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Old 06-18-2016, 11:42 AM   #1
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Angry Launch experts - I need your help!

Hi everyone.
I'm really frustrated. I put on the MT ET S/S 295/55/15 tires and I can't hook on the STREET - my back of the car is dancing on 1st - 3rd gear!

I set Tire PSI to 26-27
This is how I launched:
- Really short burnout (maybe not enough)
- Turned AdvanceTrac completely OFF (include TC)
- Put on D
- Hold the brake
- Raise rev to 1500-2000 RPM
- Left the brake and stomped the gas pedal.

It feels like it starts hooking but then it feels like one the rear tires hook more than the other and the back starts to spinning a little bit and i am loosing a lot of ET!

This is my setup in case you missed:
2014 GT A6-3.15
VMP Gen 2: 79mm, ID1000s, VMP 67mm TwinJet TB, VMP BAP
BMR UCA Adj w/ Mount, BMR LCA, BMR Relocation Brackets and BMR Adj Panhard Bar, Eibach Pro-kit springs
255/35/20 NT555 Front, MT ET S/S 295/55/15 Rear

P.S.
We don't have prep track here so i can only do it in the street.

Please help guys - what am I doing wrong??? maybe its something in my suspension?
Appreciate your help guys
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Old 06-18-2016, 01:24 PM   #2
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Drop the tire pressure a few more pounds.

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Old 06-18-2016, 01:25 PM   #3
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Drop the tire pressure a few more pounds.

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Which PSI should I set?
So you think it's all about this or there is something else?

Thanks
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Old 06-18-2016, 01:34 PM   #4
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It's hard to say without watching the car. I would start simple and drop about 2psi. If that doesn't work, drop 2 more. Depending on sidewall height and flex I would not drop below 15psi.

If you find that adjusting the air pressure is not working I would suggest mounting a camera behind the car so we can see what is happening.

It is possible that you are breaking loose and hopping due to dirt and oils in and on the asphalt. If that is the case all you can do is launch with less power. If there is little or no rubber at the launch site you are going to spin. If it is hot outside, asphalt becomes slick, and you will spin. The sun easily turn a good strip into a puddle of goo.

I really wish I could see the car launching. That would make a diagnosis much easier.

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Old 06-18-2016, 02:10 PM   #5
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It's hard to say without watching the car. I would start simple and drop about 2psi. If that doesn't work, drop 2 more. Depending on sidewall height and flex I would not drop below 15psi.

If you find that adjusting the air pressure is not working I would suggest mounting a camera behind the car so we can see what is happening.

It is possible that you are breaking loose and hopping due to dirt and oils in and on the asphalt. If that is the case all you can do is launch with less power. If there is little or no rubber at the launch site you are going to spin. If it is hot outside, asphalt becomes slick, and you will spin. The sun easily turn a good strip into a puddle of goo.

I really wish I could see the car launching. That would make a diagnosis much easier.

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Thanks for the tips man! I would try that and also try to take a video of it
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Old 06-19-2016, 12:39 PM   #6
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When had my auto, I had my mt's at 17 psi. If the tires were still slipping, I wouldn't hold revs up at all, kept it at 0 rpms. Good luck.
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Old 06-19-2016, 12:44 PM   #7
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0 rpms?
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Old 06-19-2016, 12:55 PM   #8
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0 rpms?
Definitely won't spin with the car off! Lmao
Think he meant idle ...~750 or so?
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Old 06-19-2016, 02:42 PM   #9
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When had my auto, I had my mt's at 17 psi. If the tires were still slipping, I wouldn't hold revs up at all, kept it at 0 rpms. Good luck.
17 PSI for a street run?
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Old 06-19-2016, 03:57 PM   #10
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17 PSI for a street run?
It depends on the tire. If you are running junk the sidewalls will collapse. Then again, if you're running junk you aren't going to hook anyway.

Tire pressure is different for every location, temp, and driver. You have to learn the car and what works for you.

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Old 06-19-2016, 06:40 PM   #11
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My first question would be what hole are the lower control arms in? If you don't have enough anti squat it won't bite, and if you have too much anti squat it may bite at first, but then spin. I ran 1.4 60' on a similar setup, same springs and 20 psi with 275/60/15's so it can work. I always got my best launch right off idle too . You don't want to shock the tires loose. If you are spinning one tire more than the other it's time for a proper posi. I run a true track but there are other good choices out there as well. When in doubt, do a bigger burn out. If your smoking one, your posies done.
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Old 06-19-2016, 08:53 PM   #12
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Definitely won't spin with the car off! Lmao
Think he meant idle ...~750 or so?
Yes, at idle. Lol
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Old 06-19-2016, 11:26 PM   #13
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It depends on the tire. If you are running junk the sidewalls will collapse. Then again, if you're running junk you aren't going to hook anyway.

Tire pressure is different for every location, temp, and driver. You have to learn the car and what works for you.

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I'm running MT ET S/S
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Old 06-19-2016, 11:28 PM   #14
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My first question would be what hole are the lower control arms in? If you don't have enough anti squat it won't bite, and if you have too much anti squat it may bite at first, but then spin. I ran 1.4 60' on a similar setup, same springs and 20 psi with 275/60/15's so it can work. I always got my best launch right off idle too . You don't want to shock the tires loose. If you are spinning one tire more than the other it's time for a proper posi. I run a true track but there are other good choices out there as well. When in doubt, do a bigger burn out. If your smoking one, your posies done.
I use the middle hole in the Relocation bracket.
Which part do you suspect is not posi correctly?
Is it the UCA? Or something else?
When I think about it, at the burnout the back of the car always move to the same size (don't remember which) while holding the brake completely. Is this related?
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Old 06-19-2016, 11:30 PM   #15
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I'm running MT ET S/S
You may have mentioned it already, but I don't remember (I'm studying -stupid head classes), and too lazy to scroll back. Lol

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Old 06-20-2016, 10:51 AM   #16
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Quote:
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I use the middle hole in the Relocation bracket.
Which part do you suspect is not posi correctly?
Is it the UCA? Or something else?
When I think about it, at the burnout the back of the car always move to the same size (don't remember which) while holding the brake completely. Is this related?
Posi is in the differential, it locks the two wheels together so that they both spin.
Try using the bottom hole. My LCA brackets only had 2 holes and I used the bottom.
Not sure how that relates to the new style.
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Old 06-20-2016, 02:13 PM   #17
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Posi is in the differential, it locks the two wheels together so that they both spin.
Try using the bottom hole. My LCA brackets only had 2 holes and I used the bottom.
Not sure how that relates to the new style.
I spoke with BMR and they told me I should try to top hole. I'm using the middle now
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Old 06-20-2016, 02:21 PM   #18
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I spoke with BMR and they told me I should try to top hole. I'm using the middle now
Its relative to how lowered the car is, and since I cant see the car I can only guess...mine was on the bottom hole on a 2 hole bracket. 1.4 60' is pretty damn good for a 4000 pound street car.
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Old 06-22-2016, 10:12 PM   #19
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Here you go, this is how it works....


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Old 06-23-2016, 04:22 AM   #20
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Here you go, this is how it works....


Thanks man
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Old 06-23-2016, 08:14 AM   #21
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Try leaving off idle. With a TVS on street no need to power brake it.
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Old 06-23-2016, 09:31 AM   #22
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Try leaving off idle. With a TVS on street no need to power brake it.
Great tip! Will try that.
Shall I keep turning off my TC? Or leave it on?
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Old 06-27-2016, 11:56 AM   #23
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Hey, when I do a burnout and also at hard launch my back of the car always go left and loose the hook. Is there any chance my issue is not related to traction only but also to something else? Maybe my suspension?

It's always the same side
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Old 06-27-2016, 03:36 PM   #24
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It's traction. There's a law of physics (cmon you college kids, help me out) that a rotating mass (this would be your tires) will go left/right dependant on the direction of rotation. Once the wheels brake loose, you always go the same way. Unless your south of the equator then it's opposite...wait no that's only water in a flushed toilet
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Old 06-27-2016, 03:38 PM   #25
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https://www.4physics.com/phy_demo/ne...ewton_rot2.htm
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Old 06-27-2016, 08:33 PM   #26
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You just need a better tire...
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