shock and tire setup

[fishman]

what i am looking for is basically is affect of air pressure for my application on the tires.......trying to find the normal air pressure i should be running for my application and also i have coil overs in the front and the back with just one way adjustments.....my take is setting the back stiffer will not let the tires hit so hard and softer settings will let the tires hit harder.......i am trying to figure out if i have my shocks set wrong or my air pressure or i am launching at the wrong rpm as the car loads up and then unloads for a instance and a small spin.

The car weight is 2600 lbs with me in it
wheel base is 94 inchs
rear tires are 32x14x15 with 7 to 8 psi in them
launching at 4800 rpm and torque stall is 5800 rpm
tranny is a 1.76 powerglide
motor is 383 sbc peak torque at 5300 rpm 525 ft/lbs
peak hp is at 6700 rpm 600 hp
car is 55 wieght to front and 45 to back

The other day i was playing with my shocks and tire pressure and my 670 foots went in the range of 1.38 to 1.42.......our track elevation is 2400 feet and usually corrected in the 3600-4200 range and as bad as 5300 feet

two weeks earlier i took the car to the coast and air was at 1400 corrected the worse and i ran 8 psi in tires and still would load and unload but not as bad with 1.34 60 foots.

So the biggest thing is should i loosen up the front shocks right up and tighten up the backs and go up with tire pressure and try elimanate the load and unload of the tires.....................thanks in advance

[John_Heard]

Can you get some good video of the car launching?

[fishman]

Sorry don't have any video of car launching, i realize that doesn't help but for me a better understanding of the realtion between tire pressure and shock adjustment will help me in the right direction....i changed the front end this year to coil overs from 90/10 shocks and the car is reacting diffrently and i need to learn how to tune it...........the car is not pulling the front up as high as these new shocks don't have as much travel..........i have been searching every where but i cannot find any info on the single adjusment shocks and tire pressure for drag racing....i leant my chassy book to a friend and guess what he can't find it.............i know the way the car is reacting hooking and then unloading the tires that all i need to do is fine tune the shocks and the tire pressure...................thanks

[John_Heard]

Let's concentrate on what you changed first (front end). What you're describing is soft shocks that are running out of travel too quickly is sounds like to me. The first thing to try is start tightening up the extension so that it doesn't unload the car when it runs out of travel.

If you've ran that same tire combo in the past, same weight, etc. I think you're previous tire pressure settings would be fine, not to mention that is a TON of tire for a light weight car like yours. I would be the majority of what's going on is due to the change in the front end.

Find a buddy that knows what he's doing with a video camera that can film the car from the starting line, it will help a bunch to help understand what the car is actually doing.

Last question, how old are the tires? Maybe time for a fresh set?

[fishman]

Let's concentrate on what you changed first (front end). What you're describing is soft shocks that are running out of travel too quickly is sounds like to me. The first thing to try is start tightening up the extension so that it doesn't unload the car when it runs out of travel.



Last question, how old are the tires? Maybe time for a fresh set?

The tires are 2 years old with about 150 hits on them, they are not wrinkled and there is lots of thread left

You think them tires are to big......if the car had smaller tires it wouldn't look as cool and i always thought with that short wheel base it needed big tires to plant

John with one setting on the front shock...tightening or loosening will do what.. will it only control the car coming down or will it also control hit to the back tires and also the back shock settings by going stiffer will it not hit the tires as hard and by going softer will it hit the tires harder......also what affect will this have on pulling the front end........sorry for all the questions but it seems like the more i think of it the more i can confuse myself so this is were your knowledge comes in steering me in the direction

Thanks for replying to my question and any opinions you can give me on this i welcome

[John_Heard]

Without watching the car launch, it's really hard to say. Your reduction in travel in the front along with what your describing that it hooks initially then spins some sounds to me like it's upsetting the car when the front end runs out of travel, but that's just a guess. Slowing the extension on the front shocks will change the point in time when that happens (runs out of extension) and soften the action. It may or may not like it - again, hard to say without watching it leave.

Rear shocks and how tight they are tend to control how hard it hits the tire, if you were spinning right at the hit I'd suggest softening those up some. If they are too loose and you're running out of travel then that can do the same thing to (hook then spin).

Again video of the launch will be your biggest friend on figuring out what it wants.

[fishman]

John thanks for taking the time to answer my questions greatly appreciated

I am going to the track next weekend and will try stiffing the front and the back shocks and try maybe a little more air pressure in the back as not sure what the average tire pressure for my setup going to start at 8 psi and go up a 1/2 pound from there