Autocross Videos - Tips and Discussion

[invaliduser]

Originally Posted by Kostamojen

Anyone else have this problem before? (the vibration) Trying to figure out exactly whats causing it, so before I bark out how the car is setup I'm curious if anyone else recognizes it...

Overdriving

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[Kostamojen]

Originally Posted by invaliduser

Overdriving

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Yes I've overdriven into plenty of corners, but what specifically is causing this. Ive made some suspension changes and ive never had this happen prior.

[justint5387]

All driver induced, tires vibrate because they wanna commit suicide. Your input is too rough for any tires

[Kostamojen]

Originally Posted by justint5387

All driver induced, tires vibrate because they wanna commit suicide. Your input is too rough for any tires

I can give you dozen previous videos of me driving on this course with previous setups and cars driving the exact same way, and none of them have the "machine gun" vibration occurring. Lots of squealing dying tires, but nothing remotely like that.

[ame]http://www.youtube.com/watch?v=L30oiMQxr0M[/ame]

[ame]http://www.youtube.com/watch?v=PzZfGt6yXqg[/ame]

[tigermack]

You didn't even brake before entering those corners. The two videos you linked afterwards is much slower and you actually braked before corner entry.

[Kostamojen]

Originally Posted by tigermack

You didn't even brake before entering those corners. The two videos you linked afterwards is much slower and you actually braked before corner entry.

That last corner wasnt a braking corner, but yes I did brake. The first one too late though you are right and the second one after the long sweeper was super hard braking.

But still, the point is ive done that before and the car never did that specific reaction before.

FWIW this was my "clean" run that got red flagged at the end :/

[ame]http://youtu.be/SlyJw1uJD5w[/ame]

[invaliduser]

Originally Posted by Kostamojen

That last corner wasnt a braking corner, but yes I did brake. The first one too late though you are right and the second one after the long sweeper was super hard braking.

But still, the point is ive done that before and the car never did that specific reaction before.

FWIW this was my "clean" run that got red flagged at the end :/

What tires and pressures were you running? I've seen soft sidewall tires do that when the sidewall becomes your contact patch.

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[Kostamojen]

Originally Posted by invaliduser

What tires and pressures were you running? I've seen soft sidewall tires do that when the sidewall becomes your contact patch.

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RE71R's and I did lower the pressures a bit after the first run (from 36 hot down to 33 hot)

[tigermack]

It's not tire pressure or any setup, it's just going into the corner without slowing down at all.

[Kostamojen]

Originally Posted by tigermack

It's not tire pressure or any setup, it's just going into the corner without slowing down at all.

Let me rephrase the question then.

What are the physics behind the tires violent hopping as opposed to smoothly sliding?

[invaliduser]

Re71s at that pressure on a twin will not get on the sidewalls unless they are on a narrow wheel. Pointless to continue down that thought.

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[tigermack]

Slip. Angle.

[strat61caster]

Since nobody else will say it, I've gotten the 'machine gun' too from overdriving. It's not something unique to any changes you've made. I've gotten it on OE suspension and wheels and fully modified for STX and some setups in between.

Edit: Even had another driver with about a decade experience do it in my car, didn't surprise him, he had seen it on other cars, his advice was the same, you just came in too hot, just wait for it to grip again.

[Kostamojen]

Originally Posted by strat61caster

Since nobody else will say it, I've gotten the 'machine gun' too from overdriving. It's not something unique to any changes you've made. I've gotten it on OE suspension and wheels and fully modified for STX and some setups in between.

Is it the inside tire or the outside tire?