much up and down movement. I tried large bore shocks but they broke and did not last at all. My current shock is tough dogs with 9 settings. They work like magic but come at a steep price. At setting 7 under load it works well. They have worn a bit in the last 3 years and Now need to be at setting 9 for the same result.

The reason for my post is to validate. Do I continue with those or goto x2 cheaper shocks. The second reason is that I currently need to replace the lower rubbers a few times per year that tells me I am operating on the limits

I will follow through on the advice tabled above.

(To add. The double [standard] springs at the back already eats into my kidneys when it is empty. Can longer springs add to assist the shocks without making the ride less confortable?l

Sent from my SM-G955F using Tapatalk

My humble opinion is that the problem lies with your current suspension setup. In person I do not think the Tough Dogs are heavy duty load carrying shocks.

If I were you I would have installed a complete Heavy duty Old Man EMU rear suspension. They have better load carrying capacity than the stock coils. Also their heavy duty shocks is designed to function with their matching coil springs.
Only suspension the last on Kalahari dirt roads carrying over limit loads.

[grips]

Meety arms worries me. Not sure I want to get into the mechanics of the EvoLever setup like they do on the Jeeps. Thats why I thought of just straight stiff shock at a slight angle. But something that does not push the shock more than 25-30deg at full compression. Still gives me massive droop range.

I just need to figure what angle will be comfortable for that particular shock on a 2 ton vehicle. And then I have a space challange in the front to get any angle on the shock.

All ideas I am playing with. Just weighing up the possibilities.

Sent from my SM-G925F using Tapatalk

David do not try to redesign the wheel. You are going to buy a set of truck shocks and find after numerous experiments find that they do not work on a lifted 4x4 no matter what angle.

Save up buy a descent set of Fox Shocks. They have 500mm travel, progressive action and simply gives you the best of both worlds with superb on road and off-road handling. Fox is going to out last your 4x4.

[david bfreesani]

David do not try to redesign the wheel. You are going to buy a set of truck shocks and find after numerous experiments find that they do not work on a lifted 4x4 no matter what angle.

Save up buy a descent set of Fox Shocks. They have 500mm travel, progressive action and simply gives you the best of both worlds with superb on road and off-road handling. Fox is going to out last your 4x4.

Grips, I have an open canvas under the Sani. The original little shock bolts that Nissan put in there bent and broke of many years ago. I upgraded these before the SFA even happened to Patrol shocks with 20mm bolts that go through a bracket on either side of the shock eye on a new cross member I added over the sparewheel. Still have a fair ways to go before I can pin down a shock length based on ride height and articulation once all is done.

[Apocalypse]

Thanks gents, and thank you for excellent posts. I though to wait a bit before responding, and work with more input, which I really appteciate

1. Load. I carry a custom build alucab canopy with the usual plus a few things (like 185 lt water etc.) My calc of the canopy's weight is 1.55T when loaded. The vehicle has additional mods to itself like build-in fuel tanks (90 lts) that adds up. I have taken it to a weightbridge and tge rear axle came in at 2.6T, with minor contents not loaded ( i.e. hald water and no food). Its is a lot of weight I know

2. Springs. It has the standard double spring setup the 130 comes with. I added air bags not so much for load but rather to lift the back side about 2 inches.

3. Shocks. Standard shocks works but damping is not great with too much up and down movement. I tried large bore shocks but they broke and did not last at all. My current shock is tough dogs with 9 settings. They work like magic but come at a steep price. At setting 7 under load it works well. They have worn a bit in the last 3 years and Now need to be at setting 9 for the same result.

The reason for my post is to validate. Do I continue with those or goto x2 cheaper shocks. The second reason is that I currently need to replace the lower rubbers a few times per year that tells me I am operating on the limits

I will follow through on the advice tabled above.

(To add. The double [standard] springs at the back already eats into my kidneys when it is empty. Can longer springs add to assist the shocks without making the ride less confortable?l

Sent from my SM-G955F using Tapatalk

My humble opinion is that the problem lies with your current suspension setup. In person I do not think the Tough Dogs are heavy duty load carrying shocks.

If I were you I would have installed a complete Heavy duty Old Man EMU rear suspension. They have better load carrying capacity than the stock coils. Also their heavy duty shocks is designed to function with their matching coil springs.
Only suspension the last on Kalahari dirt roads carrying over limit loads.

Agree with this.

I can't find info on the stock spring rates for the 130, but you need higher rated springs when you are loaded. maybe a kidney belt for the unioaded days?

I don't know the Tough Dog shocks at all, but the OME works well on the Defender in the applications I've seen . I wouldn't put OME near the Wrangler though!

If you upgrade the rears, you'll need to upgrade the fronts too - full kit.