Spheres

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saintjamesy89
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Spheres

Post by saintjamesy89 »

I've been having a good'ol read up on all things spherically green. The general consensus seems to be that 500ccm, 55 bar (or regassed to 60) spheres with a max bore hole size of 1.8mm are about as comfy as is safe for a BX. Higher pressure creates problems by getting too close to the operating pressure of the LHM in the sphere and so you get no travel and bigger bore sizes reduces the damping to the point that when you accelerate the back end is on the bump stops and over speed bumps you roll around like a duck in a stormy bath tub.

I have yet to see what I have on the TXD, but a post made by Jonathan_dyane (who's father owned this TXD) made a comment that he had 16 sphere's put on it and it made the ride softer than the TD ones on before hand.

My question is, what about rear spheres. These are not talked about in any of the posts. All estates had 500 ccm whilst all hatches had 400ccm spheres, I guess this is due to the load carrying capacity of the estate. If the difference between the 500 and 400 is only that there is more gas to compress in a 500 than a 400 (at the same pressure) then the only difference in ride or behavior (at the same suspension height and load/weight) would be the reaction of the sphere to a bump, in that a larger gas volume will compress less over the same bump than a smaller volume (not going into temperatures or anything, so lets say both spheres at the same temp) so even though it has the same spring rate (55 bar pressure dictates this) the rate of change of gas displacement is less as there is more gas to compress, at the peak of the bump, i.e when the wheel is at the top of it's travel, the 500 will be compressed to a lower pressure than the 400 - making it 'feel' more soft and allowing the diaphragm to move more. Mathematically though, in terms of 'spring rate', which is the force (e.g. pressure) required to move the diaphragm a certain distance, both spheres are the same.

So can I fit 500ccm to the rears? Obviously i'm solely thinking about spheres here, the rear struts look smaller than the fronts, and there is less weight here too - unless you're loaded up with luggage/passengers. I suppose estate rear struts or other design aspects must be different to the hatches to accommodate for this, and to allow 500 rears?

I'm getting tired now, and my brain is slowing down. So i'll do more figuring tomorrow, any flaws or bits you don't agree with - shout, I want to understand how these things work. Oh, and physics was always my worst class at school and college, managed to not do any at uni :D
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BX Bandit
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Re: Spheres

Post by BX Bandit »

I've been asking similar questions myself just recently.

The Estate rear cylinder is a bigger diameter than the hatch.

Apparently there is no discernable difference in ride between a hatch and estate

According to Plieieieiaaaaeedddiiieiiiidiiies, putting 500cc estate spheres on a hatch is arse dragging time.

spheres and comfort

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djoptix
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Re: Spheres

Post by djoptix »

Moderately off topic, but I have also been wondering about spheres for the 16v. BITD Luke advised me that a good combination for a 16v was standard 16v rear spheres on the front, and XM spheres regassed to 35 bar on the rear.

My question is, how does one know which spheres are which? I have two in a spares box and if they fit, I will use them...
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Re: Spheres

Post by BX Bandit »

Hmmmm, if there is no part number then physical size and bore diameter be your only guide.

400cc spheres resemble your balls when you were 18, tight, compact, purposeful and....well...hard
500cc spheres resemble your balls when they've spent a good 20yrs+ being knocked about, abused, un-emptied, un-supported, un-used and...well...soft!
As for central bore diameter, I suggest applying the same principles to your Jap's Eye dimensions......
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JayW
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Re: Spheres

Post by JayW »

Getting through that bottle then Neil! drunk

Without reference material to hand to verify, the site above says 16v rears are 30/0.7,

The V6 XM rears suggested are 30/0.5

Just before my 16v came off the road i fitted 30/0.5's all round and the results were epic, but it did suffer skip from major bumps on fast cornering. I kind of enjoyed that though as it added a bit of "widowmaker" appeal :)

My only concern with mine was the longevity of other suspension components under the extra strain.

N.B. always check spheres are stamped or printed with their values, GSF think all the green balls are the same having supplied random one's twice despite me ordering the specific ones i wanted!
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