Determining wheelie bar flex

[wideopen231]

Just build wheelie bar for fed. Everything lloks good .I was trying to determine how much flex they have after planting wheel. Was trying to figure away to measure how much frontend lift they allowed before starting to unload rear tire. Not even sure it can be figured w/o actually being a run. Started out with wheel 2.25" off floor with car level.Jacked front end up and at 6 to 7" wheel was loaded. Mesuring under axle at housing it looks like at 12" it seemed to be starting to rise,unloading tire some.Just trying to make sure they are stiff enough yet have some flex so as not to cuase unlaoding issue on inital runs.

  Question is. Is there away to figure this if so and other than my attempt give details.

[rooman]

Too many variable mate!----how quickly does the car rotate, does it squat into the tire initially, how quickly does it get up on the tire, how much does the frame flex ahead of the motor, what is the front/rear weight bias, how much does the bar flex initially and how much does it move before it starts to stiffen up (if it does). I seem to have figured out what works on my cars (even the double) but your results may vary 

Roo

[wideopen231]

So on track results only will tell. Kind of figured that was case,but never know tell you ask. Thanks

[masracingtd1167]

Chris I think it all depends on what tire you are going to use . A stiff sidewall will not squat at the hit like a soft sidewall tire ! My bar is pretty flexible and at the hit it will plant itself but my front wheels stay on the ground . As the car moves forward it starts to come up on the tire really fast and the front end starts to come up to about 8 to 10 inches . My bar is about 2 1/2 inches off the ground with me in the car . This has been working very good for me . 

[janjon]

I built this for mine. Rod end attachments at the chassis, and at the top bar mounts to the wheel. It's kinda heavy and clunky, but if the wheel hits the ground, bows the bottom bar up like a spring to make the anti-rotation effect very progressive. Drop the top attachment point to the lower hole and it's much stiffer, the upper bar centerlines more closely intersecting the wheel axle centerline.

[wideopen231]

Mines pretty much the same. I did use clevis at frame so as to eliminate any side to side movement. Only checked centerline dozen times before and after welding. Has adjustment built in to top bar connection. Also slide tube to allow pinning it up for easy loading and unloading. I have not added the crossbar set up yet. Trying to decide best way.

[dusterdave173]

My 200 inch Cenpen with MT 33x10.5 has a 48 inch bar--two top single bottom--run it close like 2 1/2 to 3 in high
I Have a plain old 350  car runs mid 5's 1/8th so no powerhouse but
I started leaveing real hard on the converter ( like 3500-4000)--it would hit the bar Hard and unload it all
Long story short
started leaving from idle car has settled right down and is a pleasure--I know what it is going to do now where before--it was different every time--
I have no braces just the three bars   It is not flexing it any I can tell now based on photos of the leave

[wideopen231]

My inital plans are to launch around 5500 with 6600 stall. Hemi  should do around 1000 hp maybe lil more. Guess different approach. I figure to hit tires hard enough to get car up on tire quick and be boarderline spinning them. Non agressive has never been my way. present tires are 15x14x32 hoosiers and plans are for simular size MT's soon.