Rear tire air pressure
 

this feels like a really stupid question. what should air pressure be in the rear tires?

i know all cars are different, some like higher than lower and that the type of car matters, as does weight. but, my question is for me and my car.

its a 9.6 full body camaro weights 3050 with me in it, i got 8 lbs in my big tire car. my 60 ft times however have no reason to them. i've been at low as 1.31 for the first run of the day and i've had 1.31 as the last run of the day. unfortunally i've also had a few 1.35 and some 1.37. this as we know is death at the finish line. your either holding a ton, or you hope that your oppounet had like a .110 r/t since you don't have a pray of running the number.

Re: Rear tire air pressure
 

I have 28x11.5 on the back of my Firebird and run between 10 1/2 to 11. This is a footbrake car. When I ran 28x9, I ran 11.5 to 12. I use M/T bias ply's.

Re: Rear tire air pressure
 

thanks bobby

but, thats not what i mean by big tire. i ran those pounds also when i had the smaller tire.

no my question was for door slammers weighting 3000 lbs with 32X14.0X15 i got 8lbs. some folks say i should have less, but the car weights so much.

your thoughts?????????

Re: Rear tire air pressure
 

OH, they are big for me, LOL. My brother runs something like a 14x32 and runs 9, I think. I usually don't check his tires. His wife does that for him. He also runs a footbrake car and M/T tires.

Re: Rear tire air pressure
 

You are close, given the variances of tire gauges at low pressures, you could run anywhere from 6 1/2 to 8 1/2 and be "correct"....it also matters whether it is a stiff sidewall, the front/rear weight balance, and how much it gets up on the rear tires for the launch.

If you aren't wadding the tires on the launch, they leave a full footprint, and wear even across the tread section, you have it right.

Sounds like you are having a hot track / tire compound issue to me.

I ease up on the burnouts when the track is hot, as well as running a "medium-hard" (Goodyear D-4A) compound for that purpose.
When the track temps exceed 110-120 degrees, I do a dragster type burnout and roll to the line.

Re: Rear tire air pressure
 

hi dave

no i don't have the corage to do a dragters type buntout. with no line lock at all, i'm not sure it would clean off the tires enough and "hook" on the hit. sometimes i'll do a shorter burn out and roll forward. its just those 60 fts not being consistant enough for my liking. just was wondering if pressure helped one way or the other.

as for the foot print yea i know about that one to. seems smooth right across, its about time to rotate them i got about 20 runs on them now, time to flip them over

Re: Rear tire air pressure
 

Don't forget to measure the rollout while you're rotating them.Joe.

Re: Rear tire air pressure
 

Why ?????

Re: Rear tire air pressure
 

I ran 8-10.5 on my 14.5 x 32's on my 3200# 65 442 clone running as quick as 9.90.
If you think you're 60's are inconsistent , try radial slicks! On a poorly prepped track my 30 x10.5 radials will 60' Either 1.50 or 1.80 ,& not much in between. Now on a decent track they'll be 1.50 all day!:)

Re: Rear tire air pressure
 

Carlos, the tires can be a differen't circumfrence even though they are the same size so measuring the rollout of each tire will tell ou this. Also in a 2500 lb car and 2700 lb car i run 6.5 to 7.0 In a 3100lbs car We run 7.5. You need to run as high as pressure as you can w/o spinning or being inconsistent. So i would start out around 7.5 and go up from there. And it does depend on the gauge, but i use two of the 80$ jegs gauges and both of them read exactly the same.

Re: Rear tire air pressure
 

vic

so if i understand you correctly. your saying that my 60 ft wow's are probally due to spinning tires. ok if i give you that, then where can i verify it on the time slip? i have my wife at the starting line but, i don't think i can explain a "wheel slip" to her and have her look for it. i could i guess give here a cmaera and just play it back nice and slow. but, i don't think she's about that either. to her its fun to be there to watch, not to anaylze the a,b,c,'s of the sport.

so, can you see wheel spin anywhere else on the time slip to confirm it. since its to easy to say hum 1.37 instead of 1.31 the wheel s spun, guess i need to drop another half pund out of the tires.....

thanks

Re: Rear tire air pressure
 

Carlos
One of the first thing I would try would be lowering your launch rpm. The car may not 60ft as quick but it may make it more consistant. Depending on what you have for suspension shock settings also make a big difference. Every thing has to work together. When making changes, just make one at a time. On my elcamino I sometimes lower the launch as low as 3200 on a slick track.

Re: Rear tire air pressure
 

I also have a question I need help on. I have a 68 full bodied camaro with a 509 engine, powerglide trans. I tried radial tires 15X33X15 goodyears, and the car had a violet wobble, the car was all over the track. I was never able to make a full pass on the radial tires. I had to go back to regular slicks to get the car to go down the track. What would cause radials not to work? Also, after several 4 link adjustments by a well known chassis shop, the car still will spin the tires after the initial hit. We can't seem to get rid of the tire spin. I now run the light weight hoosier's 15X32 with down to 8 pounds air pressure. They claim you can run up to 12 pounds, but not in my case. Any suggestions?

Re: Rear tire air pressure
 

i run the hoosier as well and mine weights 3210 with me in it and i normally run 8.0 lbs in mine their a 14x32x15 hoosier bias ply 1.48 60ft main thing to is get a constant routine on your burnout and prestage routine . normally if you do the same routine evrytime you will get very very close numbers. mine really dont like more that a 3.5 to 5 second burnout ... once in high gear!