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      10-15-2018, 02:53 PM   #1
dre99gsx
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Talking Going off track sideways at 100mph

My ego took a bit of a beating this past weekend. Here is a prime example of why turbocharged is fun, but dangerous

Start at 12:54 - You'll see what going sideways at almost 100mph near a wall is like.



This section has a crest with a slight-left bend. I usually part throttle it in 4th and try to maintain 10psi boost (car boosts 23 full). The difference between 10psi and 23psi is about 5% throttle! Turbos like to spool indefinitely if given the chance.

Well, it did this time, and spun 90deg. Snap-oversteer with no time for correction. Traction control didn't even kick in since the rear was too light for any large difference in wheel speed from-to-rear.

I remember hitting the brakes right about when the car rotate slightly backwards, hoping I could hold it in that position and go straight and not into the wall. I was VERY lucky.
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      10-15-2018, 11:39 PM   #2
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Quote:
Originally Posted by dre99gsx View Post
My ego took a bit of a beating this past weekend. Here is a prime example of why turbocharged is fun, but dangerous

Start at 12:54 - You'll see what going sideways at almost 100mph near a wall is like.



This section has a crest with a slight-left bend. I usually part throttle it in 4th and try to maintain 10psi boost (car boosts 23 full). The difference between 10psi and 23psi is about 5% throttle! Turbos like to spool indefinitely if given the chance.

Well, it did this time, and spun 90deg. Snap-oversteer with no time for correction. Traction control didn't even kick in since the rear was too light for any large difference in wheel speed from-to-rear.

I remember hitting the brakes right about when the car rotate slightly backwards, hoping I could hold it in that position and go straight and not into the wall. I was VERY lucky.
Your car is fast!! That's a sinking feeling when your no longer in control. I'm glad it worked out for you!
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      10-16-2018, 09:02 AM   #3
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Very interesting that your car's balance was thrown off so much in that section. An NA Z4M is full-throttle all the way from the exit of T7 into the entrance of T9.

I wonder if keeping it in a higher gear could help?
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      10-16-2018, 09:17 AM   #4
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I just got into 4th gear there, and 6krpm is my peak torque (~520wheel torque). I have similar gearing as well, and I believe Z4M hits that crest at around 80mph? I've seen a few Z4Ms shift into 4th right after the crest. If that's correct, powerband on z4M at 7600rpm? in 3rd is about 190wheel torque to the wheels. Big difference

No doubt the rear end got light over the hill there. I probably had 10 degrees left steering wheel input. That combination is lethal.

After the bowl, I'm sometimes on full throttle with about the same steering wheel input, never get loose, but there is not crest on that side.

Going to 5th there could help but it wouldn't make sense to be in 5th through the bowl, too low of a rev and below my boost threshold range unfortunately.

I think I just have to let off slightly just as I approach the peak, then get back on it. I noticed a few other high powered 911s are doing same thing as well.

My lesson for that day is to take into account any crests or hills on the track and be mindful of power application and steering angle. I need to also get a camera further back to study my steering wheel angle for better review.

ANOTHER thing: I wasn't 100% throttle, I was feeding it in trying to be "light" just incase I had to pull back out. You can see my TPS % is below 100%. Unfortunately, like I mentioned, 55% and above essentially guarantees full boost. In other terms:

35%-45% I can modulate 0-12psi. 50% throttle the turbo runs wild and wants 23psi. I wish I can control 14psi-18psi with throttle but it requires a lot of finesse.
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      10-16-2018, 11:30 AM   #5
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Thanks for sharing the vid, glad you and the car survived that. It's a learning experience all the time.
As long as you can walk away with pretty much just your ego dented a bit, it's a good day.

Love your car, as someone said before, it's fast.
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      10-18-2018, 01:13 PM   #6
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I'm sorry, I didn't see what happened? I was to distracted by the awesome flames shooting out of the back of that Porsche.

Glad you're okay. Wow that thing snapped around quick.
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      10-18-2018, 01:29 PM   #7
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Thanks. I'm lucky. The snap at first felt like mechanical. Later, I realized it was driver error . Felt much better actually after reviewing the video, and discovering exactly what went wrong.

That porsche is 600-700whp cup-spec racecar. Thing is an animal. He was 'taking it easy' for photo opportunities lol. You'll see him in many of my videos as we usually frequent these tracks together lately.
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      10-19-2018, 09:04 AM   #8
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Quote:
Originally Posted by dre99gsx View Post
Thanks. I'm lucky. The snap at first felt like mechanical. Later, I realized it was driver error . Felt much better actually after reviewing the video, and discovering exactly what went wrong.

That porsche is 600-700whp cup-spec racecar. Thing is an animal. He was 'taking it easy' for photo opportunities lol. You'll see him in many of my videos as we usually frequent these tracks together lately.
Glad nothing more damaged than pride and grass!
It's surprising how much traction is lost when you're at speed and just hitting a point where the pavement is falling away like where you'd just crested that hill.
Lots of spins for first timers at Daytona at the entry to the bus stop because of that. You're braking hard from high speed and if you're not straight when you cross the point where you transition into the bus stop from the trioval you're going around CCW because there's a dip there and traction drops off significantly for about 50 feet or so.
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      10-19-2018, 09:37 AM   #9
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And to add... I will admit I got complacent at that spot. I wasn't even thinking about countersteering because I assumed the car wouldn't go sideways, ever.

It makes me feel that I need to be aware at all times of losing traction and focus on steering control, NOT just steering in and out of corners. I remember looking far ahead at the apex. When it happened, I shut down and just went for the ride until the car turned 90deg, when I snapped to it and countersteered.

Lesson learned. In retrospect, if I had countered much sooner in anticipation, and kept on the gas, I could have powered through it. I guess....
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      10-19-2018, 09:25 PM   #10
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Quote:
Originally Posted by dre99gsx View Post
And to add... I will admit I got complacent at that spot. I wasn't even thinking about countersteering because I assumed the car wouldn't go sideways, ever.

It makes me feel that I need to be aware at all times of losing traction and focus on steering control, NOT just steering in and out of corners. I remember looking far ahead at the apex. When it happened, I shut down and just went for the ride until the car turned 90deg, when I snapped to it and countersteered.

Lesson learned. In retrospect, if I had countered much sooner in anticipation, and kept on the gas, I could have powered through it. I guess....
Even aliens have an off once and awhile. They just make it seem like ho hum, no big deal. This is Ian Stewart, one of our local aliens running at Road Atlanta. A number of cars had offs at T12 and crashed, he just lifted a bit caught it, got it back on the track, adjusted the mirror, and hit it again LOL. I dream of having a feel for a car and quick hands some day.
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      10-20-2018, 10:50 AM   #11
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Whoa...glad you're ok. Video is a great tool. You think you're doing one thing but really doing another!
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      10-20-2018, 04:09 PM   #12
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Quote:
Originally Posted by dre99gsx View Post
And to add... I will admit I got complacent at that spot. I wasn't even thinking about countersteering because I assumed the car wouldn't go sideways, ever.

It makes me feel that I need to be aware at all times of losing traction and focus on steering control, NOT just steering in and out of corners. I remember looking far ahead at the apex. When it happened, I shut down and just went for the ride until the car turned 90deg, when I snapped to it and countersteered.

Lesson learned. In retrospect, if I had countered much sooner in anticipation, and kept on the gas, I could have powered through it. I guess....
The old adage is "in a spin, both feet in", meaning get on the clutch and brake and use the brake to control your direction as much as you can. You particularly want the clutch in because you don't want to spin the engine backwards if you're coming around and the rear tires get some traction.
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