Foam or Gas Shocks???

[John H]

I know this is probably a complicated issue but which system is more effective in terms of shock absorbtion —

Foam cell shocks (like Tough Dogs)
OR
Low pressure gas shocks (like Old Man Emu).

The tech lowdown would be good if anyone is up on it rather than, "I've used OME's since I was five and they havnt failed me yet!"
I have a heavy Patrol with heavy 6 inch lifted coils and want some shocks that will be effective for some outback touring.

[Ryano]

I'd be inclined to go with the foam cell Tough Dogs.

For a heavy, loaded vehicle and outback touring the foam cell would be the better option.
The gas shocks are more suited to a lighter vehicle and moderate 4wdriving.
With a fully laden, heavy vehicle touring along rougher roads and offroad tracks where the shocks are working hard, there is more chance of the gas shocks fading and killing them a lot sooner.

That said if you were to be running around town in a hilux with the occassional run up the beach or less regular offroad work, the gas shock is more ideal.
Hope this helps,
Ryano

[John H]

Cheers for the advice!

[murcod]

The inlaws have got a very heavy GQ with two inch lift. They recently fitted Koni's and are very happy with the improvement. They've given it a good workout including towing a van to the Flinders and touring up around that area.

Personally I think the quality of construction would come into it more than it simply being a case of foam or gas being better in general.

[Slunnie]

I was under the impression that the design of foam shocks made it more susceptable to fade than that of a gas shock. Better again a seperated gas shock.

[dumbdunce]

I was under the impression that the design of foam shocks made it more susceptable to fade than that of a gas shock. Better again a seperated gas shock.

there are a couple of different types of 'fade' - 1) fade due to emulsification (mixing) of the oil and gas due to continuous high-speed operation can, by design, only effect twin tube gas dampers. in foam cell and mono-tube (separated gas, including remote canister twin tube design) the gas and oil cannot mix, so they are impervious to this kind of fade. 2) fade due to boiling/outgassing the damping oil - ALL dampers are susceptible to this kind of fade, also caused by continuous high speed operation, and by choosing dampers too soft for the application. gas and mono tube type will probably recover from this type of fade, but foam cell shocks will probably not, as the boiling oil tends to destroy the foam and release the gas charge, turning the oil into a soup of gas, foam bits and oil. 3) fade due to mechanical damage - also usually caused by heat from continuous high speed operation - where the cylinder, piston, seals and valves suffer catastrophic damage due to elevated running temperatures. All shocks can suffer from this however it is more likely in twin-tube designs. mono-tube shocks have the advantage of having the working fluid separated from the atmosphere (ie coolant) by only one layer of steel tubing, so they run cooler and can suffer more work without failure. the downsides of mono-tube shocks include reduced travel for a given shock length (as the one tube must house a gas reservoir at the end of the tube), and less protection from mechanical damage - you can dent a twin-tube and get away with it, but even a small ding destroys a mono. Other things to consider are whether or not you want adjustability - at the moment the only adjustable shocks on the market are monos (koni etc) or foam cell (rancho, tough dog etc), what sort of loads you are carrying, what is your driving style, where are you driving etc. If you're building a rockcrawler, adjustable foam cell are hard to go past. If you're building a pure touring machine that will see little "hard" off road use, monos win. If you want a compromise between the extremes, low pressure gas will probably suit you.

cheers

Brian

[John H]

Thanks Dumbdunce, thats the sort of info I was after. I guess I was after something to do a bit of both. It is now set up with long Rancho shocks (34inch extended) and is more a 'rock crawler'. Having said that they have survived a couple of trips across the Simpson. As I am off Cape York this winter I thought I should fit something that would offer greater comfort and less fade. The Rancho's have suffered from some fade but always recovered. I was kind of considering the Tough Dog Ralphs for their extra volume and piston surface area — plus I don't mind the adjustability as I can better match the shock to my spring rate.
With what you have said I may also check out some of those skyjacker shocks as I believe that they have good travel and a mono tube design (thick walls too).

[sootygu]

Have you condidered the 88 series Konis, these are also a larger bore shock than their standard, they were suggested for my GU ute because of the load it will carry. I have had the standard Konis on my 100 series and travelled to Kakadu, Simpson and the Cape and they never missed a beat. The good thing about the 88 series is that they are still adjustable and fully rebuildable. I beleive some of the comp guys have gone to these.

Top Performance Products in Melb should be able to make a set for the lenght you require and valve them accordingly.

[turps]

OME are no good to you since you have a 6" lift. As even if you got the Lsereis shocks, these are only good for about 4"lifts (also no warranty since they are a comp shocks). So would be to short for the sort of travel you have.
I have Koni's designed for a 2" lift and have been very happy with them. They have done lots of Vic High country and a desert trip.

[Ryano]

Cheers Dumbdunce!
Always good to hear from an educated someone who knows what they are talking about on a subject.

[dumbdunce]

Cheers Dumbdunce!
Always good to hear from an educated someone who knows what they are talking about on a subject.

shh dude, I was making it all up!

[bj42oz]

My understanding is That "Low Pressure Gas" are Hydraulic (oil) shocks the Gas used to compensate for the volume change with piston travel. Gas only shocks are High pressure. Foam cell are low pressure gas with the oil the Foam used to prevent Oil and Gas mixing. Have hammered Low pressure Gas/Oil shock in outback challenge etc with no mixing or fade so Foam plug in a twin tube doesn't gell with me, If the shock is in upright position gas it at the top and valving at bottom, so no gas in valves.

Would never trust a mono tube in oZ as one stray rock, stick etc and their gone, rebuildable or not. If your 6" is working nicely for articulation oyur shocks are going to be working their backside off I would consider twin lighter setting shocks to control the spring and not fade. Hate to see a 6" lifted heavy truck with shocks like jelly wouldn't be an enjoyable Cape trip. Save some money by installing a 2" lift for the trip you will have a list of shocks available the length of your arm and the passengers wont be chucking up thoughout the trip. Go back to the 6's and rancho's when you bet back to Sydney rock crawling.
Colin

[dumbdunce]

... "Low Pressure Gas" are Hydraulic (oil) shocks the Gas used to compensate for the volume change with piston travel. Gas only shocks are High pressure....

this is a common and understandable misconception - as they are marketed as "gas" shocks. All vehicle shock absorbers are oil filled, and they all compress a gas (air, nitrogen etc) to compensate for the volume change due to piston travel. some use a high pressure gas to (amongst other things) maintain contact between the gas/oil bulkhead to reduce vacuum cavitation at high rebound rates, and to increase the boiling point of the oil. the downside is, better sealing is required and if the seals are damaged, the performance of the shock is rapidly diminished. a low pressure gas shock will continue to work reasonably well even with a busted seal (up to the point where a significan proportion of the oil escapes) and they are less likely to leak in the first place.

cheers

Brian