...what would you do?

I have always been more concerned with handling/braking than throttle performance or ride comfort. I intend to do a lot of work to this car over the next couple of years, to include the installation of a manual trans and whatever modifications need to be done to turn the car into a real road carver, if it's possible. I realize I'm behind the 8-ball already given my choice of car but this is the goal nonetheless.

I see random suspension modifications listed in people's signatures, and vendors like Driven Man seem to offer packages (roll bars, shocks, springs, bushings, etc.) that would seem to help. I'm going to change the wheel size eventually, but I'm worried 17x8 wheels will scrape if I lower the car. That's a topic for another day, however.

One thing I wish this site had is a sticky for preset builds. When I was big into Mitsubishi Starions, someone had put together sort of a standard performance build where we could point new owners, or owners like me that are afraid of picking the wrong parts. It made modding the car pretty easy.

Absent that, I'm throwing this open to suggestions with the following rules:

1) No body modifications (i.e., no custom fender work, roll cages, etc.),
2) No major modifications/repurposing at the system level (i.e., no "use the rear end from a 1985 Porsche 944", etc.). I'm looking for mostly bolt-on suggestions and reviews.

I'm also interested in what *doesn't* work. Especially if you've bought certain parts and were disappointed with their performance.

I'm aiming for the best suspension-brake-wheel package I can put together. I've been told the brakes on these cars are fine as is but I don't feel I'm getting adequate performance out of my factory setup. And I just swapped on new pads about 1,000 miles ago.

Jess

 

Define "....handle the best it could...."

If ride comfort isn't an issue, and lack of body roll is a primary measurement of success, and your favorite canyons don't have any bumps or ruts, just have some stiff springs made up and maybe lower the car a bit. Add a rear ARB to reduce the built-in understeer. Get some sticky summer tires. Dial in lots of caster for strong self-centering to the steering.



Cheers
DD

 

Here's an interesting video clip from Top Gear comparing a Jaguar XKR prototype to an Aston Martin DB7 GT, looks like early 2000s model years. While they were quite impressed by the XKR prototype, Jeremy Clark was really impressed by the AM DB7 GT. Especially the handling. The early DB7 is closely based upon the XJS platform. Therefore I would surmise that there is significant potential for improvement to an actual XJS. I looked at a 2002 DB7 convertible and it really feels like an XJS. Don't forget Bob Tillus group 44 Trans Am champion XJS and the European Touring Car Champions. Check out the video.

 

Talk to the racers at the JEC in England. Lots of knowledge and off the shelf parts, and tyres. As Doug said, basically, harder lower springs, ditto shocks, ARB mods and uprate brakes. For brakes, EBC slotted rotors and Red Stuff pads will do the job perfectly.
If comfort is not an issue then remove as much weight as you can, this will make a huge difference even on a standard engine (ie aircon, heater, spare wheel, rear seats, bumpers, etc etc). The manual trans will also make a very big difference. All very interesting, do keep us informed, please.
Greg

 

Rivguy,

That video is quite entertaining and educational besides. I'm encouraged that someone was able to milk greater improvement from the XJS platform.

In another thread on this board, a different poster encouraged me to consider stiffening the frame by welding crossbeams in to reduce body flex in the corners. If anyone knows how that should be done, exactly, I'm all ears, although that might be a step too far.

I'm not looking to build a race car, and I doubt I'd ever even autocross it, although I'd like to have the option. I mostly want to be confident when I'm driving it in "spirited" fashion. Right now, even changing lanes to pass someone on a 2-lane road produces way too much body roll when the car crosses over the centerline and goes from leaning on the right wheels to leaning on the left. The suspension feels like a too-soft mattress. There's also way too much forward dive when I get hard on the brakes.

I've mentioned here a couple of times that I used to own a Mitsubishi Starion. I installed Tokico Blue struts and Suspension Techniques springs on that car and upgraded the brakes (steel lines, slotted rotors, performance pads). The end result was the car lowered about 2 inches, almost an imperceptible amount, but it went from being a somewhat heavy sports GT to an honest-to-goodness sports car. Coupled with a torque-y turbo four, it was a blast to drive, but what I loved most was how confident I was behind the wheel. It even handled well in wet weather despite only having ABS on the rear wheels. I never worried about it getting away from me. I ran the Tail of the Dragon at a rather stupid pace in it one time and it still gave me plenty of mistake room.

I'm older and wiser now, but I miss that level of control. I love my XJS, but even the slightest bit of rain, suboptimal pavement conditions or changes in elevation make me nervous. I'm not much for nervous driving.

Jess

p.s.: Greg and Doug, thanks for the tips. Greg, I'll look up EBC and Red Stuff products. As for "talk(ing) to the racers at JEC in England," I'd love to but would they really give some random guy from south Alabama the time of day?

p.p.s.: Here's a couple of pictures of the car, I'll add more once I have time to shoot more.

 

Here's my 2 bobs worth.

Stiffening the car too much will hurt handling, mostly due to the uneven roads most of drive on. The suspension needs enough compliance to keep all 4 tyres in contact with the road.

By far the best thing you can do for the handling of your XJS is to stiffen the chassis.

While I'm banging on lets discuss lowing a car.

Body roll in a corner is caused by the fulcrum effect between the cars Roll Center (RC) and Center of Gravity CoG). The center of gravity is obvious, Roll center is determined by drawing a line through the suspension control arms, the intersection point is the Instant Center, then draw a line from the middle of the tyre to the Instant Center and this is the RC.

When a car is lowered this changes the angle of the control arms lowering the RC, thus moving the RC and CoG further apart, in effect lengthening the fulcrum and making the car roll more requiring stiffer springs to counter this effect.

My car runs stock front springs and heavier rear springs 25mm front sway bar (ie Stock ride height). Poly rack bushes and stock wishbone bushes. It corners fabulously especially on less than perfect roads.

 

This sounds like shot shock absorbers to me, possibly allied to weak springs. My standard suspension car does not act like that. First off, bung on a set of Gaz adjustables, set about halfway and see how that feels. If better but not what you want, harder springs next and new OEM suspension rubber components throughout. Then see.
I am quite sure the guys who race will help you. PTJS also knows the name of the garage that supplies most of them, I am sure he will chime in.
Greg

 

That's easier, then.

IMHO....a basic formula will work well:

Stock springs and ride height. Added rear ARB. Larger front ARB. Premium shocks. *Replace worn suspension components, including rack bushings*. 50-60 series performance tires. Plenty of caster.

These changes will probably give you the improvement you are looking for and will work well on real-world roads

Cheers
DD

 

Doug,

This is the suspension kit I'm eyeing. Thoughts? The Driven Man - Jaguar - Springs - Specialty Auto Performance Parts & Accessories

Greg,

I'll be happy to talk with those guys if they'll talk to me; can you point me to some contact information?

Warren,

In regards to stiffening the chassis, have you done that to your car and if so, can you advise? I'll search the forum for more info. I looked at your resto blog and found a lot of good info there.

Jess

p.s.: I also should mention that I'm sure my rear end gear is in need of rebuild given that it likes to rattle and grind when turning to the right (but not the left).

 

I say first get the car correct, as Doug mentioned. You are obviously experiencing a worn out car suspension-wise.
These are the Racing guys, very helpful and very knowledgeable, years of experience. Jaguar Race Preparation, Servicing - XjRestorations
Greg

 

Jess,

No I have not added chassis stiffening yet. It will be on my todo list after my 6.8L engine rebuild. What I was planning is to add X bracing under the car google Miata butterfly brace. I now wish I had seam welded the car while it was bare metal, oh well its not a race car.

What a stiff chassis does is allow the suspension to work without the oscillation induced by the twisting of the body.

And Doug is right on the money with what needs to be done. Also add a good set of quality shocks I went Bilstein, TWR valving not Jagsport. They are more complaint in bump.

 

Find an install a rear antisway bar.
Good luck...they are hard to come by but totally necessary as a first step.

Then get 16 or 17 inch wheels and 235 or larger series tires all around.

Then install bilstein shocks all around.

Do this and it will still ride sweet yet keep up with Porsches of the same era. You will be amazed.

If its still not enough you will need much stiffer springs which will greatly diminish ride quality.

 

I guess it all depends on how hard you push the car but l think the changes that walkinshaw made to the xjs to create the xjrs certainly resulted in a car more than adequate for my driving style. Namely spring rates, bilstein shocks and steering rack spec. changes but probably the easiest and cheapest change he could have made was simply adding a rear anti roll bar. There must have been a reason he did not do that.

 

There are a hundred ways to skin a cat.

Often, when springs rates are changed, the builder does not feel the need to use a rear ARB....under the notion that the new springs rates give the desired amount of roll resistance, I reckon. Makes sense to me.

The beauty of added/upgraded ARBs is that you can get a good improvement without changing springs and/or sacrificing much comfort.

Urban legend has it that Jaguar stopped installing the rear ARB because "track testing proved it was of little benefit". I say 'fiddlesticks'. What works well on the racetrack might not be best for a road car and vice-versa. IMHO the rear ARB is a very worthwhile addition to a street driven XJS or most any other car that doesn't have one....even if it doesn't make any improvement on the race track.

Cheers
DD

 

Jaguar enthusiast club
Although based I England have members from all over world.
They will be happy to 'talk' to you. Any Jaguar enthusiast is made welcome.
Many members of JEC are also on here

Jaguar Enthusiasts Club, Classic British Cars, Jaguar Owners Club, Jaguar Tool Hire, The largest Jaguar Club covering all models including E-type, S-type, X300, XJS, XJ, Mark 2, XK8

 

What I have done on my '90 convertible:


1. Lowered front end (removed packing rings from tops of spring towers)
2. Rebushed front end with poly
3. Poly steering rack bushings (you won't believe the difference)
4. Larger front bar
5. Added rear bar
6. XK8 17" wheels
7. Tire spec to match front tire and rear tire OD as used on the TWR cars. These cars have a slightly nose-down attitude, and there's a reason- noticeably sharper handling. I ended up with 245/50 on rear and something like a 235/40 on the front to get this. I would not go lower profile that 40 for many reasons.
8. New bushings on IRS
9. New shocks and bushings for shocks, all around
10. Established tuned in ride height for rear with spring height adjustments


All this has made the car quite a bit sharper and corner nicely now. It DOES get a bit twitchy at 9/10's as regards the rear end with that rear bar. Most road racers do not use a rear bar, but resort to spring and shock tuning to get what they want. For road use, I like that bar, and 99% of the time I am no where near the break-free release point of the rear end with the bar, so I am good with it.


Where I am going next: I have a ladder brace from an XJS-C that I intend to mount to do 2 things: 1) stiffen the floor pan (convertibles are flexible), and 2) I intend to tie bushings between that ladder frame and the tie plate of the IRS to minimize/restrain cage motion under hard accel. This is a real problem with a manual box and short gearing (much torque), and I have had to be careful not to tear up the mountings. But the ladder bar should do the trick.


It's never gonna be a track car (convertibles are just too flexible- think 2 ton Miata), but, it's very competent on the twisties, now.


-M

 

One other comment, too:


There are basically two schools of thought on suspension setup. The first and most common is to stiffen everything up and lower the overall car as much as possible. Rides like a lumber truck, but hey, if you want that, you can do it.


The other school is more old school, and holds that the suspension should be softly sprung and well damped. This means, for the XJS, concentrate on the shocks, all other things being equal.


Finally, what you do will depend on whether you have a coupe, which has a pretty stiff body/chassis to begin with, or a convertible, which is much more flexible. You can take the coupe farther than a convertible, because the convertible's flexibility works against the usual approaches. And there's really no good solution unless you are willing to weld the doors closed or otherwise raise the door sills to regain the torsional and lateral stiffness lost from the removal of the roof. There are a few things, but as I said, in the limit, you will fall short of what can be done with the coupe.


As for me, I wanted to elevate the handling competence of the car, but not give up too much of that fabulous jag ride. For example, I have a friend with a really nice 94 vette coupe, and having driven that car, I can tell you I would MUCH rather have my jag. Way better car over long distance touring with its vastly better ride quality, and frankly, set up the way it is now, my car can give that '94 fits in every way possible.


-M

 

Mike,

I wanted to focus on this portion of your response: I've done a lot of reading up on XJS and the wheels you can use on the car, and the limit seems to be 17x8 or 18x8 with a specific tire size before scraping starts happening under the outer curvature of the fenderwells.

You're the first person I've seen talk about lowering the car (in the front) and still using a 17" rim size with 235/40 tires.

I plan not to use XK8 rims, but I think I've settled on 17x8 as a size and will probably use something from MOMO or another higher-end provider. My question to you is, one, do you have problems with scraping; two, what did you have to do in regards to offset, spacers, etc., to make this work.

Jess

 

Jess:


You picked probably the most thorny part of my post. I spent a lot of time on this issue, driven by my choice of XK8 Revolver wheels.


I chose those because I wanted to use OEM jag wheels, and I liked those pretty well.


But the complexities of that choice were visited upon me for quite some time.


I initially selected 245/50-17 tires, and two problems immediately cropped up: first, the front tires interfered with the fender wells at close to full lock and actually rubbed the inner fender well at full lock. Moreover, it was not possible to fit the wheel center caps, as the wheel hub's grease cap protruded too far. Second, the rear tires would come into contact with the fender wells on heavy bumps, or, moderate bumps, but at speed. The interference was worst when turning into a driveway or some such where there was also a curb. Had to be very ginger in how I did this, otherwise would run the tire into the fender.


I will get to the answer as to why, first: the whole game with the XJS and wheels has to do with offset. The jag XJS uses a very particular wheel offset, and this is why most any other wheel you would want to casually pick up and use (other than what jag themselves made for this _specific_ model) will often not work. Bernard Embden has an excellent account of this, as he ended up purchasing an aftermarket set of wheels for which offset could be specified. Even so, he claimed that 235/50's were as big as you could go. I disagree, but the 235/50 is a pretty decent stopping point. Google that site and read it yourself. You will learn a lot.


As for my own story: I ended up using hub centric wheel spacers on the front (and longer studs), to eliminate the problem of outer well interference, but could never eliminate the inner well rubbing at full lock, with 245/50's. The spacers were just enough to be able to fit the center caps, but these still stood proud of the wheel by about 1/8" and had to be RTV'd in place. No big deal, the bond is easy to break, and it is very durable until you need to pull the wheels. And it looks fine 5' out.


Full disclosure: I am running 225/45-17's on the front now, not the 40 series as I had earlier written (memory being what it is...). I would NOT go under 45 series, as you are removing precious compliance as those side wall heights reduce, and, you are seriously exposing your wheel rims to road damage. Besides, I was never a fan of the banana peel look that is in vogue for a certain segment of enthusiasts. Potatoe, Potahtoe, you know.


As for the rear: I checked my ride height first, figuring maybe it was sagging a bit. I found it to be at the low end of spec, but still very much in spec. Putting new shocks improved the situation, as the tendency to bottom the suspension (or really, the dive tendency, speaking of the rear suspension) lessened quite a bit. In the end, I very slightly rolled the inner edges of the fender lips. Not much, just a bit. These changes essentially solved the problem of interference. I should point out that others have not reported this issue with these wheels and this tire size, and I think there's an element of coupes vs. convertibles, here, in terms of how the factory built the cars. I also KNOW that there was variation in the XK8 Revolver wheel production, because I have two sets of these wheels, and they fit differently. Slight differences, to be sure, but different, none the less.


In the end, I was looking for this setup: the XJRS used these wheels:


225/50-16 on the front, with 19 mm offset. Tire OD is 24.9"
245/55-16 on the rear, with 33 mm offset. Tire OD is 26.6"


So you can see where a good deal of the nose-down attitude that the TWR XJRS has comes from. There is also a bit of overall lowering going on in the TWR XJRS, and some of this is in addition to what comes from those wheels.


The tires I am using are:


225/45-17, offset 33 mm, tire OD is 25.0"
245/50-17, offset 33 mm, tire OD is 26.6"


So I am nearly dead on to the TWR XJRS spec. I love the resulting handling, very noticeable. I also like that nose down attitude of the car. And, going to the 225/45 totally eliminated the interference issues on the front.


To tune up the ride height, I found my front end was about right on, with the 225/45's and the removal of the packing rings in the spring towers.


I found the rear still a touch too low, and I chose to use a small amount of ring spacers in the spring platforms of the rear suspension. The polymeric kind favored by the high lift sport-ute group. Those took a bit of scouting, but I found a part number that worked great. I don't recall the part number, nor the thickness, but they were at the lower end of what was made. The change I was looking for here was small, and some may argue that I didn't need to do anything, or, that I needed new springs- I really did not see that, given the measurements, and so chose a different path.


This change to the rear absolutely removed any opportunity for interference, as it moved the height up just enough to take it out of contention on anything but very very serious road/speed conditions.


The result is right at the limit of what can be done with these particular wheels- I would not want any narrower aspect tire on the front, the ride would become very harsh.


If you have the opportunity to order wheels with whatever offset you want, then, you are home free to pretty much pick the tires you wish to run. There are guys running really big rear tires (like 255/50-17's) but they do this by adjusting offset.


You are wise to approach this with caution- blindly bailing into this will end up being time consuming, expensive and frustrating. But going into it with a knowledge of how offset and tire size interplay will enable you to select exactly the setup you are looking for. Summit and other places have nifty fixture setups you can buy that bolt to the wheel hub and have adjustable tire size and offset, and will be able to tell you if you will have interference issues.


A down side to the setup I chose (and the TWR XJRS setup) is that running two very different tire sizes means that if you get a flat, your spare will not necessarily fit well. I continue to look for a space saver that might work, and which would also save some weight. But since I don't take the car that far afield, I figure I will just flatbed it to wherever if I get a flat.


One last thing: 17" wheels give clearance on the tie rod ends on the front suspension (as I recall at 33mm offset, all is good). There have been cases of guys running 16" aftermarket/non XJS jag wheels where tie rod interference is reported, so watch that part, too. Especially look at what the clearance might be if a balance weight is clipped to the inside edge--- you are very close here, potentially, at 16", and will be surprised in an unhappy way if you don't!


Good luck,


-M

 

Mike,

Thanks for that response. This is exactly what I was hoping to read and I'm very thankful you took the time to be that detailed and precise. I'm saving this post for future reference and likely will copy your setup verbatim. I'm about 98% sure of what you wrote and may want to contact you in the future (specifically about your rear suspension setup for height/clearance purposes) if you're open to it.

Jess