Bx Height Control Lever

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jeremy
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Post by jeremy »

I've always likened the Range Rover driving experience as being similar to driving an overweight blamanche. I've never understood the point of a self levelling strut in the middle of an axle - there should be one each side to keep it level, one in the middle means it settles left or right but not level.

I was also amused to find that on some bumps you could get the heap to push sideways as the front panhard rod was caught at the wrong angle!

Give me something honest like a Land Rover anyday.

Whats also interesting is that the public's insatiable desire for these things didn't (and still hasn't) triggered the production of dcent sized lightweight diesel engines. Now the problem of 90 degree V6's has been overcome (PRV V6 - as fitted to Renault 25 and others with offset crankpins to make it behave like a 60 degree engine) I would have thought that someone would have made a series of similar straight 4's, - say 2 litre, 3 litre V6 and 4 litre V8 all on the same machinery. (which was the original idea of the PRV project - but petrol engines)

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DavidRutherford
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Post by DavidRutherford »

as massively off-topic as this has gone, but...

This sort of development work did go on in British Leyland. There were plans to build a 3.5 litre V8 diesel engine, called the Iceberg, based on a strengthened Rover V8 block. I think 3 engines were made, but it was killed off as the develpment was costing the near-bankrupt BL too much money.

Shame.. it would have been a fantastic engine. Something like 150hp and 300lbf-ft were estimated.

I've often wondered if it would be possible to make some sort of V8 engine using the dimensions and parts of XUD engines... the only real problems would be a block casting, and injection pump.... Load of rubbish really.
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Post by jeremy »

Staright 8 would probably be easier! - especially if you were handy with a welding torch!

Rover made a 5 cylinder 2000 engine by welding front 3 cylinders to back 2 or the other way round - but I expect the lump of steel for a crank would cost several thousand before any work had been done. They then abandoned the project when William Martin-Hurst found the V8 while trying to sell Land Rover diesels to an american marine engine manufacturer.

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Toddman
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suspension

Post by Toddman »

The BX suspension has always been a bone of contention and I definitely do not claim to fully understand how it all works but -
Is it possible that when you raise the suspension that this applies more pressure to the gas sack thus making the spring stiffer in effect?
If so when you lower does the opposite occur until you run out of travel hence the bump stops come into play causing that awfull bouncy feeling?
Just a thought

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DavidRutherford
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Re: suspension

Post by DavidRutherford »

Toddman wrote:Is it possible that when you raise the suspension that this applies more pressure to the gas sack thus making the spring stiffer in effect?
Well done for bringing us back on topic!

Yes, but no.

Yes, it applies more fluid pressure into the strut, and hence to the sphere, but that pressure is almost instantly lost again as the car moves up.

The LHM is only there as a solid (incompressible) link between the roadwheels and the pressurised volume of nitrogen. The only times that the suspension springyness is NOT related to the volume of pressurised nitrogen is either in minimum height (when the car is resting on it's bump-stops, and the nitrogen is "relaxed") and maximum height (when the car is on it's upper stops, and the nitrogen is pressurised to system pressure)

In theory, any suspension height that allows sufficient movement to avoid hitting the limits of travel will have the same spinging rate. The only things that might affect the springing and ride quality would be the rubber bushes in the lower wishbones of the front suspension, and trying to use a differently-worn area of the strut.
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Toddman
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suspension

Post by Toddman »

Sooooo -
Spring is constant then so long as the travel remains within the bump stops.
So if travel is hitting the stops the way to prevent it is too use a smaller hole diameter to dampen the travel to keep it within bump stop limits.
Are we heading somewhere worth viditing?

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DavidRutherford
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Post by DavidRutherford »

if you use smaller damper holes, you may find that the ride becomes harsher, as less LHM is transferred into the sphere over a given time, and hence the car reacts more to the bump in the road. Although, yes, it may prevent the car from hitting the bump stops.

What would be better would be to have the ride height set so that you don't run out of travel.
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Post by jeremy »

The self-lowering systems I've referred to above (Range-Rover air, Xantia Activa and others) all have one thing in common and that is heavy use of electronics. By using the sensors (suspension and steering wheel movement) they deduce that the car is on a motorway or similar road and drop the car by 1.5 cm or something similar. This reduces drag and improves stability (and if you've got a caravan - may cause it to snake - Range Rovers have an override)

The theory is that motorways have a good surface and so the full suspension travel isn't needed.

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Post by mnde »

As anyone who has traversed the awful Surrey stretch of the M25 will testify, this is not guaranteed to be the case.

There are some ginormous craters to catch out the unaware, which give your car a good pummelling when travelling at 70mph, I can tell you!

I don't believe tweaking the ride height or fiddling with damper settings is worth doing. IMHO the heights should be within the factory limits to achieve the best compromise between comfort and other subjective factors. Even the best BX is a different animal when compared with a DS or a GS for "ride comfort".

One mod which I think can be applied to most BX's with success, is fitting small BX14/GSA spheres at the front. The front may lurch around a bit under the more powerful acceleration offered by the larger engined models - but I wonder if anyone has tried these on the 19 diesel, for example?

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Post by Way2go »

DavidRutherford wrote:if you use smaller damper holes, you may find that the ride becomes harsher, as less LHM is transferred into the sphere over a given time, and hence the car reacts more to the bump in the road. Although, yes, it may prevent the car from hitting the bump stops.

What would be better would be to have the ride height set so that you don't run out of travel.
This seems a good assessment! This is just one of the factors though as volume of the sphere, it's Nitrogen Pressure and damping hole will all affect it's response.

The following is a downloadable pdf on Shere Application that gives these factors for the various models front & back:

www.gsfcarparts.com/downloads/sphere_table.pdf

Strangely the GTi front spheres are the same as the BX14 and diesel hatches but bigger volumes (by 25%) and smaller dampers are on the estates.
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stuart_hedges
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Post by stuart_hedges »

Argh! mnde, you've just referred to my least favourite stretch of road in the whole world ever, bar none. If I never see it again it will be too soon. Oh yes... and I'll be on it on Friday evening (if my brakes last that long!). Lucky me.

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Vanny
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Post by Vanny »

damper is provided by the throttling of fluid moving in and out of the sphere. Spring rate is determined by the volume of the sphere.

When spheres fail, the pressure is lost from behind the diaphram resulting in an increase in volume. Look at the sphere pressure table and its clear that as the volume increases the ride becomes softer (16v spheres are firmer that normal spheres because of the volume), so when spheres fail they should give a higher spring rate and make the car bouncy!

So less spring = firmer ride. As mentioned a change in damper will also give a firmer ride but as it is in principle rather dificult to do this we can consider the damping to be fixed.

Now in racing practice the nitrogen sphere pressure is usually lowered to make them stiffer, this is because the pressure of nitrogen opposing the hydraulic pressure creates the 'spring' of the suspension. The pressure provided by the system is controlled by the height corrector and NOT the amount of fluid in the struts, disconnect the control arm of the HC and the struts should explode under infinite pressure (if the pump is REALLY good :), so while increasing or decreasing the pressure WILL result in some change of height it changes (more importantly) the pressure in the sphere and thus the spring rate. If you put the car in full height then it gains rock hard struts as there is no spring, and for the same reason if you have no pressure opposing the nitrogen there is also no spring which has the effect of making the ride much firmer.

In racing the change of sphere pressure allows a change of suspension dynamics while maintaining suspension dynamics, however at normal height the drive shafts will sit downwards from the diff, putting load on the CV's. When lowering the car you straighten the driveshafts and i guess reduce the load on the CV's, you cant make the drive shaft point up and drive the car as they sit too low and foul all sorts of things (specifially the bottom arms).


The BX suspension is meant to give a nice balance between real road feeling and nice 'not being on the road' feeling. One of the problems with previous HP suspensions is that customers didn't like them because they where too light on the ground (and antisink was fitted as people thought the cars where breaking if they sank!). Hence (like ALL suspension systems) the original setting is one of balance, but most manufacturers (including citroen) realise there are more than one style of driving and thus have complicated electronics in order to change the drive.


Will have to point out to any race car owner with low suspension must be a boy racer and not have a clue about suspension as the manufacturer knows best!

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Post by adamskibx »

I experimented with the height lever in my old BX14. Having it in a slightly lower than normal position seemed to smooth out the ride so long as you were on a smooth road to start with that wouldnt catch the bump stops out. I also find that having the car on the raised setting seems to make the car more "level" over undulations but transmits smaller bumps and road harshness more significantly. The handling was always superior in a lower position purely because of the lower center of gravity and the fact that the car rolled around less as a result. As has already been discussed, the pressure in the spheres esentially relies on gravity no matter what the position of the struts unless pressure is released at the lowest setting by the bump stops or increased by the top bump stops in max height. The only other variables I can see from a handling point of view are; increased wheelbase and wider front track due to the suspention geometry. Ride wise, surely the car will be smoother when the average front wishbone position is perfectly horizontal and the rear arms almost horizontal? If the front wishbones are at a downwards angle then a component of the force will be transmited directly down the wishbone to the subframe and the tyre will have to move about more. Im probably a bit off the mark in some ways here but this is always the way ive seen it.

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Post by Toddman »

Vanny wrote:damper is provided by the throttling of fluid moving in and out of the sphere. Spring rate is determined by the volume of the sphere.

When spheres fail, the pressure is lost from behind the diaphram resulting in an increase in volume. Look at the sphere pressure table and its clear that as the volume increases the ride becomes softer (16v spheres are firmer that normal spheres because of the volume), so when spheres fail they should give a higher spring rate and make the car bouncy!

So less spring = firmer ride. As mentioned a change in damper will also give a firmer ride but as it is in principle rather dificult to do this we can consider the damping to be fixed.

Now in racing practice the nitrogen sphere pressure is usually lowered to make them stiffer, this is because the pressure of nitrogen opposing the hydraulic pressure creates the 'spring' of the suspension. The pressure provided by the system is controlled by the height corrector and NOT the amount of fluid in the struts, disconnect the control arm of the HC and the struts should explode under infinite pressure (if the pump is REALLY good :), so while increasing or decreasing the pressure WILL result in some change of height it changes (more importantly) the pressure in the sphere and thus the spring rate. If you put the car in full height then it gains rock hard struts as there is no spring, and for the same reason if you have no pressure opposing the nitrogen there is also no spring which has the effect of making the ride much firmer.

In racing the change of sphere pressure allows a change of suspension dynamics while maintaining suspension dynamics, however at normal height the drive shafts will sit downwards from the diff, putting load on the CV's. When lowering the car you straighten the driveshafts and i guess reduce the load on the CV's, you cant make the drive shaft point up and drive the car as they sit too low and foul all sorts of things (specifially the bottom arms).


The BX suspension is meant to give a nice balance between real road feeling and nice 'not being on the road' feeling. One of the problems with previous HP suspensions is that customers didn't like them because they where too light on the ground (and antisink was fitted as people thought the cars where breaking if they sank!). Hence (like ALL suspension systems) the original setting is one of balance, but most manufacturers (including citroen) realise there are more than one style of driving and thus have complicated electronics in order to change the drive.


Will have to point out to any race car owner with low suspension must be a boy racer and not have a clue about suspension as the manufacturer knows best!
Not sure what to make of your comments Vanny :?
Read the first 5 lines and what are you saying? Volume increases then spring rate increases - Nitrogen leaks out thus volume increases we know this makes the spring very hard but then you say higher volume makes the ride softer or am I missing something?
Ads for the manufacturer knowing best that is laughable :D
For race applications the comfort factor is hardly an issue so lowering and stiffening the suspension is a good move and varying the hole size is not that difficult as you can strip the spjere down to customise it if you wish.
My mates have been involved in rallying since the days of the DS and they have plenty of experience with altering ride height and suspension on these cars.

I didm't ride in CWs/Andy S' BX how did it feel? I know CW was over the moon when I sent him his new spheres for it

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Vanny
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Post by Vanny »

yeah i know the logic went fuzzy but that is the way it works (stupid huh), the change in nitrogen pressure and thus the leaking out of gas doesnt change the volume very much i would assume, its not until the diaghram fails that lots of extra volume appears, but looking at schematics i still dont think there is a huge volume of gas?

I mean for these words to be my observations, as is the fact that when you lower the car it gets stiffer and certainly in my experience at high speeds it becomes easier to control.

I'd be grateful if we continue to expand this topic and figure out (or explain to me :D ) if lowering has affects on the 'spring' effect, the 'damping' effect, stiffness etc i've been part of many debates on how all these bits work and its made certain aspects of the car much easier to understand (and no smart arses who understand it ruining the fun :P )


Don't know about Andy Simpsons car as i have never driven it!


Oh more info, my car does sit slightly high at the back and has 205/40 R17's on the rear (guess that puts the boy racer nail in the coffin then), but i dont think these make any difference as the old 19rd would do much the same and stiffen up on the 165/70 r14's?