Lowering with aftermarket bolts and F55 suspension?
07-11-2009, 03:00 PM
#1
Drifting
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Lowering with aftermarket bolts and F55 suspension?
Has anyone lowered their F55 Vette with aftermarket bolts? Is there any potential problems with doing this? I love the look of a Vette slammed to the ground...
07-11-2009, 08:35 PM
#3
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lowered mine w/zip products bolts. no problems other than 1 of the rubber caps (bushings) tore and fell off. i think it was an isolated problem. other three are fine. waiting for the replacement to arrive.
07-12-2009, 12:16 AM
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Before going to a coil-over suspension for track performance, I used the F55 both on the street and the track. In my quest to modify the F55 suspension for track performance, I became acquainted with one of the lead Delphi engineer's who developed the F55 suspension for Corvette. He wrote the following reply concerning whether or not the (F55) position sensors need to be relocated in a lowered C6. He touches on another potential issue of lowering the F55 equipped C6 (reduction of compression travel).
>>The position sensors do sense position, but internal to the MR ECU a calculation (differentiation) is made to turn that information into velocity - the rate of change of position with respect to time.
Very simplistically, I’ll say that velocity is really the main signal of interest, as many handling, stability, body and wheel control strategies use this basic information in various ways. Also, don't forget that dampers are velocity devices - even though we usually say the MR device is not really damper, but an actuator. Position is used, too but that information is only critical to a few control strategies. Of course, we have a strategy to do simple position-sensitive damping control, but it's not used in the Corvette.
In the end, regardless of where we're at in the suspension travel, it's the rate of change of the position signal over time that matters - that's why we don't have to change the position sensor mounting when lowering or raising the car.
Almost everything for MR (sensing, processing, output control, etc.) is done at 1kHz or 1000 times per second.
The main reason I suggest cutting bumpstops is that "free suspension travel" is everything, in my opinion. (I'll define "free suspension travel" as the amount of travel of the shock absorber between full rebound and jounce bumper engagement.) When the car is lowered, compression travel is taken out. The jounce bumper is a secondary spring. It will engage even on relatively smooth roads (I still remember "discovering" this fact on one of the access roads at the Desert Proving Grounds many years ago, during the course of developing the profile, length and hardness of the C5 jounce bumper). Also, and maybe most importantly, during turning events the jounce bumper may engage, leading to oversteer or possibly understeer - and sometimes we can be snookered into thinking the oversteer/understeer is coming from another source like the main suspension spring rate or the stab bar or tire pressures or ?? (another story: the CERV IV had terrible max lat numbers for some time. Everybody was really upset, because these numbers were really low. Turns out, the jounce bumper was simply too long in the rear. Spring rate goes up, traction goes down.)<< (emphasis added)
My (then) F55 equipped car was leveled for the track and lowered in the process but only using the stock 'lowering bolts.' I suggest you only use the stock 'lowering bolts.' If you slam the car beyond that you risk affecting compression travel to the point of jeopardizing the effectiveness of the system. In street driving it may not matter all that much but if you really push the car on a track you'll degrade suspension performance more noticeably.
PS My other suggestion is to make sure your car is 'balanced' properly. Although I essentially leveled my car for road course performance (largely eliminating the factory spec rake) it really wasn't setup too precisely right from the factory (it was off side-to-side and diagonally). Just turning bolts an equal number of turns is no guaranty your car will be setup properly. It's not overly difficult to do but there are certain procedures to follow and measurements to take to make sure your car is setup right. Remember, every time you turn one bolt you affect the other corners of the car (the one diagonally the most). Your car might be spot on to begin with but it might be worth checking while you're lowering it.
>>The position sensors do sense position, but internal to the MR ECU a calculation (differentiation) is made to turn that information into velocity - the rate of change of position with respect to time.
Very simplistically, I’ll say that velocity is really the main signal of interest, as many handling, stability, body and wheel control strategies use this basic information in various ways. Also, don't forget that dampers are velocity devices - even though we usually say the MR device is not really damper, but an actuator. Position is used, too but that information is only critical to a few control strategies. Of course, we have a strategy to do simple position-sensitive damping control, but it's not used in the Corvette.
In the end, regardless of where we're at in the suspension travel, it's the rate of change of the position signal over time that matters - that's why we don't have to change the position sensor mounting when lowering or raising the car.
Almost everything for MR (sensing, processing, output control, etc.) is done at 1kHz or 1000 times per second.
The main reason I suggest cutting bumpstops is that "free suspension travel" is everything, in my opinion. (I'll define "free suspension travel" as the amount of travel of the shock absorber between full rebound and jounce bumper engagement.) When the car is lowered, compression travel is taken out. The jounce bumper is a secondary spring. It will engage even on relatively smooth roads (I still remember "discovering" this fact on one of the access roads at the Desert Proving Grounds many years ago, during the course of developing the profile, length and hardness of the C5 jounce bumper). Also, and maybe most importantly, during turning events the jounce bumper may engage, leading to oversteer or possibly understeer - and sometimes we can be snookered into thinking the oversteer/understeer is coming from another source like the main suspension spring rate or the stab bar or tire pressures or ?? (another story: the CERV IV had terrible max lat numbers for some time. Everybody was really upset, because these numbers were really low. Turns out, the jounce bumper was simply too long in the rear. Spring rate goes up, traction goes down.)<< (emphasis added)
My (then) F55 equipped car was leveled for the track and lowered in the process but only using the stock 'lowering bolts.' I suggest you only use the stock 'lowering bolts.' If you slam the car beyond that you risk affecting compression travel to the point of jeopardizing the effectiveness of the system. In street driving it may not matter all that much but if you really push the car on a track you'll degrade suspension performance more noticeably.
PS My other suggestion is to make sure your car is 'balanced' properly. Although I essentially leveled my car for road course performance (largely eliminating the factory spec rake) it really wasn't setup too precisely right from the factory (it was off side-to-side and diagonally). Just turning bolts an equal number of turns is no guaranty your car will be setup properly. It's not overly difficult to do but there are certain procedures to follow and measurements to take to make sure your car is setup right. Remember, every time you turn one bolt you affect the other corners of the car (the one diagonally the most). Your car might be spot on to begin with but it might be worth checking while you're lowering it.
Last edited by Wayne O; 07-12-2009 at 12:22 AM.
07-12-2009, 08:09 AM
#5
Drifting
Thread Starter
Before going to a coil-over suspension for track performance, I used the F55 both on the street and the track. In my quest to modify the F55 suspension for track performance, I became acquainted with one of the lead Delphi engineer's who developed the F55 suspension for Corvette. He wrote the following reply concerning whether or not the (F55) position sensors need to be relocated in a lowered C6. He touches on another potential issue of lowering the F55 equipped C6 (reduction of compression travel).
>>The position sensors do sense position, but internal to the MR ECU a calculation (differentiation) is made to turn that information into velocity - the rate of change of position with respect to time.
Very simplistically, I’ll say that velocity is really the main signal of interest, as many handling, stability, body and wheel control strategies use this basic information in various ways. Also, don't forget that dampers are velocity devices - even though we usually say the MR device is not really damper, but an actuator. Position is used, too but that information is only critical to a few control strategies. Of course, we have a strategy to do simple position-sensitive damping control, but it's not used in the Corvette.
In the end, regardless of where we're at in the suspension travel, it's the rate of change of the position signal over time that matters - that's why we don't have to change the position sensor mounting when lowering or raising the car.
Almost everything for MR (sensing, processing, output control, etc.) is done at 1kHz or 1000 times per second.
The main reason I suggest cutting bumpstops is that "free suspension travel" is everything, in my opinion. (I'll define "free suspension travel" as the amount of travel of the shock absorber between full rebound and jounce bumper engagement.) When the car is lowered, compression travel is taken out. The jounce bumper is a secondary spring. It will engage even on relatively smooth roads (I still remember "discovering" this fact on one of the access roads at the Desert Proving Grounds many years ago, during the course of developing the profile, length and hardness of the C5 jounce bumper). Also, and maybe most importantly, during turning events the jounce bumper may engage, leading to oversteer or possibly understeer - and sometimes we can be snookered into thinking the oversteer/understeer is coming from another source like the main suspension spring rate or the stab bar or tire pressures or ?? (another story: the CERV IV had terrible max lat numbers for some time. Everybody was really upset, because these numbers were really low. Turns out, the jounce bumper was simply too long in the rear. Spring rate goes up, traction goes down.)<< (emphasis added)
My (then) F55 equipped car was leveled for the track and lowered in the process but only using the stock 'lowering bolts.' I suggest you only use the stock 'lowering bolts.' If you slam the car beyond that you risk affecting compression travel to the point of jeopardizing the effectiveness of the system. In street driving it may not matter all that much but if you really push the car on a track you'll degrade suspension performance more noticeably.
PS My other suggestion is to make sure your car is 'balanced' properly. Although I essentially leveled my car for road course performance (largely eliminating the factory spec rake) it really wasn't setup too precisely right from the factory (it was off side-to-side and diagonally). Just turning bolts an equal number of turns is no guaranty your car will be setup properly. It's not overly difficult to do but there are certain procedures to follow and measurements to take to make sure your car is setup right. Remember, every time you turn one bolt you affect the other corners of the car (the one diagonally the most). Your car might be spot on to begin with but it might be worth checking while you're lowering it.
>>The position sensors do sense position, but internal to the MR ECU a calculation (differentiation) is made to turn that information into velocity - the rate of change of position with respect to time.
Very simplistically, I’ll say that velocity is really the main signal of interest, as many handling, stability, body and wheel control strategies use this basic information in various ways. Also, don't forget that dampers are velocity devices - even though we usually say the MR device is not really damper, but an actuator. Position is used, too but that information is only critical to a few control strategies. Of course, we have a strategy to do simple position-sensitive damping control, but it's not used in the Corvette.
In the end, regardless of where we're at in the suspension travel, it's the rate of change of the position signal over time that matters - that's why we don't have to change the position sensor mounting when lowering or raising the car.
Almost everything for MR (sensing, processing, output control, etc.) is done at 1kHz or 1000 times per second.
The main reason I suggest cutting bumpstops is that "free suspension travel" is everything, in my opinion. (I'll define "free suspension travel" as the amount of travel of the shock absorber between full rebound and jounce bumper engagement.) When the car is lowered, compression travel is taken out. The jounce bumper is a secondary spring. It will engage even on relatively smooth roads (I still remember "discovering" this fact on one of the access roads at the Desert Proving Grounds many years ago, during the course of developing the profile, length and hardness of the C5 jounce bumper). Also, and maybe most importantly, during turning events the jounce bumper may engage, leading to oversteer or possibly understeer - and sometimes we can be snookered into thinking the oversteer/understeer is coming from another source like the main suspension spring rate or the stab bar or tire pressures or ?? (another story: the CERV IV had terrible max lat numbers for some time. Everybody was really upset, because these numbers were really low. Turns out, the jounce bumper was simply too long in the rear. Spring rate goes up, traction goes down.)<< (emphasis added)
My (then) F55 equipped car was leveled for the track and lowered in the process but only using the stock 'lowering bolts.' I suggest you only use the stock 'lowering bolts.' If you slam the car beyond that you risk affecting compression travel to the point of jeopardizing the effectiveness of the system. In street driving it may not matter all that much but if you really push the car on a track you'll degrade suspension performance more noticeably.
PS My other suggestion is to make sure your car is 'balanced' properly. Although I essentially leveled my car for road course performance (largely eliminating the factory spec rake) it really wasn't setup too precisely right from the factory (it was off side-to-side and diagonally). Just turning bolts an equal number of turns is no guaranty your car will be setup properly. It's not overly difficult to do but there are certain procedures to follow and measurements to take to make sure your car is setup right. Remember, every time you turn one bolt you affect the other corners of the car (the one diagonally the most). Your car might be spot on to begin with but it might be worth checking while you're lowering it.
I'm bookmarking this thread.
07-12-2009, 01:13 PM
#6
Safety Car
My wife's C6 has the F55 option. She likes her car *low* so we went first to WCC lowering bolts. The rear bolts came apart after 4 days 
So we used cut down stock bolts which lowered it nicely but generated a couple of other problems. First, the cut bolts don't last (2 years is OK I guess.) More on point is that (as Wayne's post stated) once you lower the car that much the F55 shocks don't have enough travel and any spirited driving will quickly find the car bottoming out on the shock travel. Instant 3200 pound gokart. Not good.
So, if you intend to keep the F55 system AND you don't want to do surgery on the shocks AND you want to drive the car like it was intended to be driven, you really ought to take Wayne's advice and stick with the stock bolts.
Wayne: the solution was shorter, adjustable QA-1 shocks. And you *cannot* decouple the F55 system from the main system on a 2007 car (five different TechII experts have tried and failed.)
Z//
So we used cut down stock bolts which lowered it nicely but generated a couple of other problems. First, the cut bolts don't last (2 years is OK I guess.) More on point is that (as Wayne's post stated) once you lower the car that much the F55 shocks don't have enough travel and any spirited driving will quickly find the car bottoming out on the shock travel. Instant 3200 pound gokart. Not good.So, if you intend to keep the F55 system AND you don't want to do surgery on the shocks AND you want to drive the car like it was intended to be driven, you really ought to take Wayne's advice and stick with the stock bolts.
Wayne: the solution was shorter, adjustable QA-1 shocks. And you *cannot* decouple the F55 system from the main system on a 2007 car (five different TechII experts have tried and failed.)
Z//
07-12-2009, 01:18 PM
#7
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Lowered mine with stock bolts.
As Wayne O suggested a year and half ago. I love the ride. I also added the bigger Z06 sway bars too.
I know everyone likes the Z-51 bars. I went with the Z06 ones.
As Wayne O suggested a year and half ago. I love the ride. I also added the bigger Z06 sway bars too.
I know everyone likes the Z-51 bars. I went with the Z06 ones.
