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PostPosted: Fri Apr 04, 2014 5:43 pm 
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Location: Roundabout City (Milton Keynes)
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yeah bump stops were shortened. Maybe the springs were touted as progressive, can't remember. With car sitting normally the top coils are compressed tight and maybe 4 are open and iirc the gaps widen as you descend.

I think both the Apex and the Spax extended on their own (gas-filled?) but the Spax were almost impossible to push down with my weight (13-14 stone back then :D) whereas the Apex were softer and imo gave better handling on the 899 no ARB. I thought the Spax were faulty because of that stiffness, but had no option but to fit them at the time.

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PostPosted: Fri Apr 04, 2014 6:25 pm 
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Location: Eastern London / West Essex
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Spax may have made more then one type of shock absorber but, as best as I can recall, the ones I had did not extend on their own.

The Koni rears do and I think the fronts may do. The rears are higher gas pressure monotubes. The front are twin tubes maybe with a small bag of low pressure gas.

Fairly sure the Spax I had were twin tubes at the rear as well as front and possibly none gas pressurised.

All shock work by oil passing through a restrictive valve. The gas is there to prevent foaming of the oil by pressurising it. Once the oil has foamed, the damping reduces or ceases and you then have just a rod going up and down in foam.

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Cinquecento Sporting 1.1 1998
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PostPosted: Fri Apr 04, 2014 11:34 pm 
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Just a comment, I'm not aware of any twin tube dampers that have gas in them. As I understand it the reason for either gas or twin tube is to allow for the displacement of oil caused by the piston rod moving into the damper. Tends to be one or the other. The advantage of gas being the pressurization of the oil that raises the boiling point of the oil and reducing the tendency for the oil to foam. Ofcourse I'm always ready to be corrected!

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PostPosted: Sat Apr 05, 2014 12:46 am 
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I think all twin tubes have gas in them otherwise, as you say, the rod would not go in.

Some, eg, Koni, may have higher pressure. But nothing like the high pressure of some Monotubes.

Koni told me they'd put rival twin tube shocks (Avo which as fas as I can tell are aka LEDA and GAZ) on their machine and they'd foamed after 5 minutes use whereas the Koni did not foam.

I saw a good video showing the foam in a cut away demo Bilstein return to oil as soon as the gas pressure was applied.

There masses about it all on the internet.

I just pulled out an old knackered Koni sport front twin tube and the rod did not spring out on it's own. So no pressurised gas in there, if there ever was.

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PostPosted: Sun Apr 06, 2014 11:42 am 
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Well slap my thigh and call me Sally! You learn something new everyday! Asked this question at my local factors. Knew there was the different types and I new there was an air gap in twins and again thought it acted as a reservoir but never knew they could be pressurized!

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PostPosted: Sun Apr 06, 2014 12:13 pm 
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Stating the obvious but air is gas. I think they use Nitrogen though. But they'd have to select a pressure. If they had a strong vacuum it would suck the rod in, that doesn't happen. As the rod goes in it must increase the pressure of the gas, but it's evidently not enough to press the rod straight back out, if at all, so perhaps not enough to over come the seal resistance? I presume they select a neutral pressure, ie, 14.7psi, when the rod is about 1/2 way in.

Apparently Bilstein Monotubes use about 360psi. Which I presume increases as the rod goes in and act as a damped spring. Onthe read on my Renault this stopped the car rolling but still yielded over bumps. It was just the thing and kept the back 'planted' but stopped it bouncing off bumps, but only at higher speed, it was a bit hard at 40mph. Make for Tarmac rally when the speeds are high, normal road use might be better with a lower gas pressure. Don't know really, it may roll more again.

I guess the best is the auto variable shocks that firm up with detected G force, used by Citroen and others. Used in the Range Rover. A form of 'active' suspension.

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PostPosted: Sun Apr 06, 2014 9:02 pm 
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Location: Roundabout City (Milton Keynes)
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just found my invoice and the Spax were TAG1078 which means they were of the PSX range, and Spax say the PSX's are "filled with high pressure Krypton gas".

Can't find anything saying if they are mono or twin tube. The high pressure thing suggests mono but the "rebound adjustable only" thing that I must have got from the box/instructions suggests a twin tube?

The Krypton gas thing is touted as better "thermo-dynamic properties ensure there is no fading of the damping action" but I'm not sure if it is meant to be better than nitrogen. I'd have thought they'd use Krypton in F1 tyres rather than Nitrogen if it was better. Spax do use nitrogen in the range below the PSX so there must be some benefit, unless it's just a marketing thing (sounds Superman'ny :))

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PostPosted: Sat Jul 05, 2014 4:56 pm 
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Drives: Cinquecento sporting(POLLY)
Any other opinions on this? Car will be put back on the road shortly so looking at options for a track day on the cheap next month. Going to do the brakes. Engine any gearbox oil.

Just want to know what way to head with the suspension!? Would just whacking some cheap springs on do for now? Some cars respond better than others with lowering springs on std dampers.


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PostPosted: Sun Jul 06, 2014 11:26 am 
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Lowering springs drops the Cinquecento sporting onto the bump stops and the ride is too hard.

On mine the previous owner cut 40mm off the from bump stops as the springs were 40mm lowering. It still hits what's left of the rubber stops though.

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PostPosted: Sun Jul 06, 2014 6:49 pm 
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There can't be much bump stop left at all with 40mm cut off!!!
Maybe I should just go at it with stock suspension!!!


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PostPosted: Fri Jul 11, 2014 11:38 am 
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My bumpstops fell off a long time ago :lol:

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PostPosted: Fri Jul 11, 2014 12:33 pm 
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Drives: Cinquecento 899 sx
I cut mine down 50mm when I lowered the car.. Tbh I may as well of taken it off as it's falling apart anyway :)

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PostPosted: Fri Jul 11, 2014 9:19 pm 
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sounds like everyone is rolling around with no suspension at all if they are pretty much sitting on non-existent bumstops!!!!!


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PostPosted: Sat Jul 12, 2014 10:11 am 
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I don't seem to have any issues.

The bump stops are a bit like an hourglass and I just cut the bottoms off.

The bounce seems progressive, I've never felt like "oh, that doesn't feel ok".

Maybe all the other rattles get my attention though :D

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PostPosted: Fri Aug 22, 2014 10:50 pm 
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Drives: Cinquecento sporting(POLLY)
i went with the apex kit in the end. was a sale on so they ended up @ £285 delivered :)


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