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

[Asbjorn]

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.



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.



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.



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.

Hey first of all, thank you so much for this detailed input!

I should have been more clear, that I wanted to improve my laptimes specifically on the Ningbo circuit shown above. I do understand that each track need different setup... same for rain vs sunny track days. I am just trying to get the basics right, and optimize for one track before I move on to the next. I am obviously very new in this regard, and want to learn.

As for the tires, I did run 240tw up front, but then had 180tw on the rear (same brand and type though). This was bugging me, so yesterday I swapped the tires to 200tw both front and rear (an old set of AD08R I had lying around), to take that difference out of the equation. Now, you are right that my temps were low, but as stated, I did not push the car on the straights or in braking. Instead I went through all the turns at 90-100%, and just cruised on the straights. My approach here may have been off.

I also agree that tires matter the most. The people I compete against typically use Trofeo R or Cup 2. I am probably going for Trofeo R next as I have heard the NTs are very noisy. But I am very much undecided on that still. I however didn't realize tires with more grip would require me to start over on the camber adjustments. Great input!

As for front caster I believe I am at 7.5 deg right now (EDIT no 7.2). Also I use ET35 wheels up front to reduce kingpin offset a bit over stock Z4.

So what I conclude from your post:
1) I should consider custom work on the strut tower (better camber plates exist for the stock E89 only if running coilovers)
2) I must select the right tires first, and only then start collecting data (both temp and tire wear) on the exact track that I want to improve lap times on.
3) I probably need less camber rear, and should forget about swapping swaybars to adjust camber.

 

[Bnks334]

1) I should consider custom work on the strut tower (better camber plates dont exist for the stock E89)
2) I must select the right tires first, and only then start collecting data (both temp and tire wear) on the exact track that I want to improve lap times on.
3) I probably need less camber rear, and should forget about swapping swaybars to adjust camber.

1) Can you modify the camber plate? Bore out the adjustment range a bit more? That would help avoid hacking up the car.
2) Changing mechanical grip (tire compound) will definitely have an affect on everything suspension related.
3) I would stick to using sway bars to get the roll resistance and handling characteristics you want. Since the thread is about optimizing camber, yes, I'd recommend tweaking rear camber a bit lower and increasing front camber a bit. I don't think tweaking camber is going to drop any meaningful time off your lap times though, unfortunately.

 

[barry@3DM]

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.

BTW, I didn't say your temps were not ideal as we don't know what they truly are. What I gave you was an example of a temp spread across the tire. You need to get a probe style temp sensor, otherwise you are wasting your time with the IR sensor regardless of how quickly you read the temps after coming off the track.

I'll "steal" what @Bnks334 said about caster and broaden it and say that you need to understand that each part of the suspension has a complex relationship with every other part of the suspension.

Here is an example, I'll touch on the lowering spring part a bit... Since these are MacPherson struts, the roll center control isn't all that great. What I mean by that is when you lower the car, the roll center (RC) drops disproportionately. So if you lower the car .5" then you lower the (RC) more than .5". Roll moment is defined by the distance between the CG of the vehicle and the RC. So when you lower the front ride height you are INCREASING the roll moment. If you don't offset this with more roll stiffness (either with a stiffer spring or ARB) you are actually increasing the amount the car will roll. Again to repeat what @Bnks334 said, since the lateral control arm follows an arc, as you lower the car you get more static camber but you reduce dynamic camber gain. To the point of the complex relationship... simply lowering the car changes the roll moment, the dynamic camber gain, the static caster, KPI, scrub radius, mechanical trail, and the list goes on and on.

So I'll give you a real world reference point. When I ran in Grand AM with an e90, almost every BMW in the field didn't lower the front of the car that much. We were not allowed to change the pickup points so everyone wanted to keep the RC and camber curve in check.. Another reference point, Turner Motorsport used to run up to -4 deg camber on their e46s and e90s WITH stiff "race" springs.

If it were me I'd finish working on the foundation and low hanging fruit first (like better tires). Then start worrying about things like 10mm ride height changes.

 

[rac]

You need to get a probe style temp sensor, otherwise you are wasting your time with the IR sensor regardless of how quickly you read the temps after coming off the track.

That's right. The tyres temps measured are really low not much can be interpreted from that because the surface has already cooled so much and the outside is probably cooling faster than the inside. Even with a probe, you need to come in off a hot lap and get around those tyres asap.

 

[Asbjorn]

Point taken about the IR temp reader. I have ordered a probe type. Btw do check out this VBOX tire monitoring system.

And very interesting info on the roll center. Counter-intuitive for sure! Is the rear roll center typically higher or lower than the front on these cars?

Anyway, had the car's alignment checked today to dial out rear camber. Ended up with

Front Camber: -2.7°(left), -2.8°(right) (max with current camber plates)
Front Toe-in: 10' (left), 11' (right),
Front Caster: 7.2°(left), 7.2°(right) (max with current camber plates)

Rear Camber: -1.9° (left), -2.1° (right)
Rear Toe-in: 12' (left), 6' (right)

It is interesting how the E89 is now out of spec with "only" -2deg camber rear. Stock alignment has more negative camber.



Anyway, now I am just waiting for the rain to stop. I also need a new lpfp it seems. It has been acting up since I got injector cut-outs due to fuel starvation on track.

 

[Bnks334]

Point taken about the IR temp reader. I have ordered a probe type. Btw do check out this VBOX tire monitoring system.

And very interesting info on the roll center. Counter-intuitive for sure! Is the rear roll center typically higher or lower than the front on these cars?

Anyway, had the car's alignment checked today to dial out rear camber. Ended up with

Front Camber: -2.7°(left), -2.8°(right) (max with current camber plates)
Front Toe-in: 10' (left), 11' (right),
Front Caster: 7.2°(left), 7.2°(right) (max with current camber plates)

Rear Camber: -1.9° (left), -2.1° (right)
Rear Toe-in: 12' (left), 6' (right)

It is interesting how the E89 is now out of spec with "only" -2deg camber rear. Stock alignment has more negative camber.

View attachment 18069

Anyway, now I am just waiting for the rain to stop. I also need a new lpfp it seems. It has been acting up since I got injector cut-outs due to fuel starvation on track.

Factory settings are always skewed toward keeping the car easy to drive on the street. High rear camber and low front camber is going to dial in under-steer which is generally accepted as being "safer" and "easier to drive."

Have you tried zeroing out the front toe? Or, going a bit negative? The car will be very darty on the street, but, it will feel much more agile on turn-in.

As for role center, I went down that rabbit hole about a year ago. I started mapping out suspension components and trying to measure roll center changes. There were just way too many unknown variables to get an accurate assessment (what is my modified/lowered cars COG?). Even with an accurate assessment, I was finding I really didn't understand what the math was telling me. Like you said, the results of everything I did were counter-intuitive.

For example, spacers showed on paper as lowering the roll center; therefore, increasing roll moment (more body roll). However, a wider track width is supposed to decrease load transfer... There were just too many things I didn't understand. Maybe someone knowledgeable of suspension dynamics (vehicle engineering) do some brief assessments of some of these things to show the affects of the various mods people do. I found that actually doing the spacers resulted in a better handling car. That's all I need to know I guess but suspension tuning by trial and error is expensive and time consuming.

 

[Asbjorn]

Factory settings are always skewed toward keeping the car easy to drive on the street. High rear camber and low front camber is going to dial in under-steer which is generally accepted as being "safer" and "easier to drive."

Have you tried zeroing out the front toe? Or, going a bit negative? The car will be very darty on the street, but, it will feel much more agile on turn-in.

Last time I tried that, my braking became a little darty. But it has been several months since I tried toe out. Perhaps it would be easier to manage now that I have stiffer bushings everywhere?

However in general I do not have problems with turn-in, it is really sharp with all the upgraded bushings. My main problem is a bit of under-steer starting from mid turn when pushing towards the limit.

As to your other points - I can see a general theme here that says I better keep it simple. Ie first select better tires. Then focus on optimizing static camber based on data for each track (as long as it yields actual improvements in lap times). And finally, resist the temptation of changing anything else lol.

 

[Bnks334]

However in general I do not have problems with turn-in, it is really sharp with all the upgraded bushings. My main problem is a bit of under-steer starting from mid turn when pushing towards the limit.

First thing I would do is get some 265's or at least 255's up front in a square setup with the rear.

 

[Asbjorn]

Finally got a chance to try the new alignment settings using tires that have the same thread-wear front and rear.

Front Camber: -2.7°(left), -2.8°(right) (max with current camber plates)
Front Toe-in: 10' (left), 11' (right),
Front Caster: 7.2°(left), 7.2°(right) (max with current camber plates)

Rear Camber: -1.9° (left), -2.1° (right)
Rear Toe-in: 12' (left), 6' (right)

Before
Front: Zestino Gredge 07R (240tw) - 235/40
Rear: Zestino Gredge 07RR (180tw) - 265/40

Now
Front: AD08R (200tw) - 235/40
Rear: AD08R (200tw) - 265/35

My lap times are about the same, and the car now over-steers much more than I am used to. Examples of unintended over-steer are seen in below video:

Here's the wear found on the front tires (both sides looked like this). It looks like I still don't have enough camber with these tires?

Rear tires had no signs of uneven wear/melting. Both front and rear were at around 2.5bar (36psi) hot.

I have still have not received my new temperature probe, so I don't have any tire temp measurements from this session.

Other conclusions made today
1) My oil, coolant and transmission temps were all fine in today's 17C (62F) weather. I am able to push the car much more in this weather compared to when it was +100F outside.
2) However my race brake pads now shows signs of pad fade. I need to find out if it is because I only have 20% pad left, or if I need a new compound type.

 

[barry@3DM]

Track pads should be replaced when they have 50% of their material left so brake fade is highly likely due to pad thickness if you only have 20% left.

Out of curiosity...

What were your oil and coolant temps? Do you have a data log of them?

What is the resolution of your tire pressure gauge? Someday you will get to the point of changing tire pressures by 1 or even .5 PSI. That is .07 to .035 BAR respectively. Does your pressure gauge go down to 2 decimal places for BAR?

 

[Asbjorn]

Track pads should be replaced when they have 50% of their material left so brake fade is highly likely due to pad thickness if you only have 20% left.

Out of curiosity...

What were your oil and coolant temps? Do you have a data log of them?

What is the resolution of your tire pressure gauge? Someday you will get to the point of changing tire pressures by 1 or even .5 PSI. That is .07 to .035 BAR respectively. Does your pressure gauge go down to 2 decimal places for BAR?

Now that you ask, it doesn't show bar with 2 decimals. It jumps in 0.05bars.

Here's the best temperature data I have from Ningbo Circuit at this point:

100F day (AC on) - Ningbo Circuit during the summer
https://datazap.me/u/asbjoern/ningbo-speedpark-session-2?log=0&data=6-21-24-30
After one hot lap:
Peak coolant: 119C 246F (way too high)
Peak oil: 138C 280F (ok)
Peak dct: 100C 212F (ok)
Peak iat: 75C 167F (ok)

63F day (AC off) - Ningbo Circuit today
I meant to log, but it failed (only around 10 data points in the log). Fortunately I can read what MHD showed on my phone in the video of my first session:
Peak coolant: 105C 221F (only monitored during the first 20min session)
Peak oil: 125C 260F (definitely never saw 130C at any time today)

I have logged similar temps at other track sessions in similar ambient conditions.

My cooling setup during both sessions
MHD: stock cooling
7in FMIC (downgraded from 7.5 to avoid covering part of the coolant radiator)
CSF coolant radiator
Additional engine oil cooler (part of semi-dry oil sump system)
SSP DCT oil cooler
95C oil cooler thermostat
Intake snorkel removed (63F day only)
R+ Racing Coolant (63F day only)
Full bore NBI plus 5W40 Engine oil (63F day only)

 

[Bnks334]

My lap times are about the same, and the car now over-steers much more than I am used to. Examples of unintended over-steer are seen in below video:

Here's the wear found on the front tires (both sides looked like this). It looks like I still don't have enough camber with these tires?

View attachment 18152

Rear tires had no signs of uneven wear/melting. Both front and rear were at around 2.5bar (36psi) hot.

I have still have not received my new temperature probe, so I don't have any tire temp measurements from this session.

When I said wear bars I meant the sidewall wear indicators. The triangle/symbol indicates optimal tread usage. See attached example. Your picture of the face of the tire looks pretty normal. Brand new tires with a lot of tread like 200tw (10/32) always feels really greasy to me and sees a lot of wear on the first track day. More so than something with less tread like a hankook z214 (4/32 new).

I think it was noted that the alignment changes would orient the car more towards oversteer. The tire compound changes would as well, obviously.

You put the H&R 28mm back up front?

 

[Asbjorn]

When I said wear bars I meant the sidewall wear indicators. The triangle/symbol indicates optimal tread usage. See attached example. Your picture of the face of the tire looks pretty normal. Brand new tires with a lot of tread like 200tw (10/32) always feels really greasy to me and sees a lot of wear on the first track day. More so than something with less tread like a hankook z214 (4/32 new).

I think it was noted that the alignment changes would orient the car more towards oversteer. The tire compound changes would as well, obviously.

You put the H&R 28mm back up front?

Yes the H&R sway bar is back in. And yes, the balance is better now. Still considering those stiffer -10mm M sport front springs for a bit of extra static camber, and less front rebound though.

What I wanted to show with the tire picture is how the wear / melting is more severe on the outside compared to the inside. I do not know if it is possible to see or not. As for the triangle - got it. I actually discussed this with an instructor some time ago, and he told me to do the temperature testing instead...

Also these AD08R actually melt alot less than the Zestino 240tw which have less thread new. I think this is because the Zestino's are designed to heat up quickly, and work best on the second-ish lap.

Anyway this tells me I need R888R next...

 

[barry@3DM]

Yes the H&R sway bar is back in. And yes, the balance is better now. Still considering those stiffer -10mm M sport front springs for a bit of extra static camber, and less front rebound though.

Can you expand on what you mean by less front "rebound"?

I think you are still confused on the camber thing. The suspension has a predetermined camber CURVE. On a MacPherson strut this is mostly determined by the length of the control arm (and a little bit by the length of the strut). Meaning that as you compress the suspension the camber curve is based on an arc that the control arm follows in relation to the KPI. When you lower the car you change the STATIC point of the camber curve, you do not change the actual camber curve.

Remember how I said lowering the car increases the roll moment? When BMW lowers the car on a sport suspension (for example M Sport) it increases the roll moment which they then offset by increasing the roll stiffness with spring rate, a stiffer anti roll bar, or both. Having said that, to determine what BMW accomplished between the two springs would require modeling. My ASSUMPTION is that roll stiffness was increased just enough to offset the extra roll moment plus maybe a little more..

Think about it this way... (These numbers are TOTALLY made up to show you an example)

Non M sport springs:
Ride height: 15"
Static camber: 2 degrees
Car rolls in a turn: Suspension compresses 1.5"
Camber after suspension compressed: 2.5 degrees

M Sport Springs:
Ride Height: 14.5"
Static Camber 2.25 degrees
Car rolls in a turn: Suspension compresses 1"
Camber after suspension compressed: 2.5 degrees (the same!)

This goes back to the low hanging fruit thing. Instead of spending the time and money swapping springs out all the time, I would get adjustable front and rear anti roll bars. Then you can change roll stiffness at the track between sessions. Honestly before that I would first get a square tire/wheel setup. This allows for consistency front and rear and so you can rotate your tires to get more longevity out of them.

In the case of oversteer, if you had adjustable bars, you could have either increased stiffness of the front bar or decreased stiffness of the rear bar. Since you make a lot of power I would start with increasing stiffness of the front bar. This will help put more weight on the inside rear tire and help keep rear squat in check when powering out of a turn.

 

[Asbjorn]

Can you expand on what you mean by less front "rebound"?

I think you are still confused on the camber thing. The suspension has a predetermined camber CURVE. On a MacPherson strut this is mostly determined by the length of the control arm (and a little bit by the length of the strut). Meaning that as you compress the suspension the camber curve is based on an arc that the control arm follows in relation to the KPI. When you lower the car you change the STATIC point of the camber curve, you do not change the actual camber curve.

Remember how I said lowering the car increases the roll moment? When BMW lowers the car on a sport suspension (for example M Sport) it increases the roll moment which they then offset by increasing the roll stiffness with spring rate, a stiffer anti roll bar, or both. Having said that, to determine what BMW accomplished between the two springs would require modeling. My ASSUMPTION is that roll stiffness was increased just enough to offset the extra roll moment plus maybe a little more..

Think about it this way... (These numbers are TOTALLY made up to show you an example)

Non M sport springs:
Ride height: 15"
Static camber: 2 degrees
Car rolls in a turn: Suspension compresses 1.5"
Camber after suspension compressed: 2.5 degrees

M Sport Springs:
Ride Height: 14.5"
Static Camber 2.25 degrees
Car rolls in a turn: Suspension compresses 1"
Camber after suspension compressed: 2.5 degrees (the same!)

This goes back to the low hanging fruit thing. Instead of spending the time and money swapping springs out all the time, I would get adjustable front and rear anti roll bars. Then you can change roll stiffness at the track between sessions. Honestly before that I would first get a square tire/wheel setup. This allows for consistency front and rear and so you can rotate your tires to get more longevity out of them.

In the case of oversteer, if you had adjustable bars, you could have either increased stiffness of the front bar or decreased stiffness of the rear bar. Since you make a lot of power I would start with increasing stiffness of the front bar. This will help put more weight on the inside rear tire and help keep rear squat in check when powering out of a turn.

The reason I am considering the M sport springs, although it wont influence camber mid-turn, is because it might increase camber going out of a turn. I do not think I can adjust this with sway-bars. Is this wrongly understood?

I have under-steer coming out of turns T7-T8-T9 at Ningbo. In this 270deg right hander you accelerate by slowly increasing throttle from around 45mph to 85mph while opening the steering more and more. At the same time there is an elevation change - first you go a bit uphill, and then downhill. My thinking is that with the lower and stiffer M sport front springs, the front de-compresses less (this is what I called less rebound), and therefore maintains more camber.

As for the anti-roll bars, the rear H&R sway bar I use now is adjustable (and set to stiffest setting), but the front isn't. I found that Eibach sells an adjustable front sway bar. I will see if this product is available locally in China.

As for the power oversteer - at this point I am also thinking the AD08R simply don't offer enough grip for my power-level to begin with. I will hold back on any adjustments there until I get better tires - perhaps a square 255/35 setup.

 

[barry@3DM]

The reason I am considering the M sport springs, although it wont influence camber mid-turn, is because it might increase camber going out of a turn. I do not think I can adjust this with sway-bars. Is this wrongly understood?

I have under-steer coming out of turns T7-T8-T9 at Ningbo. In this 270deg right hander you accelerate by slowly increasing throttle from around 45mph to 85mph while opening the steering more and more. At the same time there is an elevation change - first you go a bit uphill, and then downhill. My thinking is that with the lower and stiffer M sport front springs, the front de-compresses less (this is what I called less rebound), and therefore maintains more camber.

As for the anti-roll bars, the rear H&R sway bar I use now is adjustable (and set to stiffest setting), but the front isn't. I found that Eibach sells an adjustable front sway bar. I will see if this product is available locally in China.

As for the power oversteer - at this point I am also thinking the AD08R simply don't offer enough grip for my power-level to begin with. I will hold back on any adjustments there until I get better tires - perhaps a square 255/35 setup.

When in a turn, whether the entry, mid corner, or exit, the amount the car rolls (how much the suspension compresses/rebounds) is determined by roll stiffness. Roll stiffness is determined by spring rate, anti roll bar, roll moment, shocks, etc. Therefore, any of those things will be a factor of "ride height" or "influence camber" due to roll in a corner. Again, that means at what point you are located in the camber curve.

Do you know what's the spring rate difference between the regular and M sport spring? Honestly, unless there is a huge spring rate difference, things like a 10mm ride height difference are micro suspension adjustments.

Again, I'd go after the foundation first. You need to be able to converge on the solution by using things like adjustable anti roll bars, height adjustable suspension (aka coilovers), adjustable dampers, etc. Trying to chase a handling issue with things like two different OEM fitment front springs to get a certain camber setting is going to give you a constant headache.

 

[Bnks334]

Yes the H&R sway bar is back in. And yes, the balance is better now. Still considering those stiffer -10mm M sport front springs for a bit of extra static camber, and less front rebound though.

What I wanted to show with the tire picture is how the wear / melting is more severe on the outside compared to the inside. I do not know if it is possible to see or not. As for the triangle - got it. I actually discussed this with an instructor some time ago, and he told me to do the temperature testing instead...

Also these AD08R actually melt alot less than the Zestino 240tw which have less thread new. I think this is because the Zestino's are designed to heat up quickly, and work best on the second-ish lap.

Anyway this tells me I need R888R next...

Again, I'm just speaking in generalities. The tire compound may just be inferior and not able to handle as much heat.

Those tires look perfectly fine though. The tread is gobbed up like that from turning forces... normal to see.

i have under-steer coming out of turns T7-T8-T9 at Ningbo. In this 270deg right hander you accelerate by slowly increasing throttle from around 45mph to 85mph while opening the steering more and more. At the same time there is an elevation change - first you go a bit uphill, and then downhill. My thinking is that with the lower and stiffer M sport front springs, the front de-compresses less (this is what I called less rebound), and therefore maintains more camber.

The first thing that comes to mind would be use less power, or, open the wheel up more. Second thing that comes to mind is the 235s up front might be the cause of this kind of push. Can you space the front wheels out any?

As for the m sport spring rate change, you are correct in the concept that stiffer springs would generally mean less static compression due to the weight of the car (think sitting in your driveway) and therefore you would also have less static droop (decompression as you called it). However, the msport springs are also shorter which is what achieves the lowering. This automatically moves available suspension travel toward having more rebound despite the spring rate increase reducing compression travel from the static weight of the car... this is why coilovers are so great... you can run any length spring you want and not change the suspension travel at all (you can dial out preload).

The net effect of the msport spring change on the camber curve would be the complete opposite of what you're expecting. You keep chasing this idea that camber loss is something you need to address to make the car faster... it's really not. Imo it's a grossly blown out of proportion phenomenon. Pirelli world challenge cars are limited to 3.5/3.0 and they have no issue setting lap records with production cars lol...

Also, a stiffer spring will NOT reduce front end lift when you power out of a turn... the wheels will just lift off the ground once you run out of front droop travel (decompression). When accelerating, the front end of the car lifts as the rear end of the car squats. Meaning, it's rear compression travel that dictates how much front end "decompression" you get.

 

[Asbjorn]

Amazing explanations guys. Really appreciate it.

 

[rac]

Here's the wear found on the front tires (both sides looked like this). It looks like I still don't have enough camber with these tires?

I have 400 lb/in coil over up front and a 27mm sway and I now ended up with fairly even tyre wear on a r-spec 235 tyre (z221) with about 2.5 - 2.8 deg.
I imagine the AD08R are going to roll more onto the tyre's edge.

on the topic of temperature probes, it was great data at first but in the end I got lazy and stopped using it. you have to be very consistent in your measurement process, how you come off track, how quickly you do it and what you did those last few laps to get consistent numbers. And even still, if you do your hard corners early in the lap and late in the lap you have a long straight followed by a slow corner into pit, the outside of the tyres may have already significantly cooled and so the temps are not representative of the work the tyre is doing through the earlier corners.

the best information I ended up getting out of it was a general idea of what the average tyre temps were and how long it had taken to get there in different ambient conditions, which helped explain why I did a few grass tours on cold nights, and whether or not I could get away with using a soft, medium, hard compound based on manufactures optimal temperature windows.

 

[Vdkk]

These are the threads I join forums for. God damn the info is so good.