Hi All,

I'm trying to calculate the optimum sphere pressures and volumes and although most of the info I require is available I'm stuck on this one. Does anyone know the ratio of XM front to rear weight distribution with, say, driver and 5 gallons of fuel on board? 65/35? 60/40? 55/45?

Derek

Hi Derek

Engine dependant of course but im sure when i put mine on the weighbridge with about 9gals and me in it there was about 950kg on the front axle and 4 or 500kg on the back axle, if you want accuracy i can go to work and weigh it this weekend for you? since i will be going past on sunday.

D

Hi Derek

Axle weights are given in the owners manual. I estimate that someone in the front seats is at the one third point between the axles while the fuel tank is at the two thirds point.

John

Thank you both for that info.

Dean, don't put yourself out but appreciate the offer. I'm going to have to make some assumptions so I think the figures you and John have given me will give me a good foundation to work from.

Derek

Well, im driving right past the yard on sunday so i will weigh it now purely because you have got me interested

D

Jolly good, look forward to seeing the results.

Might I ask why you are going to all this trouble? Too much free time?
Uhh, no, you are aiming at the optimum ride for Derek, who drives the car mostly without passengers. But why the small amount of fuel?

Those were the days eh

John, the book only gives maximum allowable weights so it's not what I'm looking for. For example, the 2.1TD estate has greater weight on the rear axles than the front.

So Dean, I'm relying on you and your weighbridge.

Jan-hendrik, As I'm long retired and it's getting too cold to work outside then yes, I do have time on my hands and I've never been one for watching telly. It has nothing to do with my cars but there has been much discussion about sphere pressures and I decided to try to calculate the theoretically optimum spheres for each design of car. I thought it would be interesting to then compare my theoretical calculations with the ones fitted.

It was obvious to me that the calculations should be based on minimum load, the system automatically compensates for increased loads but not necessarily vice versa.

You may well think that what I am planning to do is a waste of time, but it's my time and you are not me.

Derek

This post has been edited by DerekW on November 21, 2008 07:43 pm

I wasn't thinking along those lines at all. I was just curious and certainly don't want to offend you

This post has been edited by Jan-hendrik on November 22, 2008 03:34 am

Of course not Jan-hendrik and I'd be mortified if I offended you.

When (if) I finish my calculations I'll post them on the forum for general discussion. I suppose my reasons are twofold, to try to come up with a definitive logical answer to the sphere question and to exercise the grey cells.

Derek

Derek,

Can I also retire and join u in calculating, measuring and testing our sphere'd-cars....

cheers
G

Hi Derek

Unfortunatly my van broke down in a rather spectacular fashion this weekend which kind of disrupted my plans somewhat and being very busy at work at the moment i wont get a chance to get the old girl on the scales this week, but i will 100% be taking the car that way this weekend (to do what i was supposed to this weekend just gone) so if you can wait till saturday i will post the results then.

Regards
D

That's OK Dean, at your convenience. You are my Last Chance Saloon!

George, you can't retire until you finish your final thesis! But by all means join me, the principle I'm working on is that once I know the front/rear weight distribution and knowing the ram(front)/piston(rear) sizes I can calculate the static load pressures. By measuring the ride height difference between normal and low I can work out the ram/piston movement and thence the fluid displacement. This should let me work back to the initial charge pressure. Of course I'm going to have to make some suppositions, for example that Dean's weight distribution is the same for all engine combinations. Whatever, it should be an interesting exercise and I look forward to seeing how my results compare with the Citroen fit.

Derek

This post has been edited by DerekW on November 24, 2008 07:39 pm

I know, I know....


BTW I'm positive I had read weight data (can't remember *where* though) according to which the V6 PRVs have a 63%-37% distribution while the 2lts are much nearer the 60-40 mark.

Had also found the XM's strut piston surface and the C5's equivalent but also can't remember where! I only remember that the C5 has marked a switch to a smaller piston surface (thus smaller liquid displacements) which is why they use 350cc spheres as opposed to 400+cc on XMs etc.

G