So after much searching and deliberation, I reached out to Spires and thought I'd give it a shot. I did some research on parts, and the seats/perches and other surrounding suspension components of XKRs before 2012 were largely the same, so it told me that the Spires springs would fit without issue. And this was also later confirmed by Spires via emails.

The spring rate, however, is identical to the OEM springs. So essentially, you're lowering your car, without any change in ride quality. Still, I was very hesitant, but I decided to take the gamble and it paid off! The Eibach-sourced springs fit terrific. No noises or squeaks. Moreover, there is no increase in harshness.

The car settled to its .75-.80 inch drop, and it's settled beautifully after some cycles. Took about 2-3 drives. Handling has also dramatically improved. The initial pitch and lean is significantly reduced when going into a corner. It carries momentum around a bend so wonderfully that it puts a massive smile on my face.

As far as alignment, this drop is the absolute maximum you can lower without the need for camber kit and such. My Jag dealer was just able to get the alignment back into perfect spec, but my tech stated that if the drop was any lower, it'd need a kit.

The only drawback to some people would be the following: scraping and bottoming out. The car sits lower, and because the spring rate is the same, the suspension will compress the same as OEM. So if you live in an area with really poor roads that are ridden with holes, have lots of dips, etc...don't lower your XKR (probably best not to lower it with any set of springs, actually). You increase the likelihood of hitting the bumpstops.

On my usual routes of driving around, I have purposely aimed at some bumps and dips here and there...and all has been fine. Leaving certain areas here in central Florida still requires me to use lots of caution, to avoid scraping because of the water runoff easeways, but that's only in some areas - and I use the same caution in my XF too.

So all in all, yes you can install these on your car. They fit. They work. They make a terrific difference in handling. And I do recommend them highly.

I'll post pics once the rain stops.

 

Thanks for sharing, many here will probably be very pleased to hear that. Compared to other options, I believe these custom Eibachs offer perfect ride height and improved handling without sacrificing anything. I am very pleased with mine and have had no issues with various road surfaces in Central Florida.

Which dealer did you have install them?

 

I guess I am missing something here. If the spring rate is the same then wouldn't the suspension travel be the same. Also what was changed to lower the car or is it just the length of the spring. I would assume if it turns flatter then the new springs would be stiffer . If that is the case then the ride would be harsher then the OEM ride. Just need a little learning here. How about some before and after pictures.

 

I felt the same way. Spring rates being the same, the spring would need to be shorter a 'X' percent to lower the car 'Y' amount which makes me curious about what the dynamic systems are doing to improve the ride vs. lowering changing the geometry. From the commercials the XKRS makes 3k pounds of down force at high speed which I think would do the same thing to the chassis as lowering it. Makes me wonder how compressed the lowered stock rate suspension is now going to be at speed and if there is a safety issue involved? It'd be a real bummer to go solid at 130 mph.

Personally the only reason I'd ever lower a car is if it had a goofy gap between the rubber and the fender. My '07 XKR with + 5% profile tires doesn't have a goofy gap and handles damn nice without a rough ride. The spring rate is a little higher than I'd like but that is the trade off for a performance version of the car. It only bothers me on rough stretches of the interstate.

 

I believe there is a misunderstanding regarding these spring rates. I believe the idea was to create a ride quality similar to stock by increasing the rates to compensate for the shorter springs and to prevent bottoming out (what would happen if you simply cut the stock springs).

I've been well over 150 mph with no issues.

 

Other than that grin you just can't get rid of?

 

Books have been written on suspension springs, quite complex these days..
Our XK is stock, but my experience with Eibachs on other cars has been good, pretty much as described here. Had H&Rs on an Audi S4 and they were stiffer.
Springs do not have a constant rate, but progressively get stiffer as they compress, achieved by coil spacing and their diameter.
Those Eibachs may have a similar rate when sitting still, but it will increase quicker than stock when compressed, resisting roll and also reducing the maximum compression when encountering bumps.
The big coils on some stock springs can actually touch together, often having rubber bits on them to stop the clanging
Bump stops these days are typically part of the spring system, designed to start compressing way before solid things come in to contact, which is REALLY not good.
Just shortening a spring will make it stiffer, the number of coils is just one of the variables, along with wire diameter, coil diameter,coil spacing and ....
My little Mazda RX8-R3 is my good handling track toy, Bilsteins and sport springs, the XK is our tourer, handling okay but could be improved, I find many cars like slightly higher front tyre pressures than the rears, but our XK feels "nervous" unless the fronts are a couple of pounds lower (early Corvairs??). and then the changing damper rates, not sure that is really good either?
Glad to hear that those Eibachs are good.
Cheers

 

Jaguar of Orlando.

Spring rate changes the stiffness of the spring and the weight required to compress it a full inch. The rate is usually increased when the spring is shorter. In this instance, it isn't and it's supposed to be almost the same as stock. The suspension travel on our cars is pretty long as is, so the likelihood of hitting the bump stops with a .75 drop is still extremely low.

Correct.

Just want to specify that what you're describing about springs not having constant rates and being progressively stiffer isn't exactly correct (not in this instance). When they get progressively stiffer, that's a progressive spring. That's essentially the difference between progressive springs vs. linear springs. Our Jag's OEM springs are linear (equal length coils from top to bottom). And my replacement Spires/Eibachs are also linear.

Progressive springs are partly equal length and then towards the bottom tightly coiled. See image:




Essentially, most of my performance enhancement is aided by the lower center of gravity, as opposed to any kind of stiffness. Springs that stiffen up into corners can usually cause understeering tendencies, and if disturbed in mid-corner with a bump, can cause snap oversteer. Suspensions with linear springs are more predictable, because the load on them continues, and they are also generally softer, which allows more grip through a corner and less risk of snap oversteer. Generally, almost all OEMs use linear springs.

 

Your / our springs may be constant rate, but your handling improvement did not happen just because the car is sitting .75in lower.
The bump rubbers, on most cars (I have not seen ours) are very engineered to provide increasing sprng rate, as the car compresses the outer springs in a turn.
When you lowered the car, with the same bump stops, they will now come in to play that same .75in sooner, this is what gives you the reduced roll..
I am quite sure that production cars in general do not utilise a total constant spring rate, they would have an unacceptable ride / handling combination.
The Spires site shows 4 springs, one pair have plastic coated coils, so that you will not hear them when they touch together, ie - progressive...

 

Arnoldkay beat me to it.

 

Steering and Handling dynamics aside, I can barely get my *** out of my stock XK. Why would I lower it? Maybe I could just sort of roll out of it?

Ah humor...

 

I promised pics. They're very large.

And of course...the good ol' finger measure. It's 1.5 fingers. Down from 3.5.

 

Thanks for the pics. Nice ride.

 

Beautiful! Enjoy.