So with a chassis that is now going on 5 years old, and as many or more performance designators (XK, XKR, 4.2L, 5.0L and on and on), has anyone put together a list of available factory sway bars?

I'm simply curious to know what changes in diameter have been released over the years. (Thinking more of checking junkyards for sadly retired XKR's to gain a little less body roll in the corners on my base XK.)

Any info in this area?

 

OK to answer my own question and for others info:

According to my documentation, for the 4.2L NA and SC (06-09) chassis,
Front: 32mm
Rear: 17mm
Convertible Rear: 16mm

Darn, no easy swap of XKR parts for us XK owners.....


Now, has anything changed on the 5.0L side of the house?


Vince

 

The XK needs a 21-22 mm rear bar with poly bushings for good, controllable neutral handling. Unfortunately I have not been able to locate anything, like that. The aftermarket does not seem to make too many items for our cars.

With my '05 XK I installed a second factory swaybar in parallel with the original one and even that stiffness was not quite enough. On the '08 XK I looked but, they ran the bar through the suspension where it would be a good sized job just to exchange it. I gave up on it.

Albert

 

I'm thinking that the bigger motor (not sure, but is it a new block or did they just stroke the 4.2?) may have required a beefier bar. Maybe even the XKR-S where ride comfort takes a back seat to all-out performance?

I understand we have very few options, and I'm not sure what I would do once I knew they existed... but step one is to find out if any changes occured on the OEM side of the house.

If I had access to a parts breakdown for this chassis, I'd just look up the bars and see if part numbers changed as the model progressed between '07 and '12.

Just thinkin' out-loud....
Vince

 

Shouldn't you be beefing up the springs first anyways, and possibly be leaving the roll bar stock?

Bruce

 

Not sure I'm wanting to head down that path either. But it certainly will remain a possibility.
Unlike several of my past cars, I like how my Jag rides. Comfort is becoming a key preference over my bone jarring race prepped suspensions of the past.
And...... I think I'm starting to mellow and remain a little more safe and sane in the canyon twisties than I was in younger days.

Bear in mind I haven't owned her through a summer, so I have yet to really evaluate her limits in detail, but once I buy 18" rims and sticky summer tires I'll get a chance to see where her dark side is and know more about where I'm going from there.
Light sway bar increases are harmless if used to fine-tune oversteer and understeer in the corners without sacrificing ride quality, so after tires it may be all the further I go.

Summer will tell me more! Come On Summer!

Vince
Oh... right now its snowing outside... grrrr

 

Bruce

You probably DO NOT want to go in that direction.

Let me say it first; Jaguar and all other manufacturers know exactly how to dial-in a perfect near-neutral handling. The reason, however, that they do not do so is a matter of safety and liability. A car that has ideal, neutral handling will be prone to rear-end spin-outs if the driver goes into a corner even slightly too fast and hits the brake in a panic move. A heavily under-steering car, on the other hand, like our XKs, will force the driver to dial-in more steering in order to get around the corner and the crossed up rubber on the tires will rub off some speed, hopefully enough to keep the car on the road. Factories tend to default to under-steer so they do not get sued, as Porsche did years ago for producing the 911s that had a built-in tendency for spinouts.

So, the ideally set up cars are for skilled drivers only. Most drivers on the road are not skilled enough to safely handle such setup under all circumstances. Having said all that, in order to make a car handle more neutral, my preferences are the following; please note that all changes are a compromise, you will always trade off something for something else.

In order to reduce the roll, or body lean under heavy cornering, you would need to drastically increase the spring rates. Like, at least 50 - 100 percent. If you do that the car's handling will fall apart; the factory shocks will not be able to dampen the drastically increased spring forces thus, the car will be out of control on bumpy, uneven surfaces. If you hit a bump in the middle of a fast corner, the car would likely bump and skip itself off the road, or at the least, make the hair stand up on the back of your neck. My general guideline is to increase spring rates no more than 10 -15 percent max over the factory rates. If I can keep the factory rates with shorter springs and still not bottom out the shock travel or the suspension, I may even stay with factory rates. The softer springs will reward you with good dampening and road compliance, not even talking about ride quality.

So, the primary means to reduce the roll is with a larger sway bar. Most of the time just increasing the rear bar substantially, while keeping the front bar stock with hard bushings, will produce very significant reductions in body roll. As I mentioned everything is a tradoff. What you will trade for much better overall handling is a reduction in the independence of your suspension. Sway bars tie the two wheels together and will reduce the independent movement on the opposite sides. Most of the time it is a worthwhile trade-off, if one really appreciates improved handling. A much larger REAR sway bar will not only reduce body roll but, tighten up the steering a whole lot. You will need to crank on much less steering angles to go around a corner than with the softer bar. The car will feel like as if it moved on rails with a more precise steering to boot.

Like I suggested, given the weight of our cars, you probably need a minimum of 0.75" rear bar but, preferably a 7/8". You will not know it until you try it, unless others have tested it before you.

I'd love to replace my rear sway bar but, I have not found any available.

Albert

 

Albert,

You mention some of the discussion points necessary before addressing a desire to reduce body lean. My questioning him about beefing up spring rates was actually not intended as a recommendation to do so, or to adversely affect ride quality or height, or to change the balance of the car. Spring rate changes can definitely necessitate a damper change, and I suspect the availability and costs involved would make it prohibitive. And stiffer sway bars may not be the answer either.

I'm sure once Vince determines if he wants to make any change we'll have a good opportunity for a lively exchange of ideas...and depending on his findings my first suggestion might be to trade for an XKR

Bruce

 

Here you go:

http://www.ebay.co.uk/itm/1998-2005-Jag ... 2325e2d58e

and:

Ultra Racing, Venair Silicon Hose items in D-Way Motorsport store on eBay! (that only says hoses - has sway bars)

'cos our roads have corners

 

Thanks for the link. My '05 XK is long gone, replaced by the new gen. XK, which is also gone, replaced by an XJL and an XF.

Finally an available swaybar that the '05 XK REALLY needed. Being only 35 percent stiffer than stock, however, is not enough. I ended up mounting a second factory swaybar in parallel on that car for a 100 percent increase in rear roll stiffness. Even that was not truly enough to bring the car into neutral behavior.

Albert

 

The 5.0L cars appear to have the same size sway bars.

The 2008ish XKR-S has a different rear one though, part number C2C4318 and bush part number is XR845062. Unfortunately I can't find any info on what size it is. The ride height was reduced by 10mm as well.

 

https://www.jaguarforums.com/forum/s...44/#post722556

Don't have any info on the earlier XK8/R though...