Tire pressure at the track

Posted By: Chargerfan68

Tire pressure at the track - 09/01/11 06:44 AM

Hey Fellas,

I understand everyone's car is different and you have to see what each car needs. With that said, when are you checking and adjusting your tire pressures. I check them cold before the run and then after. I had them adjusted at 12.5 cold, and my buddies at the track kept nagging me to lower them to about 10 when they were hot. I know that is a big drop (cold to hot). I gradually lowered them each run finally to 10.

My 60 ft. did get slightly faster (1.65 to 1.56), but when I got home and watched the videos, It looks like the sidwall is distorting too much at 10 psi. My car is a street car and weighs 4000 with me.

What do you think looking at the pics.

(These photos are in reverse order)

Thanks for any input.

Posted By: Mr.Yuck

Re: Tire pressure at the track - 09/01/11 12:18 PM

Ran these last time out at 17 cold Hoosier drag radail). Back to back 1.60 sixty foot. Once I get the good axles in I'll try 15 and come out harder. 10 seems too low. Go up by 2lbs until you see it fall off. I'm guessing 13-15 cold will be good. One way to tell is to heat them up and do a burn out and look at the contact patch. Easy to tell if they are cupping or not.
Nice car

Posted By: Islandcuda

Re: Tire pressure at the track - 09/01/11 12:57 PM

Does the car bounce at all on leaving the line? looks like you are getting a bit of a ball in front of the tire which could cause that. It also at the same time looks like the rear is hitting real good. I,ve always been told to run as much air as you can get away with. Ie. bouncing off the line or hard to steer at top end with to low of pressure.

Posted By: Mr.Yuck

Re: Tire pressure at the track - 09/01/11 01:13 PM

Chargerfan I see you are running cal-tracs. How much did they shave off your 60 foot? Right now I'm just running stock XHD's w/ a snubber and 3.91's.

Posted By: MR_P_BODY

Re: Tire pressure at the track - 09/01/11 04:00 PM

Your KILLING your side walls... up the pressure and
if need be start adjusting the suspension to correct
for it(preload on the caltracks and shock settings)
set the front end loose

Posted By: 440Jim

Re: Tire pressure at the track - 09/02/11 01:13 AM

Quote:

Your KILLING your side walls... up the pressure and
if need be start adjusting the suspension to correct
for it(preload on the caltracks and shock settings)
set the front end loose

That is killing the tire. If you need to run like that to prevent spin, you need to work on the chassis. Can you give us more info on what was happening when you dropped the air pressure and improved sixty foot time? i.e. spin, hook then spin, turn the tire then hoook, etc. Just the number doesn't tell enough of the story.

Posted By: Chargerfan68

Re: Tire pressure at the track - 09/02/11 04:29 AM

Quote:

Does the car bounce at all on leaving the line? looks like you are getting a bit of a ball in front of the tire which could cause that. It also at the same time looks like the rear is hitting real good. I,ve always been told to run as much air as you can get away with. Ie. bouncing off the line or hard to steer at top end with to low of pressure.

You hit the nail on the head....The car was bouncing, but I attributed that to my shock adjustment. I knew the tire pressure was too much. Next time I don't listen to my buddies. Thanks for the tip.

Posted By: Chargerfan68

Re: Tire pressure at the track - 09/02/11 04:34 AM

Quote:

Your KILLING your side walls... up the pressure and
if need be start adjusting the suspension to correct
for it(preload on the caltracks and shock settings)
set the front end loose

Thanks...The front end is very loose, and I have just about 5 1/2 inch of travel. I notice on the vids, when I dump the clutch, the rear just drops violently. I have my shocks on 21 out of 24 stiff. needs more stiffness I guess. I believe the track was not as good as previous times. This was a track rental, and I was just about the only car there running. There was no fresh rubber down. So instead of adjusting my preload and shocks, I started chasing with air. My mistake.

Posted By: Chargerfan68

Re: Tire pressure at the track - 09/02/11 04:44 AM

Quote:

Quote:

Your KILLING your side walls... up the pressure and
if need be start adjusting the suspension to correct
for it(preload on the caltracks and shock settings)
set the front end loose

That is killing the tire. If you need to run like that to prevent spin, you need to work on the chassis. Can you give us more info on what was happening when you dropped the air pressure and improved sixty foot time? i.e. spin, hook then spin, turn the tire then hoook, etc. Just the number doesn't tell enough of the story.

My friends at the track said the tire was spinning and I should lower air. After slowly lowering air, my 60s got slightly better, but I think that was the track getting a little better with some fresh rubber.

After looking at the vids of the first few runs, the tire just spun 1-2 times then hooked. That's the ideal situation that should result in better 60s.

I didn't touch the bars all day since the car was launching straight ...just barely touching on Drivers side, 3/4 turn preload on pass. Shocks set on 21 rebound/16 compression. Tires run 1 set to 12.5 lbs, and adjusted 4 times down to 10 hot for the 10th and 11th run.

My fasted 60 foot was 1.49 at different track , but it was 6 degr. cooler that day and an event day.

Any other info needed?

Thanks.

Posted By: Chargerfan68

Re: Tire pressure at the track - 09/02/11 04:50 AM

Quote:

Chargerfan I see you are running cal-tracs. How much did they shave off your 60 foot? Right now I'm just running stock XHD's w/ a snubber and 3.91's.

The caltracs really helped my car get much more consistant. I ran the super stock springs before this setup with an adj. snubber, and within a month on the street, the front segment of the springs bent and when launching on a deserted road, the rear axle moved forward and cut brand new MTs et steets with the front quarter panel lip. I pulled the springs out and put the caltracs on and never looked back.

Depending on the track, they do seem very consistant.

Good luck.

Posted By: MR_P_BODY

Re: Tire pressure at the track - 09/02/11 11:41 AM

On a good biting track you can have your shock tight
but on a bad or not so good of biting track you want
to loosen the shocks up... what hole so you have your
caltracks in... you will need them in the lower
hole and then start on the shock adjustment
EDIT
Are you foot braking or trans brake... if I launch
at lower rpms I need more air pressure than if I
launch at higher rpms

Posted By: 383man

Re: Tire pressure at the track - 09/02/11 02:42 PM

I run theses 30 x 9 Hoosier radial slicks and I run at least 15 or more as on good tracks they will hook with almost 20 in them. And I have been driving on the street with them for almost 2 years. I see your best 60 is 1.49 and thats a great 60 for a low 11 car. Guess them Cal Tracs really work. I would definetly try as everyone says and raise the psi so they dont wad up. How old are the tires ? Ron

Posted By: joedust451

Re: Tire pressure at the track - 09/02/11 02:46 PM

Quote:

On a good biting track you can have your shock tight
but on a bad or not so good of biting track you want
to loosen the shocks up... what hole so you have your
caltracks in... you will need them in the lower
hole and then start on the shock adjustment
EDIT
Are you foot braking or trans brake... if I launch
at lower rpms I need more air pressure than if I
launch at higher rpms

He says he's dumping the clutch & from his pic looks like the bars are in the lower hole.

I would start out with 11 psi "cold" & play with shock settings, Like MrP said, at a better hooking track you can have a tighter shock setting, you just need to balance out the 2, shocks/tire pressure, all your really after is the best hook/60ft without slamming the suspention, alittle bit trickier on a stick car.

I notice too the front end isn't coming up much, your right, it is good to have a little bit of tire spin for best 60fts on a stick car, gets you past any boggs.

Posted By: joedust451

Re: Tire pressure at the track - 09/02/11 02:49 PM

Quote:

I run theses 30 x 9 Hoosier radial slicks and I run at least 15 or more as on good tracks they will hook with almost 20 in them. And I have been driving on the street with them for almost 2 years. I see your best 60 is 1.49 and thats a great 60 for a low 11 car. Guess them Cal Tracs really work. I would definetly try as everyone says and raise the psi so they dont wad up. How old are the tires ? Ron

Ron, i think those are ET streets Bias ply.

Posted By: MR_P_BODY

Re: Tire pressure at the track - 09/02/11 03:35 PM

Quote:

Quote:

On a good biting track you can have your shock tight
but on a bad or not so good of biting track you want
to loosen the shocks up... what hole so you have your
caltracks in... you will need them in the lower
hole and then start on the shock adjustment
EDIT
Are you foot braking or trans brake... if I launch
at lower rpms I need more air pressure than if I
launch at higher rpms

He says he's dumping the clutch & from his pic looks like the bars are in the lower hole.

I would start out with 11 psi "cold" & play with shock settings, Like MrP said, at a better hooking track you can have a tighter shock setting, you just need to balance out the 2, shocks/tire pressure, all your really after is the best hook/60ft without slamming the suspention, alittle bit trickier on a stick car.

I notice too the front end isn't coming up much, your right, it is good to have a little bit of tire spin for best 60fts on a stick car, gets you past any boggs.

Yeah I forgot about it being a stick car.... but all
of the same aspects still apply

Posted By: 383man

Re: Tire pressure at the track - 09/02/11 03:38 PM

Quote:

Quote:

I run theses 30 x 9 Hoosier radial slicks and I run at least 15 or more as on good tracks they will hook with almost 20 in them. And I have been driving on the street with them for almost 2 years. I see your best 60 is 1.49 and thats a great 60 for a low 11 car. Guess them Cal Tracs really work. I would definetly try as everyone says and raise the psi so they dont wad up. How old are the tires ? Ron

Ron, i think those are ET streets Bias ply.

No believe me they are the radial slicks. The same kind many of the NHRA stockers run. No tread on them. Ron

Posted By: joedust451

Re: Tire pressure at the track - 09/02/11 06:17 PM

Quote:

Quote:

Quote:

I run theses 30 x 9 Hoosier radial slicks and I run at least 15 or more as on good tracks they will hook with almost 20 in them. And I have been driving on the street with them for almost 2 years. I see your best 60 is 1.49 and thats a great 60 for a low 11 car. Guess them Cal Tracs really work. I would definetly try as everyone says and raise the psi so they dont wad up. How old are the tires ? Ron

Ron, i think those are ET streets Bias ply.

No believe me they are the radial slicks. The same kind many of the NHRA stockers run. No tread on them. Ron

Oh OK, well then he's running way to low pressure.