Do high pressure gas shocks raise ride height?

[Paul Drawmer]

Now I find this difficult to believe, but I'm told that some HP gas dampers (Koni quoted to me) will raise the ride height of a car.

I am of the opinion that the damper can't resist weight, and will sink to the normal ride height.

Has anyone met this suggestion before? Since I'm not an expert, I can only offer opinion, can anyone offer knowledge about this?

[GreenV8S]

Gas pressurized dampers do have a small tendency to extend due to the internal gas pressure acting on the end of the rod, but the effect is utterly negligible compared to the weight of the car, and in any case you would set the ride height via the spring seats anyway.

[PhillipM]

Slightly, the amount depends on the supension design and the damper itself

[Mr2Mike]

I have heard people suggest this before but it's rubbish. It's entirely possible that some aftermarket struts have the spring seats welded on at a slightly different height of course (assuming not just replacing inserts).

[trackcar]

Its not rubbish .. whilstever you have an upwards force on a damper piston rod it must raise the ride height, all other things being equal. However .. the force isn't great (you can still push gas pressure dampers in by hand if you're pretty strong ) .. so the net effect might be measured in milimeters or fractions thereof, so in practical terms it's nothing to be concerned about.

[PhillipM]

Depends on the damper design, if they have a large piston and are of a high pressure design then you'll not compress them much more than a few mm even if you sit on them.

[Paul Drawmer]

Let me display my ignorance here: Does this type of damper extend by itself if there is no load?

If not; then how can it raise the ride height?

Baffled in Banbury.

[Mave]

Koni yellow have height adjustable perches don't they?

[PhillipM]

Paul Drawmer said:

Let me display my ignorance here: Does this type of damper extend by itself if there is no load?

If not; then how can it raise the ride height?

Baffled in Banbury.

Yes, they do, often quite rapidly!

[Paul Drawmer]

PhillipM said:

Yes, they do, often quite rapidly!

Sounds as if you've been smacked by one!

Well, thanks for that. Now I understand that they must increase the ride height.

The car in question is a fairly heavy thing without adustable spring platforms.

[GreenV8S]

Paul Drawmer said:

The car in question is a fairly heavy thing without adustable spring platforms.

If you change the dampers and the replacements have different spring seat positions or are different lengths, this can throw the ride height right out. Maybe this is what you were being warned about.

The gas pressure effect is real but utterly irrelevant to the ride height since the effect is so small. You won't be able to measure it let alone notice it when driving.

[PhillipM]

Paul Drawmer said:

PhillipM said:

Yes, they do, often quite rapidly!

Sounds as if you've been smacked by one!

Well, thanks for that. Now I understand that they must increase the ride height.

The car in question is a fairly heavy thing without adustable spring platforms.

I have, several times - but most of the dampers I have used have large pistons and 200-500psi of gas pressure - on some of them you can happily run the car without springs.......

For reference, the new rear dampers for my Pug 306 raised the rear ride height by 12mm compared to before, and that's with a relatively poor damper/wheel travel ratio for leverage (1:2.7)

Edited by PhillipM on Saturday 12th July 10:20

[Mr2Mike]

You almost always get a raised ride height after dismantling and re-assembling the suspension, but it should settle down after a few hundred miles.

[PhillipM]

I doubt it, they're designed to due to the gas pressure acting as a spring assist!

[Mr2Mike]

No, you are incorrect in the general case. So called 'Gas dampers' have pressurised gas to help prevent aeration of the oil (which does the actual damping), nothing to do with spring assistance.

If the gas was used for spring assistance (i.e. the gas damper contributed significantly to the spring rate), consider what would happen in operation as the damper heated up!

[PhillipM]

Mine are, and do, which is why they have heatsinks on the body!


But either way, back to more normal dampers, ~200psi of nitrogen on any decently sized piston will make some difference.

Edited by PhillipM on Tuesday 22 July 22:49

[GreenV8S]

PhillipM said:

But either way, back to more normal dampers, ~200psi of nitrogen on any decently sized piston will make some difference.

It's the rod area that matters, not the piston area. Do many dampers run at 200 PSI? That sounds unfeasibly high to me.

[PhillipM]

Well he said high pressure gas, which would be a decent monotube, 200 psi is a fairly conventional figure for one, mostly they range between 100-400psi.

Mine run at 420psi currently, most Ohlins start out around 150-200 (depending on application), Bilsteins range anywhere from 120 to 360 on the ones I've seen, Fox are nomally set at 200psi but can go anywhere from 120-350...

Edited by PhillipM on Wednesday 23 July 12:09