Daily, we get calls and emails from people that go like this:
"I've got a (-insert your vehicle here-) with a 3" lift kit, and I'm chasing shocks that extend out 3 inches more than original, but compress down to the same amount as the factory shocks..."
It's not an unreasonable question. I can see the logic here. Unfortunately (in practise) it's wrong.
Firstly, lets assume that a vehicle fitted with a 3" suspension lift kit, will benefit from 3" longer shocks (more about this in a minute).
You can't have a shock that is 3 inches greater in extended length, yet compresses to the same body length of the original unit. This is because the shock body (which is your compressed length) must be greater in order to allow for the increase in rod length (extended length).
Memorise this.
- The body length of the shock must be greater in order to provide the increase in rod length (extended length).
- The body length of the shock must be greater in order to provide the increase in rod length (extended length).
- The body length of the shock must be greater in order to provide the increase in rod length (extended length).
The extended length of a shock, is determined by the length of the chromed piston rod, combined with the length of the shock body itself. On full compression, the chromed piston rod is contained within the shock body.
If we made say, just the chrome piston rod longer, and left the shock body length the same, on full compression of the suspension, the shock's chrome rod would simply smash through the base of the shock body.
Game over.
Back to the bit about needing shocks 3 inches longer, for a vehicle with a 3" suspension lift....
Perhaps your 4WD does need such an application. However, often this is not the case.
On the lifted vehicle, the extra movement or travel between the shock mounting points may be minimal. This can be due to the way that the suspension is configured relative to the positioning and angle of the shocks to the axle and the wheel.
It may be that the sway-bar mechanics on the vehicle are holding the travel of the suspension back (rather than the shocks).
It could be (in the case of heavy-duty springs) that the extra spring rate creates less flexibility in the suspension, negating the benefit of fitting a longer shock.
If we go ahead and fit the 3" longer shock (in the case of a coil-sprung vehicle), the coils may not remain captive on extended travel (the coil falls out).
That's a big deal.
On compression travel (because the shock body is longer) you might crunch (destroy) the shocks, as the vehicle's suspension pushes down past what the shock body length specification will allow.
Ouch!
If the longer shocks do allow for more suspension travel than original, your brake lines may be too short (stretch and tear).
You might put extra load or tension on your sway-bar. In some cases, your drive-shaft or tail-shaft may pull apart.
I'm not a drama queen (really), so this is how it works...
On most popular Australian-sold vehicles with a suspension lift of up to 50mm, the shock absorber length supplied (in almost any brand in the marketplace) is about the same as the original unit.
This is because in most cases there is sufficient travel in the shocks stroke to allow for this type of lift. Particularly as the amount of stretch between the shock mounting points is usually less than the amount of suspension lift height.
I'm not saying you can't get extra travel by fitting a longer shock, but the modifications and checklist involved are usually more than what the average family-orientated 4wd owner wants to be involved with.
"But I want maximum travel!"
OK. I hear you.
If your vehicle can benefit from fitting longer shocks, and you are happy to do what you have to do to make it work - here are some guidelines to start with.
First, determine the suspension travel your vehicle is capable of with no shocks fitted (none). You usually need to drive your vehicle up onto a dedicated travel ramp. If you don't have access to a travel ramp, you can achieve the same thing by jacking up each corner of the car with a forklift (one corner at a time), or finding some off-road terrain (or adapting some) that allows you to fully work the suspension.
Do this with great care. Regardless of the method that you use, you don't want the vehicle to roll over and crush you. In the case of a coil-sprung vehicle (as the shocks are removed) you don't want the coils to drop out.
Record the distance between the shock mounts at full suspension travel, for each direction of movement.
Also for reference, measure the distance between the shock mounting points while the vehicle is parked on flat ground. This measurement is called the 'static' or 'rest-height' position.
Then work with your supplier of shocks for the closest match in an appropriately valved product to both the open and closed measurements. The closed (upward travel) is just as important as the extended (downward travel). This is because in the case of a solid-axle suspension system, one side of the vehicle must be leveraged up in order for the opposite side to be pushed down.
Traditionally, a technically perfect application sees a shock absorber opened to the half-way position while the vehicle is parked on flat ground. So, if a shock has 10 inches of travel, the shock (at normal ride) would have the ability to extend out 5 inches before coming to the end of its travel, as well as compress 5 inches from the normal ride height position before crunching the shock.
A technically perfect application is not always possible, due to shock length availability, or the travel characteristics of the vehicle (may have more travel in one direction than the other). Essentially, as long as you have optimum travel in both directions, according to what your vehicle is capable of - you have a good long-travel shock application.
I mentioned earlier about modifications required to fit genuine long-travel shocks.
In most cases, extending the axle bump-stops is required. This is to protect the shock from 'crunching' and becoming damaged on full compression of the suspension as ...the body length of the shock must be greater in order to provide the increase in rod length (extended length).
Extending the axle bump-stops means you are reducing the bump-stop gap, so the rubber bump-stop makes contact with the metal striker plate before the shock crunches into itself. Extending the axle bump-stops (reducing the bump-stop gap) sounds counter-productive to the intention of maximising wheel travel.
The benefit of doing so (together with the longer shocks) still outweighs the performance of a vehicle fitted with a suspension kit and factory-length shocks - particularly in the case of bigger lifts.
A way of eliminating the need of extending the axle bump-stops can be to relocate the 4WD's shock mounting points, so that they are spread further apart. Weld-on shock hoops are one example of how to do this. It means that you can fit a shock with a massive amount of travel (more travel than what the vehicle is capable of in any direction).
So here, no need for extended bump-stops or inefficiencies in travel. No need to worry about crunching the shock on full compression of the suspension.
Next, check your brake lines. Purchasing extended-length ones is often required, because the suspension may now articulate further than factory design.
Check (in the case of a coil-sprung vehicle), that the coils remain captive (can't fall out) under the full travel of the suspension.
Check the stress on the other related components on the vehicle such as sway- bar and link pins. If you fit longer link pins or extend the original ones, this might alleviate some problems - It might also create new problems too!
The extra suspension travel available may also mean that parts of the suspension or axle may make contact with other parts and accessories on the vehicle.
You will need to counteract and compensate for this. Lots of extra travel can even allow your CV's, drive-shaft and tail-shaft to be damaged, slip out, or fall apart.
Again, you need to compensate for this.
All the things you need to do and check for are beyond the scope of this post.
Also, (and this is where I have to do the legal talk) you need to make sure that any modification you make to your suspension will not affect the safe and reliable operation of the vehicle, or contravene any applicable regulations, rules, laws or insurance requirements.
This is your responsibility. Don't shoot the mail-man!
An alternative we could look at to eliminate a lot of hassles associated with long-travel shocks, is if we started to make them out of rubber. This way, a customer could simply stretch the new rubber shock out and in to whatever length they want.
They could get the exact open length they would like, together with the ideal closed length they wish for also.
It would be good business sense for us too. We would only need to stock one part number on the shelf, rather than the hundreds of different part numbers we currently do.
I'd probably get a raise!!!
So, if you are interested in purchasing the new rubber shocks for your next suspension application, please click here.
