sphere specs

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deian
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sphere specs

Post by deian »

hi,

sorry to brint it up again, i did notice i posted about spheres earlier in the day

spheres are obviously specificed by their volume, pressure and damping hole size,

Can someone explain to me what the effects of higher/lower volumes, and higher/lower pressure and bigger/smaller damping holes will have on the cars ride and the combinations of each,

as i understand it, the bigger/heavier the car is the higher the volume needs to be, the cx had 500 spheres with quite high pressures of 75 on the front (was it very heavy on the front), with massive damping holes, was it these damping hole that gave it the soft ride, or was it the fact that it also had double wishbones?

anyway non-hydrative cars have bigger damping holes with the exception of the estate version which apparently doesn't have a damping hole at all (?)

as for hydractive cars, obviously the damping holes will be smaller for the harder ride, but the pressure is smaller, and the centre sphere for the front is 70 where as the rear is 50, would it be bad to put 70 on the back too? cos if i accelerate hard or go fast on the corners the center will be locked out right.

how about putting estate spheres on a saloon rather than the non-hydractive ones for the softer ride?

all lots to think about, and it can all go wrong so easily.

oh, one more thing, i understand they ALL use the same thread?

thanks so much
Last edited by deian on 27 Dec 2009, 22:51, edited 2 times in total.
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Post by Peter.N. »

Hi Dei

All suspension corner spheres have a damping sized hole, the only ones that dont are the accumulator and hydractive centre spheres, and possibly anti sink, but I've never had one of those.

The size of the hole determines the rate at which the fluid passes through it, so the smaller the slower and therefore the harder the ride. Hydractives have smaller holes on the corner spheres because in normal mode the centre sphere is in circuit which has no damping at all giving a much softer ride, in sport mode the centre sphere is switched out leaving the corner spheres with very small holes giving a much harder ride.

If you fitted spheres without any restriction to the corners you would have a wonderfully soft ride but it would lean a lot when cornering - that's the sort of suspension I like but it might not be very safe.

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Re: spheres specs

Post by admiral51 »

deian wrote:
as i understand it, the bigger/heavier the car is the higher the volume needs to be, the cx had 500 spheres with quite high pressures of 75 on the front (was it very heavy on the front)
Sorry to make this a nonsense reply Dei but with that amount of spheres it was always going to be heavy :lol: :lol:

Colin
Last edited by admiral51 on 27 Dec 2009, 22:53, edited 1 time in total.
deian
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Post by deian »

so what the deal with the volume and pressure?
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Re: spheres specs

Post by deian »

admiral51 wrote:
deian wrote:
as i understand it, the bigger/heavier the car is the higher the volume needs to be, the cx had 500 spheres with quite high pressures of 75 on the front (was it very heavy on the front)
Sorry to make this a nonsense reply Dei but with that amount of spheres it was always going to be heavy :lol: :lol:

Colin
what i meant was 500cc (?) spheres, :roll:
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Post by Peter.N. »

I shall be interested in a logical explanation of that myself :D
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Post by Xaccers »

Larger the volume/pressure means further travel of the suspension.
Think of it like conventional suspension with longer springs, able to tavel further before hitting the bump stops.

So for an estate, higher pressure means that it can carry more weight in the boot without the internal balloon being totally compressed, so it still gives suspension travel.
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Post by admiral51 »

Not too sure if this is going to logical but.......

Taking it as given that the spheres all have the same internal area and the placement of the membrane being the same then the amount of gas within that compartment will increase the pressure within that compartment the higher the volume of gas.Assuming the membrane is flexable then the higher the volume/pressure of gas will reduce the available area left within the sphere.The area remaining needs to be filled with fluid (LHM).The normal suspension height will be when the pressure of the gas and the lhm are equal within the sphere.As the suspension is lowered the forces exerted on the gas will increase its pressure and therefore the amount of fluid inside the sphere will lower.This needs to be forced back into the sphere to counter act the downward force of the suspension/gas.
The lower the gas pressure within the sphere the easier it is for the fluid overcome the forces exerted on it.So no gas/pressure means the sphere is full of fluid and as fluid will not compress very easily we get a firm ride.
As for the damping holes the larger the hole the easier it is for the fluid to enter the sphere,again making a firmer ride.The smaller the hole the higher the pressure required to get the fluid into the sphere and it takes a little longer so hence the suspension travels that little bit further giving a softer ride.

Now all this is probably a load of b"^^"*&^ but just how i see things in my own little world here in deepest dorset :lol: :lol:

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Post by xantia_v6 »

Another way of looking at it...

Think of the rated pressure of a sphere as just a convenient way of measuring the mass of Nitrogen within the sphere, the pressure number itself becomes meaningless as soon as the the suspension is pressurised with LHM. So a higher pressure sphere has more gas in it.

While the suspension is pressurised, the diaphragm in the sphere moves to equalise the pressure on the LHM and Nitrogen sides of the sphere.

The actual pressure in the sphere is determined by the weight of the car, dynamic forces due to the mass of the car bouncing up and down, and the size of the strut pistons. It is not (in any practical way) affected by the mass of gas in the sphere.

The working volume of gas in the sphere is determined by Boyle's Law, and is proportional to the mass of gas in the sphere. Because the working pressure in the sphere is much higher than the original filled pressure, the working volume of gas is only a small proportion of the sphere volume.

Boyle's Law also tells us how stiff the "springing" is, because to bounce the suspension up and down the working volume of the gas in the sphere must change, and Boyle tells us how much force is needed to change the volume (note that it is a hyperbolic, not linear curve).

The apparent stiffness of the suspension is affected about equally by the stiffness of the springing and the stiffness of the damping. The stiffness of the damping is, for slow movement of the suspension, set by the size of the damping hole.

For rapid suspension movement (e.g. sleeping policemen encountered at speed), the damping is controlled by a much larger "blow off" hole which is normally closed by a sprung valve, and it is the strength of this spring that determines how smoothly such obstacles are handled.
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Post by lexi »

Added to all of this your double wishbone just has to give a nicer softer ride than struts.
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