Tire Pressure tech

Ok so without a conclusion or tons of answers saying I need to put weight on the front of my car because it does
wheelies, lets try a different aproach using the givin known facts. The rear end is straight, and it is sqaure, the diameter of both
tires are equal in circumfrance, the tire pressures are the same, the wheelie bars are set equal, and the car does have a very nice
balance on all four corners and front to rear with 54% on the rear, and with me in it ready to run weighs 1882 lbs.
Here is my next test, but need to confere with the experts on which way to go. The rear tire pressure.
I have been running 7 lbs in the 33.5x17x16 the latest ProStock tire, it bights very well, but it is dead hooking.I have tried launching at lower rpm and as High as 5300rpm. What I do know is that if I launch the car lower than say 2800 it wants to wonder, but if I launch more aggressively say 4000-5000 it goes straight, I want to get the tire to spin, so I have been trying to figure out which way to go on tire Psi.. I have ran the wheelie bars as low as 2 inches and it dont like that 3.5 to 4 inches is were it just balances the wheelie ride.
I know with big power 2500-3500hp the lower the pressure
the more the tire will cup say for a National event track that has steelar grip, giving it wheel slip/spin 5 1/4 to 5 3/4, and by adding Psi it creates more grip/footprint say for a loose track 6 to 6 1/2 ,.. but,..is it not the opposite with lower HP motors such as 900hp to get wheel slip/spin, by increasing the tire Psi ?
I know about using the wheelie bar to help unload the tire, or to get it up on the tire, or create the wheel speed,..I just need to get a scense of which way on the tire Psi to go to, and that will help me set my bars to help in the launching tune.

any help appreciated.

Thanks
Vic

 

If you need more shaft speed at launch to 1.0 or 1.5, lower tire pressure. I don't know many that run more than 5.5, I'd start at 5.5 and go from there. I'd say until you get the car w/ the wheelspeed you want, I wouldn't worry about tuning it with the wheelie bar. Once you get really really close...bring the wheelie bar in....a load sensor on the bar would be beneficial at that point. Now....I'm a dragster guy but to me wheelspeed is wheelspeed.

Sidenote: After reading "Wannabe" he brings up some important info. I would run Hoosiers and nothing else, even on our Q-8/Outlaw dragster nothing worked like a Hoosier. I know several guys that run Altereds/FC's and M/T didn't/won't work for them either. The tire of choice in my mind is the Hoosier 34.5-17.0/16 C2055.

Brandon Booher
NHRA TAD #35

 

I really wish I could help. The only thing we found is that our solid mount funny cars absolutley hate tires created for suspension cars. We went to alcohol and fuel tires and have never looked back. Sure you are dragging more down the track, but they launch like they are meant to.
If you ever get around here, I will let you borrow a few different 34.5's I have laying around.

 

I agree with Wannabe, there are a lot of guys trying to run the Prsotock tire on cars that arent meant for them (read solid mounted rear ends). These tires have stiffer sidewalls for supended cars. Lower air pressure takes less power to make the tire "work" or "take a set". It seems counter intuitive, but it allows the sidewall to wrinkle and reduce the final drive ratio for launch, conversely the more pressure you have the more power it will take to wrinkle the sidewall and create the same gear reduction effect.

Have you tried running the tire at 5 psi or lower yet? maybe as low as 4.5 psi.

Also, have you thought about running smaller tire? I have had cars that when I wanted to go faster, I put a narrower tire on it, becasue it takes less power to turn. look at a C/D they run 6 sec on a 12in. tire.

 

QPM,...Wouldnt running too low of pressure cause the tire to wadd up from not having enough horse power to keep it spinning..??? I am at 900hp 700ftlbs

But no,.. I have not ran less than 7
I am limited on diameter for my halibrand 16x13 wheels

I did run the 34.5 in my cars first 8 passes but with the gear change to the 4.10`s and the tire diameter to the 105 roll out from the 110, I did not want to give up much down low.
The idea behind the question was to determine which way in tire pressure I should go because of being low HP.
Guess there is only one way to find out,..testing.

thanks for the input guys.

VicMiller

 

Just give it a try in the 5 range and see what happens. Where did you get the 7 psi number from? Just curious, I know a couple of people that tried that when the fuel cars had to go to it and they have struggled, they were blown alterd/funnys car with a lenco.

I have an injected dragster with about 800 horsepower and 1700lbs i usually run about 5.25 on a 32x14.5Wx15 it is a stiffer sidwall, it is a hoosier comp elim. tire, that is what fit my 15x14 wheels.

 

whats the best size/compound goodyear tire to run under a 2300 lb Pro mod type car? We have some GY 34.5's that barely fit on a new car, may have to do some body work on an all fiberglass body.... or just put some pro stock 33.5 X 17's under it.... What would be best? cut the fiberglass or smalelr tire? roll out is 4 inches diff but GY says the 34.5 is a high growth tire built for Pro mod......

 

Vic, on a bitchen track, we'll dip down to about 6.5 on my 12.00x16 spec fuel tire. On a crappy track, we are up around 8.

On a good track if we go get up to 7.5 or 8 it'll shake so damn hard i have to back up & pick up parts

 

Vic....
i figured that i would throw in about a cent and a half....
first of all, don't even think about running a 34.5 Hoosier on your car....way too much tire. i would set the wheelie bars at the usual height with about 4.5-5psi in the tires and leave around 5000. i think that will get you close. keep us posted on testing.
Darren