Removing under steer

[FASTFATBOY]

I have a 2013 ZL1 and a 2015 1LE, both under steer like a snow plow.

Putting a DSE rear bar and more front camber helped the ZL1 but by far did not correct it.

I go to the Tail of the Dragon and run those roads a few times a year, as a former track day guy I drive the car harder than most.

Before I get replies as to what tires, tires don't matter, car balance is car balance no matter what the tire is. My C5 Z06 on brick tires didn't under steer. Tires are BFG Comp2 A/S for reference purposes. Before you critique the tire, go on Tirerack and compare this tire to the Michelin PS4. Both tires are almost mirror images of each other.

I don't want to rip out everything under the car to correct it, I am selling the ZL1 and keeping the 1LE.


I drive 7 hours to get to Tail of the Dragon, even with -1.75 camber in the front the ZL1 was wearing the inside of the tire from normal driving and killing the outside of the tire in the mountains.

Look at how far the front tire is pulled under the car, destroying the outer edge of the tire.

What is the fix? Is there a fix? If not how do you make it better?

[KillboyPowerhead]

If you're selling the ZL1 then I guess you're more concerned about the 1LE? I'd say for the ZL1 try a square tire setup, and as the 1LE is already square try the DSE rear bar. Using factory shocks/springs? I have JPSS bars (27mm front, 32mm rear), solid rear mounts, BC racing coilovers (8kg front, 12 kg rear spring rates) and factory rear RS/SS wheels all around (275/40 tires) on my V6 and it's more biased toward oversteer.

FYI if you increase caster you'll get more camber while turning and so you won't need as much static camber - to do so would require either camber/caster plates or drilling/grinding out the inner (at subframe) radius rod bolt holes and adding offset washers (also sold by DSE, or one could make them themselves).

[FASTFATBOY]

Originally Posted by KillboyPowerhead

If you're selling the ZL1 then I guess you're more concerned about the 1LE? I'd say for the ZL1 try a square tire setup, and as the 1LE is already square try the DSE rear bar. Using factory shocks/springs? I have JPSS bars (27mm front, 32mm rear), solid rear mounts, BC racing coilovers (8kg front, 12 kg rear spring rates) and factory rear RS/SS wheels all around (275/40 tires) on my V6 and it's more biased toward oversteer.

FYI if you increase caster you'll get more camber while turning and so you won't need as much static camber - to do so would require either camber/caster plates or drilling/grinding out the inner (at subframe) radius rod bolt holes and adding offset washers (also sold by DSE, or one could make them themselves).

Yes, keeping the 1LE.

I have put the DSE rear bar in the middle hole on the ZL1 and it went too far to loose.

I currently have ZL1 tire sizes.

I don't want coilovers, too much brain damage.

I would like to make what I have better, if I could just get 50% of it out I'd be happy. With 50% out on some 200 tread tires I could make the Vettes I run with up there look bad lol.

To corner faster the key is entry speed, when I start adding entry speed the car just plows.

I may just put some lowering springs on it and the DSE rear bar on it and it will be what it'll be. I can't turn it into a Vette, it's physics.

[CamaroCracka]

I got my Z28 setup from an SCCA racer who helped develop the DSSVs on the Gen5 with GM and GM had him move the mounts on the front shocks down 1 inch and only a half in inch in the back. He said the half inch of rake was to decrease the understeer. I believe the ZL1 springs lower the rear less than the front too, but only by about a quarter inch.

Justice Pete recommended a +5mm difference between the front bar and the rear bar to address understeer.

The 1LE has the same springs as the SS, so I think you have the right idea with changing springs.

[FASTFATBOY]

Originally Posted by CamaroCracka

I got my Z28 setup from an SCCA racer who helped develop the DSSVs on the Gen5 with GM and GM had him move the mounts on the front shocks down 1 inch and only a half in inch in the back. He said the half inch of rake was to decrease the understeer. I believe the ZL1 springs lower the rear less than the front too, but only by about a quarter inch.

Justice Pete recommended a +5mm difference between the front bar and the rear bar to address understeer.

The 1LE has the same springs as the SS, so I think you have the right idea with changing springs.

1LE bars are 27mm front and 32mm rear from GM.

The DSE rear bar is 35mm.

[CamaroCracka]

Originally Posted by FASTFATBOY

1LE bars are 27mm front and 32mm rear from GM.

The DSE rear bar is 35mm.

1LE bars are 27/28. ZL1 25/28. Both the 1LE and the ZL1 use the same rear bar. Z28 are only 25/26.

[FASTFATBOY]

Originally Posted by CamaroCracka

1LE bars are 27/28. ZL1 25/28. Both the 1LE and the ZL1 use the same rear bar. Z28 are only 25/26.

Google was wrong.

Maybe the lowering springs and the DSE rear 35mm rear bar will make it better.

I called JDP and talked to him, he is looking for a specific set of springs to sell me to help this issue, waiting on a return call. He knows what they are, he is looking to see if they are available.

Wondering what a ZL1 25mm front bar and the 35mm rear bar would do, probably be ass happy.

[KillboyPowerhead]

Justice Pete recommended many a' time the 5mm difference between front and rear bars, although I remember in his more later posts he said that he was liking more and more the stock SS front bar with his rear bar (10mm difference). Believe both were in reference to a square tire setup which he also suggested was best for the 5th gen.

Regarding the DSE bar, I remember reading somewhere that it is hollow and about equivalent to a 32mm solid bar stiffness-wise. Not sure if the 1LE and/or ZL1 bars are hollow or solid; believe SS is solid? Or were changed to solid at some point? Something else to keep in mind.

[acammer]

Here is the key:

Originally Posted by FASTFATBOY

I currently have ZL1 tire sizes.

Get the staggered width out of it. Per factory the 1LE was square with intention - the staggered width you added is definitely going to hurt the chassis balance and exacerbate understeer. You can work the sway bars and spring rates, but you'll always be fighting against that stagger.

[FASTFATBOY]

Originally Posted by acammer

Here is the key:



Get the staggered width out of it. Per factory the 1LE was square with intention - the staggered width you added is definitely going to hurt the chassis balance and exacerbate understeer. You can work the sway bars and spring rates, but you'll always be fighting against that stagger.

I have never understood this.

If you are off the gas on corner entry this should not matter at all, now at apex on gas I can see where it would.

My issue is at turn in off the gas, once the car settles I crack the gas on but I have to wait an eternity for that to happen.

This is my ZL1 in stock form at NOLA, look how bad the under steer is...it's rediculous.

Turn up the volume and listen to the front tires.


I have to waaaiiiit and drive around the under steer.

[acammer]

Originally Posted by FASTFATBOY

I have never understood this.

If you are off the gas on corner entry this should not matter at all, now at apex on gas I can see where it would.

My issue is at turn in off the gas, once the car settles I crack the gas on but I have to wait an eternity for that to happen.

This is my ZL1 in stock form at NOLA, look how bad the under steer is...it's rediculous.

Turn up the volume and listen to the front tires.


I have to waaaiiiit and drive around the under steer.

A big part of the problem is that these are just big, heavy cars for the amount of tire under them. Understeer does not equate to a grip level, it simply relates to balance. You eluded to this yourself when you said something like "don't tell me it's the tires" - and I agree with that, tires impact grip level and even responsiveness, but not steady-state chassis balance.

However, there is something to be said for getting the chassis rotating into the corner better by getting the chassis balance closer to where you want it. Just because the front tires are loaded much heavier than the rear tires on entry does not mitigate the fact that more rear grip will keep that end of the car more firmly stuck to the track. That shows up as understeer, and will hurt entry, and can even hurt the maximum cornering speed.

The chassis designers of these cars had some decision to make, and in the case of the ZL1 that was their high power, grand tourer. Having the biggest power, the compromised on chassis balance into vs. out of the corner, and put some extra width on the rear to help corner exit deal with all that supercharged power. However, the 1LE and Z/28's cars with less power and more grip (yes, the 1LE has the same tires, but it's significantly ligther) got the squared treatment to improve that balance.

40mm of tread width difference isn't going to be life changing to the chassis balance, but it absolutely does matter. On a regular SS chassis you have 245/275 and so that difference is a little more noticable when getting square, and I can promise you that it helps get the chassis closer to neutral. You can get there with enough swabar/spring rate as well, but unless you're got a pretty powerful setup I suspect you probably don't need the 305 out back on slow corner exits as much as you'll appreciate better chassis balance everywhere else. If you square the wheel and tire, then you can rotate, and that will definitely get more life out of the tires by getting the fronts to the back when you start to murder the shoulders.

Just my two cents.

[FASTFATBOY]

Originally Posted by acammer

A big part of the problem is that these are just big, heavy cars for the amount of tire under them. Understeer does not equate to a grip level, it simply relates to balance. You eluded to this yourself when you said something like "don't tell me it's the tires" - and I agree with that, tires impact grip level and even responsiveness, but not steady-state chassis balance.

However, there is something to be said for getting the chassis rotating into the corner better by getting the chassis balance closer to where you want it. Just because the front tires are loaded much heavier than the rear tires on entry does not mitigate the fact that more rear grip will keep that end of the car more firmly stuck to the track. That shows up as understeer, and will hurt entry, and can even hurt the maximum cornering speed.

The chassis designers of these cars had some decision to make, and in the case of the ZL1 that was their high power, grand tourer. Having the biggest power, the compromised on chassis balance into vs. out of the corner, and put some extra width on the rear to help corner exit deal with all that supercharged power. However, the 1LE and Z/28's cars with less power and more grip (yes, the 1LE has the same tires, but it's significantly ligther) got the squared treatment to improve that balance.

40mm of tread width difference isn't going to be life changing to the chassis balance, but it absolutely does matter. On a regular SS chassis you have 245/275 and so that difference is a little more noticable when getting square, and I can promise you that it helps get the chassis closer to neutral. You can get there with enough swabar/spring rate as well, but unless you're got a pretty powerful setup I suspect you probably don't need the 305 out back on slow corner exits as much as you'll appreciate better chassis balance everywhere else. If you square the wheel and tire, then you can rotate, and that will definitely get more life out of the tires by getting the fronts to the back when you start to murder the shoulders.

Just my two cents.

The 1LE I am keeping makes 550 wheel, I am not flooring the car on exit up there anyway as the car is too unpredictable in it's current state. Power does you no good in the mountains, it's all about entry speed and momentum at Tail of the Dragon.

I will lower the car and put the DSE 35mm rear bar on it and see what happens.

I learned to drive in the ass happy platform that is the 4th gen Fbody so a little loose doesn't phase me.

[morepowerjoe]

Please let us know how it goes as I am very interested.

[fz4k98]

This spring i installed adjustable coilovers in front and did a track day. I could adjust the coilovers to increase corner speed but the understeer would be the same, just at higher speed.

The understeer on my car was the same on original shocks as the coilovers, just different corner speed.