I came from a Porsche 944 Turbo before my XKR recently, and am inspired to make the XKR as much of a dialed-in driver's car as possible with my slushbox GT. Unfortunately, I have an added hindrance with the convertible in this effort and wonder what options are available to tighten the car up more in the bends. Make it even more of the brute British roadster it is. There's a big, flat, metal brace behind the backseat that seems to be the only thing holding the sides apart. Are there strut braces available for the rear that will do a better job? What about for the front that would fit under the bonnet?


I'm also planning to get an alignment, make sure my control arms and bushings are in good shape, try disabling the steering rack boost, and removing the rear seat (the mod Phil did earlier this year) to perhaps save a little weight, though there aren't many great options for the latter there. Thoughts?

 

Fully weld the doors!

 

In another thread "sandiegomac" (creator of the MacLeod MK II exhaust system) mentioned that an untintended but beneficial side-effect the installation of his larger diameter stainless exhaust tended to increase chassis stiffness. I'll hunt for the exact post and edit this one with a link-back when I find it.

Edited.... Reference to chassis stiffness is -> Here <- from the xk8-exhaust-without-center-muffler thread.

 

In addition there are some frame tightening mods you can do. I've done the polly bushings and the stiffer anti-roll bar. Search for Ultra Racing and Jaguar on eBay: Ultra Racing 20mm Rear Anti Roll Sway Bar Stabilizer 96 06 Jaguar XK8 XKR X100 | eBay


They even have a shock tower brace (but it is XK8 only). Jaguar Specialties is working on their own stiff anti-roll bar but it is still in test.


Oh on the Polly bushings there are two levels. The black ones are especially stiff. Powerflex is the source: PowerflexUSA - XK8 - XK8R (97+)

 

Y'know, I'm just tall enough that climbing in may not be a problem so long as I leave the top down all the time. Usually possible in Texas. :P

Ha, I read that yesterday! Am looking into exhaust options too as you saw. Odd benefit of that system- those must be some hangers. Duly noting this option...

That's what I'm talking about. Much thanks! Bookmarking both of these. I think the bushings would be a great start.

 

Lowering springs are usually stiffer as well, made a good improvement on my car, including stiffer shocks, which should actually be done when you get stiffer springs as well to complement them. This combination not only gives a much tighter feeling, it actually has improved handling. I prefer just the stock rubber bushings, and I may experiment with the thicker front sway bar and thinner rear (the ones used on the Jaguar R Performance pack).

 

Ultra racing also has front and rear chassis braces available:
Jaguar XK8 4.0 (1998) Aftermarket Performance Parts / Accessories / Spare Part - Ultra Racing Product Catalog

I can say that a full set of poly bushes really made the car feel better, even without changing anything else.

Upper shock mounts and lower shock bushes break down too. You can check tie rod ends too, which aren't too awfully expensive from SNG Barratt.

Is you have the original shocks, at 127k they might be tired too. Not too terrible to replace is you have regular ones but if they are CATS... ouch.


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Just as an aside on the CATS shocks: One thing I have been thinking about is that if we could find a place that rebuilds them in the US like Avos has done in Europe, that we could start a hand me down program and pass used sets on to the next forum member who needed a set.

They could rebuild them without needing to decommission their car, install and then hold their old set until the next member came along.

I figure these parts will get harder and harder to find and probably more expensive, so it's a sort of preservation program.

I bit the bullet and bought a set of 4 new ones (the stiffer R package type) so will have a set of used CATS shocks that we could seed the rebuild program in the not too distant future.

 

Thanks, avos- not sure why I didn't mention suspension, but I think I'm too focused on just getting a somewhat-loose convertible chassis firmed up more. But a proper sport suspension would certainly lend itself well to that, and I've had the Mina kit on my 'plans' list (or what would you recommend?).

Thanks also, Charlie- bookmarking that! And great idea for the CATS hand-me-downs. I also have a CATS system, but it's disabled as usual. I'd be happy to contribute to that effort whenever I replace my suspension with something along the lines of what avos has. It's a great idea for those here who prefer it.

 

Please, clarify. I dont get it.

Disabled means stiff, and while fun in the corners, you dont want that driving in a straight line all day as it makes the car bouncy.

If I had a convertible, I would do the Ultraracing front and rear underbraces immediately.

Larger rear anti roll should reduce the massive understeer. I would have already done the 20mm bar (vs the stock 17mm we all have, non R pack) by UltraRacing had I not learned of the upcoming 22mm + bar coming from JaguarSpecialties.com any time now.

Other person has written about custom front top shock plates to improve steering but no one else did it.

I'd like a tighter ratio but "steering quickner" devices NOT highway legal.

Former Boxster driver myself (5 years) so I too am eager for handling improvements and upgrades.

One idea from current Chevy Camaro SS , 1LE option, de stagger the wheels and tires. I may try that, as in sell my frony wheels for two more rears that I would use in the front. Camaro same power and weight range.

R Pack option for 2003-2006 did NOT change magazine reviewer impressions of massive understeer so no point repeating slightly larger front roll bar (1mm) and smaller rear (-2mm). Sorry AVOS, for us tight turns guys, not following the factory on that one.

 

Don't know what they tested, but a smaller rear bar will allow for more grip on the rear wheels with the open diff (as the inner one is lifted less in tight turns). Going thicker will lift the rear wheel more, and give you more oversteer but as the wheel lifts more you will also have less power with the open diff. Anyway, as I haven’t driven different setups I can’t speak from experience, and when l start experimenting, it will only give info for cars that have a little more power with a clutch lsd, and with eu tight corners ;-).

 

I was surprised how well the chassis took it, as at some point that one will take on the load of course being a convertible; at least that is what I would expect. Of course it isn’t a go-cart, and not something I would want to turn this car into, but overall the tighter feel (ok less wobbly may be a better starting point) makes it better for me.

 

Avos, so in another thread called called increasing your rear (sway bar)

https://www.jaguarforums.com/forum/showthread.php?t=111770

... we have a second vendor offering a larger rear bar. Emphasis is in reducing understeer, and the Chevy people made a significant improvement in that regard with larger rear bar too (again, similar weight and power on Camaro SS, which was dominated by undesteer before the 1LE pack with larger bars and unstaggered wheels).

Ccfulton, what has your experience with your UR larger bar?

I recall modifaction crazy Enderle saying his larger rear bar diminished sway enough that he found subsequent lowered springs to be of minimal effect

 

Are you certain that it actually reduced understeer or just made the rear end break loose before the front end? Common misperception from the inexperienced.

By the way, welding the doors shut only helps if you normally find yourself driving with the doors open...

 

You need to look here my friend, watch the video as well, this applies to you directly

http://www.ebay.com/itm/ULTRA-RACING-20MM-REAR-ANTI-BODY-ROLL-SWAY-BAR-STABILIZER-96-06-JAGUAR-XK8-X100-/171216340163?pt=Motors_Car_Truck_Parts_Accessories &hash=item27dd4a04c3&vxp=mtr

 

Peculiar thing about the strut brace is that the XK8 doesn't have struts. It employs a double wishbone suspension and both upper and lower control arms are mounted to the same isolated structural cross-member/subframe. While the upper spring mounts are indeed mounted to the body structure that has little to do with the suspension geometry other than a small, potential influence on ride height. Undoubtedly the cross brace would enhance body rigidity and possibly play a minor roll in cowl shake reduction.

Reducing body flex, short of a full-on cage setup, would best be accomplished by employing stronger sills, extending braces from the cross brace above to triangulate both forward to the radiator support and back to the cowl. Follow that with a tall center backbone through the passenger compartment, connected to the front cowl structure and to a similar reinforcing structure to the rear.

Tightening the suspension to the body by replacing suspension subframe to body mounts with items of less compliant materials, while definitely destroying ride comfort and real world drivability, would enhance responsiveness. Changing the mountings before strengthening the body structure would be a gross mistake. Also, consideration must be given to the durability of the front alloy subframe if stiffer mountings were employed as they also serve to allow the body a certain amount of flex without unduly stressing the structure.

 

Over in the other thread about increasing the rear antiroll bar, I posted a question about the larger rear bar also making the steering sharper. Years ago someone with CoventryWest added a second rear sway bar in parallel to achieve more rear stiffness and he noted the steering was sharper as well as providing less oversteer.

Whether that is with the UltraRacing 20mm bar or JaguarSpecialities upcoming 22+mm bar is going to be interesting. As a coupe owner, I already enjoy better chassis stiffness than the convertible by a wide margin (for this gen of Jag, not so much the next one in 2007 and on), so I suspect my car can handle it

 

Welded in roll cage:
http://www.rsfabrications.com/wp-con...5/cimg1625.jpg

 

Now that will get the job done!

 

I kinda think you're missing the point... Let's say you can negotiate a turn at 45 mph but the front is understeering. Adding more bar to the rear will make it seem that the front is understeering less as the back end will now break out at about the same time. However, you're now only able to go through the same turn at 38 mph because the entire car is sliding out. Sometimes a driver can use that to his advantage, sometimes not.

The proper thing to do is to shove the front wheels forward or the weight to the rear. Look at a Corvette. The seat backs are pretty much at the rear tires, allowing the engine to set further back and the front control arms are pretty much ahead of the engine. You could increase the tire contact patch in the front but go too far and you'll probably end up with some new problems as a result.

 

Be sure to clarify who may be missing a point. I am guessing you mean me. I appreciate the feedback so thank you.

The people at CoventryWest are no strangers to Jaguar, and they were quite clear about that 2nd rear sway bar experience. In addition, I still refer to the current model Chevy Camaro SS and the difference between it and the optional 1LE package that drastically reduced understeer to the applause of every magazine that reviewed it (Car and Driver, Road and Track, MotoTrend, Automobile).

I have not heard anyone with the UltraRacing bar, which is 3 mm thicker than stock, regretting the decision aside from some initial squeaks (Deuce2000 comes to mind). JaguarSpecialties wrote back about the same concern that was expressed earlier by AVOS. Check out the thread.

Setting the larger bar aside, you against replacing rear bushings with PowerFlex "purple" series bushings? XKRacer Tony of ParagonDesign fame likes 'em.