Dear All,
I have been saying for some time that I would design a kit to upratethe rear anti-roll bar (ARB) on the X300 to complement my uprated front ARBdrop links. Well, I have finally done it. The kit is intended as a directreplacement for the standard rear ARB, requiring just a substitution of partsand no modification of existing parts. The kit is based around an aftermarketrear ARB for the XK8. This revised ARB is 20mm in diameter compared with 15mmfor the standard X300 rear ARB. The stiffness of a circular bar in torsion isproportional to the diameter raised to the 4th power (you’ll have totrust me on this, or else look it up in an engineering text book). This meansthat changing from a 15mm ARB to a 20mm ARB will actual increase the rollstiffness by a factor of 3. You might bethinking that this may be too stiff. However, due to the difference ingeometries between the front and rear ARBs, and how they mount to the suspension,the 20mm rear ARB results in a roll stiffness at the rear wheels which is stillonly 75% of the stiffness at the front wheels.

The uprated XK8 rear ARB will not mount directly to the standard X300 droplinks so these have been replaced by my own design of drop links usingspherical bearing rod ends to provide full articulation. I have seen single rodends used as one end of a drop link, but these do not provide full articulationto take account of the relative movement between the wishbone and the end ofthe ARB. By not using the standard Jaguar XK8 drop links I have alsoeliminated the compliance in the standard rubber bushes used in these parts.This also increases the effective roll stiffness. I have enclosed the rod endsin rubber boots to prevent dirt ingress. These are the same design of rod endsthat I have been using successfully on my uprated front anti-roll bar droplinks for the last 6 years.

The installation can be performed in less than 1 hour, with standard handtools.

Below are some photos that I have taken of the finished installation.

The car is off the road now for winter, so it will be a few monthsbefore I have a chance to experience the effect of theincreased rear roll stiffness on the handling.

If anyone is interested in one of these kits, then please email me directly on andystodart@metronet.co.uk

 

In the photos you can see that I have added a spacer between the rear ARB bushes and the brackets on the rear wishbone tie. This is necessary because of the way in which I have designed the lower ends of the drop links to attach to the wishbones

 

Thanks Andy, will be very interested in hearing how it performs for you.

 

At what point do we need to worry about cracking the ARB mount on the lower control arm off? I am not up on my strength of materials for cast iron.

 

That's a good question. The mounts are 9mm thick cast iron and about 25mm wide and 25mm long. Assuming the bending force required to exceed the tensile stress of cast iron is applied at the mid point from the free end, it would be equivalent to a mass of 400kg (880lbs) (assuming tensile strength of cast iron is 130MPa).

 

Hi Andy, just wondered if you've had a chance to test this new modification out yet?

 

Yes, I got the car out of storage at the weekend and drove it for the first time since fitting the uprated rear anti-roll bar. At the same time I had also fitted new springs which lowered the car significantly, and stiffer dampers. The combination of these changes has transformed the handling of the car. I'm really pleased with the results. I would not have believed that such a big car could handle as it now does.

 

Hi Andy,

As mentioned to you off forum, I am eager to buy one of these kits whenever they are available. So hopefully your test drive gives you the confidence to proceed ;o)

Cheers,
nickdabs

 

Hello, would you be willing to sell this kit? I would be really interested.

 

As a number of people have expressed interest in my uprated rear anti-roll bar kit, I do intend to make it available. I just need to get some costs for plating some parts to provide corrosion protection. Once I have all the cost information I will let everyone know.

 

Hi Andy

could you also share what shocks did you use? I am asking as I changed from old and tired KONI specials (with three step adjustment) to original Bilsteins (green) in the front and the results were not very good. Bilsteins are quite floaty, they feel to be with very little rebound dampening.

 

I fitted the original equipment dampers specified for the German market:-
front = MNA2140BA
rear = MNA3540EB

 

I have now worked out the cost of producing my rear anti-roll bar (ARB) drop links. I use these in conjunction with an Ultra Racing AR20-293 20mm diameter uprated rear anti-roll bar originally designed for the XK8 from 19996-2002. I have included details so that anyone can check that this part can be sourced locally. I'm sure that there are also other manufacturers of 20mm rear ARBs for these model years of XK8 Please send me a private message for more details of my rear ARB drop links

 

 

I haven't changed the front anti-roll bar itself. However, I do offer uprated front anti-roll bar drop links. These remove the compliance associated with the standard metallatic bushes in the OEM drop links by replacing them effectivewith spherical bearings. This makes a noticeable difference to the effective front roll stiffness.

The standard rear anti-roll bar provides a great deal less roll stiffness than the standard front anti-roll bar. I propose a stiffer 20mm diameter rear anti roll bar (standard rear anti roll bar is 16mm), so that the rear roll stiffness, increases towards the front roll stiffness. This revised roll bar is fitted in conjunction with uprated drop links, similar to those that I offer for the front.

I haven't tried just the changes to the rear without having already made the changes to the front, so I can't comment on how this would feel. The changes to the rear are more significant, but are more expensive because the anti-roll bar itself changes. Owners might wish to consider changing the front drop links first, as this is lower cost. If they appreciate the benefit in the handling by changing the front drop links, then they will really appreciate the effect of the change at the rear.

 

Hi XJREngineer,

This is very exciting, I've PM you, I have the revised drop links on the front and they were a great improvement to the front, so very keen to try out the mods to the rear.

Thanks,
Nick

 

@XJRengineer is there an alternative rear anti-roll bar you'd recommend for use with your links? It's just that I ordered one from Ultra Racing in October last year and the lead time for them to be sent from the manufacturer to the supplier here in the UK keeps stretching, so I'm having to consider other options if there are any. Thanks.

 

Hi general_piffle,

I bought the Ultra Raching anti-rollbar and it took months to come. In the meantime I bought the same spec anti-rollbar for my X100 from Powerhouse, so you could try them, I think they make it themselves.

Thanks,
Nick D

 

I used the UltraRacing AR20-293 bar because it is designed to replace the standard anti-roll bar on an XKR. Any aftermarket anti-roll bar that is sold as a replacement for the XKR or possibly XK8 should work, as it should have holes in the ends to take 10mm bolts, these holes should be the right distance for the rotational axis of the bar, and these ends should be the correct distance apart. I chose the AR20-293 because it is 20mm in diameter, so similar to the front anti-roll bar.

 

https://www.demon-tweeks.com/uk/ultr...r-uruar20-293/

This is where I got one