Interesting additional info 04XJR.

IMHO, CATS is more of gimmick. Holds flat in a turn was the only thing I particularly noticed. An interesting feature but I prefer my car to lean a bit, you can feel what the suspension is actually doing and I feel more secure in pushing it when I choose to than artificial help.

Why are you saying that the aftermarket coilovers 'cheap out' on their Bilsteins? Someone gave me a part number off their Bilsteins and it was a stock shock, as far as I could tell. Or that the conversions don't use the S specific shock?

On a side note, I kinda laughed at Bilstein's video, they must be getting hurt by not supplying their "OE quality" (repeat, repeat) that often start to leak at fairly low miles...consistently.

 

I read through the thread you posted and I see - the S type uses a Bilstein shock that incorporates CATS. So basically it's two stage, hard and soft damping?

Interesting.

 

There are multiple choices from Bilstein. Dual and monotube, CATS and non-CATS. They are some of the best shocks out there, and well made. The real issue is that none of the conversions really approach this issue with CATS and the way in which the XJ vehicle dynamics really work.

When designing a suspension, there are a ton of factors to take into account, and not everyone sees the same performance as "preferable" to them. If you are going to want a performance feel when cornering and a soft ride in strait forward driving, you have some real tough decisions to make. Engineers at Jaguar chose the air modules so they could adjust ride height while in operation, and variable damping to help in cornering and vehicle dynamics like braking. Smaller air chambers for sport, and the regular size for comfort. You are correct in your assertion of on/off soft/hard profiles from the shocks.

I said this before, if I were to ever change from the original design, (and I have recently replaced all of mine with Bilstein B4 air modules, and the new shocks made a surprising difference) I would elect to build my own, although it would not be the cheapest method, but more than likely come in less than replacing the air modules at about $3500 for the 4, which is what I spent. I would start with H&R progressive rate springs. Drop the stock ride height no more than about 3/4 inch, and 1 over 2 progressive rate. This is where the shock would then come into play using the Bilstein B4 comfort monotube S-type w/CATS shock. (green body) Obviously a height sensor calibration would need to be made, as this is an integral part of CATS selection method of shock tuning.

“Progressive rate springs” are generally classified into two sub-types: 1) constantly increasing rate springs and 2) a “dual-rate” spring with two linear rates connected with a rate-transition range.

The first type (constantly increasing rate) of springs are most often used as “load-compensating springs” on the rear of a vehicle when the vehicle will often see significant load changes in the cargo area. These are most often stock replacement type suspension springs. They are identified most easily by continually varied spacing between the coils. One area of racing where constantly increasing rate springs are used is dirt modified racing where pull-bar springs, using a constantly increasing spring rate, are used to control rear axle wrap during acceleration. These springs are not suspension main springs, but are supplemental springs.

The second type of progressive rate suspension springs, the dual-rate spring with two linear rates connected with a rate transition range is a much more sophisticated suspension spring. The design is much more focused on the specific use for the spring. These types of springs are used primarily in road racing and high performance street and GT applications where the vehicle trim package will stay in a very predictable range. These springs are easily identified by having a few closely wound coils at one end and then wider, equal spaced coils at the other end. They have rates described as 200/425lb/in. This means that the spring has an initial rate of 225lb/in through some range of deflection and then the rate transitions to 425lb/in through a deflection range of 1”-1.5.” The big advantage of these springs is that they can provide “roll control” in addition to roll control provided by sway bars.

Let’s discuss roll control provided by springs. For “linear rate springs” the discussion is easy. They provide no roll control! (and this is what you are being sold in your conversion kits) Think about taking curve at a very high speed. The side of the car on the outside of the turn rolls over and the side of the car on the inside tends to roll up. For discussion sake, let’s assume we have 300lb/in linear rate springs on the front of our car and the car is rolling too much and cornering speed suffers. If we move up to a set of 400lb/in springs in an attempt to “stiffen” the suspension, we fail because the linear rate springs provide no roll control. Think about it. As you enter the same curve at the same speed your vehicle is rolling onto a higher rate spring; BUT the inside of the vehicle is being pushed up by a higher rate spring, also. So there is not improvement with roll control. With linear rate springs, all roll control must come from the sway bar (anti-roll bar).

Roll bars are, and should be your last resort to control body roll, not the first. The stiffer the roll bar, the less independent the suspension will be. This is the first mistake made by those who don't understand how to properly design suspensions. Properly operating spring and shocks should contribute the greatest amount of control for body roll, and one of the greatest shortcomings of these conversions on the XJ, and the first complaint that their new shiny conversion kits don't do squat to help control body roll, and they reach out to change the roll bar. Wrong decision, wrong spring, wrong shock to start with.

 

David, do I understand that you replaced your original Bilstein air shocks by "B4" air shocks?
If so, are these B4 different (improved, i.e. more resistant to leaks?) from the original ones?

 

The B4 air modules are the same air bag as the "comfort" modules originally produced by Bilstein for Jaguar production. Do they have any improvements over the original ones? There are some minor variations, but I would not want to purchase NOS (new, old stock) due to aging and deterioration of rubber when left to sit for years. You have to deal them just as you would tires. Any air module with over 10 years or 100k have certainly lived it's service life. Mine made it 115k/12 years before one started leaking at the upper seal in the mount. I included in my purchase decision the cost of new air modules in the overall purchase price when I picked up the car, and had already started to set money aside for them. If I get the same service life out of these, I will feel it money well spent.

 

David,
Thank you for the advice.
My air shocks are original and my Super V8 is 10 years old.
Although I have completed only 60.000 km right now, I suspect the PO already replaced the compressor seal using the Bagpipingandy kit.
I had myself a first "suspension too low" and then ASF on past winter, with the compressor failing to rise the car (the car dropped back repeatedly after a few attemps by the compressor). Surprisingly, the car recovered by itself on the following day, the compressor then succeeding to keep the car level with no further faults since then.
I therefore suspect tired shocks that do not seal perfectly when it's too cold.
Would you advise to change them prevently to avoid a failure while parked in the cold, and would you change the four of them by these B4 that seem the best option to me?
And sorry to hijack the thread, hoping it's still on subject.

 

The symptom you describe is generally how the issue starts with a failed upper seal in the mount. The reason I purchased my vehicle was specifically because of the advanced ride control, and chose to retain the air module, and the Bilstein B4 was my choice due to factors I already stated with NOS, as well as cost. Bilstein made the originals for Jaguar. I will say the vehicle's dynamics was pleasantly improved by new modules.

 

Not that experienced with replacing air shocks. But just as an aside I purchased Black Dog "improved" neoprene upper seats for XK8 suspension. I installed the 2 front neoprene seals in the metal retainers (pop-rivited and no chance of errors in installation or stress other than in retainers). Came out the next day to finish installing them in car - both sets were split!! I could not believe that - it was even before installing shock upper attachment and they split!! How could they ever work with a shock working the neoprene.

Reason for writing is that Black Dog did not even reply to my write-ups on this (including photos). I do not believe I would ever buy from them again.

Just a heads up. Take care

R

 

Sorry, I would do my notes as I see it was said for all suspension theory, if not, I take my words back and sorry again for misunderstanding

Wrong. Not last and not always first and it just can be the only, from budget perspective for example.
Right. However on practice there're also lots of other contributors weakening this straight attitude, for example many rubbers which should first take out all its plays before start doing business.
Very vague.
Wrong. Just two examples of very different extreme setups: Rally car with maximum independence and susp travel required still has rollbars, as well as circuit racing car with stiffest springs and shock still has rollbars. You need rollbars.
Just separate apples from oranges. First, set the target you want to get from your setup. More comfort, sharper handling, faster cornering (more grip), all of them in balance etc. If you claim it re all suspension theory - it's far far from true. If just stick to XJ conversions, I would recommend take each particular setup and sort it out in relation to target set, but results won't be applicable for all suspension theory. Rollbar, springs, shock valving and tires grip - these four key contributors to vehicle dynamics on the road and the trick here is to adjust one of them sacrificing some in others to get what you prefer better. You can't win all of them, just choose some. Sorry I feel I'm vague in my comments as well and don't want to go deeper here as this is real science, but I just to hold your bullets for those who will read it and keep for all occasions.

 

Box is entitled to his opinions. I just completly disagree with him.

I know what im looking for in a car and sway bars have always gotten the effect I've desired: Flater and faster cornering with predictacble and more controlled handeling.

It worked in my 1986 Alfa Romeo GTV6, my 1985 Audi 4000S Quattro, my 1979 and 1973 Mercedes 450 SLCs. and it will work in my XJR.

There is nothing magic or different about my 2004 XJR. Im not looking for a pillow ride. These cars were always criticised in the auto press for lacking the cornerinmg and handeling abilities of the cars that they were competeing in the market against. THE XJR..not the VDP

That was by design, Jaguar thought we all wanted a softer ride. I dont.

So the purist trolls can all suck it, becuase its my car and I can and will modify it ANYWAY I DAMM WELL PLEASE. Why they want to pepper us with their opinions in posts that are clearly devoted to modification possibilities and not orginiality obsessions I will never know... but I respect that its their right to do so. Just as its my right to completly ignore them.

keep sharing the valuable info folks... we're all in this together!

 

And you received your Engineering degree from where? And if not a degree in Engineering, what auto manufacturer have you worked for? And if not, what race team have you designed suspension components for? And if not, where have you received your factory training from? And if not, where have received your technician training from, and what certifications do you hold? If you are running your XJ in rally races or Baja... well...

There is ample information from numerous sources out there from suspension manufacturers, as well as tuners that you can glean information from, and what you will find, my information doesn't come from a vacuum. I didn't say there wasn't a place for roll bars, I said it is the last in the equation. Educate yourself first.

 

It is your vehicle, and I don't really care if you want to place curb feelers on it, and drag the pavement, or raise it and put a lift kit and place 28" wheels on it. Go for it... Some folks like their vehicle to look like this... I'm sure they handle just as well.

 

Gentlemen,

Stop having a pissing match in my thread! It's about suspension options, not who can lay it on the table and see who's is bigger.


The CATS system is not the dogs bollocks when it comes to suspension anymore, IMO, and it seems air suspension has been moved past too (too many issues/warranties?) with many manufacturers. Stock suspension is always a compromise for engineers, price plays a big part.

I smiled when I got a free copy of the Jag club magazine this weekend with my lower a arms - there was a review of the new F-Pace and the reviewers comments was along the lines of 'suspension much better than the old CATS system'.

I'd love to see a proper coilover done by, say Ohlins, but I doubt the market is big enough. I've never been a fan of bilsteins valving, stock valving, but that's in other makes I've driven/tracked.

I'm not in with Box, but he's passionate and entitled to his opinion.


Keep it happy, and about suspension options.

 

Apples and Oranges. F-Pace is a SUV, not a Sports Coupe or Saloon. It's a truck chassis. And, contrary to your assertion, the F-Pace options include “Adaptive Dynamics” system, which is a new fancy name for eCATS, as well as major automakers like GM using the same style of system in their vehicle lines. Dodge now includes air systems in their new truck lines for self-leveling and road control. Mercedes, Ford, BMW... the list goes on.

 

Well we can argue back and forth over what is/isn't the same...the apples and oranges argument applies both ways.
I'm saying that technology has moved on and having the same stock jaguar suspension is certainly not the end all be all.
In another thread you posted of your amazement of people cutting corners or similar on a $70k car. The reality is that these are not $70k, they're $8-$15k cars...and if you drop $5k on new air suspension at the dealer...that would come across as a poor investment to most people - especially when there are much cheaper alternatives that do just as well.

 

I dropped about $3400 for all 4 with new Bilstein B4's about a year ago. When I purchased the vehicle, it was part of my total cost of ownership, knowing it would need them, and was part of the buying decision. I still came out in my opinion, where I wanted to be. I have watched folks spent literally thousands on audio upgrades/mods on the XJ's. It all comes down to what you value. Honda Civics are 8-15k vehicles, Jaguar XJ8's are luxury high priced vehicles, and have a high cost of ownership. If your ego can't afford the maintenance, better to stick with a Civic you can afford.

 

More elitist/purist nonsense.
As cool as these cars are, the resale value just didnt hold up...(maybe because of people like you telling prospective buyers to prepare to drop almost half the car's value on old technology shocks) you're not here to help anyone man.... You just want to push your dogma. Sad

 

I'll say it again, I couldn't care less what you do with your vehicle. What I do care about, is the safety of those who drive them, and the others on the road whom are placed at risk by unsafe maintenance that shade-tree mechanics provide, and poor advice. Do with that whatever you wish.

 

and let's get back to the topic again...the B4's were not out when I wrote this, I'll see if I can add them to the review.

 

The intrinsic characteristic of air modules, in relationship to cornering and roll, is that as you remove weight and begin to extend, it's pressure decreases and actual pressure in the upwards direction begins to fall, and conversely, when you compress it, it's pressure rises and it's rate increases. This is not so with regular linear springs, which pressure remains constant throughout its travel. This is one feature Jaguar engineers utilized in it's efforts when the X350 was released. After 100k miles on a set, when you place a new set on the vehicle, there is a marked improvement, as any new set of shocks will do for a vehicle, but it is the dynamics of cornering that you see the biggest improvement, and is completely lost in most coil-over setups, and certainly lost with the removal of eCATS. Just sayin'...