I know Andy (XJREngineer) has it on his to-do list to engineer a better rear anti-roll (sway) bar for the X300 XJR, but I just noticed that Powerhouse UK suggests they have already designed an improved rear bar for the X308:

Powerhouse Automotive | Jaguar Roll Bars


The parts diagram and part number for both the X300 and X308 rear bar are the same MNA3500DA so if Powerhouse has developed a better bar for the X308, it likely will fit the X300.

Now what does "better" mean? I have no idea But I thought it was an interesting discovery.

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I suspect it would be at least larger diameter....but maybe a different configuration as well? The original bar is short. Maybe theirs is longer so that the end links attached further outboard? Would that be a good thing?

I dunno. Just guessing. I don't know all the ramifications of anti-roll bar design

Cheers
DD

 

Agreed, I have no idea what "uprated" means in this context either, but thought it was interesting that someone was at least supposedly making one.

I've sent them an email asking for more information, and I'll report back if I receive anything helpful.

More of a curiosity really than need, but nevertheless interesting ....

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Does anyone know if the x300 race cars (JEC races) use anything other than standard ARB?

 

Here's the reply from Powerhouse:

 

Also just confirmed with Powerhouse that shipping to the east coast of the USA is £23.

They are currently out of stock, but expect more stock in about four weeks.

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Based on their eBay stats, they seem to sell several of these. Wonder if anyone has any personal experience with how they impact handling versus the stock rear ARB on the XJR6?

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Not on the XJR, but I do have uprated bars on my V12 XJS. It's 1" front ( stock 7/8"), and rear is 7/8" (stock 9/16"). It corners very flatly, there is hardly any body roll.

For circular section bars, the stiffness varies by the third power of radius, so it doesn't take much added to the diameter to make a very large difference in stiffness.

 

From my understanding the front anti sway bar and the rear bar should match. Example: the stock XJR is 1" front & 5/8" on the rear, the stock X300 is 7/8" front and comes with no bar in the rear. In other words is it beneficial in regarding handling just installing a rear bar without touching the front bar, btw this not the way Jaguar did it, also is "upgrading" to a thicker bar w/o going to a thicker front bar pro or counter productive. I believe most cars that came with a "sport type" suspension or high performance engine came with a rear bar and bigger than stock front bar.

 

Yes, the front and rear ARB should "match" in that they should be designed together as part of a system, and just tossing on a larger ARB (front or rear) may not deliver predictable or desirable results ...hence my question if anyone had tried this bar alone, and curious what their experience was when all other stock parts such as the front ARB remained the same.

It be an injustice and folly (more because I am no expert!) for me to attempt to describe all the parameters that go into designing and tuning a suspension by changing spring rates, shock rebound/damping and anti roll bar specs. But all play together as a system, and because the system would be tuned toward a specific goal in mind (e.g. understeer, oversteer, traction, road surface, tires, etc) for any vendor to say just changing to their one part is "better" doesn't mean much as we'd have to define what "better" means.

And there is no "rule of thumb" such as matching ARB sizing. Again, it depends on the geometry, spring rates, shocks/dampers, and goal of the suspension formula. I can say there are many cars with larger front ARBs than the rear, as it just depends on the goal and other issues like being FWD, AWD, RWD, etc. For example the kits for my Riviera have a larger front ARB.

I have seen Andy (XJREngineer) say that he thinks the rear ARB on the X300 XJR could be improved, and that when he has time it may be on his list to look into one day.... but beyond that I've not seen any evidence that for a given "design goal" a certain sized or ratio front & rear ARB is specified as an alternative to the OEM yet.


Again, that all being said, the cost of this aftermarket bar isn't really too bad, so it would be interesting to hear if anyone has fitted it and what their experience is.

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Correct, because, almost universally, manufacturers want to maintain an 'understeer' condition....as it is considered easier to control and safer.

Adding a rear bar without increasing the size of the front bar might bring the cornering closer to neutral ...which is a good thing....but it is also more likely to create an 'oversteer' situation in aggressive, power-on cornering.

Some prefer and actively seek out this 'tail out' cornering characteristic. In my experience it isn't pleasant. Reeling-in a 4000+ Jaguar that has 'gotten loose' isn't always easy

Cheers
DD

 

You're right!

And I disagree

I feel safe making some rule-of-thumb remarks, based on experience and common sense

- On most cars it is safe to up-size the ARBs for flatter cornering if you follow the well known advice about not letting things get too far out of balance

- Most everyone prefers flatter cornering. I know I do. That's the 'better' that most of us seek. But there is more to 'good cornering' than just lack of body roll.

- In the real world a too-stiff suspension can be a detriment. In the real world corners can be rough and bumpy. A too-stiff suspension can be a detriment here as the tires skitter rather than stick. If you are losing adhesion you are not improving your car.

- My non-engineer formula of added and/or bigger ARBs, performance type shocks, and soft/stock springs has given me the improvement I've been looking for in every case. Additionally I always ask the alignment guy to dial in the max allowable amount of caster for a strong self-centering, responsive feel to the steering

Cheers
DD

 

Yes it has often been true that a standard formula of soft(er) springs, with strong(er) damping and heavy(er) ARB has been a good recipe for a nice ride and controlling real world rough roads versus a smooth race track

But it just depends on what one is looking for and the existing capabilities of the car.

Anyway, I'm mildly interested in this bar, so it will be interesting to hear who has fitted it and how it has worked out for them specifically.
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Too true; everything is a compromise. It's all a matter of what aspects you want to improve and which ones you're willing to sacrifice


Cheers
DD

 

Al, you asked interest in fitting the rear bar.First Let me point out, I AM NO SUSPENSION TUNER! I installed mine (stock 5/8") along with the 1" front bar, all from a stock XJR donor because it was available, almost free. New Bilstine's & bushings all around. No Poly bush's, reputation of squeaking too much. IMOP the best way to do this is to drop the IRS.
Yes, the only way I would do it all again IF the IRS needed to be dropped for"on the floor work/repair" and the bar & ALL related parts were almost FREE. IMOP its not worth the expense or time to install a rear bar for the average Jag sedan if driven normally by the average driver. In the end after a 4 wheel alignment, AGAIN, IMOP! my 95 VDP I didn't notice any more WOW than a Jag with new shocks & bushings when driven normally.
Lawrence

 

Thank you for your feedback Lawrence, but I'm not inquiring into fitting a rear ARB to an X300 that was not already equipped. That indeed is a significant job.

I am asking about fitting this aftermarket larger rear ARB from Powerhouse UK to my 1997 XJR which already has the factory OEM rear ARB. My question was to inquire if anyone has fitted this bar with everything else OEM and what their experience was driving afterwards.

Of course this is exactly what Kopi has done in the following thread, fit the Powerhouse UK larger rear ARB with everything else stock. So I am interested in hearing his longer term experience with the larger rear bar:

https://www.jaguarforums.com/forum/x...ostrut-163427/


But to install the aftermarket bar on a car already equipped with the OEM rear ARB is merely a bolt off/on affair of removing the end links and saddle mounts, probably 30 minutes work

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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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