Modern Suspension Tech ('02 Z06)--I need HELP

[Ralph LoGrasso]

Hey guys,

My problem is actually a fairly simple one: I'm looking to lower my '02 Z06 using the factory adjustments. I plan on lowering the car all the way on the factory bolts, maybe one turn back. I plan on having the car aligned to factory specs immediately after lowering.

I am hesitant to do this because I'm afraid lowering the car will adversely affect its performance. (I've been told that lowering it can cause mid-turn bump issues (or something of that nature) due to the suspension not having enough travel. More specifically, the shocks not having enough travel, and bottoming out). Others say the car will be fine if it's lowered on the factory bolts, citing that GM wouldn't have put them there if they didn't intend for you to use them.

There are even those who claim to have lowered their cars way past what the factory settings will allow (longer bolts, removed front bushing) with no ill effects. I find that hard to believe, and I generally find these individuals to be show-car or drag guys who are not hard on their cars in the turns.

My car is a serious 4x4 (I can fit four fingers between the tires and tops of the fender/quarter panel) and in desperate need of being lowered. I believe GM recommends lowering the car around 7/8 - 1" as they were originally raised in order to get them on the trucks for delivery. I'm only looking to lower it slightly more than that as I believe the factory bolts only allow for a maximum adjustment of 1-1.25" (maybe 1.5").

I need some TECH here! Has anyone raced (or driven near the edge) a Z06 or C5 that has been lowered all the way on stock bolts?

I often push this car at or near its limit and I'm really not looking to find out that my suspension lacks sufficient travel in such a situation.

Can anyone give me a definitive answer on this? Will the shocks have enough travel (i.e. not bottoming out) or won't they? Is there any "easy" way for me to determine the amount of travel the shocks have?

Any input on this topic would be greatly appreciated, especially from those with C5 experience, though all opinions are definitely welcome.

Thank you,
Ralph

[Ralph LoGrasso]

Similarly, if it's determined that there will not be enough suspension travel with the factory shocks, can anyone recommend an aftermarket shock that will have sufficient travel when lowered?

The Bilstein sports look good, but I can't find any information as to whether they're shorter than the factory shocks or the same length.

[David Pozzi]

Ralph, I'm no corvette guru but I'd check on the Corvette forums and do some searching on the topic.
For the shocks, I think the issue would be under bump conditions, you don't want them to bottom out, that would damage internal valves and ruin the shock. For rebound, the shock will be fine, since there is plenty of room for shock extension.
David

[Ralph LoGrasso]

Thanks for the help, David!


For the shocks, I think the issue would be under bump conditions, you don't want them to bottom out, that would damage internal valves and ruin the shock. For rebound, the shock will be fine, since there is plenty of room for shock extension.


Gee, I look silly already. I'm not sure why I thought it was shock rebound, but what you described is my concern. Under bump conditions, having the shock bottom out and causing the car to lose control. Thanks for the correction! I have gone back and edited my post.

Unfortunately, I've done a lot of searching on the corvetteforums, and maybe I'm just looking in the wrong places, but I haven't found an answer that I'm truly happy with. Or better yet, an answer that I trust. It seems most people say it will be fine from their own experience, but can not back up their statement with any tech. I also get the feeling (and I don't mean to generalize) that those individuals are people who just cruise and never really push the car to its limits.

Thanks again!

[Damn True]

Search over on CC.com for threads by "Varkwso". He regularly tracks a C5-FRC and a ZO6.

LG is a member there as well.

You'll be fine there as you are capable of crafting a cogent sentence.

[chicane67]

To stay off of the bump stops = increase spring rates.

Geeze... Ralphy disappears for two years to come back with this !?!!

Seriously, out of all the lowerings that I did at Guldstrand... the bolts, remove the rubber pucks from the springs and install poly wedges, more aggressive alignment... was increasing the spring rate. We typically used the Z51 springs in lowered applications just to keep the chassis off of the bump stops, increase roll resistance and improve the high speed stability.

You want some real tech Ralph ?? Go get some MOTON or Penske coil overs and get it over with. Other than that... you will be fine.

[Ralph LoGrasso]

Search over on CC.com for threads by "Varkwso". He regularly tracks a C5-FRC and a ZO6.

LG is a member there as well.

You'll be fine there as you are capable of crafting a cogent sentence.

Thanks, True. I started searching there last night and plan to do some more research today. So far, I've only found one post that referenced lowering on stock bolts. It was mentioned in passing, but the guy was using his car for auto-x and had just installed some coilovers. He mentioned that his previous setup was simply being lowered all the way on stock bolts.

[Ralph LoGrasso]

Thanks, Tom!


To stay off of the bump stops = increase spring rates.

Are the Z06 springs stiff enough already? The car definitely rides much "stiffer" than a regular C5.


Geeze... Ralphy disappears for two years to come back with this !?!!

:lmao: I know--it's weak. I said it was a fairly simple problem. These sunday-drivers on other forums have me paranoid though. In one thread, a definitive answer is given that it's cool to install longer rear bolts, remove the front bushings and drive with the car slammed. No one opposes this opinion. Then, the following week, in another thread, you've got people claiming that the car will not have sufficient travel if lowered on the stock bolts only. There are warnings of people losing it mid-turn due to hitting a bump. This had me concerned...

:lmao: And hey, I only disappeared for a year, not two! :lurk:


Seriously, out of all the lowerings that I did at Guldstrand... the bolts, remove the rubber pucks from the springs and install poly wedges, more aggressive alignment... was increasing the spring rate. We typically used the Z51 springs in lowered applications just to keep the chassis off of the bump stops, increase roll resistance and improve the high speed stability.

Are the Z51 springs stiffer than the Z06 springs? High speed stability is another thing I wanted to improve on this car--I'm going to send you a PM.


You want some real tech Ralph ?? Go get some MOTON or Penske coil overs and get it over with. Other than that... you will be fine.

So, lowering on stock bolts, as-is (shock and spring wise), I will be fine? This is the info I'm looking for, thanks! If I had the cash, those coil overs would already be on the car. :6gears:

Thanks for the help and you've got a PM!

[chicane67]

If you are just going for a lowered look for right now... I say you'll be fine. But... (you knew that was coming)...

The C5 Z06 spring rates are 525/714... with the valving to match that, at the shipped ride height. If/when you lower the suspension... effectively all you actually change is the ride height and its position in the kinematic geometry. You don't however, increase the rates. This is where you will run into problems... kind-of. Once you get to a certain point in ride height... you do run out of travel. If this is all you were going to do... meaning, not going too low and you wanted to leave it alone when you were done... I would use the stock bolts, C6Z springs and HD 'Steins... is an affordable way to go. The C6Z spring rates go to 531/793... so its not too much of an increase, but... it will help keep the chassis off of the bump stops in hard impacts or high speed use. The Bilstein "HD"... as they have been referred to... have a shorter stroke and double digressive valving which works the best with lowered suspensions. You are basically tightening the window of usable travel and you need to put the chassis back into that window when you change it from factory.

Now... if you are not going to cross the lowering line, per-say... I think that the stock bolts will give you sufficient lowering... about an inch total. Anything lower and you will need 7.000" bolts. But either way you go... the dampers will need increased rebound valving. That is where most who lower... FAIL... to complete the required work and regain the balance that they are screwing with.

If you are still screwing with "ride comfort"... then its a toss up. The stock OE C5 or C6 Z06 springs are not too bad. If you don't care about losing another few percent in ride quality... I would opt for the T1 springs... mind you that they are the quote -un- quote... factory race springs. They are 582/793. Which in reality, are not all that bad either. Considering... a true race spring package is really more around 625/850 in the specific model year.

In the end... coil-overs are the cats meow. Its really easy to change rates... and its even affordable to do so. Most of all coil-overs set ups come with an adjustable damper... so, it kind of kills two birds with one bullet. You can set it up some what soft for the street and then... click click click... your set up for some squirrelly driving.

The only down side... is initial cost. But... (you knew that was coming)... it pays the dividends 10 fold.

Phadt
LG
Guldstrand
Penske
Moton

But for now... have fun with the stock bolts. I mean, you already have them... and all you need is a wrench and an alignment.



PM back at ya !!

[Ralph LoGrasso]

If you are just going for a lowered look for right now... I say you'll be fine. But... (you knew that was coming)...

The C5 Z06 spring rates are 525/714... with the valving to match that, at the shipped ride height. If/when you lower the suspension... effectively all you actually change is the ride height and its position in the kinematic geometry. You don't however, increase the rates. This is where you will run into problems... kind-of. Once you get to a certain point in ride height... you do run out of travel. If this is all you were going to do... meaning, not going too low and you wanted to leave it alone when you were done... I would use the stock bolts, C6Z springs and HD 'Steins... is an affordable way to go. The C6Z spring rates go to 531/793... so its not too much of an increase, but... it will help keep the chassis off of the bump stops in hard impacts or high speed use. The Bilstein "HD"... as they have been referred to... have a shorter stroke and double digressive valving which works the best with lowered suspensions. You are basically tightening the window of usable travel and you need to put the chassis back into that window when you change it from factory.

Now... if you are not going to cross the lowering line, per-say... I think that the stock bolts will give you sufficient lowering... about an inch total. Anything lower and you will need 7.000" bolts. But either way you go... the dampers will need increased rebound valving. That is where most who lower... FAIL... to complete the required work and regain the balance that they are screwing with.

If you are still screwing with "ride comfort"... then its a toss up. The stock OE C5 or C6 Z06 springs are not too bad. If you don't care about losing another few percent in ride quality... I would opt for the T1 springs... mind you that they are the quote -un- quote... factory race springs. They are 582/793. Which in reality, are not all that bad either. Considering... a true race spring package is really more around 625/850 in the specific model year.

In the end... coil-overs are the cats meow. Its really easy to change rates... and its even affordable to do so. Most of all coil-overs set ups come with an adjustable damper... so, it kind of kills two birds with one bullet. You can set it up some what soft for the street and then... click click click... your set up for some squirrelly driving.

The only down side... is initial cost. But... (you knew that was coming)... it pays the dividends 10 fold.

Phadt
LG
Guldstrand
Penske
Moton

But for now... have fun with the stock bolts. I mean, you already have them... and all you need is a wrench and an alignment.



PM back at ya !!

THIS is what I'm talking about! Thanks so much, Tom!

For this season, I'm just looking to get the car a little lower and maybe improve the performance a little bit.

Eventually (hopefully, next season) I want to install some coil overs and go lower. Because of this, I really don't want to spend much, if any, money on springs or shocks right now.

If it will really help, though, I'll spring for the $450 or so for the Bilstein HDs. I can always sell them next year.

PM Sent!

[68sixspeed]

For a slight lowering (as you aren't going to lowering bolts for a big drop) you should be ok on the stock stuff. You might want to do a bump steer check-- there are people selling kits for correcting this on lowered cars. (Pfadt may have more info) The bilstein sports are good for the money. I put them on my c5 last year with which has z06 bars, etc and tracked it twice last year. They aren't koni's, but they are a lot better than worn gm. A lot of guys are using c6z06 shocks on c5's with good results too, and they are pretty cheap.

one note main reason I posted - if you go coil-overs get the heavy (Pfadt) sway bars at the same time. They are adjustable, and by removing the cross-leafs you get rid of the cross talk in the suspension. (typically causing more roll).

Have fun!! -Dan

PS- Bilstein were going for around $300 last year?

[Ralph LoGrasso]

For a slight lowering (as you aren't going to lowering bolts for a big drop) you should be ok on the stock stuff. You might want to do a bump steer check-- there are people selling kits for correcting this on lowered cars. (Pfadt may have more info) The bilstein sports are good for the money. I put them on my c5 last year with which has z06 bars, etc and tracked it twice last year. They aren't koni's, but they are a lot better than worn gm. A lot of guys are using c6z06 shocks on c5's with good results too, and they are pretty cheap.

Thanks, Dan! I'm starting to consider the Bilsteins more and more. The stuff on my car is pretty fresh as the car only has 13,000 miles on it, so the current shocks aren't really worn. But, I'm thinking they might be a nice little upgrade anyways. I was looking at C6Z06 shocks also, but I've heard they're a little bit taller and will actually raise a lowered car back up some.


one note main reason I posted - if you go coil-overs get the heavy (Pfadt) sway bars at the same time. They are adjustable, and by removing the cross-leafs you get rid of the cross talk in the suspension. (typically causing more roll).

Have fun!! -Dan

PS- Bilstein were going for around $300 last year?

I'm going to go with coil-overs in a year or so (when cash becomes available), and definitely will look into the sway bars. I was considering going with slightly larger sway bars to limit roll anyways.

$300 wouldn't be bad at all for the shocks. I've gotta do some checking around.

Thanks again,

[chicane67]

www.SHOX.com

[93Polo]

My old C5 FRC has over 40k miles of regular street driving and some track use by the current owner with Z06 springs lowered on stock bolts. If you cut the bushings you really have to watch ground clearance and IMO just is not worth it.

http://www.ls1howto.com/index.php?article=20 has some info on the springs.

Corvetteforum, check out the road racing section too and Z06vette should have plenty of info.

[Payton King]

go to corvette forum, under general corvette there is an autocross/roadrace section. Lots of racers over there so post up your question. I have spent some time over there because of the C5 sub and geom on my car. If you get on Pfadts web site they have reccommended alignment specs as well.

[Ralph LoGrasso]

My old C5 FRC has over 40k miles of regular street driving and some track use by the current owner with Z06 springs lowered on stock bolts. If you cut the bushings you really have to watch ground clearance and IMO just is not worth it.

http://www.ls1howto.com/index.php?article=20 has some info on the springs.

Corvetteforum, check out the road racing section too and Z06vette should have plenty of info.

Thanks! That's great to hear. I assume the car is running C5 Z06 springs, not C6 Z06 springs? Also, there are no issues with the rear of the car "stepping out" under mid-turn bumps?

I'm definitely going to stay away from cutting the bushings.

Thanks again,

[Ralph LoGrasso]

go to corvette forum, under general corvette there is an autocross/roadrace section. Lots of racers over there so post up your question. I have spent some time over there because of the C5 sub and geom on my car. If you get on Pfadts web site they have reccommended alignment specs as well.

Thanks, Payton! I need to try to remember my username and password for corvetteforum--it's been so long since I've been on there, I've forgotten both of them. :banghead: I can always re-register.

I will check out Pfadt's site for the alignment specs. All I have right now is the stock specs.

[Ralph LoGrasso]

Another question--

If I lower the car as-is and align it, will I need to re-align it if I switch out the stock shocks for Bilstein's a few weeks later?

What about the same situation, but with the springs. If I lower, align and then go back and change to C6Z06 springs, will I need to re-align it?

I was thinking yes for re-aligning with the springs, but no for just the shocks?

Thanks,

[LateNight72]

I was thinking yes for re-aligning with the springs, but no for just the shocks?
Correct

[Payton King]

with corvettes usually means you have an alignment is off in the rear. Think bump steer. The wrong shocks will do it as well, but since you are using the factory ones right now, your alignment is off.

I know I have read this over at corvette forum in the last 6 months under the autocross/roadrace section.

For a dual purpose car, lots of folks over there swear by the Pfadt sway bars and shocks.

[93Polo]

Thanks! That's great to hear. I assume the car is running C5 Z06 springs, not C6 Z06 springs? Also, there are no issues with the rear of the car "stepping out" under mid-turn bumps?

I'm definitely going to stay away from cutting the bushings.

Thanks again,
Yes I was running all '04 C5 Z06 take off parts for the suspension from Phoenix Racing as they do alot of T1 conversions. It had the '04 Shocks (Nurburing valved one year only), C5Z06 springs, and C5Z06 swaybars. I was running '01 Z06 wheel with it. The car handled very well and was stable never had problem mid turn. One of my favorite twisty roads has a decreasing radius turn with a pavement change about 2/3rds in no problems running in the middle of 3rd gear. If it did step out just roll out of the throttle. The car had heads and cam so getting it to step out once the tires were a little worn was no problem. ;)

The bilsteins I believe are valved a little stiffer than the '04s. If you lower it to far then you run into bottoming out the shocks but that is not a problem on stock bolts without cutting.

http://s19.photobucket.com/albums/b181/leadfoot_mf/?action=view&current=Picture140.jpg for pics

I was planning on converting to the Pfadt stuff as I wanted to go more agressive and track the car when I sold the car.

I also recommend frame savers from A and A Corvette.

[Ralph LoGrasso]

with corvettes usually means you have an alignment is off in the rear. Think bump steer. The wrong shocks will do it as well, but since you are using the factory ones right now, your alignment is off.

I know I have read this over at corvette forum in the last 6 months under the autocross/roadrace section.

For a dual purpose car, lots of folks over there swear by the Pfadt sway bars and shocks.

Thanks, Payton. The rear of the car does seem to want to step out at times during mid-turn bumps. It's not bad, but you can definitely feel the rear hop and step out a little and then catch traction and stick. I will check the alignment when I lower it, as it sounds like it might be off a little bit. The car only has 13,000 miles though, so I'm not sure how far it could be off?

[Ralph LoGrasso]

Yes I was running all '04 C5 Z06 take off parts for the suspension from Phoenix Racing as they do alot of T1 conversions. It had the '04 Shocks (Nurburing valved one year only), C5Z06 springs, and C5Z06 swaybars. I was running '01 Z06 wheel with it. The car handled very well and was stable never had problem mid turn. One of my favorite twisty roads has a decreasing radius turn with a pavement change about 2/3rds in no problems running in the middle of 3rd gear. If it did step out just roll out of the throttle. The car had heads and cam so getting it to step out once the tires were a little worn was no problem. ;)

The bilsteins I believe are valved a little stiffer than the '04s. If you lower it to far then you run into bottoming out the shocks but that is not a problem on stock bolts without cutting.

http://s19.photobucket.com/albums/b181/leadfoot_mf/?action=view&current=Picture140.jpg for pics

I was planning on converting to the Pfadt stuff as I wanted to go more agressive and track the car when I sold the car.

I also recommend frame savers from A and A Corvette.

Thanks! Yeah, when the car hops and steps out a bit now, I just roll out of the throttle and let it stick and then roll back into it. Most of the roads that I like to carve around here are very bumpy, so you can see why this was a concern of mine. Hearing of your experience definitely helps to ease my mind, though.

Now all I need to do is find a free day where I can lower it (can do this anytime) and then align it.

I had heard the frame savers mentioned a bunch of times, but never the manufacturer. I will definitely be putting them on the car.

[93Polo]

Thanks! Yeah, when the car hops and steps out a bit now, I just roll out of the throttle and let it stick and then roll back into it. Most of the roads that I like to carve around here are very bumpy, so you can see why this was a concern of mine. Hearing of your experience definitely helps to ease my mind, though.

Now all I need to do is find a free day where I can lower it (can do this anytime) and then align it.

I had heard the frame savers mentioned a bunch of times, but never the manufacturer. I will definitely be putting them on the car.
Understood. IMO stability did not chage that much with lowering. They twitch a little bit but you get used to it.

I stated it wrong you want the rocker rails to keep the fiberglass that wraps around the frame from getting scuffed. They also make jacking the car much easier. I didn't go with the frame savers. http://www.aacorvette.com They are listed under C5 exterior.