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      10-31-2018, 06:57 PM   #1
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Just got back from running Streets of Willows with OnGrid this past Sunday and was experiencing bad under steer, and am trying to understand why.

My set up is:
Falken Azenis
Front 285
Rears 315

Brembo 380mm bbk front and rear
Endless pads

US MDM

Camber is 3.8 front and 3.2 rear

Running a front GTS style splitter also

Best time was 1:30, my friend ran a 1:28 with my car as well

Any thoughts as to what is causing the under steer? I was also over heating the front brakes, I think the mdm was kicking in waaaay too early and causing issues

I should also add that while the rear tires were being used to the fullest, as the wear marks were spot on, the fronts were scrubbing and not hitting their wear marks. Too much camber?
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      10-31-2018, 08:57 PM   #2
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What are your toe settings? Camber is one piece of it.
I have ran here a handful of times, and it is a tight track. I am sure the stagger set up doesnt help with the understeer.

Also since its a smaller track, I noticed while excited in the beginning of the day, I was overdriving with Euro MDM, and experiencing some "push" and understeer. I turned TC off and made me focus on not overdriving and I was able to shave 2 seconds off the time (1:28+ ->1:26)

I dont think you're going fast enough on this track to activate aero, etc.

Just my 2 cents.
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      10-31-2018, 09:04 PM   #3
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Yes our cars are very sensitive to toe. Damping also can cause massive understeer. I experienced bad understeer with worn dampers, and when my front damping was set much lower than rear (on Ohlins).

Too much rear aero can also cause massive understeer.
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      10-31-2018, 09:45 PM   #4
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Overdriving or too much throttle too soon.
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      10-31-2018, 09:47 PM   #5
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Quote:
Originally Posted by italyix View Post
Just got back from running Streets of Willows with OnGrid this past Sunday and was experiencing bad under steer, and am trying to understand why.

My set up is:
Falken Azenis
Front 285
Rears 315

Brembo 380mm bbk front and rear
Endless pads

US MDM

Camber is 3.8 front and 3.2 rear

Running a front GTS style splitter also

Best time was 1:30, my friend ran a 1:28 with my car as well

Any thoughts as to what is causing the under steer? I was also over heating the front brakes, I think the mdm was kicking in waaaay too early and causing issues

I should also add that while the rear tires were being used to the fullest, as the wear marks were spot on, the fronts were scrubbing and not hitting their wear marks. Too much camber?
any videos?
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      10-31-2018, 09:52 PM   #6
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Quote:
Originally Posted by roastbeef View Post
Overdriving or too much throttle too soon.
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      10-31-2018, 10:23 PM   #7
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Wow appreciate the replies!!! Toe I believe is zero front and a 1/16 rear.

I was a bit aggressive, but the throttle too soon is an interesting point, considering it would lift the front and cause the understeer.

No videos unfortunately, I really want to get the AiM setup and fine tune my driving.

Thanks guys!!!
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      10-31-2018, 11:48 PM   #8
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I think 3.8 front camber is too much for this car.
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      10-31-2018, 11:49 PM   #9
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Would depend on the driver but asking here leads me to agree
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      11-01-2018, 12:28 AM   #10
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You might be going to fast into the corners. A slower entry speed could yield more grip and a better exit.

So many different possibilities, as others have already mentioned
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      11-01-2018, 10:16 AM   #11
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a) too much entry speed is usually the reason, on a tight course like streets, for understeer. If your friend was able to knock 2 seconds off your time, I think that's probably a big part of it. Especially running with MDM on and overheating the brakes. That tells me the car was struggling mightily to save you from yourself

b) that seems like a lot of rear camber, necessary to fit the tire? If not, stand up the rear tires a bit. I'm assuming you're using an 11" wheel in back, if so, 315's on an 11 are still a bit pinched and you're going to roll over a bit, plus the outside rear takes a lot of load but it's transient, it's not like the fronts, a little rollover isn't going to cord the outsides of the rears. This sounds like what the 295/315 hoosier setup I had did, the rears looked like they were rolling over more than the fronts from the wear marks, but the fronts still wore the outside shoulders faster because you grind on them harder in corners whereas the rears are only rolling all the way out for a short time during traction events. Different tires and setups, but keep that in mind when interpreting wear marks, they mean different things on different axles

c) Sounds like you need to drop front pressure a bit too, seems like a lot of front camber too, those two are interrelated. I understand from others the 615K+ likes pretty low pressures, but, grain of salt I've never run them
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      11-01-2018, 01:04 PM   #12
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I'd say a big part of the issue is "Falken Azenis Front 285 Rears 315" You've overloaded the rear and undergripped the front. Try 295 square with a better tire.
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      11-01-2018, 01:16 PM   #13
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I agree with the others, it sounds like too high a corner entry speed. Also, don't squeeze on the throttle until after the apex. If you're on throttle at corner entry, it will guarantee to understeer.

For set up, you can try lowering the front tire pressure a bit and reducing the front camber a bit. Without seeing the way the car is set up, it's hard to say though.
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      11-01-2018, 02:30 PM   #14
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Quote:
Originally Posted by Richbot View Post
running with MDM on and overheating the brakes. That tells me the car was struggling mightily to save you from yourself
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      11-01-2018, 03:10 PM   #15
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Quote:
Originally Posted by Datka View Post
I think 3.8 front camber is too much for this car.
I've been running maximum camber---whatever the Vorshlag will allow---in the front for at least 4 years on track, and I think most people would agree that my car is capable of putting down solid lap times. (I bring up lap times only to establish some sort of credibility for the car.) Max camber on Vorshlag usually equates to -3.8 to -4.1 depending on the day and place you measure it. The more camber I've run, the happier the front tire outer-edges are, and turn-in feels great. On this car, running much less camber with a grippy (soft) front tire results in outer edges that get destroyed too quickly, leaving the rest of the tire unused. I ruined tire edges in the front very quickly with lower camber.

I have not felt any degradation in braking performance either. My car still can pull 1.5G+ in braking deceleration. And I'm not squirming or sliding around when I'm on the brakes.

My friend with a very similar setup as me had been running max camber (around -4) successfully for some time----meaning his tire edge wear was good and he could run 1:51 at Buttonwillow 13CW. He went to a high end alignment shop who told him it was too much. He left the alignment shop with -3.2 in the front. He showed up at the next track day at Buttonwillow with new Hankook TD's. Two sessions in, his front tire edges were well on their way to being fully destroyed while the rest of the tire looked almost new. He promptly slammed the camber back to maximum and he slowed the edge wear down back to what he was used to seeing.

It's worth noting that a more street oriented tire will resist edge wear longer than a soft track tire simply due to the harder rubber, so you won't see the effects as quickly. But that does not mean it's the correct way to run.

As far as rear camber, I've been running -2.2 and my rear tire wear has always been perfectly even across the face of the tire. It's amazing how much you have to fight the fronts, but the rears are so easy.
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      11-01-2018, 04:51 PM   #16
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Quote:
Originally Posted by dogbone View Post
Quote:
Originally Posted by Datka View Post
I think 3.8 front camber is too much for this car.
I've been running maximum camber---whatever the Vorshlag will allow---in the front for at least 4 years on track, and I think most people would agree that my car is capable of putting down solid lap times. (I bring up lap times only to establish some sort of credibility for the car.) Max camber on Vorshlag usually equates to -3.8º to -4.1º depending on the day and place you measure it. The more camber I've run, the happier the front tire outer-edges are, and turn-in feels great. On this car, running much less camber with a grippy (soft) front tire results in outer edges that get destroyed too quickly, leaving the rest of the tire unused. I ruined tire edges in the front very quickly with lower camber.

I have not felt any degradation in braking performance either. My car still can pull 1.5G+ in braking deceleration. And I'm not squirming or sliding around when I'm on the brakes.

My friend with a very similar setup as me had been running max camber (around -4º) successfully for some time----meaning his tire edge wear was good and he could run 1:51 at Buttonwillow 13CW. He went to a high end alignment shop who told him it was too much. He left the alignment shop with -3.2º in the front. He showed up at the next track day at Buttonwillow with new Hankook TD's. Two sessions in, his front tire edges were well on their way to being fully destroyed while the rest of the tire looked almost new. He promptly slammed the camber back to maximum and he slowed the edge wear down back to what he was used to seeing.

It's worth noting that a more street oriented tire will resist edge wear longer than a soft track tire simply due to the harder rubber, so you won't see the effects as quickly. But that does not mean it's the correct way to run.

As far as rear camber, I've been running -2.2º and my rear tire wear has always been perfectly even across the face of the tire. It's amazing how much you have to fight the fronts, but the rears are so easy.
This has been my experience as well. I'm at -3.5 front and I'm still hammering the outer edge of my tires. I tried some setup changes hoping to alleviate the issue (stiffer front sway bar setting, full SPL arm conversion, camber increase from -3 to -3.5, wider wheels and tires (went from 10 with 265 to 10.5 to 285)). I'm left thinking I need to adjust my driving style and/or increase the camber even more. Based on your post I think more camber will help. Improving my driving is a given
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      11-01-2018, 05:12 PM   #17
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I've run the Falken tires before on my old Evo. The RT615K have very stiff sidewalls. The amount of grip it has is actually not as high as the stiff sidewalls give the confidence to drive.

If the tires are not wearing to the outside edge as it should, it is probably too much camber or tire pressure for these tires with the current set up.
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      11-01-2018, 05:49 PM   #18
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what suspension are you on?

you're compression settings might be too stiff.
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      11-01-2018, 08:40 PM   #19
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1. Switch to 295 square all around
2. Dab brakes slightly and get initial turn in started before weight transfer shifts back
3. Slow down entry speeds, ease on power through and exiting.

Every M car (well, to be fair, nearly all street legal performance cars) will want to understeer at the limit. The three ways to solve that is more front tire, less entry speed, and tweaking stiffness/suspension settings. The first two are easy.

The exit of the corner is much more important than the entry. I always laugh when someone gets right up on my bumper into the braking zone but then I gain 4-5 car lengths by corner exit.
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      11-01-2018, 10:25 PM   #20
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Passes are usually made as brakes are released on corner entry...why not not suck at both?
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