So, I am under the rear of my XJR for the first time today, about to start tackling the rear shock replacement, and in taking in a general observation of the rear suspension components.... one thing I notice is how small the rear sway (anti-roll) bar is for such a large heavy car.

I know we are talking about two different cars and suspension designs, but the rear sway bar on my 1995 Buick Roadmaster has to be at least twice as thick in diameter and dwarfs the XJR bar. Even my 1995 Buick Riviera rear sway (which also is an independent rear suspension, but front drive) is quite a bit larger.

But in reading various reviews/tests when this generation XJR was new, it appears that they thought the car handled well for its size/weight, pulling high .8x g's on the skid pad for example.

So with that in mind, I wonder if in reality this relatively small/thin sway bar on the XJR is actually the appropriate size when combined with the rest of the rear geometry?

If not, it is interesting to note that Addco makes what appears to be a larger front and rear sway bar for the XJ6:

http://www.summitracing.com/search/p...guar/model/xj6


I wonder if anyone has tried these out?

I know the Addco bars are very popular in the Buick Riviera owners' forums.


Here is an interesting write-up on Jag Lovers on the topic, and does touch on the Addco bars specifically:

http://www.jag-lovers.org/books/old-...ensionmods.htm



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The larger stabilizer bar is opposite the drive wheels.
A rear drive car will have a larger FRONT bar and there might not be a bar at all in the rear or it should be SMALLER diameter.

bob gauff

 

Presumably Jaguar did some homework and came up with a decent compromise....but Jaguar always compromises in favor of comfort over performance. I've looked for something a bit bigger (for both front and rear) but have been unable to find anything.





Those Addco bars you're looking at are not for the X300. They are for the older platforms; XJS, and sedan prior to XJ40.

I've used them on my older Jags.

The 7/8" rear bar is too big for the XJS, that much I can say for sure. Unless, of course, you actually *enjoy* heading for the ditch, backwards, trying to reel in a 4000 pound Jag that has gone from neutral steering to gross oversteer in about one nano-second


Cheers
DD

 

Thanks for clarifying the application is for the Series III cars Doug.

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Al,
One of my longer term projects is to design a new rear anti-roll bar arrangement. The torsional stiffness of an anti-roll bar is proportional to the diameter raised to the 4th power, so the rear bar is a fraction of the stiffness of the front. Added to which the ends of the bar are along way from the wheels, thereby reducing the angular rotation for any given wheel movement. This effectively further reduces the stiffness. Also the anti-roll bar mounts to the rear sub-frame are a long way from the ends of the bars. I would expect this to cause bending rather than rotation in the bar, which also changes its stiffness characteristics. From what I have read on chassis engineering, increasing the rear roll stiffness on a rear wheel drive car will change the handling characteristic from understeer to oversteer, as Doug has said. I'm sure it will take some track time to get the stiffness of my new design correct.

 

Great, I'm sure everyone will be very interested to hear what your testing produces.

 

I noticed how short the rear sway bar is. This has to have a effect on its size. I'm no engineer, but seems it being so short, doesn't allow for torsional twist as much as a longer bar.

 

Your right. torsional stiffness is inversely proportional to length, but if the rear bar were say half the diameter of the front bar, then it would be 1/16th the stiffness if it were the same length. If the torsion is applied over half the length of the front bar, then it is still effectively 1/8th the stiffness. Then you have to take into account all the suspension geometry to relate wheel movement to angular movement of the bar to calculate effective roll stiffness.

 

..... and with that in mind, we'll again be very interested to hear what you figure out Sounds like a lot of engineering, testing and a bit of luck to figure out what will work best.... which of course all equals a whole lot of time and effort. So that will be much appreciated.

On a related note, is it your opinion that the front sway bar is adequate, and the rear may simply benefit from some enhancement?

Again, look forward to what you find works best.


Still plan to pick up some of your rose/heim jointed links for the front at a later date when funds allow.


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Please don't take this the wrong way, but do you actually know what you want to achieve by fitting 'better' ARBs?

As alluded to by Doug above, simply fitting the stiffest bar you can find is very unlikely to be a good idea. ARBs are a compromise: a thicker bar doesn't just mean less roll, it also means less ability for the rear suspension to act independantly for example, and ultimately less grip!

Another thing to consider is that you should look at front and rear ARBs together (along with springs & shocks) as changing just front or just rear will alter the roll coupling of your car overall.

I'm not trying to put anyone off here - indeed ARBs are often neglected when they can make a massive difference to handling - but a bit of thought now could save you a lot of wasted effort later...

 

So, ran across the following on eBay:

1997 2003 Jaguar XJR X308 Performance uprated Rear Suspension Anti Roll Bar | eBay


Is the X308 rear sway bar interchangeable with the X300 directly, or with minor drop link modification?

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I like my rotational stiffness and don't try to play with it.

 

True, not suggesting it is "better" as there is more to consider than simply "bigger is better" when tuning suspension.

I'm just curious about interchangeability for anyone considering it.

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I'm sure Andy is busy, and any research is ongoing, but I thought I'd bump this thread too see how his rear ARB 'improved design' is going.

I was also curious if fitting male heim/rose joints to the rear as replacement for the OEM "metal-lastic" rubber bushed end-links might be a simple improvement in connecting the rear sway/anti-roll bar to the lower suspension arm? This would be very similar to the upgraded heim/rose joined front end links that Andy makes.

It would be a relatively inexpensive task if worth the effort, assuming one could find and fit all the right parts of course. As long as one could find a male rose-joint link with the correct diameter hole for the end of the sway bar, and a long enough and proper diameter male shaft to bolt to the lower control arm perhaps with flat some poly bushings that are already available for the OEM links, then it should be a bolt-on affair?

Just thinking out loud


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exactly, and you cannot just change one without the other being tuned for the change and knowing if you want to/how to reduce understeer. neutral/oversteer. I prefer balanced neutral with throttle induced oversteer. You can also(and easier) go to stiffer and or shorter springs. There is more than one way to reduce roll. custom variable rate shocks etc. and adjustable spring heights. on the XJ make sure it has the triangular 1 piece brace to the rear diff carrier and not the twin single ones. And If putting out upgraded power and or on stickier tires you need to fully weld and maybe even brace the mounts in the body for those brace. I have customers tear them out of the body on R's and seen on here too. Go to wider taller better tires and wheels for much better traction and for sticking in the corners. I went to 01 XKR wheels 18" on my 95 and going to 20" Takobas for the 04 XJ. The change in cornering speeds was night and day(speaking of the 7 sweaping 90* corners to and from work that are rated at 45mph are very easy to go almost double that and sticks very well)

 

XJREngineer's thread on upgrading the rear ARB, latest news should be found here:

https://www.jaguarforums.com/forum/x...ension-184197/

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