Car enthusiasts, rather, Jaguars enthusiasts in our case, all have in common in that we enjoy our cars. From their design to their driving dynamics, these Jags exude a charm distinct from more mainstream cars. Certainly a case can be made for these as some of the most beautiful cars from the late 90's and early 2000's. The shape harkens back to the 60's E-types. The now famous quote by Enzo Ferrari, who called it the most beautiful car in the world, was probably not lost on Geoff Lawson and team, who designed the X100 taking inspiration on the E-types beautiful and curvaceous body. The E-type was a pioneering sports car at the time. It innovated by being one of the first to have a fully independent rear suspension along with double-wishbones in the front. The IRS underwent various iterations and became a staple of Jaguar's magical ride. So good was this suspension that it gained popularity as a swap into resto-mod trucks of the 50s. This suspension system also underpins the Aston Martin DB7. With a racing pedigree to match, the sporting image the XKR invokes belies its true nature as a grand tourer. On the Aston, this suspension was tuned a little more sportingly. Although, I have never driven a DB7 to know how different it feels.

If you are like me, you want your car to be the very best example of its kind. Whether it be in showroom or mint condition, in tip-top mechanical shape, or upgraded for higher performance. Of course, it's always possible on the XKR to change pulleys or swap in a twin screw for higher power. Despite this, power is nothing if it can't be controlled. Even in as new conditions, the suspension on these X100s, even with the CATS suspension and/or the handling pack, is still tuned for comfort rather than sporting pretensions. The goal is not to make the XKR into a track weapon. There are much better options for that, such as the perennial club sport favorite MX-5 on the low end, to the Porsche's and Lotuses if money is no object. I think the goal a car that is more planted and sure-footed in the back roads. A car equally at home in canyon runs as it would be on cross-continental road-trips or in the daily commute. I believe it is possible to stiffen the shocks and springs and still end up with a comfortable ride.

To the effect of improvements in handling, elsewhere in this forum these have been reported to be obtained via the use of polyurethane bushes, thicker front and thinner rear anti-roll bars, and, Limited Slip differentials. Those upgrades have been discussed in other threads and are not the purpose of this review. Instead, I focus our attention on the coilover. The coilover is a simple concept. A unit which includes a shock absorber of either fixed or variable rate, which has on its body a spring perch for an adjustable height and adjustable rate spring. The more expensive units allow you to adjust height, spring rate, and damper rate independently. The ideal way of setting these up is to have the car corner balanced at the desired ride height. The result will be a more stable and planted car in the corners that is also more responsive. Depending on the chosen setup and spring and damper rate, the ride may become either slightly or much more harsh. A good setup and good tuning is key. The biggest issue with lowering the X100 is that the camber will go out of spec, towards excessive negative camber. On cars with McPherson struts, the solution is to use camber plates where the shock mounts to the body. On double wishbone systems like in our cars, this camber correction is more complex. The rear suspension can be corrected with thicker half-shaft shims, as detailed here and here. The front suspension is much more difficult to correct. The official method is to use eccentric bolts in the lower rear control arm pivot. A better method is to use an adjustable upper wishbone. To date, the only existing adjustable upper wishbone, that I could find, is the one-off custom unit that Deuce2000 fabricated for his own car.

As I was perusing the threads on this forum regarding coilover options for our cars I found the following:

• Ohlins coilovers - Deuce2000 was able to have these made for him, but apparently there were issues in so that the stock bushes couldn't handle the stress? Price was/is around $4400. Coincidentally, I noticed he is no longer a member of the forum, what happened there? Ohlin's thread
• The Nitron kit. No reported issues that I could find. It however, does not have helper springs. Can be obtained via Tom Lenthal. Can't seem to find the price, and am not sure if it's still for sale, but was reportedly pricey as well. Nitron thread
• The NTP Eibach-Bilstein coilovers, also around $4500. No reported issues with that one. But apparently less adjustable than the Ohlins. NTP-Eibach-Bilstein Thread
• There's mention of a Spire's coilover, but I couldn't find any specific threads about it. ccfulton mentioned in this thread about the Spires
  Quote:

  There is an adjustable coil over kit from Spires in the UK. It is built on standard Eibach springs, so you can choose any spring rate, they are height adjustable and they offer different damping rate options. It also comes in CATS and non CATS form.
  and in the Ohlin's thread linked above, pking51 mentioned post #7 that the shocks on the spires kit look like non-adjustable Bilsteins.
• Cheaper kits, from brands of questionable reputation such as Ceika, PB-Brakes, and Gecko Racing, offer coilovers in the $1200 range. One thing these all have in common: they do not ship with a rear spring and require the use of either the OE spring or the use of an aftermarket lowering spring. At which point, you're better off just going with one of the available lowering spring options from Mina, Adamesh, H&R, or Eibach, to name a few.
• Given the lack of full-coilover kits that included rear springs for our cars, Mjs128 decided to make his own coilover for the rear using the PB-brakes's incomplete kit.

One avenue for coilovers that I have not seen explored by anyone on the forum is the AVO GTZ kit offered by the good chaps at Swallow's Racing. I learned about these from the Drivetribe YouTube videos: Project XKR. It's possible that few on this forum paid attention to that if they watched. The price, converted to USD is about $1500. Which is undercuts the Nitron, Ohlins, and NTP Eibach-Bilstein kits and is only marginally more expensive than the questionable chinesium kits that do not include a rear spring in their coilover kit.

The AVO GTZ kit certainly looks nice. Although a few things do come to my attention. It's the only kit I have seen so far that retains both the OEM Upper shock mount for both the front and rear as well as the lower shock bushes. Whether the OEM parts can survive the abuse is unexplored. Deuce's experience with the Ohlin's kit, which used the OE top mounts, suggests that they may likely fail. However, the AVO kit also uses the stock lower bush. Would that help matters or make it worse? Hopefully someone with more knowledge than I can chime in. As for the top bush, I have reason to believe that Wayne's (cjd777) and Baxtor's Poly front upper shock mounts may be up to the task of surviving the abuse of the AVO shock mount.

On the subject of CATS systems, when replacing with a non-CATS system, eliminating the "Suspension Fault" warning is as easy as disconnecting the CATS module in the trunk. Do not let the possibility of warning messages be of discouragement to switching to a different system. This is attractive for those looking to save money by buying OE non-CATS shocks and also applies when switching from the CATS system to swap in a coilover.

I hope this long-winded review of the available data on this forum is of help to anyone considering refreshing their suspension or upgrading from their existing OE Bilsteins, be they CATS or not. If anyone takes the plunge with trying out the AVO GTZ coilovers available from Swallows, please report back on their ride, handling, and durability. The X100 coupes are a good platform for upgrade that has been largely ignored by the aftermarket. And what little aftermarket is available to these cars is limited in their offerings, the prices are stratospheric, and the longitudinal real world data from owners concerning the available options is also lacking.


Merry Christmas!!

 

I did look at those systems and the Spires and Swallows shocks but in the end I went down the route of sticking to OEM shocks and lowering springs. There isn't really enough info on these kits and the performance they bring for me to really go down that route in my opinion. I figure these companies are more focused on track driving then road driving so the ride will be much too stiff and performance will suffer as a result. It would be interesting to see people who have these kits chime in though, that would be nice.

 

Gian, lots of research and should head anyone thinking of this upgrade in the right direction.
On that thought, Baxtor was showing something he was messing with that adjusted the spring length. Where we have a problem getting springs that are rated for the purpose of control is our springs are different diameters top and bottom, great for comfort but not a consistent control through the turning range, like loading the front wheel at the apex.
Can the standard adjustment on the electric shocks put enough restriction in the four wheels to allow a controlled spirited drive? Sorry to say, never been where I or the driver was trying to feel any difference.
Poly bushings all around could help but these cars are heavy and the springs would have more control to keep things level through the corner and of course a bit of negatives camber. Now you are looking at making it unroadworthy for normal day to day use.
We have done the track car to street car and reverse on lots of AutoX cars (MG and Triumph), I must admit, over a period of time not something that works for both ways.
Will follow your thoughts and see what you come up with, thanks.
Wayne

 

I run Nitron - true front and rear coilovers - and have them available at the link below.
Nitron does not have helper springs and set at the softest setting rides like an OEM+ feel. Basically what you would expect the R to ride like if it was a modern car, comfortable but firm with no body roll. Another perk is they have a completely different design for the front upper shock mount, so no longer have to deal with the collapsing issues.

https://www.ebay.com/itm/32528102318...Bk9SR8bdj6aUYw