XKR Suspension notes and discussion (long)
#1
03-24-2014, 08:45 PM
XKR Suspension notes and discussion (long)
Discussion Subject: Why XKR variants lack traction on the racetracks in the hands of qualified test drivers? (Street-only drivers, no need to pay attention)
Most pro-test drivers complain for a lack of traction and twitchy handling when exiting corners at racing speeds.
Disclaimer: All conclusions are for my own use and represent no recommendations for anyone to follow.
So, this morning I got down and dirty under and into the XKR and took a bunch of (about 20) different measurements on the various suspension components. Then, I entered those values into software to calculate existing sway bar rates and the desired rear spring rates.
Software:
I used 3 different suspension software to calculate spring and sway bar values. Unnervingly, the 3 provided different answers with the same exact parameters entered. So, the calculated values I am listing below is from my trusted source, my race car sponsor’s proprietary software that reflects decades of racing and high performance driving as well as shop ownership experiences. I used that software to set up many of my own street and of race cars and I know that those values work.
Front anti-sway bar.
Installed Bar diameter = 1.25 inches. Very large diameter bar but, it comes with long, 17” side arms that soften the bar’s torsion effects considerably. The sway bar link’s location on the lower suspension “A”-arms are almost the same for the front and rear bars, about 3.5” from the outer bushings.
Calculated Front Sway Bar Rate = 555 lbs/inch.
Wheel Rate – 355 lbs/inch (takes into account the “lever” effect of the suspension “A” arm)
Rear anti-sway bar.
Installed Bar diameter = 0.71 inches. Much smaller diameter bar than up front but, it comes with much shorter, 9” side arms.
Calculated Bar Rate = 204 lbs/inch
Wheel Rate =132 lbs/inch
Sway Bar Conclusions:
The front sway bar rates appears perfectly sufficient for the weight of the car. The rear bar rate, however, is insufficient to control the body roll under maximum cornering loads. Installing a 7/8” bar would result in 471/306 lbs/inch combination that maybe too much but, if the bar’s arm length is extended (adjustable) an other 1.5” the results change to 348/226. That would be my starting value. Reminder: it would have to be used in combination with softer rear springs, otherwise too much oversteer (dangerous) could result.
Sway Bar Bushings and shimming:
The bushings appear to be hard rubber. Some benefit could be gained by changing them to polyurethane that compresses even less.
As to shimming the sway bar, my sponsor who raced all his long life and owned a racing shop for long decades, was just as clueless as I was when I heard Spires’ suggestion. He also agreed that any shimming equally on both sides would have zero effect on the operation of the bar.
XKR rear spring rates
Some cars, like the new Corvette Stingray visibly squat at their rear-end considerably under full acceleration from low speeds. Some “squat” can have a very beneficial role in track racing as it helps to transfer weight to the rear tires for improved traction under hard acceleration. Look at rear-end squat on drag racers.
What I could see from the software values that the use of high rate, 544 lbs/inch (calculated from many inputs) rear springs for the XKR is justified. My original “gut feel”, was, since I do not have any experience setting up cars that weight 4000 lbs, that I would start with much softer, 350 lbs rear springs. The difference between my numbers and the XKR’s numbers comes down to the available shock piston travel specs. When I entered into the software an additional 1.0 inch of available shock travel (3.5”), the recommended rear spring rates dropped from 544 to near my recommendation, to 382 lbs. Jaguar appears to calculate with a 2.5” maximum shock piston travel, which seems to be close to what I actually measured on the car (with great difficulties). However, in my experiences, factories tend to spec cars to accommodate the worst-case conditions. Yes, if you run over a 2x4 on the freeway the 544 lbs springs+damper valve settings combo should prevent the dampers and the suspension from bottoming out. That is an important consideration as if you hit that major bump in the middle of a fast corner and the dampers/springs do bottom out, the rear spring rates rise to infinite values (become basically a solid suspension at such point) and the rear of the car will violently loose traction and spin around while car flies off the road, looking for a big tree to hit.
But, in real world street and race driving conditions we can generally make do with softer springs and still not bottom out anywhere (unless you hit the 2x4, which is why I tend to leave some cut-down bump rubber in the lowered shock setup.) To show what I’m saying, if I enter the parameters for my 2600 lbs RX-7 the software recommends 341 lbs rear springs. I am running 275 lbs on a lowered suspension and never bottomed a single time since I have the car for 9 years now. I never bottomed my previous RX either that I raced for years with the same rate springs/dampers. I do have great traction out of the corners and with the adjustable-arm 0.75” rear roll bar set on stiff, completely flat cornering. What I see with Jaguar is a conservative spring setting that is quite similar to how manufacturers set their engine operating parameters to safe values, so the engine won’t scatter during a worst-case-operating scenario. If you are willing to go out on the limb a bit with an after-market engine tune, you have seen the gains to be made on engine power and similar gains are waiting with suspension tuning. My starting values would be 375 lbs rear springs and a 7/8 rear swaybar with adjustable side arms. If the car bottoms, go up in the spring/damper rates. When I raced, I used to lower my coil-over ride height to where the chassis would just bottom at the worst dip on the racetrack, then raise it 0.25”.
Lowered suspensions:
Stock (non-lowered) damper travel = 2.5”.
If such stock car is lowered 1.3” with springs only, the available damper travel is reduced to 1.2”. Such scenario requires the installation of extra stiff springs that do not compress beyond that reduced travel. In our case the 544 stock springs would have to be changed to 1100 lbs/inch to not exceed 1.2” spring travel at the XKR’s rear weights. Of course damper valving can also be tightened to control compression travel. The ideal scenario when lowering a car is to also install new dampers with shorter body and a close-to-stock piston travel. If only installing the lowering springs and cutting the piston travel drastically, the needed ultra stiff springs and damper rates can make the car basically jump and skip over pavement irregularities encountered during hard cornering. In other words the springs/dampers will be unable to dampen the ride over surface irregularities. The resulting traction loss, coming from the very sudden up/down movements of the car’s mass, will make the car very scary and cause unpredictably changing tire traction pressures against the pavement. It looks very suspicious to me as the very reason why testers find the XKR(S) handling so twitchy.
Not sure what are the electronic adjustment parameters on the XKR dampers. In my case when I ran my street cars on the track I always selected dampers which were at least rebound adjustable. That allowed me to have an acceptable street ride on full soft settings and tight track handling on near full stiff settings. Of course, “full soft” is relative as my suspension in that mode was/is pretty stiff, still. I still have to drive my XKR more to encounter some surface bumps at high speeds to evaluate the degree of damper rebound control. If a car is allowed to rebounds too fast after the damper/spring compression from hitting a bump, the mass of the car will bounce upwards, lessening the tire pressure against the pavement, which can also cause the same dangerously twitchy sensation.
Tires
A tire thread will increasingly slant from horizontal as camber increases. For a 285 wide rear tire the amount of slant is 0.175” per degree of camber. Thus, a 3 degree negative camber will result in the tire’s outer thread-edge being 0.525“ higher than the inside tire edge. In practice the tire will deform enough to plant the entire thread surface on the pavement but, the inside tire edge will have lot higher pressures (and deformation) against the pavement when compared to the outer edge. That will result in increased heat for the inside edge as well as increased tire wear under regular driving conditions.
While for most spirited street driving 1 – 1.2 degree negative camber is ideal for a 285/30/20 tire, on race tracks more, around 2 degrees could work well. As an extreme example; NASCAR teams that use 10” wheels run as much as 10 degrees negative camber on high speed ovals on their outside wheels and 8 degree positive camber on the inside wheels. Of course, they use high aspect ratio racing tires with tall sidewalls that tend to deform a lot more than our low, 30-aspect-ratio rear tires.
As to what changes would I make to my XKR’s suspension? The answer is; probably not much. I do not intend to track the car and the availability of sway bars is next to nothing and even if sourcing one the installation is a real bear. With the wheel spacers installed I find the factory handling quite fun and would have no problem going VERY fast with this car on my local winding roads, if so desired. Any extra speed above the present capabilities could only be realized under all out, 10/10th track conditions.
More
I’ve just finished working on my car for today, having painted my brake calipers and installed 20mm front spacers and 15mm rear spacers. During the test drive I could definitely tell the extra 40/30 mm track width while cornering. I made sure that I washed up nicely and changed into clean clothing before taking that test drive. Then, just yards from my driveway a young woman flagged me down, telling me that her horse had just thrown her. The horse ran away. I looked at her condition (no bleeding) but plenty filthy for landing in some muck and was ready to recommend that she kept walking (my sense of helpfulness only goes so far…) She must have read my mind as she yanked the door open and threw herself into the passenger seat of my ultra-clean XKR with whites stitching on the seat, muck and all, demanding that we go horse-hunting in a Jaguar…. We did find her horse about a mile up the road, she exited without thanks and my car needed some serious interior cleaning. Lessons learned…. &$%#&????
Edit: Pictures show painted front calipers and car with 20mm front and 15mm rear wheel spacers.
Most pro-test drivers complain for a lack of traction and twitchy handling when exiting corners at racing speeds.
Disclaimer: All conclusions are for my own use and represent no recommendations for anyone to follow.
So, this morning I got down and dirty under and into the XKR and took a bunch of (about 20) different measurements on the various suspension components. Then, I entered those values into software to calculate existing sway bar rates and the desired rear spring rates.
Software:
I used 3 different suspension software to calculate spring and sway bar values. Unnervingly, the 3 provided different answers with the same exact parameters entered. So, the calculated values I am listing below is from my trusted source, my race car sponsor’s proprietary software that reflects decades of racing and high performance driving as well as shop ownership experiences. I used that software to set up many of my own street and of race cars and I know that those values work.
Front anti-sway bar.
Installed Bar diameter = 1.25 inches. Very large diameter bar but, it comes with long, 17” side arms that soften the bar’s torsion effects considerably. The sway bar link’s location on the lower suspension “A”-arms are almost the same for the front and rear bars, about 3.5” from the outer bushings.
Calculated Front Sway Bar Rate = 555 lbs/inch.
Wheel Rate – 355 lbs/inch (takes into account the “lever” effect of the suspension “A” arm)
Rear anti-sway bar.
Installed Bar diameter = 0.71 inches. Much smaller diameter bar than up front but, it comes with much shorter, 9” side arms.
Calculated Bar Rate = 204 lbs/inch
Wheel Rate =132 lbs/inch
Sway Bar Conclusions:
The front sway bar rates appears perfectly sufficient for the weight of the car. The rear bar rate, however, is insufficient to control the body roll under maximum cornering loads. Installing a 7/8” bar would result in 471/306 lbs/inch combination that maybe too much but, if the bar’s arm length is extended (adjustable) an other 1.5” the results change to 348/226. That would be my starting value. Reminder: it would have to be used in combination with softer rear springs, otherwise too much oversteer (dangerous) could result.
Sway Bar Bushings and shimming:
The bushings appear to be hard rubber. Some benefit could be gained by changing them to polyurethane that compresses even less.
As to shimming the sway bar, my sponsor who raced all his long life and owned a racing shop for long decades, was just as clueless as I was when I heard Spires’ suggestion. He also agreed that any shimming equally on both sides would have zero effect on the operation of the bar.
XKR rear spring rates
Some cars, like the new Corvette Stingray visibly squat at their rear-end considerably under full acceleration from low speeds. Some “squat” can have a very beneficial role in track racing as it helps to transfer weight to the rear tires for improved traction under hard acceleration. Look at rear-end squat on drag racers.
What I could see from the software values that the use of high rate, 544 lbs/inch (calculated from many inputs) rear springs for the XKR is justified. My original “gut feel”, was, since I do not have any experience setting up cars that weight 4000 lbs, that I would start with much softer, 350 lbs rear springs. The difference between my numbers and the XKR’s numbers comes down to the available shock piston travel specs. When I entered into the software an additional 1.0 inch of available shock travel (3.5”), the recommended rear spring rates dropped from 544 to near my recommendation, to 382 lbs. Jaguar appears to calculate with a 2.5” maximum shock piston travel, which seems to be close to what I actually measured on the car (with great difficulties). However, in my experiences, factories tend to spec cars to accommodate the worst-case conditions. Yes, if you run over a 2x4 on the freeway the 544 lbs springs+damper valve settings combo should prevent the dampers and the suspension from bottoming out. That is an important consideration as if you hit that major bump in the middle of a fast corner and the dampers/springs do bottom out, the rear spring rates rise to infinite values (become basically a solid suspension at such point) and the rear of the car will violently loose traction and spin around while car flies off the road, looking for a big tree to hit.
But, in real world street and race driving conditions we can generally make do with softer springs and still not bottom out anywhere (unless you hit the 2x4, which is why I tend to leave some cut-down bump rubber in the lowered shock setup.) To show what I’m saying, if I enter the parameters for my 2600 lbs RX-7 the software recommends 341 lbs rear springs. I am running 275 lbs on a lowered suspension and never bottomed a single time since I have the car for 9 years now. I never bottomed my previous RX either that I raced for years with the same rate springs/dampers. I do have great traction out of the corners and with the adjustable-arm 0.75” rear roll bar set on stiff, completely flat cornering. What I see with Jaguar is a conservative spring setting that is quite similar to how manufacturers set their engine operating parameters to safe values, so the engine won’t scatter during a worst-case-operating scenario. If you are willing to go out on the limb a bit with an after-market engine tune, you have seen the gains to be made on engine power and similar gains are waiting with suspension tuning. My starting values would be 375 lbs rear springs and a 7/8 rear swaybar with adjustable side arms. If the car bottoms, go up in the spring/damper rates. When I raced, I used to lower my coil-over ride height to where the chassis would just bottom at the worst dip on the racetrack, then raise it 0.25”.
Lowered suspensions:
Stock (non-lowered) damper travel = 2.5”.
If such stock car is lowered 1.3” with springs only, the available damper travel is reduced to 1.2”. Such scenario requires the installation of extra stiff springs that do not compress beyond that reduced travel. In our case the 544 stock springs would have to be changed to 1100 lbs/inch to not exceed 1.2” spring travel at the XKR’s rear weights. Of course damper valving can also be tightened to control compression travel. The ideal scenario when lowering a car is to also install new dampers with shorter body and a close-to-stock piston travel. If only installing the lowering springs and cutting the piston travel drastically, the needed ultra stiff springs and damper rates can make the car basically jump and skip over pavement irregularities encountered during hard cornering. In other words the springs/dampers will be unable to dampen the ride over surface irregularities. The resulting traction loss, coming from the very sudden up/down movements of the car’s mass, will make the car very scary and cause unpredictably changing tire traction pressures against the pavement. It looks very suspicious to me as the very reason why testers find the XKR(S) handling so twitchy.
Not sure what are the electronic adjustment parameters on the XKR dampers. In my case when I ran my street cars on the track I always selected dampers which were at least rebound adjustable. That allowed me to have an acceptable street ride on full soft settings and tight track handling on near full stiff settings. Of course, “full soft” is relative as my suspension in that mode was/is pretty stiff, still. I still have to drive my XKR more to encounter some surface bumps at high speeds to evaluate the degree of damper rebound control. If a car is allowed to rebounds too fast after the damper/spring compression from hitting a bump, the mass of the car will bounce upwards, lessening the tire pressure against the pavement, which can also cause the same dangerously twitchy sensation.
Tires
A tire thread will increasingly slant from horizontal as camber increases. For a 285 wide rear tire the amount of slant is 0.175” per degree of camber. Thus, a 3 degree negative camber will result in the tire’s outer thread-edge being 0.525“ higher than the inside tire edge. In practice the tire will deform enough to plant the entire thread surface on the pavement but, the inside tire edge will have lot higher pressures (and deformation) against the pavement when compared to the outer edge. That will result in increased heat for the inside edge as well as increased tire wear under regular driving conditions.
While for most spirited street driving 1 – 1.2 degree negative camber is ideal for a 285/30/20 tire, on race tracks more, around 2 degrees could work well. As an extreme example; NASCAR teams that use 10” wheels run as much as 10 degrees negative camber on high speed ovals on their outside wheels and 8 degree positive camber on the inside wheels. Of course, they use high aspect ratio racing tires with tall sidewalls that tend to deform a lot more than our low, 30-aspect-ratio rear tires.
As to what changes would I make to my XKR’s suspension? The answer is; probably not much. I do not intend to track the car and the availability of sway bars is next to nothing and even if sourcing one the installation is a real bear. With the wheel spacers installed I find the factory handling quite fun and would have no problem going VERY fast with this car on my local winding roads, if so desired. Any extra speed above the present capabilities could only be realized under all out, 10/10th track conditions.
More
I’ve just finished working on my car for today, having painted my brake calipers and installed 20mm front spacers and 15mm rear spacers. During the test drive I could definitely tell the extra 40/30 mm track width while cornering. I made sure that I washed up nicely and changed into clean clothing before taking that test drive. Then, just yards from my driveway a young woman flagged me down, telling me that her horse had just thrown her. The horse ran away. I looked at her condition (no bleeding) but plenty filthy for landing in some muck and was ready to recommend that she kept walking (my sense of helpfulness only goes so far…) She must have read my mind as she yanked the door open and threw herself into the passenger seat of my ultra-clean XKR with whites stitching on the seat, muck and all, demanding that we go horse-hunting in a Jaguar…. We did find her horse about a mile up the road, she exited without thanks and my car needed some serious interior cleaning. Lessons learned…. &$%#&????
Edit: Pictures show painted front calipers and car with 20mm front and 15mm rear wheel spacers.
Last edited by axr6; 03-24-2014 at 09:13 PM.
#2
03-24-2014, 09:13 PM
Veteran Member
consider both rear camber and toe.
there is nothing like the old live axle for putting down power coming out of a turn because they have zero toe and zero camber.
i am running a hair greater than zero and it cured stability problems in slush ... slush is like pavement ... you just reach the limits faster
there is nothing like the old live axle for putting down power coming out of a turn because they have zero toe and zero camber.
i am running a hair greater than zero and it cured stability problems in slush ... slush is like pavement ... you just reach the limits faster
#3
03-24-2014, 09:15 PM
Veteran Member
She must have read my mind as she yanked the door open and threw herself into the passenger seat of my ultra-clean XKR with whites stitching on the seat, muck and all, demanding that we go horse-hunting in a Jaguar…. We did find her horse about a mile up the road, she exited without thanks and my car needed some serious interior cleaning. Lessons learned…. &$%#&????
#4
03-24-2014, 09:29 PM
consider both rear camber and toe.
there is nothing like the old live axle for putting down power coming out of a turn because they have zero toe and zero camber.
i am running a hair greater than zero and it cured stability problems in slush ... slush is like pavement ... you just reach the limits faster
there is nothing like the old live axle for putting down power coming out of a turn because they have zero toe and zero camber.
i am running a hair greater than zero and it cured stability problems in slush ... slush is like pavement ... you just reach the limits faster
Rear cambers: -1.2 and -1.5. Not too bad but, i will likely bring the rear toe back to likely 0 to 1/16 IN. Front toe will come back to 0.
Will set both front cambers to 1.5 (narrower front tires need more camber than wider rears). Rear camber is non-adjustable (thanks Jaguar).
#5
03-25-2014, 11:12 AM
Veteran Member
Albert,
Thank you for taking the time to put all of this together.
So running a lowered suspension at around 1.3 inches which is roughly where I am the higher rear spring rates and stiffer dampers make sense. At that height should the rear springs still be stiffer than the front? The compression is also dampers but I have no idea how much due to the Adaptive dynamics.
So looking at your information for a lowered car, it seems as though I'm pretty close other then the 1100LBS rear spring rate which I'm a bit over 600 plus stiffer dampers. My car has hit the rear bump stops once and that was in a construction zone going over some VERY rough sections at highway speeds. On the track it hasn't come close.
As far as alignment, if I could get the rear even at -1.7ish I'd be happy right now I have one at -1.7 and the other at -2.0 with my fronts at -1.7.
Sorry if I read this to quickly I'm trying to meet a deadline and recover from the advanced driving class.. Man I run 50 miles a week and am fairly fit, but nearly 6 hours, 4 straight at race speeds in a car wears you out! I've never had a track day physically kick my butt before.
Thank you for taking the time to put all of this together.
So running a lowered suspension at around 1.3 inches which is roughly where I am the higher rear spring rates and stiffer dampers make sense. At that height should the rear springs still be stiffer than the front? The compression is also dampers but I have no idea how much due to the Adaptive dynamics.
So looking at your information for a lowered car, it seems as though I'm pretty close other then the 1100LBS rear spring rate which I'm a bit over 600 plus stiffer dampers. My car has hit the rear bump stops once and that was in a construction zone going over some VERY rough sections at highway speeds. On the track it hasn't come close.
As far as alignment, if I could get the rear even at -1.7ish I'd be happy right now I have one at -1.7 and the other at -2.0 with my fronts at -1.7.
Sorry if I read this to quickly I'm trying to meet a deadline and recover from the advanced driving class.. Man I run 50 miles a week and am fairly fit, but nearly 6 hours, 4 straight at race speeds in a car wears you out! I've never had a track day physically kick my butt before.
#6
03-25-2014, 03:26 PM
Albert,
Thank you for taking the time to put all of this together.
So running a lowered suspension at around 1.3 inches which is roughly where I am the higher rear spring rates and stiffer dampers make sense. At that height should the rear springs still be stiffer than the front? The compression is also dampers but I have no idea how much due to the Adaptive dynamics.
So looking at your information for a lowered car, it seems as though I'm pretty close other then the 1100LBS rear spring rate which I'm a bit over 600 plus stiffer dampers. My car has hit the rear bump stops once and that was in a construction zone going over some VERY rough sections at highway speeds. On the track it hasn't come close.
As far as alignment, if I could get the rear even at -1.7ish I'd be happy right now I have one at -1.7 and the other at -2.0 with my fronts at -1.7.
Sorry if I read this to quickly I'm trying to meet a deadline and recover from the advanced driving class.. Man I run 50 miles a week and am fairly fit, but nearly 6 hours, 4 straight at race speeds in a car wears you out! I've never had a track day physically kick my butt before.
Thank you for taking the time to put all of this together.
So running a lowered suspension at around 1.3 inches which is roughly where I am the higher rear spring rates and stiffer dampers make sense. At that height should the rear springs still be stiffer than the front? The compression is also dampers but I have no idea how much due to the Adaptive dynamics.
So looking at your information for a lowered car, it seems as though I'm pretty close other then the 1100LBS rear spring rate which I'm a bit over 600 plus stiffer dampers. My car has hit the rear bump stops once and that was in a construction zone going over some VERY rough sections at highway speeds. On the track it hasn't come close.
As far as alignment, if I could get the rear even at -1.7ish I'd be happy right now I have one at -1.7 and the other at -2.0 with my fronts at -1.7.
Sorry if I read this to quickly I'm trying to meet a deadline and recover from the advanced driving class.. Man I run 50 miles a week and am fairly fit, but nearly 6 hours, 4 straight at race speeds in a car wears you out! I've never had a track day physically kick my butt before.
Again, for optimum track suspending, think of the Stingray; I do not know the spring rates it uses (transverse fiberglass springs) but, many pictures I have seen clearly show the car accelerating out of track corners, with a definite rear-squat stance. There is serious weight transfer taking place onto those rear tires. I would bet money that it has rather soft rear springs. Would not be surprised if the value would be equivalent to coil spring rates of 300-325 lbs/inch. The car is super planted in corners, has tons of traction accelerating out of corners and is predictable, which are some of the obvious reasons that it puts a shocking 10 seconds/lap at VIR and 4.5 sec/lap at Laguna Seca on the XKR-S which has 90 more HP.
An other telling bit about the Stingray's spring rates that when you set the dampers into "tour" mode, the car rides like a Cadillac. That is only possible if there are some soft spring rates used in combo with adjustable magnetic dampers and sway bars. The XKR, due to the stiff springs, will never ride like a Cadillac, no matter what rates the electronic damper selects. Needless to say, I prefer the Stingray philosophy for providing a super comfortable cruise to the race track but, with a quick change in the damper settings, it becomes a supercar-killer on the track.
Yes, race driving can be VERY tiring. When watched on TV it appears that those race cars are just out for a Sunday cruise....ha...ha....ha.... Nothing is further from the truth. The more tire adhesion a race car has the more work it is to drive. My formula car with dual-wing downforce was a lot more work than my GT car. The arms get tired from wrestling the small steering wheel and your body gets worn out from all the G-forces in the corners.
Last week a few of us went over to the local indoor-go kart track and I ran 3 consecutive sessions, 66 laps altogether. The next few days saw two large black and blue bruises on my back where the racing seat side-bolster pressed into it, as well as ultra tight lower arms from wresting the little thing around those tight corners. Yes, it is HARD work to race, despite the appearances.
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MaximA (03-26-2014)
#7
03-26-2014, 08:13 AM
Veteran Member
Yes track days at full speed session after session are tiring to say the least, I'm just now feeling back to normal... I can only imagine driving a high downforce car for that amount of time. One reason I'm sticking to GTs for now, although I'm seriously considering a Caterham R500.
I looked around the internet and can't find C7 spring rates but found the C6 rates which surprisingly are much stiffer than I expected as the cars are rather lite for production cars. I ran much lighter springs on my C4 with coilovers but can't remember what the exact rates were. I'll ask some of my friends that track their C7s if they know the rates.
C6 Z06, 531/782
C6 T1 Kit, 582/850
C6 Z51, 526/645
C6 Base, 420/657
I looked around the internet and can't find C7 spring rates but found the C6 rates which surprisingly are much stiffer than I expected as the cars are rather lite for production cars. I ran much lighter springs on my C4 with coilovers but can't remember what the exact rates were. I'll ask some of my friends that track their C7s if they know the rates.
C6 Z06, 531/782
C6 T1 Kit, 582/850
C6 Z51, 526/645
C6 Base, 420/657
The following users liked this post:
axr6 (03-26-2014)
Trending Topics
#8
03-26-2014, 08:54 AM
Yes track days at full speed session after session are tiring to say the least, I'm just now feeling back to normal... I can only imagine driving a high downforce car for that amount of time. One reason I'm sticking to GTs for now, although I'm seriously considering a Caterham R500.
I looked around the internet and can't find C7 spring rates but found the C6 rates which surprisingly are much stiffer than I expected as the cars are rather lite for production cars. I ran much lighter springs on my C4 with coilovers but can't remember what the exact rates were. I'll ask some of my friends that track their C7s if they know the rates.
C6 Z06, 531/782
C6 T1 Kit, 582/850
C6 Z51, 526/645
C6 Base, 420/657
I looked around the internet and can't find C7 spring rates but found the C6 rates which surprisingly are much stiffer than I expected as the cars are rather lite for production cars. I ran much lighter springs on my C4 with coilovers but can't remember what the exact rates were. I'll ask some of my friends that track their C7s if they know the rates.
C6 Z06, 531/782
C6 T1 Kit, 582/850
C6 Z51, 526/645
C6 Base, 420/657
Remember when in 1993 I test drove the RX-7 R1 model that I eventually purchased and raced. With the salesman next to me I crossed over the local railroad crossings at normal, slow speeds and the suspension banged hard as if I hit a 4x4 at full speeds. Shocked, I told the salesman that something broke in the suspension and we needed to pull over. He laughed and said that this was "normal" for the R1 (track version). Definitely the stiffest stock suspension I have ever experienced.
Yes, the stock R1 had non-adjustable dampers, set to full racing stiff. The car was a total pain over regular road surfaces, shaking every filling loose from your teeth. A big reason why Mazda did not sell many of them. When I changed to adjustable dampers, what a difference it made. Still stiff but, a LOT more liveable on the streets. On the other hand, the R1 ran away with all stock car competition titles for years. Nothing, no Porsche, Ferrari or anything could touch it on tracks or in autocross. With my mods, double the stock power, killer-lowered suspension, still very few cars would keep up with it despite the fact that it is 21 years old.
#9
03-26-2014, 10:41 AM
Veteran Member
Those are all stock spring rates but I'm sure the wheel rate is very different due to the positioning of the transverse leaf spring.
I have a friend that runs some of the track day events and has a C5 with coilovers. I'll ping him to see what kind of rates hes running and see if he can get some more information on the C7 rates.
I have a friend that runs some of the track day events and has a C5 with coilovers. I'll ping him to see what kind of rates hes running and see if he can get some more information on the C7 rates.
#10
03-26-2014, 10:49 AM
Veteran Member
#11
03-30-2014, 06:57 PM
Veteran Member
I do not know if you have read this article yet, but according to Ollie Marriage, the springs on the GT are 68 percent stiffer in the front and 25 percent stiffer in the rear.
First drive: Jaguar XKR-S GT - BBC Top Gear
First drive: Jaguar XKR-S GT - BBC Top Gear
#12
03-31-2014, 12:27 AM
I do not know if you have read this article yet, but according to Ollie Marriage, the springs on the GT are 68 percent stiffer in the front and 25 percent stiffer in the rear.
First drive: Jaguar XKR-S GT - BBC Top Gear
First drive: Jaguar XKR-S GT - BBC Top Gear
"Special mention to the steering, too. It's not super-precise and brimming with jiggly feedback, but after a while you realize how well synced it is to the chassis, how you know exactly what the car is up to."
That "jiggly steering feedback" drives me bunkers in my XJL, I simply HATE it. To me it is most important that a steering wheel be "calm" in my hands regardless how stiff the suspension is. A jiggly or vibrating wheel disturbs my concentration that I need when driving fast.
#13
03-31-2014, 06:33 AM
Veteran Member
Those high rates also make bring the need for a lot or rebound damping which the stock XKR lacks IMO. My car stock was literally frightening at 150MPH. One bump and the rear would bounce way to much.
The XKR-S and the cars with the Dynamic Pack didn't have to deal with this. With the coilovers the cars perfect for me, although some adjustability in the sway bars would be nice.
The XKR-S and the cars with the Dynamic Pack didn't have to deal with this. With the coilovers the cars perfect for me, although some adjustability in the sway bars would be nice.
#14
03-31-2014, 10:57 AM
Those high rates also make bring the need for a lot or rebound damping which the stock XKR lacks IMO. My car stock was literally frightening at 150MPH. One bump and the rear would bounce way to much.
The XKR-S and the cars with the Dynamic Pack didn't have to deal with this. With the coilovers the cars perfect for me, although some adjustability in the sway bars would be nice.
The XKR-S and the cars with the Dynamic Pack didn't have to deal with this. With the coilovers the cars perfect for me, although some adjustability in the sway bars would be nice.
One thing I always demanded or built-into from my cars were: "stupid foolproof handling". That meant that anybody could just get into it and drive them fast with full confidence. I'm convinced that my GT race car that I won so many Championships with could have made a winner out of just about any average racing driver.
I generally avoided cars that were twitchy and required special conditions to drive at 10/10th (Porsche 911 or, even my mid-engined Lambo). When you go all out on a track or street the slightest lack of confidence in the car's handling will (should) slow you down. As an Engineer, those steering wheel jigglinesses drive me up the wall, draw my attention to what I perceive is an undesired behavior and keep me from 100 percent concentrating on the task ahead.
All 3 of my present Jags drive with "some" of that jiggliness; with the XF and XKR I can live with it, with the XJL it is plain freaking irritating, particularly when you expect a luxury smooth ride from a huge luxury limousine. Not sure why Jaguar prefers such irritating steering/chassis feed back. On the other hand, I have read several posters on these forums who see it as "good road feel". IMO, you do not want to be kept busy by the car telegraphing and amplifying every single ant that you have run over on perfectly smooth roads.
Not sure where the future takes me with my XKR. At this time I am happy to have the car as it is, a spectacular GT car with decent, moderate handling capabilities. I could improve on it (I never had a "perfect" stock car) but, not sure that I'm going to have the urge to do so. The way I look at the XKR is that it is good enough to where a race-qualified driver will more than keep up with some superior track machines driven by the average fast drivers. I think that the best "aftermarket" mods one can aspire to is to take race driving training and practice them enough to keep up with the skills. Practice makes Champions....
#15
03-31-2014, 11:12 AM
Veteran Member
#16
03-31-2014, 11:24 AM
For spirited canyon carving, I like the effect of lowering springs and spacers. But beyond that I am unlikely to go with this car.
Ditto on track exhaustion. For me, it's not primarily physical, it's mental. Hours of being ultra sharp at speeds double or more of normal driving, running 6 inches from retaining walls, etc. does a number on my central nervous system. I always come back toasted, doing 60 in the right hand lane, then collapse in a happy heap at home...
Ditto on track exhaustion. For me, it's not primarily physical, it's mental. Hours of being ultra sharp at speeds double or more of normal driving, running 6 inches from retaining walls, etc. does a number on my central nervous system. I always come back toasted, doing 60 in the right hand lane, then collapse in a happy heap at home...
#17
03-31-2014, 11:40 AM
Veteran Member
Doesn't matter how well a car drives, how good it handles, whether it's a Jaguar or LaFerrari, i want a relaxed steering wheel.
My XF has been fine, but my steering wheel started left to right jitters recently and i can't stand it. I think it's any passionate driver's nightmare or should be.
My tires are very uneven and quite worn, which is the reason for it. Should be getting a new set in a month or so, with an alignment to accompany it.
BTW, hope you got the chance to clean the interior from the messy and thankful horse-lady.
#18
03-31-2014, 11:42 AM
Veteran Member
Ha.Ha.Ha... That was great Albert. I am going to make that my own too.
Doesn't matter how well a car drives, how good it handles, whether it's a Jaguar or LaFerrari, i want a relaxed steering wheel.
My XF has been fine, but my steering wheel started left to right jitters recently and i can't stand it. I think it's any passionate driver's nightmare or should be.
My tires are very uneven and quite worn, which is the reason for it. Should be getting a new set in a month or so, with an alignment to accompany it.
Doesn't matter how well a car drives, how good it handles, whether it's a Jaguar or LaFerrari, i want a relaxed steering wheel.
My XF has been fine, but my steering wheel started left to right jitters recently and i can't stand it. I think it's any passionate driver's nightmare or should be.
My tires are very uneven and quite worn, which is the reason for it. Should be getting a new set in a month or so, with an alignment to accompany it.
#19
03-31-2014, 06:01 PM
Veteran Member
Mine was rock solid at 180, but autobahns are pretty smooth. Also, it has the Dynamics Pack, so is about 30% stiffer. However, there were couple of undulations that you'd probably never notice at sane speed, but were significant at max v; they didn't unsettle the car. I expected to be having to deal with front-end lift, turbulence from other vehicles' wakes - nothing. I did back off a bit when coming up to pass trucks, though.
#20
03-31-2014, 07:15 PM
Mine was rock solid at 180, but autobahns are pretty smooth. Also, it has the Dynamics Pack, so is about 30% stiffer. However, there were couple of undulations that you'd probably never notice at sane speed, but were significant at max v; they didn't unsettle the car. I expected to be having to deal with front-end lift, turbulence from other vehicles' wakes - nothing. I did back off a bit when coming up to pass trucks, though.