[Z06] Stock transverse leaf spring properties
11-23-2008, 01:04 PM
#61
Former Vendor
As the wheel goes into bump
1.Spring rates increase
2.Shock control decreases
3.In the sweet spot its pretty linear
My next post will be my a thread I started about bottoming out shocks and how to test if this is happening. I would avoid the jumps for the test because it's not a baja truck, and getting it to work for just those couple spots will decrease lap times. Work on the parts of the track were there is the most time to make up.
DRM (our company) and LGM both build good coilovers for the late model cars. I know of one other Bilstein coilover, and the reviews aren't that good.
Bilstein also makes a shorter (sport and HD) shock that work very well.
Randy
11-23-2008, 01:13 PM
#62
Former Vendor
Very few did the homework, kinda sad
http://forums.corvetteforum.com/c6-z...-homework.html
Good luck
Randy
PS Just talking suspension on a Sunday afternoon
http://forums.corvetteforum.com/c6-z...-homework.html
Good luck
Randy
PS Just talking suspension on a Sunday afternoon
11-24-2008, 07:06 PM
#63
The only problem with this picture is.
The one side has a ton of bump travel, which the car will never see because the stock shocks are bottomed out by then.
The other problem, the other side, to show this myth of a swaybar affect doesn't work either. GM has always used no attachment point for the way up. The pads on the front only act under bump and the rear has bolts. This theory would be ok if they attached the upper part of the spring.
Randy
The one side has a ton of bump travel, which the car will never see because the stock shocks are bottomed out by then.
The other problem, the other side, to show this myth of a swaybar affect doesn't work either. GM has always used no attachment point for the way up. The pads on the front only act under bump and the rear has bolts. This theory would be ok if they attached the upper part of the spring.
Randy
I am really surprised that you would claim that GM isn't going for a sway bar type effect given that Michael Lamm's book states that GM was going exactly for that effect when they first used this arrangement on the 1984 front end. Additionally I can point to patents from Honda, Ford and others specifically mentioning the anti-roll affects of this sort of spring arrangement.
You are correct that the setup used in the Corvette doesn't allow the spring to pull up. However, in this illustration the beam was flat in the unloaded case. If the spring acted like a Z-bar or promoted roll as some (not you) have proposed then we would see the bar push down on the opposite side. As is we have to imagine that the ground is always pushing the suspension up into the spring. What we can see here is the static position of this spring is higher when the right side is deflected. Let's assume the left side is now 1" from static. Well to deflect it 1.1" would require almost no force at all as we are only deflecting that side 0.1". The first 1.0" was force free.
If we let the right side back down we need to deflect the left side 1.1" and push against the spring the whole time.
Anyway, I am open to suggestions that would make that image more clear. It was shown next too an image of a beam fixed in the center (similar to a C4 rear end) as well as a beam with a central pivot. If a central pivot mount promotes roll and a fixed mount makes the spring left-right independent, it only stands to reason that this set up must do the opposite of a central pivot and thus would resist roll.
Last edited by wishihad1-2; 11-24-2008 at 09:09 PM.
11-24-2008, 10:37 PM
#64
Former Vendor
The spring isn't shown to any particular scale. The deflections are exaggerated by the FEA software and again illustrate the general deflection rather than the specifics of the Corvette parts. The GM leaf spring is not constant in section so the shape I've shown is only approximate.
I am really surprised that you would claim that GM isn't going for a sway bar type effect given that Michael Lamm's book states that GM was going exactly for that effect when they first used this arrangement on the 1984 front end. Additionally I can point to patents from Honda, Ford and others specifically mentioning the anti-roll affects of this sort of spring arrangement.
You are correct that the setup used in the Corvette doesn't allow the spring to pull up. However, in this illustration the beam was flat in the unloaded case. If the spring acted like a Z-bar or promoted roll as some (not you) have proposed then we would see the bar push down on the opposite side. As is we have to imagine that the ground is always pushing the suspension up into the spring. What we can see here is the static position of this spring is higher when the right side is deflected. Let's assume the left side is now 1" from static. Well to deflect it 1.1" would require almost no force at all as we are only deflecting that side 0.1". The first 1.0" was force free.
If we let the right side back down we need to deflect the left side 1.1" and push against the spring the whole time.
Anyway, I am open to suggestions that would make that image more clear. It was shown next too an image of a beam fixed in the center (similar to a C4 rear end) as well as a beam with a central pivot. If a central pivot mount promotes roll and a fixed mount makes the spring left-right independent, it only stands to reason that this set up must do the opposite of a central pivot and thus would resist roll.
I am really surprised that you would claim that GM isn't going for a sway bar type effect given that Michael Lamm's book states that GM was going exactly for that effect when they first used this arrangement on the 1984 front end. Additionally I can point to patents from Honda, Ford and others specifically mentioning the anti-roll affects of this sort of spring arrangement.
You are correct that the setup used in the Corvette doesn't allow the spring to pull up. However, in this illustration the beam was flat in the unloaded case. If the spring acted like a Z-bar or promoted roll as some (not you) have proposed then we would see the bar push down on the opposite side. As is we have to imagine that the ground is always pushing the suspension up into the spring. What we can see here is the static position of this spring is higher when the right side is deflected. Let's assume the left side is now 1" from static. Well to deflect it 1.1" would require almost no force at all as we are only deflecting that side 0.1". The first 1.0" was force free.
If we let the right side back down we need to deflect the left side 1.1" and push against the spring the whole time.
Anyway, I am open to suggestions that would make that image more clear. It was shown next too an image of a beam fixed in the center (similar to a C4 rear end) as well as a beam with a central pivot. If a central pivot mount promotes roll and a fixed mount makes the spring left-right independent, it only stands to reason that this set up must do the opposite of a central pivot and thus would resist roll.
Your picture does show that the inside "tire" would have less spring rate as the outside loaded "tire". No swaybar about it. It does have some effect on the overall roll of the car, but not much at all. A coil spring acts in very simular ways with decreasing spring rate as the car goes into droop. And increases as the car goes into bump.
Randy
11-25-2008, 01:13 AM
#65
Your picture does show that the inside "tire" would have less spring rate as the outside loaded "tire". No swaybar about it. It does have some effect on the overall roll of the car, but not much at all. A coil spring acts in very simular ways with decreasing spring rate as the car goes into droop. And increases as the car goes into bump.
Randy
Randy
Let’s assume we have fixed the car’s chassis to a test rig and removed the anti-roll bar. Now assume we connect the left wheel to a force gauge and hold it at static ride height (call it 0.0” and say 750lbs of force). Now compress the right tire to say 1” compression. The left side will say 0.0” (because we said it was fixed) yet the force of the spring on the wheel will be reduced to something less than 750lb. If we perform the same test with coil springs and no mater what the movement of the right wheel, the left will always say 0.0” and 750lb. We get no force transfer via the coil springs.
The force the coil applies to the suspension is a function of ONLY the compression of that coil. If I don’t compress or droop the wheel the force of that coil will stay the same. The force the left half leaf applies is a function of both how much we have compressed/deflected it AND the position of the right half of the spring. You your self have talked of this cross talk so I know you understand this.
So what the leaf spring is doing is taking displacement on the right and translating that into a change in spring force on the left. That is exactly what an anti-roll bar does. After all, if we draw things up as a free body diagram and look at forces we will se the anti-roll bar is nothing more than a difference spring. Push up the right wheel and the anti-roll bar pulls up on the left. The pulling up cancels out some of the force of the coil spring and we have higher roll rates.
That is NOT to say the car has no roll stiffness with just coils. Even without an anti-roll bar a coil spring car will have some roll stiffness. It’s just not as much as we typically want.
I don’t see how you can say that GM gets no appreciable anti-roll out of this setup. That is both inconsistent with Michael Lamm’s book. His book was written with GM’s help and states that GM was hoping to get enough anti-roll effect to avoid the front anti-roll bar all together. It also would have to ignore the patent literature filed by Honda, Ford and others specifically mentioning this anti-roll property as a benefit of the spring layout.
This is one from a company in England mentioning the anti-roll effect.
http://www.google.com/patents?id=Ee8...se+leaf+spring
This one comes from GM and mentions the anti-roll effect; “thus provides a high spring rate in roll with a low spring rate in heave for a high roll ratio.”
http://www.google.com/patents?id=wQY...se+leaf+spring
The evidence is pretty clear, GM feels the anti-roll properties of that spring are important and not simply coincidental.
Last edited by wishihad1-2; 11-25-2008 at 01:26 AM.
11-25-2008, 09:25 AM
#66
Le Mans Master
Apparently, as you mentioned earlier in your post, it's not as much as they want. Corvettes still come with fairly hefty sway bars, even on base models. So the affect must be fairly minimal.
Last edited by robvuk; 11-25-2008 at 09:31 AM.
11-25-2008, 10:25 AM
#67
Team Owner
One thing I have not seen mentioned in a long time about Coilovers is how well the upper mount can handle the additional loads placed on it by the fact that now in addition to handling the shock aborber, it is also handling the entire loads of the suspension. No question, the upper mount is simply not designed for the additional load of a coilover replacing the leaf spring.
This is okay in racing applications where there is most likely additional bracing (in true race cars) and race cars are likely inspected between every race. Also, race tracks don't have potholes to deal with. But what about the harsher enviroment of the street and the likely lack of regular inspection?
This is okay in racing applications where there is most likely additional bracing (in true race cars) and race cars are likely inspected between every race. Also, race tracks don't have potholes to deal with. But what about the harsher enviroment of the street and the likely lack of regular inspection?
11-25-2008, 01:24 PM
#68
It would be interesting to see if GM used rear anti-roll bars in their FWD sedans with used the same spring arrangement. It would also be interesting to see if they added an anti-roll bar when they switched to coils on the back of the W-body cars.
js,
If I'm not mistaken the Corvette's bump stops are on the shock (like most cars which use a coil on damper setup). As such the highest suspension loads (bump stop) are already absorbed by the shock mount. The forces due to the ride spring is almost certainly small with respect to those from "bottoming" the suspension.
11-25-2008, 03:21 PM
#69
Team Owner
Not as much as they wanted is not the same thing as minimal. If GM were to replace the leaf spring with a pair of coils giving a similar ride spring rate they would have to increase the anti-roll bar stiffness to maintain the existing roll rate. The Lamm book seemed to suggest the problem was the suspension engineers couldn't place the spring mounts far enough apart to completely avoid needing a front anti-roll bar. The C4 rear used a centrally mounted spring with no inherent anti-roll effect and thus needed a rear bar.
It would be interesting to see if GM used rear anti-roll bars in their FWD sedans with used the same spring arrangement. It would also be interesting to see if they added an anti-roll bar when they switched to coils on the back of the W-body cars.
js,
If I'm not mistaken the Corvette's bump stops are on the shock (like most cars which use a coil on damper setup). As such the highest suspension loads (bump stop) are already absorbed by the shock mount. The forces due to the ride spring is almost certainly small with respect to those from "bottoming" the suspension.
It would be interesting to see if GM used rear anti-roll bars in their FWD sedans with used the same spring arrangement. It would also be interesting to see if they added an anti-roll bar when they switched to coils on the back of the W-body cars.
js,
If I'm not mistaken the Corvette's bump stops are on the shock (like most cars which use a coil on damper setup). As such the highest suspension loads (bump stop) are already absorbed by the shock mount. The forces due to the ride spring is almost certainly small with respect to those from "bottoming" the suspension.
With coilovers, you have the entire weight of the vehicles being supported by the coilover (along with stresses as the springs/shocks absorb normal road irregularities). With the leaf spring, the bulk of the weight is carried by the leaf spring mounting locations.
To further explain, consider this. With the leaf spring, you can remove the shock absorber all together and the car will just barely sag at all as the spring is holding the car up. But if you remove the spring but leave the shock attached, the car will sag all the way down to the bump stop because a shock has almost no compression effect without the spring in place. That tells you that the springs are what is holding the car up off the suspension.
Here is a thread regarding this subject....
http://forums.corvetteforum.com/c5-t...-concerns.html
Last edited by jschindler; 11-25-2008 at 03:32 PM.
11-25-2008, 04:00 PM
#70
I do understand you mean the top shock mount. You are right that when the car is sitting the spring is basically supporting all the weight. However, the forces on the dampers are very high. Consider what happens when you hit a pot hole. The load on the spring will go up but that very quick hard shock is primarily absorbed by the damper. All the forces the damper absorbs it applies to the chassis via the top shock mount. Now consider the bump stop. If you hit something so hard that you bottom out the suspension what part actually carries that load? The spring again only takes say 1500lbs of force (I'm guess the load on the front tires when the spring is all but bottomed out). Any force beyond that (and in the case of a pot hole or say getting some air) must be carried by the bump stop. Remember that the bump stop is effectively a very stiff rate spring that doesn't make it's self felt until the last inch or so of travel. That means it needs to be stiff which means any thing that supports it needs to be strong.
If the top shock mounts really were inadequate for use with coil overs I suspect we would see far more mount failures. I think the one Z06 failure is the only one that has been reported. That involved a car with lowered suspension and if I understand correctly dampers which were too long to use a proper bumps stop.
If the top shock mounts really were inadequate for use with coil overs I suspect we would see far more mount failures. I think the one Z06 failure is the only one that has been reported. That involved a car with lowered suspension and if I understand correctly dampers which were too long to use a proper bumps stop.
11-25-2008, 04:56 PM
#71
Team Owner
I do understand you mean the top shock mount. You are right that when the car is sitting the spring is basically supporting all the weight. However, the forces on the dampers are very high. Consider what happens when you hit a pot hole. The load on the spring will go up but that very quick hard shock is primarily absorbed by the damper. All the forces the damper absorbs it applies to the chassis via the top shock mount. Now consider the bump stop. If you hit something so hard that you bottom out the suspension what part actually carries that load? The spring again only takes say 1500lbs of force (I'm guess the load on the front tires when the spring is all but bottomed out). Any force beyond that (and in the case of a pot hole or say getting some air) must be carried by the bump stop. Remember that the bump stop is effectively a very stiff rate spring that doesn't make it's self felt until the last inch or so of travel. That means it needs to be stiff which means any thing that supports it needs to be strong.
If the top shock mounts really were inadequate for use with coil overs I suspect we would see far more mount failures. I think the one Z06 failure is the only one that has been reported. That involved a car with lowered suspension and if I understand correctly dampers which were too long to use a proper bumps stop.
If the top shock mounts really were inadequate for use with coil overs I suspect we would see far more mount failures. I think the one Z06 failure is the only one that has been reported. That involved a car with lowered suspension and if I understand correctly dampers which were too long to use a proper bumps stop.
I only bring these issues up as points of discussion. I understand supensions, but don't claim to be an expert in any way. Thanks for the replies
11-25-2008, 11:14 PM
#72
Coils are only superior in two regards; In general they are more universal and thus the same part can be used on more cars. They cost less than leaf springs (this even applies to traditional truck springs).
For the C5 it was a space issue which forced GM's hand. For what ever reason GM felt that using coils would force them to move the shock mounts. I have some speculative ideas why this might be so but I don't know for certain.
What is really superior in the aftermarket systems is likely the dampers. Look at the ZR1 reviews. Not a single review has mentioned the skittish at the limit handling mentioned when talking about the Z06. The tires and dampers are the big changes. If the benefit of aftermarket coil overs were in the springs, why wouldn't people just buy stiffer leaf springs then call it a day? The key is the dampers and I suspect the cost constraints (and maybe other constraints) limit GM's OEM shocks. If nothing else consider how expensive a set of these nicer dampers are as compared to a set of OEM like replacement shocks.
For the C5 it was a space issue which forced GM's hand. For what ever reason GM felt that using coils would force them to move the shock mounts. I have some speculative ideas why this might be so but I don't know for certain.
What is really superior in the aftermarket systems is likely the dampers. Look at the ZR1 reviews. Not a single review has mentioned the skittish at the limit handling mentioned when talking about the Z06. The tires and dampers are the big changes. If the benefit of aftermarket coil overs were in the springs, why wouldn't people just buy stiffer leaf springs then call it a day? The key is the dampers and I suspect the cost constraints (and maybe other constraints) limit GM's OEM shocks. If nothing else consider how expensive a set of these nicer dampers are as compared to a set of OEM like replacement shocks.
11-26-2008, 12:17 AM
#73
Melting Slicks
Member Since: Sep 2006
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Would you please comment on designs that remove the bump stop, ie where something else bottoms out before the shock runs out of travel?
11-26-2008, 12:50 AM
#74
Are their any systems that bottom out on parts other than the shocks? The bump stop basically pads that last bit of shock travel before the damper is fully compressed. Even without the rubber part I think the shock is the first part to run out of travel but now it does it "all at once" rather than over about 1" and with a much higher peak load being transferred to the shock mount.
11-26-2008, 10:30 AM
#75
Former Vendor
Are their any systems that bottom out on parts other than the shocks? The bump stop basically pads that last bit of shock travel before the damper is fully compressed. Even without the rubber part I think the shock is the first part to run out of travel but now it does it "all at once" rather than over about 1" and with a much higher peak load being transferred to the shock mount.
Randy
11-26-2008, 10:38 AM
#76
Former Vendor
Why is it when a coilover car has a issue, it adds fuel to the fire. But when others have had broken leafs, dropped corners because of this. Once in the C6 tech there was two different people with problems on the first page. No one even bothered to reply. SO I even posted that they need some assists. And still no one replied.
Kinda funny
Randy
2 C4 coilover issues
1 C6z
Kinda funny
Randy
2 C4 coilover issues
1 C6z
11-26-2008, 02:17 PM
#77
Our systems don't get into bump stops at all. We run a shorter body and shaft. The tire would run into the inner fender before bottoming out the shock. I know LG system also uses this same design. Funny how the two companies that have winning with Corvettes have simular shock ideas.
Randy
Randy
11-26-2008, 03:17 PM
#78
Former Vendor
11-26-2008, 03:37 PM
#79
Burning Brakes
well ive read all this and its grear but i went with VBp leafs 1250 fr 950 rear and the T1 bars and i like it...... good nuff for me..... and i drove pursuit cars, limos and such so i know a wee bit about driving...
11-26-2008, 04:19 PM
#80
Team Owner
Why is it when a coilover car has a issue, it adds fuel to the fire. But when others have had broken leafs, dropped corners because of this. Once in the C6 tech there was two different people with problems on the first page. No one even bothered to reply. SO I even posted that they need some assists. And still no one replied.
Kinda funny
Randy
2 C4 coilover issues
1 C6z
Kinda funny
Randy
2 C4 coilover issues
1 C6z
On the other hand, companies like DRM and LG are trying to convince customers that they need a completely different spring arrangement, and a very small number have been sold. When we read of a failure, it makes us take pause before investing in a system that is not of the same design as the car was intended to have.
I'm not saying the coilovers are not reliable - I don't have enough information to know. I'm answering the question you posed though.