I just received an industry email on the following video posted today. It is on evo. Go to Jaguar xkr-s vs mercedes sl63 amg evo track battle. It is a farewell to the xk series and its comparison to a much more costly amg

 

Sadly, I think the only variant where Jaguar got the traction and handling part right has to be the XKRS-GT.

 

Now that I put in a couple of days worth of driving with my '10 XKR I believe that I definitely see why testers find it difficult to control the car at the limits. For some reason, Jaguar believes in using very high spring rates and relatively low sway bar rates, particularly on the rear of the car.

The video clearly shows that the XKR-S rolls too much, the result of not enough roll stiffness in the rear. The lack of tire traction, in all likelihood, is the result of springs that are far too stiff. As the owner of an XJL, XF and XKR, IMHO, all 3 are suspended far too stiffly. I can handle the XF and the XKR stiffness but, the ride of the XJL does not belong in a luxury car. Jaguar appears to subscribe to the philosophy for controlling body roll with spring rates. I couldn't disagree more and the proof is the constant complaints from all track testers for the lack of traction.

I'd love to try much lower spring rates, closer to 300-350lbs/inch on the rear of the XKR in combination with a healthy increase in roll bar rate. I think it would allow for much better tire bite and would produce a car that is less nervous. On the other hand, when the car is driven at less than all-out, it behaves just fine. So, most of the street drivers at cornering speeds below the insanity threshold should not be disappointed. Just that it could be better with such minor changes...

 

How rite you are!!! It wasnt the big nuances that sunk the xk series it was the small minor annoyances, such as spring rate, coupled with a laundry list of other crimes that kept the xk from being a world class competitor. The designers at Jag Corp would have been wise to put you on their R&D team!!

 

Ha...ha...ha... thank you so much for your vote of confidence. The only offer I ever got for a suspension specialist job was when I invited a pro-NASCAR racing driver to drive my street/autocross championship-winning Mustang GT back in the mid 80s. He was speechless at the handling of my GT and kept bugging me to please take the job as his suspension crew chief. Of course, I had better jobs than wrenching for someone else...

BTW - I was running 275 rear springs on the Mustang, less than half of what the XKR has.

 

not to sound like a basis fan boy, but I do not buy convertibles how they preform on the track. I guess could say the BOSS 302 new mustang would smoke them both on the track for 1/3rd of the price.

1. highway/day to performance
2. looks
3. fit/finish
4. fun factor
5. maintenance cost/price

are how I look at what car to buy vs. magazine racing etc

 

There is no question when you have a high torque 500+HP car that you will struggle with traction. That is really the question to ask, how much hp does one need to have fun? Most competitors in this hp range are going to AWD. The actual improvement in 0-60 times is just not there if you just ump the hp and torque.

I am sorry but looking at his laps (and I am by no means a skilled track driver), as a matter of fact all these so called "reporters" they drive totally sloppy. I am absolutely sure that a true race driver would put down a much faster and smoother lap.
These "reporters" are just entertainers and their driving skills are limited to entertain. These cars with such high torque, front engine and rear wheel drive are very difficult to drive fast.

Just look at how smooth Randy Probst is in this video, yes the tire still light up coming out of the turn but more so from torque and NOT from entering the turn too fast and losing grip from accelerating too hard too soon, translating into a sideway drift. As long as you are going for a fast lap IMHO you have to practice until you get a lap without drifting out of a turn.

 

Albert,

I'm all for trying it if I could find someone to make a larger sway bar. What are your thoughts on front and rear spring rates and sway bar sizes?

Thanks,
Max

 

I agree that he does not look like a very skilled driver, I rode with Davy jones and Roberto Guerrero around homestead at speeds much faster than he was going any they had zero wheel spin and total control of the car. I drove the same car and didn't have any of those problems.

One thing a lot of drivers never learn is each car has its own character and have to drive that car the way IT wants to be driven. Some cars you brake earlier, some later, some you can power on through turns others you feather after the apex. Don't get in the XKR-S and start driving it like a Corvette it wont work.

This guy needs some damn driving lessons, he drives like a tool.

 

500hp is truly enormous amount of power that can produce ton of force. Take away all safety features, 95% of the people on the road couldn't handle 350hp. And, that includes car enthusiasts/reporters.

 

Agreed! This guy needs to stick to racing a Prius.

This is much better around a fairly technical and tight track like Seca.. Yes there is wheel spin but 550HP so respect the throttle. One thing I've noticed on the track is in Dynamic Mode the throttle is way too sensitive, and makes it very easy to give it to much throttle.

 

It cant help that Jaguar puts the lowest rated summer tires (PZero) on a car like this. There are several other brands that make a better/stickier tire but I guess Jag has a contract with Pirelli. I personally noticed a huge increase in traction going from the PZero to the Pilot Super Sports, and the 305's fit on the rear no problem. Anyone having traction issues with their XKR-S needs to try this setup. It also helps that things are warming up outside, since tire grip is largely variable by temperatures.

The XKRS-GT uses R-Comp tires, the P-Zero Corsa's, which are much stickier than the crappy regular PZeros. I know it plays into the equation with the addition to the suspension changes on why that car grips better.

 

It is hard to tell from a few takes of his hands on the steering wheel how good a driver he is. First, he did what most testers appear to do these days; he burned tires, tossing the car sideways just to impress viewers. Then, he settled down to do a quick lap where sideways driving should NOT be an option for quick times. In both cars he had the steering wheel spinning during the footages but, we can not be sure if those footages were taken during the actual quick-laps or spliced-in from the "hero-sideways-displays".

As a long timer racing driver, I suggest, that you should practically never have to move your hands from the 3 and 9 position during hot laps. Definitely no free-spinning steering wheel, as was shown. If you do, either the car is a terribly handling one or, the driver is not competent.

I think that we can accept a lot of his criticism, since we have heard the same from nearly all testers of various XKRs and XKR-Ss.

Drive the car at 7/10ths and it will be a great GT. At 10/10th the car, by all common accounts, is a handful with traction as the primary complaints.

As to the spring rates that I would prefer to try; I would probably start with something in the range of 400 front and 325 rear. The front sway bar on my XKR is a full 1.25" in diameter that I think is sufficient for the car. The rear bar I measured at 0.7, could definitely be increased at the time when the spring rate is decreases. Also replacing the bar bushings would be a must. You don't want that heavy body roll that the video was showing as it kills the transitional moves under track conditions.

Personally, where I am right now after having quit racing, I could live with the car as it is for my street driving. But, no doubt, it would be better for me with the lower spring rates (better ride, better road surface compliance, better tire bite).

I was having dinner with my old racing friend a couple of night back and, since I forgot exactly what spring rates I used in my stiffly suspended GT-2 race car, I asked him since he still racing a nearly identical racing car. He said he was using 300 lbs/inch springs on the rear. Of course it is a 2100 lbs race car vs. 4100 lbs for the XKR but, a race car should always be far stiffer than a street car. So, right around 300 that I would like to try first on the XKR. In my previous cars it took several tries of different spring rates to perfect the handling. Given the lack of availability of springs for the XKR this would be a challenge. Not sure what style springs your coil-overs use but, hopefully it uses standard size racing springs that are available in 25 lbs/inch increment for very low prices. Than, you could have a good chance for dialing the suspension, assuming that the proper sway bar could be paired with it. There, I would likely start with a 7/8" bar.

I will agree with anyone claiming that they purchase the car for the looks, comfort, fun factor, etc. Same with me these days. The only thing I would add that when the Jaguar made the XKR-S and dressed it in full battle gear with killer looks it should have also given it the sword that is sharp enough to fight off the challengers. That, Jaguar has failed to do.

Albert

 

Thanks Albert,

My coilovers use Eibach race springs to I can go to any spring rate I like within the range of the dampers.

I was looking at the Sway bar links yesterday and they really look sloppy, and probably a good place to start with urethane bushings or better custom made links.

As far as his driving it just looks irresponsible and "showy" even the Top Gear guys when driving the XKR seriously didn't do that. I don't know I've driven them stock over 7/10s on a track and if you're careful with the throttle I only got minimal oversteer, but I tend to like oversteer as I can control the car with the throttle and steering.

 

Great news. Tempting for me to go for coilovers.

Yes, I just poked at the sway bar bushings and they appeared to be fairly soft. Polyurethane bushings would definitely help. So would the more solid end-link. With those two minor components, you should be able to feel the difference. As I looked from one side only at the bar, the bushing change on the rear should not be all that difficult. Not sure about the front bushing locations.

 

Looks like Jethro has been to a few well established places: EVO, Car and Driver, and Car Magazine and tested many high end exotics sports cars including the Ruf Yellow Bird. That being said, I remember him testing the 2010 XKR75 and I thought he said that car was a great handling car. You would think the XKRS would be even a better handling car. He also crashed a Ferrari FF during launch day. Oops!

What I like to see is XKRS-GT vs SLS Black Series.

 

Worthless review showing and describing performance that bears no resemblance to what an actual owner would experience at a track day. The difference is the EVO driver uses his skill to exceed the tire's grip rather than optimize it. He's driving with Stability and Traction Controls turned off to allow his drifting and tire smoking antics. I turn them off to allow for the "minimal" tire slip that enhances cornering speed, steering with the throttle, and exit speed as conditions warrant.

I don't believe the car exhibits too much body roll at all. Some street cars with even excessive body roll handle incredibly well on track, and BMW has certainly made a number of them. It depends on the suspension's design, and it's ability to maintain optimal tire contact patch under cornering loads. It also depends on the dampers ability to control the body's transition as it leans over. I can only speak for the stock XKR I track, and it has about as neutral handling as you could hope for, meaning that both the spring and sway bar ratios are near ideal front to rear. Stiffening one end or the other would throw off that balance, and a particular driver's preference might desire that. Stiffening either springs or bars at both ends could be done and still maintain the car's neutral balance, but I'm not sure that's the first step to improve handling or grip.

My experience tells me that an improvement in damper valving will pay dividends on the street and track, and become even more critical as the suspension is stiffened with springs or bars. This will have a larger impact on maintaining tire contact with the pavement than changes to springs and bars. The active dampers receive inputs from the steering wheel, and as you turn into a corner they stiffen to prevent body roll. That also reduces their ability to modulate the wheels motion as it tries to follow the road's uneven surface, and would have a similar negative effect as low profile tires with stiff sidewalls. The objective is to maintain tire contact with the road, and focusing on eradicating minor body roll may not do that.

Albert, what are the stock spring rates that you used to formulate your suggested rates?

Max, the new dampers in your coilovers will hopefully make an improvement. I'd first swap out springs to change rates as you monitor that effect and impact to street ride, and then finish your tuning with bars "if" needed. And at that point an adjustible rear bar is preferred to fine-tune for different tracks and use.

Here's a video of my stock XKR on track. You can tell when it is cornering on the limits of adhesion as the rear dances around a little, and note the minimal body lean.
BruceLCMT092513 - YouTube

Bruce

 

Bruce,

The coilovers and improved dampening have made a huge difference, the car feels very planted but you can feel the rear step or even jump a bit out a little over rough areas but its controllable and not scary. You can definitely tell the dampers are working overtime keeping the car planted. The car feels very stiffly sprung, much more than a XKR-S even though the spring rates are close. I need to push it hard on a track to see where it is close to 100%. Keep in mind its also lowered 1.25 inches so body roll is minimized.

Looking at the mounting of the rear sway bar looks a bit sloppy and the link has a lot of play. I think a better link will actually allow the sway bar to "work"


I'm sticking to this guy can't freaking drive, why is he a tester? Looks like hes been fired buy a few magazines.

 

Bruce

The spring rates I referenced were the ones posted by MaximA. I don't have the time right now to find the post but, if I remember correctly the front stock springs were softer than the rears and when I converted the spring rate numbers it come to way over 500 lbs/inch for the rear.

While I used stiffer springs on the rear of my mid-engined formula racing car, it is nearly unheard of (by me) for a front engined car. It is almost a rule-of-thumb that the rear springs have to be softer than the front springs.

As to the body roll; the video clearly shows too much body roll with the XKR-S. I would not use your personal track video as a reliable reference as you even stated when you first posted that video that you were far from driving at 10/10ths. As a matter of fact, you seem to be very disciplined at not driving near the edge and thus, not risking a crash that may happen at 10/10th. Judging from the way the car that follows you was driven, you were likely not even exceeding 7/10th in that video. So, of course, you would not have much body roll or traction problems. When these guys are going for the hot lap, they really are supposed to push the car right to the edge.

When I drove my XKR around those nice corners at far less than even 7/10th, yes, there was no body roll and the car felt just fine. But, while we may criticize this particular test driver, it is difficult NOT to pay attention to every single track driver, Randy Pobst included (he declared the XKR-S the car that was most likely to spin on the race track) who criticizes the lack of traction near the limit for the XKR variants. As much as I know about suspension, I still believe that the lack of traction goes hand-in-hand with overly stiff suspension setup. The XKR-S GT appears to invalidate my theory as it is judged finally to be well handling by the testers but, remember that the GT is using R compound tires which will increase traction by a great deal just by itself. It would be an automatic 3-5 sec/lap improvement at places, like Laguna Seca.

 

I'm going to try to find aftermarket bushings, and see if I can get the end links remade with something that doesn't resemble a straw. Thats a fairly decent sized bar in the back but the with slop in the end links of course they won't work very well.