[Henry427]

Congrats on the sway bars Paul! I told you I couldn't feel any ride difference in my butt meter! I just noticed the black chrome wheels in your signature, can you share some pics?

Check out post #324 in Blade Silver thread (6/30/16).

 

[Richard Brubaker]

Check out post #324 in Blade Silver thread (6/30/16).

Just checked them out Paul and they really pop. Great choice.

 

[Jerry U]

Z51 Mag Ride cars have the same front bar as the 'regular' Z51, and an even stiffer rear bar than the regular Z51. I think the mag ride base car still has the same front bar and no rear bar as the base car without mag ride, but I'm not 100% certain.

Putting a larger rear bar on the car without a larger front will result in less understeer (or more oversteer) than the smaller rear bar. With the regular Z51 bar set, the car still understeers, but less than with the stock setup. One person who put the mag ride bars on his base Stingray reported the handling is close to neutral, with maybe a bit of oversteer at the limit. For most drivers, terminal understeer is much safer than terminal oversteer.

If one confirms that the mag ride base Stingray has no rear bar, my recommendation would be to go with the regular Z51 bars, not the bigger mag-ride rear bar. Note that my advice may be worth exactly what you've paid for it.

Agree with your statement I put in bold. According to Tadge, they even eliminated the front air dam on the Z06 (and no doubt the Z51) because it created excess downforce at speed, promoting oversteer. They state, as you note, that understeer is preferred (safer.)

For someone who had a modified Corvair (even though a '67 without swing axles, which Ralph Nader used to reinforce his argument that '60 thru '64 swing axle Corvairs were "unsafe,") that oversteered significantly requiring quick reactions to counter having the rear slide off the road in fast turns! Messing with anti-roll bar balance should only be done if you're a skilled driver or want to try drifting! :smile-new:

Getting a matched pair of bars for the spring stiffness in the car, from a knowledgable vendor is more prudent.

 

[meyerweb]

My understanding is that base rear spring is designed to provide additional 'anti-sway' properties (compared to Z51 rear spring) so a rear bar is not necessary. Adding a Z51 bar to base gives more 'anti-sway' than a Z51 rear set up.

First, I don't know any way the spring can provide more "anti-sway" other than being stiffer, and it's not. The springs on the base model are softer than those on the Z51. And having driven a Z51 on the track at Ron Fellows, and my base + Z51 sways on the track at the Corvette museum track, I don't think my car has more anti-sway than the Z51.

 

[STINGmole]

The only handling characteristic that really bothers me about my base C7 is the understeer. I wish it was more neutral.

 

[Jerry U]

First, I don't know any way the spring can provide more "anti-sway" other than being stiffer, and it's not. The springs on the base model are softer than those on the Z51. And having driven a Z51 on the track at Ron Fellows, and my base + Z51 sways on the track at the Corvette museum track, I don't think my car has more anti-sway than the Z51.

Agree with your comment about it not being anti-rill more with a less stiff spring unless the mounting was different, which it is not.

My post 40 is just a brief summary of why the mounting method of a transverse spring does add to the anti-sway (roll.) Lots written on the subject. Looks like GM discovered the issue with the C4 and C5 but it may be from old cars that also used transverse rear springs including some race cars.

I recall that large center mounted rear transverse spring on my first car, a '41 Ford Opera Coupe. As on the early Corvettes it's center mounted location does not add any anti-roll. It's the center section between the mounts in newer Vettes and the C7 that bends in an S shape that provides that function.

 

[autoxal]

Keep an open mind... Just because you can't see it... and others agree, doesn't mean it isn't so... I had a finite element analysis engineer friend explain it to me (much of it going over my head) a long time ago. The anti-sway properties of the FRP transverse spring have been used on the Corvette since the 1984 model. The spring rate and anti-sway are designed into the spring (and it's mounts) independently of one another... as one goes up, the other can be designed to go go down. Google Corvette leaf spring, and read the Wiki page (more in depth info can be found). The base car HAS more anti-sway designed in, than the Z51 REAR spring. This is complex engineering, designing the profile of the spring, both outboard of the mounts, as well as between them. Putting the Z51 bar on a base car will give more TOTAL anti-sway THAN Z51 total. And your handling computer programing will NOT know you made this mod. Though it may FEEL good in 'normal' driving... when you exceed limits of tire traction, you will be in for a big surprise (potential 'snap' spin)... THAT'S why Chevy recommends this not be done (as someone else had noted).

 

[autoxal]

Having written all that... adding the Z51 front bar (with the rear bar) to a base suspension car, would reduce this oversteer (loose) condition.

 

[meyerweb]

The only handling characteristic that really bothers me about my base C7 is the understeer. I wish it was more neutral.

Adding the mag-ride Z51 sway bars will do that.

 

[Mobius]

Putting the Z51 bar on a base car will give more TOTAL anti-sway THAN Z51 total. And your handling computer programming will NOT know you made this mod. Though it may FEEL good in 'normal' driving... when you exceed limits of tire traction, you will be in for a big surprise (potential 'snap' spin)... THAT'S why Chevy recommends this not be done (as someone else had noted).

Just to make sure I understand your points, regarding the 2nd, are you saying that Chevy does not recommend the Z51 sway bars be installed on the base car? I'm surprised, since Chevy dealers market the upgrade kit nationally, including on this forum. Chevy Performance also sells the T1 suspension package for the base and Z51 Stingrays - it substantially changes the suspension, but there is no change required to the EBCM or StabiliTrak program.

My understanding is that StabiliTrak is an extension of the TC system, and constantly monitors driver input, wheels speeds and vehicle accelerations. If you get into an serious oversteer or understeer situation, StabiliTrak will come to the driver's aid, and modulate braking and power (to the extent it can) to correct the situation. This is all done independently of suspension stiffness characteristics.

​

 

[meyerweb]

I simply don't believe that the base car has more anti-sway than the Z51. Period. I've driven both, and the base car rolls like a cruise ship in a hurricane compared to the Z51. And my base car with Z51 bars STILL has more body roll than the Z51. But a lot less than without the Z51 bars. The base car + bars is far more controllable near the limit than without the bars, based on both fast street driving and fairly hot laps around NCM motorsports track. And the car still understeers in this configuration.

I'd like to see some actual proof of autoxal's contention that the base car spring has more anti-roll built in than the Z51 springs, not just conjecture or statements without any actual data. Many people on both Corvette forums have done this mod, and not one has reported any snap oversteer. Some have done the mod wtih the even larger MSRC rear bar, and reported very neutral handing with a touch of oversteer (not "snap" oversteer) at the limit.

Finally, I don't believe there are any sensors looking at body roll, so that's not something the "handling computer" is looking at. Traction control is based on lateral acceleration, steering angle, and tire slip (variation in speed from one tire to the next). Anyone who's taken the Spring Mountain Corvette Owner School can tell you how well the stabilitrak works, even if you turn the wheel full lock while driving straight ahead.

One can believe the experiences of those who have done the mod, or one can believe unsubstantiated theory.

 

[Sauraus]

Can someone perhaps post the part # for the Stingray & Z51 front and rear springs?

 

[autoxal]

If 'unsubstantiated theory' refers to me... I am working on it. And I have taken the Spring Mountain three day school (as well as years of track days at Summit Point Raceway), so am aware of the handling capabilities of the C7, as well as how a car feels 'at the limit' on a closed course. My comment that rear bar addition was discouraged by Chevy, was specifically referring to a previous post that had indicated this was the case. As far as the handling program, maybe I'll concede it might catch the additional oversteer... >maybe<. But I can't imagine how the program could anticipate changes to tires, springs, brake pad and bars. (I need to apply this much brake, to this tire, using this brake material, suspended on this spring, while stabilized by this bar... exaggerated a bit, but you get the idea). To be continued...

 

[Jerry U]

Keep an open mind... Just because you can't see it... and others agree, doesn't mean it isn't so... I had a finite element analysis engineer friend explain it to me (much of it going over my head) a long time ago. The anti-sway properties of the FRP transverse spring have been used on the Corvette since the 1984 model. The spring rate and anti-sway are designed into the spring (and it's mounts) independently of one another... as one goes up, the other can be designed to go go down. Google Corvette leaf spring, and read the Wiki page (more in depth info can be found). The base car HAS more anti-sway designed in, than the Z51 REAR spring. This is complex engineering, designing the profile of the spring, both outboard of the mounts, as well as between them. Putting the Z51 bar on a base car will give more TOTAL anti-sway THAN Z51 total. And your handling computer programing will NOT know you made this mod. Though it may FEEL good in 'normal' driving... when you exceed limits of tire traction, you will be in for a big surprise (potential 'snap' spin)... THAT'S why Chevy recommends this not be done (as someone else had noted).

Agree, suspension analysis is complex. Anti-squat and anti-sway are different. I recall a Prof in an engineering dynamics class many years ago drawing a block on the board and showing why a car squats down in the rear when accelerating. However a few of us car buffs argued that a ~50 Olds actually raised, which he would not accept!

If I recall correctly the way the Olds suspension arms and springs were arranged had the front and rear raise but the front rose higher making the Profs free body diagram work!

 

[Mobius]

My comment that rear bar addition was discouraged by Chevy, was specifically referring to a previous post that had indicated this was the case. As far as the handling program, maybe I'll concede it might catch the additional oversteer... >maybe<. But I can't imagine how the program could anticipate changes to tires, springs, brake pad and bars. (I need to apply this much brake, to this tire, using this brake material, suspended on this spring, while stabilized by this bar... exaggerated a bit, but you get the idea

My understanding is that TC and StabiliTrack are feedback control systems, meaning that they each constantly monitor vehicle dynamics. When these feedback control systems are activated, based on vehicle dynamics, they provide both braking as well as reduced power (up to the limits of the algorithms) to return the vehicle to a "controlled" configuration.

TC is simpler to describe - TC constantly monitors wheel speed, and when a mismatch in wheel speed is identified (between fronts and rears, or between the two rears) TC begins to apply rear wheel braking and power reduction until this wheel speed mismatch is removed. TC doesn't care that you swapped out your Z06 Pilot Sport Cup 2 ZP tires with Continental Extreme Contact DW summer tires; TC sees tire spin occurring and works to correct it. The TC system also has no information regarding the road surface (sand, snow, wet, etc.), but is able to effectively limit wheel spin without this information, just by monitoring the vehicle response to the braking and throttle position changes that TC is implementing.

StabiliTrack is similar in operation, based on a feedback control loop, constantly monitoring both the inputs it has authority over (differential braking, throttle position) and the vehicle outputs (vehicle accelerations, steering angle, wheel speeds). The system knows nothing about suspension and tire mods, powertrain mods or road conditions, but can still operate effectively through a controlled feedback loop to counter oversteer and understeer. The level of differential braking and throttle reduction that StabiliTrack applies is determined dynamically, probably at the millisecond level, to the constantly changing vehicle dynamics.

Regarding the post made by someone that GM discourages the addition of the rear bar only, that's a post I've never seen on the forum. If you could find that post, let us know so we can take a look.

 

[meyerweb]

The closest I've seen to a post that GM discourages it was a post from someone who said their dealer refused to install them "because GM didn't recommend it." That's a long way from GM actually stating that it's not recommended.

I've driven my car on the NCM Motorsports track with the Z51 sways on, and there's simply no question that it still understeers.

 

[autoxal]

Here's where I was looking... go to post #25 in this thread, follow the first link, then look at post #12 there. Then look at (Glen E's) post #15.

 

[Mobius]

I spent some time looking for the reported GM bulletin and came up empty. I did find this, however:

Talked to a friend at a local Chevy dealer, no bulletin about installing them on base cars but they mentioned a notice quite a while ago that Z51 sway bars only should be ordered for service replacement. Most likely they are in short supply and they want them to build new cars.

 

[rdslon01]

My understanding is that TC and StabiliTrack are feedback control systems, meaning that they each constantly monitor vehicle dynamics. When these feedback control systems are activated, based on vehicle dynamics, they provide both braking as well as reduced power (up to the limits of the algorithms) to return the vehicle to a "controlled" configuration.

TC is simpler to describe - TC constantly monitors wheel speed, and when a mismatch in wheel speed is identified (between fronts and rears, or between the two rears) TC begins to apply rear wheel braking and power reduction until this wheel speed mismatch is removed. TC doesn't care that you swapped out your Z06 Pilot Sport Cup 2 ZP tires with Continental Extreme Contact DW summer tires; TC sees tire spin occurring and works to correct it. The TC system also has no information regarding the road surface (sand, snow, wet, etc.), but is able to effectively limit wheel spin without this information, just by monitoring the vehicle response to the braking and throttle position changes that TC is implementing.

StabiliTrack is similar in operation, based on a feedback control loop, constantly monitoring both the inputs it has authority over (differential braking, throttle position) and the vehicle outputs (vehicle accelerations, steering angle, wheel speeds). The system knows nothing about suspension and tire mods, powertrain mods or road conditions, but can still operate effectively through a controlled feedback loop to counter oversteer and understeer. The level of differential braking and throttle reduction that StabiliTrack applies is determined dynamically, probably at the millisecond level, to the constantly changing vehicle dynamics.

Regarding the post made by someone that GM discourages the addition of the rear bar only, that's a post I've never seen on the forum. If you could find that post, let us know so we can take a look.

For those who have not taken multiple graduate-level EE courses in controls, please skip this post. Mobius, I assume you have, so this post is primarily directed to you.

It seems to me that Al's point is that some of the entries in the vehicle's state matrix are functions of the variables he listed in some of his previous posts. He also wrote that his focus was about a car "at the limit".

Now, the question before us boils down to the following: if some of the entries in the state matrix are allowed to be perturbed, can the closed-loop system, for the same input, still be driven to the same output which would occur for the unperturbed system? The answer to that in this case is clearly yes, except possibly at the boundaries of the state space between controllable and uncontrollable subspaces.

Al's point was made about a car "at the limit" which is, of course, on the boundary between controllable and uncontrollable subspaces. Will a perturbed state matrix result in that boundary slightly shifting? Probably it will. Will it change the boundary "significantly" (where each person is free to define what "significantly" means to them)? I don't know, but that point isn't really the one for debate anyway: Al's point wasn't if it was significant or not, but rather just that it would modify the vehicle's behaviour "at the limit".

Finally, your point about the car being able to brake and/or reduce power to keep the system in the controllable region will have all of its entries appear as part of the time-varying input control vector. That will not affect the system matrix. However, you will probably argue that the car will be able to effectively stay away from the boundary between the controllable and uncontrollable subspaces by varying that input control vector nearly a thousand times per second. Although true, this is not addressing the problem posed by Al: his basis for departure in this discussion was that there was a car "at the limit". As such, if the car finds itself at a boundary between controllable and uncontrollable subspaces, and if that boundary, due to the perturbations in the system matrix, has slightly shifted with the uncontrollable side taking some locus of points which were previously in the controllable side, then he is correct, and no amount of changes in the input control vector will be able to save it.

Is that scenario unlikely? I would surmise that it is, especially if TC and StabiliTrack are on to keep the car away from that boundary in the first place. Does that change the fact that Al is almost surely correct in the strictly technical sense of what he has written if the car is, somehow, already at the limit? No, it does not.

In summary, my take is that Al is technically correct in what he has written, but that few, if any, people will actually encounter it while driving, especially if TC and StabiliTrack are on to keep the car away from that boundary in the first place.

 

[Henry427]

Rodney, of course I understood very little of this post except for the last paragraph, which is all us non engineers need to know. What I do know is I was unhappy with the amount of body roll with my base Stingray and the Z51 sway bars are a significant improvement at a modest cost.