Need help - fine-tuning camber to improve lap-times

[Asbjorn]

In order to squeeze out the next lap time improvements, I would like to dial in my camber properly. I have never done this before, so I would love your inputs and experiences on the topic.
I recently re-installed OEM springs up front (replacing Eibach pro-kit), and at the same time more or less maxed out camber both front and rear.

Track info
Track: Ningbo Int'l Speedpark
Track length: 4km (2.5miles), full circuit, 13 left hand turns, 10 right
Ambient temp: 14C, overcast
Track temp: 15C (59F)

Setup
Tires: Zestino Gredge, 235/40R18 front, 265/35R18 rear
Dambers: Koni FSD
Springs: OEM front (non sport), Eibach Pro-kit rear
Sway bars: H&R front / rear (stiffest setting rear)
Most bushings replaced with stiffer types or bearing kits / solid mounts.
Cold tire pressure: 2.2bar @ 25C (Using nitrogen air)
OEM toe and caster settings (ie slight toe in front and rear)

Tire temp measurements after 20mins at the track
I went through most corners and braking zones at 80-100%
Only did half throttle on straights




Front L R
Outer Mid Inner | Inner Mid Outer
57°C 57°C 64°C | 64°C 57°C 59°C
135F 135F 147F | 147F 135F 138F

Tire pressure: 2.65bar (38psi)
Camber: -2°44

Rear L R
Outer Mid Inner | Inner Mid Outer
41°C 44°C 49°C | 54°C 50°C 48°C
106F 111F 120F | 129F 122F 118F

Tire pressure: 2.50bar (36psi)
Camber: -2°20*
*this number was taken from memory, and may be off...

Evaluation of balance
Corner entry: Fairly neutral (over-steer if trail-braking violently)
Mid corner: Slight under-steer at the limit. Got worse on the last laps.
Corner exit: Not evaluated today
Braking: OK, but not the best I have felt in this car on this track

Optional changes
1) Install the softer OEM sway bar up front, keep H&R rear
2) Reduce hot tire pressure to 2.2bar front and rear (manufacturer recommends 2.2 - 2.4bar (32-35psi))
3) Reduce camber front and rear, but how much?

I am not sure if the inner tire temps are high because tire pressure is too high, or because camber is too negative.

Please let me know your thoughts.

 

[barry@3DM]

Are you using an IR temp reader? If so you really need to get a probe style. They go down below the surface of the rubber and get a more core temp reading which is what you want. The surface cools off quickly and will give you false readings with an IR sensor. This is what I use: Temp Sensor

I'm going to do everything in Fahrenheit and PSI and I'll let you convert.

What you are looking for is about a 20F degree difference between the inside and outside. So for example you want:
Inside: 180F
Middle: 170F
Outside: 160F

The reason is because as you turn, lets say to the right for example, the left wheel (outside wheel) has the whole tire on the ground. The inside wheel (right wheel) only has the inside part of the tire on the ground. Then you turn left and the opposite happens. Therefore the inside of the tire is always getting heated up and will give you a higher temp number compared to the middle and outside.

You will typically see a higher spread on the front tires because you have steering ackerman also dragging the inside wheel. The rear you might end up with less of a spread between inside and out, more around 10F but 20F is fine, too.

For pressures what you will want to do is adjust up or down to get the middle tire temp in between the outside and inside temps. You want to target no more than 40PSI hot.

 

[Hydra Performance]

I also think it would be prudent to run ~0.8-1.0 less negative camber on the rears compared to the fronts. Reason being that the rear multilink setup has more camber compensation with roll by design vs the front struts. Plus we're pretty much always front-end limited when it comes to overall grip, and traction limited when it comes to corner exit. Therefore I would suspect that optimizing your setup for less R camber would result in an improvement in lap times.

 

[Asbjorn]

Thanks @barry@3DM for the very useful advice. I have updated my original post with F and psi values for what it is worth.

Based on this I can see that I could actually do with more camber up front. That is, if my IR readings are correct. I did the front tires within 1min of coming off the track.

Btw do you recommend increasing caster on the E90 front suspension?

@hydra also thanks for your input. I wonder what the differences are in terms of camber behavior between E46 and E90. The Z4 I drive has a very E46 M-like rear. I have installed M RTAB and limiter, outer (poly) bearings, as well as solid subframe mounts. Inner bushings are stock rubber - they are rather small, so they cant deflect much anyway.

 

[barry@3DM]

100% agree with @hydra. The multilink rear camber curve is much better than the front MacPherson strut. Even though the e90 and E89 rear suspensions differ they control camber in much the same way with upper and lower control/camber arms. Not sure of the curve differences off hand but they are going to be similar.

As for camber numbers, I agree, you need to go with more camber up front. You wrote -2°44, is the 44 minutes as in -2°44' (-2.75°)? If so i'd recommend at least -3° even as much as -3°30' (-3.5°).

What to you mean by "Outer (poly) Bearings"? The Z4 comes from the factory with a bearing (ball joint) on the top and a bushing on the bottom. The trick is to put the same bearing from the top on the bottom. Part number: 33306852895

As for caster yes I would run more caster than stock. You will get more front end grip in low speed turns that have higher steering angles without affecting high speed balance (low steering angles). win win.

 

[Asbjorn]

As for camber numbers, I agree, you need to go with more camber up front. You wrote -2°44, is the 44 minutes as in -2°44' (-2.75°)? If so i'd recommend at least -3° even as much as -3°30' (-3.5°).

What to you mean by "Outer (poly) Bearings"? The Z4 comes from the factory with a bearing (ball joint) on the top and a bushing on the bottom. The trick is to put the same bearing from the top on the bottom. Part number: 33306852895

As for the rear, I totally agree. I actually tried to source the BMW ball joint you mentioned. Ended up getting the wrong part number, and just installed powerflex polys instead. Not proud of it, but fortunately they are easy to service in that location. Here's the latest overview of my setup:



As for the front camber I realize I am maxed out with -2.75. I looked into other camber plates, such as the Vorschlag types, and it seems they also max out at that angle. Now I believe these are my options:

1) Lower front springs (currently have non-M sport springs)
I have asked by buddies @fmorelli @jts1981 et al if they still have their M adaptive springs lying around. They are hard to find in China as the Z4 35i was sold with non M sport suspension here. The M springs should provide a 10mm decrease in ride height. This still wouldn't bring me down to -3.5deg though. But as it is now, I am not willing to lower the car more than that.

2) Softer sway bar (currently using H&R)
A softer front sway bar should increase dynamic camber. I also assume the H&R setup has retained the balance of the OEM setup, which is probably balanced towards understeer/safe behavior. The part is easy to swap, so I intend to do some A-B testing of the H&R vs the OEM front sway bars at track next week.

3) Custom work on the strut tower
Probably not...

4) Adjustable control arms? (Already have the M control arms)
Having learned how toe behavior changes with control arm bushing type, and realizing running M control arms with a non-M hubs may not be optimum, I am greatly concerned if adjustable control arms is the right direction to go?

Thanks so much for your support on this!

 

[Asbjorn]

I am very curious what others have done to achieve -3.5deg camber with the E9x front.

Quick follow up on the options I identified above:

Softer sway bar
So I have these options available:
Bushing: Poly (H&R) vs Rubber (OEM)
Bar: H&R vs OEM non-M sport

This is how they compare for those interested:


I have decided to compare the H&R setup against a mixed setup consisting of the OEM bar and the H&R poly bushings. I am keeping the rear full H&R and at its stiffest setting.

Adjustable control arms (Already have the M control arms)
I am told that adjustable control arms may bind with stock suspension or even street-type coil-overs. I am also told that such products are mainly for correcting roll center on cars that are very low.

Lower front springs (currently have non-M sport springs)
Still haven't found any M sport front springs. Again, I am not able to go any lower than -10mm up front. As for coil-overs, I am told that doing stock ride height on one of those systems typically puts the damper out of it's optimal range. Apparently they need at least at -15mm drop to work well. Now question is if that is -15mm from M sport or non M sport. In any case, even a -20mm drop wont put me at -3.5deg static camber.

 

[Hydra Performance]

Remind me again, why do you even want -3.5 F camber with your soft suspension?

 

[Asbjorn]

Remind me again, why do you even want -3.5 F camber with your soft suspension?

Because the temperature delta across my front tires is not ideal according to @barry@3DM. I do not have enough camber up front. Rear looks fine.

I am not saying I need exaclty -3.5deg camber though, I am just really curious how others have achieved that number. Perhaps -3deg is enough. I will adjust according to the data that I collect.

 

[Hydra Performance]

@Asbjorn
I suggest you measure your tire temps properly with a probe before adding more F camber, but my gut feeling is that you should not need more than what you are currently running

 

[Asbjorn]

BTW, now running the oem sway bar front. Car leans like a boat even the rear still has the H&R bar set to the stiffest setting. I did not expect this.

 

[Rob09msport]

Its cause you dont have enough spring. A sway bar can transfer load but you still need spring rate to transfer it to that's prob why your getting a wallowing feel you need resistance and it just isnt their.

 

[barry@3DM]

I am very curious what others have done to achieve -3.5deg camber with the E9x front.

Quick follow up on the options I identified above:

Softer sway bar
So I have these options available:
Bushing: Poly (H&R) vs Rubber (OEM)
Bar: H&R vs OEM non-M sport

This is how they compare for those interested:
View attachment 17955

I have decided to compare the H&R setup against a mixed setup consisting of the OEM bar and the H&R poly bushings. I am keeping the rear full H&R and at its stiffest setting.

Adjustable control arms (Already have the M control arms)
I am told that adjustable control arms may bind with stock suspension or even street-type coil-overs. I am also told that such products are mainly for correcting roll center on cars that are very low.

Lower front springs (currently have non-M sport springs)
Still haven't found any M sport front springs. Again, I am not able to go any lower than -10mm up front. As for coil-overs, I am told that doing stock ride height on one of those systems typically puts the damper out of it's optimal range. Apparently they need at least at -15mm drop to work well. Now question is if that is -15mm from M sport or non M sport. In any case, even a -20mm drop wont put me at -3.5deg static camber.

Anti Roll Bar...
How did you use the larger diameter H&R poly bushing on the smaller OEM sway bar? A softer bar will only increase dynamic camber because you compress the suspension more. But your chassis is rolling more which then counter acts that extra camber. There is a whole lot of other things the softer bar (compared to rear) will affect. It takes load off the rear inside tire which will reduce the ability for you to put power down coming out of a turn. It adds more load to the outside front tire which will overheat it faster causing understeer problems towards the end of a session. List goes on and on...


M control arms/ adjustable control arms...
I never said the toe change was "bad". I said it was different than what the factory intended. This is a case where replacing rubber with a ball joint is better for handling and steering feel. What I meant was that it could be even better if the geometry was changed to account for it (like the M3).

I agree with not going with an adjustable front control arm. Not needed for your application. It introduces more complexity and reduced longevity than I think you want with your car.

 

[Asbjorn]

Anti Roll Bar...
How did you use the larger diameter H&R poly bushing on the smaller OEM sway bar? A softer bar will only increase dynamic camber because you compress the suspension more. But your chassis is rolling more which then counter acts that extra camber. There is a whole lot of other things the softer bar (compared to rear) will affect. It takes load off the rear inside tire which will reduce the ability for you to put power down coming out of a turn. It adds more load to the outside front tire which will overheat it faster causing understeer problems towards the end of a session. List goes on and on...


M control arms/ adjustable control arms...
I never said the toe change was "bad". I said it was different than what the factory intended. This is a case where replacing rubber with a ball joint is better for handling and steering feel. What I meant was that it could be even better if the geometry was changed to account for it (like the M3).

I agree with not going with an adjustable front control arm. Not needed for your application. It introduces more complexity and reduced longevity than I think you want with your car.

As for the sway bar bushing, I believe the H&R is 27mm whereas the OEM is 26.5mm where the bushings mount. But I did not check this data myself.
Anyhow, I already installed the H&R sway bar back as I did not like how the non-M sport sway bar felt on track yesterday. As you predicted, I got more oversteer on corner exit, and the front end just felt wobbly. I got more mid-turn adjustability, but rather due to the rear giving up earlier than better front end grip.

Looking at the bars, I thought they where unbalanced towards a stiffer front end, and that I would balance things out with the OEM sway bar up front. It turned out I was wrong.

Thanks for your recommendations regarding the control arms. I really appreciate your input.

So I have pretty much hit a wall here - unless I drill new holes in my strut towers.

 

[gmx]

Remind me again, why do you even want -3.5 F camber with your soft suspension?

You need more with soft suspension to compensate for the load transfer (roll).

No one makes camber plates for the E89?

 

[Asbjorn]

You need more with soft suspension to compensate for the load transfer (roll).

No one makes camber plates for the E89?

Yes, here's my setup

Without camber plates I would have never gotten past -1 deg camber. They however max out before -3 with stock ride height.

With strut modifications you can install other E9x camber plates as well - this was documented in @fmorelli 's build thread.

EDIT - Race camber plates from gc exist as well if you have coilovers. They need the lower diameter springs.

 

[Asbjorn]

A good read that also explains why more load transfer is not beneficial to overall grip:

https://jalopnik.com/the-engineering-behind-the-new-bmw-3-series-handling-1830257906

I learned here that grip does not increase linearly with force due to inherent properties of rubber.

 

[gmx]

That G20 article further cements my notion that BMW no longer make sports cars. It's a shame...
Well yes, what happens when you overload the RL on a right hander? Oversteer.

 

[Bnks334]

You seem to be reading all sorts of stuff and imagining up problems that don't exist lol... Also keep in mind that a lot of the above recommendations should only be taken as starting points.

Based on this I can see that I could actually do with more camber up front. That is, if my IR readings are correct. I did the front tires within 1min of coming off the track.

The temperature differential you'll see across the tire is going to vary by the track you are running on; therefore, changes to get the ideal alignment, tire pressure, and suspension stiffness are all going to be track specific as well. There are too many variables for anyone to give you a meaningful adjustment. You're temperatures aren't off so drastically that there is some glaring suspension issue. The temps are pretty low though, but, I guess low is good for the street tires you are running. You can try dropping tire pressure a bit. 38/36 is a bit high for me usually. I like to see 34-36psi hot. I usually go on at like 26-28psi.

With that being said, @ -2.44* I really don't think you should need any more front camber on 240tw street tires. Forget tire temps and look first at how your tires are wearing. All tires have wear bars that show you the ideal usage per the manufacturer. Tweak things like tire pressure to make full use of your tires first.

@-2.2* I think your rear camber might be a bit high for 240TW tires. More rear camber can help keep the rear stable in corners (keep the car more oriented toward understeer) but driving on the inside edge of the tire decreases your ability to put down power. I'd drop more toward -1.75* to -2.0*.

For reference, I had perfect tire wear F/R with 200tw tires and -2.4*/-1.75*. When I moved to stickier 80tw r-comps I needed to dial in -2.6*/-2.0* to achieve the same wear bar target. Tire sidewall stiffness also plays into this... A soft sidewall tire is going to deflect more and the scenario might call for more PRESSURE rather than static camber to get ideal wear.

Btw do you recommend increasing caster on the E90 front suspension?

Caster changes aren't really going to make you any faster. Speaking conceptually, caster can help offset camber loss during cornering and peopel generally bump the caster up a bit. But, caster changes also affect steering feel/feedback. You need to understand the complex relationship between scrub radius and king pin inclination to understand how caster changes might affect the car. Suspension and wheel setups/offsets can drastically change the affects of caster changes from car to car. Stock is around 6.x*? With my setup, my caster floor is 7.6*. I could probably get it close to 10* but aggressive caster settings don't generally agree with daily driving. Further, I've read aggressive caster is generally not a good thing on a BMW. I'd keep it under 8*, personally, but experiment with it yourself.

1) Lower front springs (currently have non-M sport springs)

I have asked by buddies @fmorelli @jts1981 et al if they still have their M adaptive springs lying around. They are hard to find in China as the Z4 35i was sold with non M sport suspension here. The M springs should provide a 10mm decrease in ride height. This still wouldn't bring me down to -3.5deg though. But as it is now, I am not willing to lower the car more than that.

2) Softer sway bar (currently using H&R)
A softer front sway bar should increase dynamic camber. I also assume the H&R setup has retained the balance of the OEM setup, which is probably balanced towards understeer/safe behavior. The part is easy to swap, so I intend to do some A-B testing of the H&R vs the OEM front sway bars at track next week.

3) Custom work on the strut tower
Probably not...

4) Adjustable control arms? (Already have the M control arms)
Having learned how toe behavior changes with control arm bushing type, and realizing running M control arms with a non-M hubs may not be optimum, I am greatly concerned if adjustable control arms is the right direction to go?

2) A softer sway bar does not help dynamic camber gain. While you do get better camber gain due to more STATIC suspension compression (braking), you also experience more camber LOSS in dynamic situations (cornering)... You need to consider the NET change, and, in general, a softer suspension is going to net you more dynamic camber loss. That doesn't necessarily mean that a soft suspension setup is"slower" or "worse," but, you need to recognize this affect and recognize the trade-offs. If you want less dynamic camber loss then you would've wanted to move to a STIFFER sway, but, I would NOT be looking at sway bars as a primary method of changing the dynamic camber curve. The affect of sway bar changes on camber is completely overplayed. The car still rolls and you still lose camber in roll. Suspension travel is pretty much always dictated by bump-stop engagement unless your driving a purpose built track car with teeth chattering spring rates. Hence, why we all run fairly high static camber for track duty regardless of sway bar stiffness.

Also consider driving style! Are you trail-braking into the corner, or, are you heavily braking and loading up the front tires? Driving style might need to change drastically depending on how you set the cars balance up. You generally tweak sways to balance the car. As you noted, less front bar produced more front grip for turn-in, but, the balance changed produce too much forward bite and the rear got loose. You might want to try the M3 front sway as a compromise. Keep in mind that the rear sway is basically STRAIGHT. It is very effective. The front bar has many curves. Therefore, you can't just compare the diameters of the front/rear bar to determine "balance."

1) Same as above... lowering the car generally produces a net camber loss in cornering. There are other reasons why we lower cars, but, reducing camber loss in dynamic roll is generally not one of them.

3) This is actually a fairly common/reasonable option... Or, you can just get better camber plates if you really think you need more camber.

4) I'd also agree that making the camber links longer is not advisable without actually understanding the dynamic suspension changes that result. More static camber might be great, but, messing up the cars suspension geometry does't sound all that great to me...

Have you considered moving to a better tire lol? Put a street-able tire like an NT-01 on the car and you'll pick up several seconds alone... Maybe then you'll be able to pinpoint any other tweaks you might want to make. You aren't going to be setting lap records on street tires. That's just facts. EDIT: I see that the tires you are running do come in semi-slicks. Are you using the street tires or the slicks? Next to tires I'd also look into spacing out the wheels as wide as possible while keeping things square/balanced.

 

[Bnks334]

That G20 article further cements my notion that BMW no longer make sports cars. It's a shame...
Well yes, what happens when you overload the RL on a right hander? Oversteer.

Huh? The F-series and G-series both make improvements over the outgoing E8x/E9x chassis. More potential is there once you strip away all the "frills" that make it heavy and bloated. BMW has always produced "super saloons" and not "race cars." BMW's, even M cars, have always been compromise cars... Speed vs luxury and comfort. BMWs aren't common at the track because they are the fastest sport car out there. Although, with work, they do make very good/fun race cars.