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tire psi help on a hardtail

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Post  Racerdad96 April 19th 2015, 1:16 pm

Recently switched from Goodyear to Hoosier rear tires while also going from roughly 750hp to 1000hp. Having issues making car hook off the line. It wants to wheel hop real bad.I was wondering if anyone has a similar setup that could help me with what toe psi they are running. First night out it was cool and car hooked good 7.5psi track was warmer last night wound up dropping psi to 7.1 car got better but still shaking tires slightly.
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Post  maverick April 19th 2015, 1:50 pm

I'm no dragster specialist, but a hardtail bouncing on launch sounds like squashing the sidewall too much to me. I'd air 'em up a little more and see if things improve. Also, my old friends with hardtails usually preferred to run tubes...said it cut down on the bounce during shutdown, too.
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Post  Racerdad96 April 19th 2015, 2:08 pm

That's what I thought initially went up with pressure problem got worse. I had a friend video tape a run it appears to spin first then go into tire shake. I believe I'm going in the right direction by lowering pressure. I was just hoping someone on hear either has a similar setup or used to have a similar setup that could tell me if I'm in the ballpark with psi or if I'm way off.
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Post  QtrWarrior April 19th 2015, 2:48 pm

Just speaking from my experience with my Undercover hardtail..
I've always run mine between 5.0 and 5.5 lbs...
Usually a little closer to 5.0, also always ran my tubeless.

That "wheel hop" on the launch is probably tire shake from it trying to hook-spin - hook...
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Post  Racerdad96 April 19th 2015, 4:22 pm

Thanks for the input. I will keep going down with the psi see what happens.
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Post  dfree383 April 19th 2015, 8:56 pm

Got the right convertor setup too?
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Post  sg86coupe April 19th 2015, 9:24 pm

5 to 5.5 is what I run

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Post  Racerdad96 April 19th 2015, 9:39 pm

I am new to the dragsters my whole family has always raced door cars. We have the convertor that was in our door car that weighed 2300 pounds I believe it is a 5500 stall.
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Post  dfree383 April 19th 2015, 9:47 pm

Racerdad96 wrote:I am new to the dragsters my whole family has always raced door cars. We have the convertor that was in our door car that weighed 2300 pounds I believe it is a 5500 stall.

After you try the tire pressure changes and if it's still doing it might want to get the convertor worked over specifically for the dragster, the requirements can be different.
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Post  Racerdad96 April 19th 2015, 9:55 pm

I was planning on buying a new convertor as soon as my budget allows. Thanks for the input.
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Post  Curt April 20th 2015, 2:37 pm

I'd go to 5 psi and work in 1/4lb increments up/down and see what the car likes. Also, be extra careful in the shutdown because you're going to see a little more bounce.
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Post  maverick April 20th 2015, 8:15 pm

Curt wrote:I'd go to 5 psi and work in 1/4lb increments up/down and see what the car likes. Also, be extra careful in the shutdown because you're going to see a little more bounce.

I think that's why my buddys went to the tubes...to cure the shutdown bounce. I believe stopping was much easier with the tires on the ground.
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Post  QtrWarrior April 20th 2015, 8:34 pm

maverick wrote:
Curt wrote:I'd go to 5 psi and work in 1/4lb increments up/down and see what the car likes. Also, be extra careful in the shutdown because you're going to see a little more bounce.

I think that's why my buddys went to the tubes...to cure the shutdown bounce.  I believe stopping was much easier with the tires on the ground.

I found that shutdown bounce was caused by getting on the brakes too hard and the chassis flexing.
That caused the back to get light and start hopping..
In my case.. tubes didn't help.
I had to start dragging the brakes to scrubbing off speed at the finish and then hit the brakes harder once it slowed some...
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Post  FalconEh April 20th 2015, 9:19 pm

I know I was told not cutting the throttle at the stripe helps the bounce (AKA easing out of it on the brakes)
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Post  Curt April 20th 2015, 9:40 pm

QtrWarrior wrote:
maverick wrote:
Curt wrote:I'd go to 5 psi and work in 1/4lb increments up/down and see what the car likes. Also, be extra careful in the shutdown because you're going to see a little more bounce.

I think that's why my buddys went to the tubes...to cure the shutdown bounce.  I believe stopping was much easier with the tires on the ground.

I found that shutdown bounce was caused by getting on the brakes too hard and the chassis flexing.
That caused the back to get light and start hopping..
In my case.. tubes didn't help.
I had to start dragging the brakes to scrubbing off speed at the finish and then hit the brakes harder once it slowed some...

Yeah, you don't want tubes in a big slick.

Mike, a lot of the tracks I ran at with my hard tail were pretty short. It was a dance that was manageable, but you had to be prepared. But that was with about 750hp. I'd hate to try it with over 1000.
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Post  maverick April 20th 2015, 9:51 pm

QtrWarrior wrote:
maverick wrote:
Curt wrote:I'd go to 5 psi and work in 1/4lb increments up/down and see what the car likes. Also, be extra careful in the shutdown because you're going to see a little more bounce.

I think that's why my buddys went to the tubes...to cure the shutdown bounce.  I believe stopping was much easier with the tires on the ground.

I found that shutdown bounce was caused by getting on the brakes too hard and the chassis flexing.
That caused the back to get light and start hopping..
In my case.. tubes didn't help.
I had to start dragging the brakes to scrubbing off speed at the finish and then hit the brakes harder once it slowed some...

I know this isn't everybody's deal but as I recall (some years ago) there was a little bump in our home track a little past the traps. That got things going for the hardtail guys...getting on the brakes naturally aggravated the hop. A friend's front engine A/Fuel nostalgia car broke in half when he ran out of pavement while bouncing....chirp....chirp....chirp.....chirp....chirp....chirp.....POW. His 'chute hung in the wheelie bar, brakes would've done the job if the tires had spent more time on the pavement. At that time, most of the hardtail guys fared better with inner tubes.

Better tracks, better tires, fewer hardtails, better solutions.......

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Post  QtrWarrior April 21st 2015, 4:18 am

Curt wrote:
QtrWarrior wrote:
maverick wrote:
Curt wrote:I'd go to 5 psi and work in 1/4lb increments up/down and see what the car likes. Also, be extra careful in the shutdown because you're going to see a little more bounce.

I think that's why my buddys went to the tubes...to cure the shutdown bounce.  I believe stopping was much easier with the tires on the ground.

I found that shutdown bounce was caused by getting on the brakes too hard and the chassis flexing.
That caused the back to get light and start hopping..
In my case.. tubes didn't help.
I had to start dragging the brakes to scrubbing off speed at the finish and then hit the brakes harder once it slowed some...

Yeah, you don't want tubes in a big slick.

Mike, a lot of the tracks I ran at with my hard tail were pretty short. It was a dance that was manageable, but you had to be prepared. But that was with about 750hp. I'd hate to try it with over 1000.

Agreed Curt..
I could run the short tracks with my "little" motor
But with the wife driving and not being as experienced, I decided to get the car we have now.
I can run the big motor in the swingarm car at the same tracks and have no issues stopping..
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