Front lifting on high speed corners

[AriuSen]

I know I will get a lot of different opinions, but I wanted to know why you think is doing that and how to fix it.
Got some opinions already, but happy to hear some from here

Set up:
500/550 lbs hyperco springs
Jrz rs pro
Hotckis front sway bar and no rear bar
Camber shouldn?t matter here.
Obviously the car is understeering on high speed corner due to the lift.
Thanks!

[CorruptCommie]

Did you send it through a curb in that picture, or is that how it normally looks through a corner?

[1MOREMOD]

Originally Posted by CorruptCommie

Did you send it through a curb in that picture, or is that how it normally looks through a corner?

Yeah looks like you went dukes of hazard. Should pick up inside rear at least mine does all the time.

[roastbeef]

i presume the car was corner balanced? do you think that took away from the front end rake and transferred the lean to the rear?

another thing that comes to mind is caster. has the caster been changed in a way that when you turn, the front tires want to "stand on their tippy-toes?"

i don't have any real world experience with this, these are just my initial thoughts. interesting subject.

[JsL]

Originally Posted by AriuSen

...
Hotckis front sway bar and no rear bar
...

So you have a front sway bar and no rear sway bar? I think that's the cause.

The rear is rolling and the front wants to roll, but can't as easily with a sway bar so it just lifts up the front.

[Richbot]

Check front bar for bind (looks like essentially no droop travel?), more rear spring are the first places I'd look. I bet if it's only happening in high speed corner your wing and diffuser are just too much for the front aero to handle, the Z4 body seems lifty up front

We were just talking about bumpstop tuning on aero cars lately in another thread

[The HACK]

Need less front rebound.

[AriuSen]

Originally Posted by CorruptCommie

Did you send it through a curb in that picture, or is that how it normally looks through a corner?

No curb.

[CorruptCommie]

Yeah, that would explain the understeer. Maybe try rear sway bar, higher spring rate, lower front ride height - some combination of those. What kind of tires are you running? Front splitters need low clearance otherwise they lose a lot of the downforce.

[Richbot]

static ride height seems fine. Makes me think aero at 90+ coupled with not enough rear spring could be changing rake especially if not a true coilover

The track appears to be falling away there too, could just be asking too much from the car

[The HACK]

Riverside/Telledega counter-clockwise? There's a slight bank/camber in towards the apex. Track's not falling away, might be a trick with the angle in which the photo was shot. I suspect the "lift" is more of an optical illusion because that turn places tremendous amount of load to the outside tires, thus with the rear having no swaybar, the inside wheel extends fully to remain in contact with the ground while the front inside is lifted off of the ground due to a combination of not enough rebound control AND stiff front swaybar AND no rear bar in comparison.

[Chuck's M3]

Dunno why, but this came to mind...

[dogbone]

Based on the couple pix I've seen of your car, you must have a TON of rear grip. You have a big rear wing, a rear diffuser and no rear sway bar. How are you balancing all this out in the front? In my opinion, you're not. The simple front splitter on a stock bumper is not enough given the powerful rear setup. The proof? The picture showing you driving on three wheels under high speed, high-G situations.

The tools you can use to combat this lifting wheel are: (in order that I would try)

-Reduce stiffness of front sway bar (if possible): Reducing stiffness of the front sway bar could reduce inside wheel lift on rounders like this.

-Lessen Angle-Of-Attack of rear wing: Reducing AOA of wing would reduce pressure on the rear of the car which would allow weight and grip to return to the front and reduce understeer in general. (I believe that right now, you have more rear grip than you need---that this car is so rear-focused, that the front is literally lifting in the air.)

-Stiffer rear springs: Stiffer rear springs might be able to give the rear of the car a bit more support given the huge forces happening in the rear. And at the same time shift weight to the front.

-Put a sway bar in rear: A rear sway bar could share the duties of leveling the car with the front sway bar. This would reduce the amount of work the front sway bar has to do.


I went to the Hotchkis website to check out your sway bar. Hotchkis doesn't specifically make a sway bar for a Z4M. Which version of Hotchkis sway bar are you using? The E46 M3? Even if it does generally fit, who's to say that the stiffness of the bar is appropriate to your car? The Z4M is lighter than an E46 M3. And if you've lightened the car even further for tracking, perhaps this bar is just too stiff for a light Z4. Plus, given that it's the only sway bar on the car, the duties of keeping the car level on a long turn like Riverside are falling on the outside springs/dampers and the front sway bar. No rear sway bar to help. I think the front passenger damper is compressing so far and the sway bar is so stiff that it's just lifting the inside wheel. As Richbot mentioned, there doesn't seem to be any droop happening with the wheel that's in the air. This means that it is actively being pulled upward. The only thing that could pull that wheel upward so hard would be the sway bar.

I think a combination of the four things mentioned above can bring more balance to a car that seems to be very rear-focused.

(I can share some other thoughts if you're interested.)

[AriuSen]

Originally Posted by roastbeef

i presume the car was corner balanced? do you think that took away from the front end rake and transferred the lean to the rear?

another thing that comes to mind is caster. has the caster been changed in a way that when you turn, the front tires want to "stand on their tippy-toes?"
i don't have any real world experience with this, these are just my initial thoughts. interesting subject.

Yes, CB....I have less rake in the front, so that wouldnt be the case here.
Caster? hmm I have about 6.7 caster.....not sure if that can affect in anything, but something to consider =)

Originally Posted by JsL

So you have a front sway bar and no rear sway bar? I think that's the cause.

The rear is rolling and the front wants to roll, but can't as easily with a sway bar so it just lifts up the front.

correct!...i need to put my rear sway bar back, but the problem is that the z4m chassi is very very stiff, and when I had the rear sway bar, my car was super twitchy....thats why I run soft spring rates in the rear.
I could do 2 things here.
1. add rear sway bar + add 100lbs springs in the front to try to keep the car balance the way it was without the rear sway bar

Originally Posted by Richbot

Check front bar for bind (looks like essentially no droop travel?), more rear spring are the first places I'd look. I bet if it's only happening in high speed corner your wing and diffuser are just too much for the front aero to handle, the Z4 body seems lifty up front

We were just talking about bumpstop tuning on aero cars lately in another thread

thanks for the comments! the wing however has nothing to do with this.....a wing doesnt put that much force to lift a car.

Originally Posted by The HACK

Need less front rebound.

yeap...that is one of the things to change. I was running +11 front and +10 rear, because I like the front grip coming out of the corner, but now I need to go less in the front

Originally Posted by CorruptCommie

Yeah, that would explain the understeer. Maybe try rear sway bar, higher spring rate, lower front ride height - some combination of those. What kind of tires are you running? Front splitters need low clearance otherwise they lose a lot of the downforce.

I am running pirelli slicks....your tips are what I heard too....thanks!

[AriuSen]

Originally Posted by Chuck's M3

Dunno why, but this came to mind...
Attachment 1676638

best solution ever!! lol

[AriuSen]

Originally Posted by dogbone

Based on the couple pix I've seen of your car, you must have a TON of rear grip. You have a big rear wing, a rear diffuser and no rear sway bar. How are you balancing all this out in the front? In my opinion, you're not. The simple front splitter on a stock bumper is not enough given the powerful rear setup. The proof? The picture showing you driving on three wheels under high speed, high-G situations.

The tools you can use to combat this lifting wheel are: (in order that I would try)

-Reduce stiffness of front sway bar (if possible): Reducing stiffness of the front sway bar could reduce inside wheel lift on rounders like this.

-Lessen Angle-Of-Attack of rear wing: Reducing AOA of wing would reduce pressure on the rear of the car which would allow weight and grip to return to the front and reduce understeer in general. (I believe that right now, you have more rear grip than you need---that this car is so rear-focused, that the front is literally lifting in the air.)

-Stiffer rear springs: Stiffer rear springs might be able to give the rear of the car a bit more support given the huge forces happening in the rear. And at the same time shift weight to the front.

-Put a sway bar in rear: A rear sway bar could share the duties of leveling the car with the front sway bar. This would reduce the amount of work the front sway bar has to do.


I went to the Hotchkis website to check out your sway bar. Hotchkis doesn't specifically make a sway bar for a Z4M. Which version of Hotchkis sway bar are you using? The E46 M3? Even if it does generally fit, who's to say that the stiffness of the bar is appropriate to your car? The Z4M is lighter than an E46 M3. And if you've lightened the car even further for tracking, perhaps this bar is just too stiff for a light Z4. Plus, given that it's the only sway bar on the car, the duties of keeping the car level on a long turn like Riverside are falling on the outside springs/dampers and the front sway bar. No rear sway bar to help. I think the front passenger damper is compressing so far and the sway bar is so stiff that it's just lifting the inside wheel. As Richbot mentioned, there doesn't seem to be any droop happening with the wheel that's in the air. This means that it is actively being pulled upward. The only thing that could pull that wheel upward so hard would be the sway bar.

I think a combination of the four things mentioned above can bring more balance to a car that seems to be very rear-focused.

(I can share some other thoughts if you're interested.)

Hey,
The car doesnt have a TON of rear grip, this car is loose in the rear by nature.....aerodynamics are the minimal issue here....the main issue is what you said....either soften front sway bar, I was in medium setting, add more spring rate in the rear, or put my rear sway bar back on..

Putting the rear sway bar back is the last alternative since this car tries to kill me when I have them on
I like to test my car one change at a time....so for now I will soften the front sway bar, and lower front rebound....if its still lifting, I will add rear spring rates.....and if its still not working, I will put my rear sway bar back, and increase front spring rate.

About hotckis you are correct. Its an m3 e46 sway bar,.
However both OEM sway bar is the same 27mm.
The hotckis is only 3mm stiffer in the soft setting.
the e46 is only about 100lbs heavier than the z4m.

thanks for the observations!!

[dogbone]

Originally Posted by AriuSen

Hey,
this car is loose in the rear by nature.....aerodynamics are the minimal issue here....

Let's consider these statements at different speeds. Is the car loose at slow speeds or high speeds or both?

At low speeds, I agree, aero requires minimal thought. However, at high speeds, aero is quite formidable and needs much more consideration. Don't underestimate all that aero you have on there!

I totally understand if you say the car is loose at low speeds. My E90 M3 became loose too after it was gutted and caged since most of the weight came out from the rear and the cage stiffened the chassis. The aero is a big fancy decoration at low speeds. I still fight looseness at slow speeds. Exiting a tight corner requires patience, a smooth throttle and grippy tires to really put power down. The Off Ramp corner is a constant source of challenge. (And the pavement there doesn't help.)

But, I would be VERY VERY surprised if you said the car, with this setup, is loose at high speeds. I mean, c'mon, you have a big rear wing, a rear diffuser, no rear sway bar and only 550 lbs springs. If you are going near 100mph at the apex of Riverside, you are generating a TON of downforce on the rear in that turn. On high speed rounders, like on Riverside, I believe the rear aero is a very large consideration.

And it is worth noting that Riverside is a bit unique. In California, the Riverside turn is perhaps the most prominent example of a basically flat, very high speed, long, fairly steady rounder. No other track around here offers the same scenario. Big Willow Turn 2 is going up a hill. Big Willow Turn 8/9 is probably the closest. It's faster and flat but isn't a steady single turn because you can straighten out the middle of 8 and then Turn 9 is decreasing radius. ACS has higher speeds and a steady loading on Turn 1/2, but it is a banking Nascar Oval so there's a whole lot of other things going on there. Chuckwalla doesn't offer speeds as high on it's flat rounders. No on Thermal. Moving further away----No at Laguna Seca. No at Sonoma (Turn 6 goes downhill). Thunderhill's Turn 2 is fairly similar, but even then the speeds are still slower (more like Chuckwalla). Anyway, all this to say that if your car is presenting some seemingly odd challenge at Riverside, part of it is due to the fact that the car doesn't see this exact combination of parameters many other places.

In this picture, I'm guessing you are around 100mph on Riverside. This is THE defining moment where all that rear downforce should shine and become formidable. And I would say, looking at your picture, it is doing exactly that (along with all the other factors we already mentioned).

And one last thing to consider (which usually should be a primary consideration): weight transfer based on gas/brake pedal activity----on Riverside, I'm always trying to be on the gas if possible. This is one more thing to shift even more weight to the rear of the car.

[Richbot]

I'm not saying the aero is necessarily lifting the front of the car. Who cares what the car's attitude is through the corner if it's fast? Nobody, that's who. I'm saying higher speed understeer = aero imbalance, IMO, and aero imbalance piled on top of soft rear springs and no rear bar means lots of rear grip and more the faster you go. Lifting an inside front once in a while doesn't necessarily mean the suspension is set up poorly, especially with a steampunk horse and buggy E46 front suspension

I'm not a fan of big rear bars on cars like ours, so I agree leave it off if you can get away with it, and I think you can if you up the rear spring some

[M3 Number 86]

Originally Posted by The HACK

Riverside/Telledega counter-clockwise? There's a slight bank/camber in towards the apex. Track's not falling away, might be a trick with the angle in which the photo was shot. I suspect the "lift" is more of an optical illusion because that turn places tremendous amount of load to the outside tires, thus with the rear having no swaybar, the inside wheel extends fully to remain in contact with the ground while the front inside is lifted off of the ground due to a combination of not enough rebound control AND stiff front swaybar AND no rear bar in comparison.

This is sunrise. Turn 1.

[AriuSen]

Originally Posted by The HACK

Riverside/Telledega counter-clockwise? There's a slight bank/camber in towards the apex. Track's not falling away, might be a trick with the angle in which the photo was shot. I suspect the "lift" is more of an optical illusion because that turn places tremendous amount of load to the outside tires, thus with the rear having no swaybar, the inside wheel extends fully to remain in contact with the ground while the front inside is lifted off of the ground due to a combination of not enough rebound control AND stiff front swaybar AND no rear bar in comparison.

that picture is sunrise.....not riverside.
im going probably at 60-70 mph
dogbone

[AriuSen]

Originally Posted by dogbone

Let's consider these statements at different speeds. Is the car loose at slow speeds or high speeds or both?

At low speeds, I agree, aero requires minimal thought. However, at high speeds, aero is quite formidable and needs much more consideration. Don't underestimate all that aero you have on there!

I totally understand if you say the car is loose at low speeds. My E90 M3 became loose too after it was gutted and caged since most of the weight came out from the rear and the cage stiffened the chassis. The aero is a big fancy decoration at low speeds. I still fight looseness at slow speeds. Exiting a tight corner requires patience, a smooth throttle and grippy tires to really put power down. The Off Ramp corner is a constant source of challenge. (And the pavement there doesn't help.)

But, I would be VERY VERY surprised if you said the car, with this setup, is loose at high speeds. I mean, c'mon, you have a big rear wing, a rear diffuser, no rear sway bar and only 550 lbs springs. If you are going near 100mph at the apex of Riverside, you are generating a TON of downforce on the rear in that turn. On high speed rounders, like on Riverside, I believe the rear aero is a very large consideration.

And it is worth noting that Riverside is a bit unique. In California, the Riverside turn is perhaps the most prominent example of a basically flat, very high speed, long, fairly steady rounder. No other track around here offers the same scenario. Big Willow Turn 2 is going up a hill. Big Willow Turn 8/9 is probably the closest. It's faster and flat but isn't a steady single turn because you can straighten out the middle of 8 and then Turn 9 is decreasing radius. ACS has higher speeds and a steady loading on Turn 1/2, but it is a banking Nascar Oval so there's a whole lot of other things going on there. Chuckwalla doesn't offer speeds as high on it's flat rounders. No on Thermal. Moving further away----No at Laguna Seca. No at Sonoma (Turn 6 goes downhill). Thunderhill's Turn 2 is fairly similar, but even then the speeds are still slower (more like Chuckwalla). Anyway, all this to say that if your car is presenting some seemingly odd challenge at Riverside, part of it is due to the fact that the car doesn't see this exact combination of parameters many other places.

In this picture, I'm guessing you are around 100mph on Riverside. This is THE defining moment where all that rear downforce should shine and become formidable. And I would say, looking at your picture, it is doing exactly that (along with all the other factors we already mentioned).

And one last thing to consider (which usually should be a primary consideration): weight transfer based on gas/brake pedal activity----on Riverside, I'm always trying to be on the gas if possible. This is one more thing to shift even more weight to the rear of the car.

dogbone, have you walked at the track in buttonwillow?
Its amazing how I thought riverside was flat too, but when you walk at the track, you will get shocked how banked the turn is....specially if you stick to the center on the turn.....outer part of the turn is pretty much flat.
anyway, i take riverside at around 109.

I know aero makes a huge difference at 100+mph, but trust me....its not the main factor of the lift.....not that I mean it doesnt have any affect....its has some....but the main reason is due to no rear sway bar, and soft springs combo in the rear, and not due to the aero.

[The HACK]

Originally Posted by AriuSen

that picture is sunrise.....not riverside.

Ah. Okay, then the track is definitely falling off there.