Suspension Data for Possible Upgrade

[GizmoQ]

Hello good people, I have a problem and would like to document my research and development on the forum for others to possibly benefit. I will need some expertise from others on the forum (Cadillac Tech, Whit, 1BADXLR, madcurl, and probably many others).

Here's the rub - I'm tired of having my ass handed to me by a pair of 03 Corvettes and an RX-8 on the autocross circuit. O.K., yes I admit they are better drivers with significantly more experience, but if I can get 20% closer in my lap times, my indexed times will allow me to stay in the #1 position in championship points. I know Elwood is heavier and not as sport tuned, so I have begun researching mods to get me close. Keeping the roof down helps with weight transfer; fatter, stickier tires will give me better traction; and upgrading the suspension should improve the loose rear end.

Wheels and tires are all I've done so far. RACING ONLY wheels are C-5 OEM 18x9.5 wrapped in 265/35/18 Michelin Cup tires. The wheels are the lightest available without jumping into custom 3 piece wheels. The offsets will be adjusted with spacers. The tires are almost 2" shorter than OEM but should only affect Speedometer accuracy since they are all the way around.... although the magride might get confused (haven't tested that yet).

What I'm currently researching is parts compatibility between the XLR and the various Corvette models. I know I have to change my front sway bar to reduce the loose rear end. And after talking to several Vette owners replacing the springs should lower/stiffen the car to compete directly with the Corvettes. Before the shouting begins, I know its an XLR not a Vette. I just want to take it up a notch for the race season and will then return it closer to stock when I'm done. I'm pretty sure the best setup for me is going to be ZR1 front sway bar and Z06 Front spring.



First lets establish some basic information. We know the XLR and C6 Corvette share several components especially in the suspension. The corvette, however, has several models. These different models also have different suspension packages. So correct me if I'm wrong but the base model has FE1/FE2 (F55 mag ride) suspension, the Z06 and Z51 have FE3/FE4 or F55 suspensions where the specs on the front are the same but differ in the rear, and the ZR1 has the FE5 suspension.


XLR Front Spring (part # 15233394) is the exact same part number as an 08 Corvette spring (FE1). Hollander Interchange says the XLR and C6 FE1/FE2 share Sway Bar Interchange Part #524-00528A. Yet, the Front Sway bar is very close to the ZO6 part# (XLR:25919501; Z06/FE4:25919502). Based on reading night and day for weeks, I can only assume the XLR front sway is 30MM vice the Z06 31MM, but they are completely interchangeable. As a matter of fact, all the sway bars front and rear (04-09 XLR, 97-04 C5, 05-12 C6) are completely interchangeable.

So lets start with the Sway bars.

GM Sway Bar Measurements:
C5 Base:.....................23 MM Front / 19.1 MM Rear / 3.81mm/2.0mm thickness
C5 Z51 (97-99):...........25.4 MM Front / 21.7 MM Rear
C5 Z51 (00-04): ..........28.6 MM Front / 23.6 MM Rear / 4.15mm/3mm thickness
C5 Z06:......................30.0 MM Front / 23.6 MM Rear / 4.5mm/3.5mm thickness
C6 Base:.....................25.5 MM Front / 17.5 MM Rear
C6 Z06/Z51.................31 MM Front / 27.9MM Rear /25.6 MM Rear
Hotchkis:....................31.75 MM / 25.4 MM
C6 ZR1:......................33 MM Front / 31 MM Rear
Pfadt Johnny O'Connell:.34.9 MM Front / 28.6 MM Rear
T1:............................38.4 MM Front / 27.5 MM Rear
LG Msprts G1:..............39.7 MM Front / 27.0 MM Rear

Not too surprisingly, the price/MM curve is exponential with the C6Z06 at a little over $100 and the T1 (full pro race setup) a little over $1000.



Whereas, the sway bars have different diameters, the springs have different bows and stiffness.

Corvette Springs:
Model Front Rear
FE1/Base 420 657
FE2/F55 420 657
FE3/Z51 502 645
FE4/Z06 526 714

So not only will the spring upgrade improve stiffness. but also lower the car more than we could ever get with just the lowering bolt. I'm afraid the ZR1/FE5 spring will throw everything out of kilter, so I plan to install the Z06/FE4 spring and adjust the lowering bolt to suit the racetrack. Nobody within 500 miles of me has the springs in stock so I'm going to have to buy one and try it. I'm 80% confident that it will fit, but performance is just a guess.

Comments, questions, (Fire suit on) flame away!

 

[richardyoo]

First off - all those sway bars should not be compared directly like that... some of them - like the hotchkis (which I have) are adjustable... I believe the pfadt are also adjustable... so using the diameter as a reference may not work for comparison for stiffness.

As for the springs - why not just go to a coil-over set up? They are completely adjustable, including ride-height

For lowering - I went with the the hardbar lowering bolts, and they were so low I had to get longer bolts to bring them up to a reasonable height... you can pretty much get the car to tuck the tires in the wheel arches with the hardbar bolts.

As for weight - although 3-peice wheels are much lighter (the forgelines I have are light enough I can pick one up with one hand), you can also look at 2-piece rotor big brake kit... they also shave a lot of weight off... I couldn't believe how much lighter the 2-peice rotors were compared to the solid iron rotors... and the calipers (although physically larger) are also lighter than the stock units...

just my 2 cents

 

[1BADXLR]

Definitely a good thread to start and learn from as many people as possible.

I have to agree comparing just the size of the sway bars seem irrelevant when you can adjust them appropriately. I also have the Hotchkis F&R w/ all new hardware and bushings. Set up on the middle of the three holes provided on the rear sway bar. You could find a better deal from ls1tech or any other corvette forums that are selling them from their c6. Believe I paid $250 brand new.

As for the shocks, I've said I am going with the pfadt coilovers for the specific reason of living on the road course. Adjusting the stiffness and ride height would help in every way. Although I may compromise the soft ride the XLR had, I can already tell the (more corvette feeling) difference of the low profile tires I have.

Now, do you need to spend a ton of money on the suspension to go fast, NO. First thing is first, I learned it from my dad growing up, learn the car! Take it to a parking lot and throw it around and feel it out, feel the limits. My first road course in the XLR I hesitated alot, because the last time I drove it hard I threw it into an overpass wall, lol. But after working out the first butterflies, I laid down some great numbers. Learning that keeping the car in manual shift mode (mostly 1st) knocked off 3 seconds, because the car kept upshifting.

Like I said, I would learn the car as much as you can to where your keeping up with similar competition before you throw suspension pieces on it. That way with your upgrades, you'll drive the car hard and wont think twice, and smoke em all! In my bracket I smoked a few nice cars, including a Z06, Audi r8, the "Crusher" '70 Camaro, and a handful of mustangs and camaro's.

Btw, GizmoQ, Like what you've done to your XLR, If I've beat the cars I have with 236 rwhp, imagine what I could do with your 501 rwhp, I'd love to take her on the course!!

 

[GizmoQ]

First off - all those sway bars should not be compared directly like that... some of them - like the hotchkis (which I have) are adjustable... I believe the pfadt are also adjustable... so using the diameter as a reference may not work for comparison for stiffness.

I have to agree comparing just the size of the sway bars seem irrelevant when you can adjust them appropriately. I also have the Hotchkis F&R w/ all new hardware and bushings. Set up on the middle of the three holes provided on the rear sway bar. You could find a better deal from ls1tech or any other corvette forums that are selling them from their c6. Believe I paid $250 brand new.

You're right and there are three more from Pfadt that I didn't list(Full pro race setup) that are also adjustable (over the top stiff!). I saw somewhere a graph comparing all the sways and the hotchkis and Johnny O'Connell's first two settings were equal to the Z06 and ZR1. Their highest settings is where they really differ with the O'Connells being slightly stiffer than the Hotchkis. Adjustables are nice, but if you're only going to use the ZR1 setting, the ZR1 sways are much cheaper and fewer parts to possibly fail. I got a company all ready to sell me the ZR1 front and hardware for $135 shipped. I know I don't need the rears.

As for the springs - why not just go to a coil-over set up? They are completely adjustable, including ride-height

As for the shocks, I've said I am going with the pfadt coilovers for the specific reason of living on the road course. Adjusting the stiffness and ride height would help in every way. Although I may compromise the soft ride the XLR had, I can already tell the (more corvette feeling) difference of the low profile tires I have.

The Corvette racers keep telling me the same thing, but I want to keep the magride for roadtrips. One of the guys has the coil-overs and showed me how quickly they can be adjusted and he loves them, but I don't want to introduce too many changes at the same time. If I keep racing in this series next year, I may have to consider them.

For lowering - I went with the the hardbar lowering bolts, and they were so low I had to get longer bolts to bring them up to a reasonable height... you can pretty much get the car to tuck the tires in the wheel arches with the hardbar bolts.

HardBars are already on order! As I said above, given the shorter wheels height, I need to drop the car a good bit.

As for weight - although 3-peice wheels are much lighter (the forgelines I have are light enough I can pick one up with one hand), you can also look at 2-piece rotor big brake kit... they also shave a lot of weight off... I couldn't believe how much lighter the 2-peice rotors were compared to the solid iron rotors... and the calipers (although physically larger) are also lighter than the stock units...

Ooooh, new info. Hadn't considered that. But its too late to upgrade for this season - already got the C5 wheels and those calipers wont fit. My current rotors are a little lighter cause they're drilled and slotted and I'm really happy with the brake setup I put on the car last year. I'll have to research how much weight we're talking about.

Now, do you need to spend a ton of money on the suspension to go fast, NO. First thing is first, I learned it from my dad growing up, learn the car! Take it to a parking lot and throw it around and feel it out, feel the limits. My first road course in the XLR I hesitated alot, because the last time I drove it hard I threw it into an overpass wall, lol. But after working out the first butterflies, I laid down some great numbers. Learning that keeping the car in manual shift mode (mostly 1st) knocked off 3 seconds, because the car kept upshifting.
Like I said, I would learn the car as much as you can to where your keeping up with similar competition before you throw suspension pieces on it. That way with your upgrades, you'll drive the car hard and wont think twice, and smoke em all! In my bracket I smoked a few nice cars, including a Z06, Audi r8, the "Crusher" '70 Camaro, and a handful of mustangs and camaro's.

Been there, done that. Four road courses, five drag strips, and 25-30 autocross sessions. I have a mentor/instructor in autocross that thought I was underdriving the car till he finally took a turn - he now says I'm at 80-85% of the car's capability (I like having a safety margin). I do drive it hard and will admit I could brake less and later, but that will come with practice. Our courses are setup to where I stay in 2nd gear and the nannys turned down.

just my 2 cents

Much appreciated!

Btw, GizmoQ, Like what you've done to your XLR, If I've beat the cars I have with 236 rwhp, imagine what I could do with your 501 rwhp, I'd love to take her on the course!!

I'd look love to sometime when you get back. Be safe out there.

I'm going out today and collect all the different GM part#s for the springs and sways. Wish me luck.

 

[richardyoo]

I know I don't need the rears.

In my set up - I noticed the most change with adjusting the rear sways... the stiffer fronts kept my nose level during turns, but the rears really tamed the rear...

The Corvette racers keep telling me the same thing, but I want to keep the magride for roadtrips. One of the guys has the coil-overs and showed me how quickly they can be adjusted and he loves them, but I don't want to introduce too many changes at the same time. If I keep racing in this series next year, I may have to consider them.

I also keep hearing great things about coil overs... I also hear that they ride great in daily driving when adjusted for a softer rate after you're done at the track... I also like the mag ride, but it doesn't sound like I'm as serious of a track driver as you are.

Ooooh, new info. Hadn't considered that. But its too late to upgrade for this season - already got the C5 wheels and those calipers wont fit. My current rotors are a little lighter cause they're drilled and slotted and I'm really happy with the brake setup I put on the car last year. I'll have to research how much weight we're talking about.

My new rotors are slotted and dimpled... I had slotted rotors before, and I assure you the weight difference is shocking between the iron rotors and the 2-peice with the aluminum center... I wish I had put them on a scale before I mounted them.

 

[GizmoQ]

Its not nearly complete, but here's my preliminary data on the suspension.





I'm still waiting for the Corvette forums to give me the data on the ZR1 springs, but those are probably outside the needs of most of us.

I was quickly corrected about how the FE# match up to the models:

FE1 = Base narrow body "Soft Ride" suspension.
FE2 = Base narrow body "Soft Ride" suspension with Mag Ride Shocks added in place of standard shocks.
FE3 = Base narrow body "Z51 Sport" suspension (not available with Mag Ride Shocks).
FE3 (hybrid) = Wide body Grand Sport. Same springs and front sway bar as Z51 but with Z06 rear sway bar and front shocks; unique GS rear shocks.
FE4 = Z06 suspension (in later years available with Mag Ride Shocks)
FE5 = ZR1 suspension with modified Mag Ride Shocks




I also found a graph by Pfadt Racing that shows how the different sway bar specs line up.

Looking at this graph makes me a little more comfortable with the ZR1 front/Z51 rear sway combination. IMHO, It basically mirrors the front to rear bias of the racing setups with decent street ride handling. Again, I'm not shooting for a full race setup, just fix the loose rear end and match the setup with my "race" tires.

 

[madcurl]

My new rotors are slotted and dimpled... I had slotted rotors before, and I assure you the weight difference is shocking between the iron rotors and the 2-peice with the aluminum center... I wish I had put them on a scale before I mounted them.

I had a chance to weigh my Baer Eradi speed Corvette Z51 13/14 brake upgrade from a wreaked Corvette. I purchased the HRE 3-piece wheels too, but the brakes went onto different car, but the wheels (years later) for the XLR.
58.5 pounds total weight for 13/14 combo

 

[GizmoQ]

Yesterday I took another trip to the Chevy dealership for part numbers. I will say I'm still a little confused. Luckily the guys over on the Corvette forums tried to help me out. One of the guys gave me a great summation on the different suspension packages for the C6:

FE1 = Base narrow body "Soft Ride" suspension.
FE2 = Base narrow body "Soft Ride" suspension with Mag Ride Shocks added in place of standard shocks.
FE3 = Base narrow body "Z51 Sport" suspension (not available with Mag Ride Shocks).
FE3 (hybrid) = Wide body Grand Sport. Same springs and front sway bar as Z51 but with Z06 rear sway bar and front shocks; unique GS rear shocks.
FE4 = Z06 suspension (in later years available with Mag Ride Shocks)
FE5 = ZR1 suspension with modified Mag Ride Shocks

Other than the FE1 and FE5, everything in-between kinda has a mix and match freestyle for the Z06, Z51, and GS models that I don't completely comprehend, but here are the part numbers I was able to gather.



Its bad enough that Chevy has such a jumble of mix and match parts (that I'm sure they tested extensively to determine the best suspension dynamics for each model), but I'm gonna mix 'em up again on my car. Interestingly, many of the Corvette forum guys agreed the FE1 package is for "cruising the boulevard only" , "A SUNDAY DRIVER and should not be driven any other way" and our suspension is softer than that!

I start ordering parts next month, wish me luck.

 

[Stella]

I guess one question is what's the difference in the car weights? The conv. top mechanism has to put alittle extra weight. I had gotten the z51 front and rear set for 175 off eBay about two years ago. I went from a new owner and it didn't have one on the rear. To upgrading the front and adding the rear and I really liked the difference. Before the car did dive in the cornering which now it stays pretty level. As for the springs. Besides dropping the ride height why would you wanna change them. Unless you'd put less spring in and add coil overs to compensate?

 

[GizmoQ]

As for the springs. Besides dropping the ride height why would you wanna change them. Unless you'd put less spring in and add coil overs to compensate?

My race rubber is 265/35/18 - 25" high, 2" less than show rubber. Need to lower at least the front.

 

[GizmoQ]

Having my setup on the street for a week now, some observations. Stiffening and lowering the front suspension makes a big improvement in the handling; steering input and response is quick and tight, body roll and braking dive is almost completely eliminated. Did a couple high and low speed transitions and this combo meets my needs and fits my driving style. The low speed transitions flow smoothly from side to side and the high speed transitions keep the rear wheels planted and biting. For the first time in high speed cornering, the rear wheels didn't break loose and the front tires squealed before the rears. I'm sure if I get the rears hot enough, they'll still drift, but I've achieved my goal of having them stick longer at higher speeds. Now its down to the tires only to determine how much lateral Gs I can achieve.

Interestingly enough, now that the front end is so tight, now I notice the rear spring is bouncy dunno:always something... should be reduced when ride height gets adjusted this weekend).

I guess one question is what's the difference in the car weights? The conv. top mechanism has to put alittle extra weight. I had gotten the z51 front and rear set for 175 off eBay about two years ago. I went from a new owner and it didn't have one on the rear. To upgrading the front and adding the rear and I really liked the difference. Before the car did dive in the cornering which now it stays pretty level. As for the springs. Besides dropping the ride height why would you wanna change them. Unless you'd put less spring in and add coil overs to compensate?

Your choice of the Z51 sways was probably the best option for the street. The ZR1 front sway is overkill for a street cruiser. I'll be torquing the system up next weekend at a 2-day autocross. We'll see then if the front sway is too much for racing.

The Z06 spring was chosen for its higher spring rate knowing I was lowering the car. This was done in hopes to keep from bottoming the shocks during hard, fast cornering and for faster, more controlled transitions.


BOTTOM LINE: All C6 suspension parts are direct replacement parts for the XLR. Any mix of springs and sways can be installed, but your results may vary.

 

[05 GRAND DADDY]

My race rubber is 265/35/18 - 25" high, 2" less than show rubber. Need to lower at least the front.

Giz what brand name rubber you running???


Sent from my iPhone using Tapatalk Thanks Dan

 

[GizmoQ]

Giz what brand name rubber you running???

Michelin Pilot Sport Cup now, but may be getting a deal on Hoosier A6 set.

 

[05 GRAND DADDY]

Good sticky tire I put the super sport on Roxy last year!


Sent from my iPhone using Tapatalk Thanks Dan

 

[GizmoQ]

Good stuff!

i am a bit intrigued on the spring setup. Retaining the stock height but fixing the non-corvette handling (keep mag ride control), what is the recommendation?

will not track my v, but am a bit disappointed as to the handling.

Like I told Stella, if you just want to tighten up the body roll and stick the rear end a little more, the Z51 swaybar set with polyurethane bushings and some good tires is all you need. If you want to keep the stock ride height and you're not tracking the car - don't bother with the spring.


Besides supporting the weight of a vehicle, the leaf springs control the ride height and keep the tires in contact with the road. A harder spring like the Z06 one I have lowers the car about a half inch versus FE1 which is OEM. I then used the HardBar lowering bolts to lower my car another inch. Most experts say this is going to reduce the remaining life of my shocks by half if not more - you don't want that. I do because autocross is all about transitions, not power or speed. The smoother I can make the transitions the faster I go.

 

[Johnxlrv]

Thx GizmoQ!

I am not against improving body roll with the z51 sway bar set you mentioned, but want to keep shock life. Alas, I'll keep the run flats until I need to replace...but stock tires and rims (v) will still work here to some degree?

like what you are doing btw....thanks for sharing the details here!

 

[GizmoQ]

Thx GizmoQ!

I am not against improving body roll with the z51 sway bar set you mentioned, but want to keep shock life. Alas, I'll keep the run flats until I need to replace...but stock tires and rims (v) will still work here to some degree?

like what you are doing btw....thanks for sharing the details here!

Thanks.

It should give you the "feel" you're looking for, but tires are going to then become even more noticeable as the limiting factor.

 

[GizmoQ]

I'll be torquing the system up next weekend at a 2-day autocross. We'll see then if the front sway is too much for racing.

The Z06 spring was chosen for its higher spring rate knowing I was lowering the car. This was done in hopes to keep from bottoming the shocks during hard, fast cornering and for faster, more controlled transitions.

What was that old quote,

"Life is not a journey to the grave with intentions of arriving safely in a pretty well-preserved body, but rather to skid in broadside, thoroughly used up, totally worn out and loudly proclaiming ... WOW! What a ride! "​

I actually knocked 5 seconds off my average today and I'm still trying to find the limits of this suspension/tire combination.

WOW! the suspension mods and the sticky tires made a world of difference and I never even got the tires loose today. The rear end sticks like its on rails, the front barely twitches transitioning abruptly from side to side, and there's little to no dip under hard braking. This thing races like a totally different car than what I started with last year.

Now comes the hardest mod of all: improving my driving skills.

 

[fcarga]

Congrats! 5 seconds off is a great achievement!

 

[05 GRAND DADDY]

Hey Giz 5 seconds don't seem like much time! But then again it depends what that 5 seconds is archiving right!
Sound like your at least heading in the right direction! Keep it move that way great news !!


Sent from my iPhone using Tapatalk Thanks Dan