Technical How much load is on wheelie bars?

By the claw...the Bandito is revealed! (Bernoulli observing Newton's unsigned ****ysis)
Looks good Mr. Bean. I wonder just how much time is needed (Ex: 0.1 sec), as it has a huge influence on the resulting force. We divide the same m*** (M1) by an accel value that gets ever smaller, when taken to the second power (squared). It results in a huge (calculated) force.

 

Holy cow Pitman, I had no idea..but I'm sure glad somebody out there did! I am pretty sure this kind of math is literally child's play for you. That 0.1 second value troubles me a bit too..it's just so imprecise the way I had to measure it. The only comfort I get is that I have seen some other enourmous numbers like this actually measured and not calculated (like in a heavyweight boxers punch). I have to agree that if I'm off on that..and I probably am a bit..it could skew my results.
...really need to look at that video in slo-mo.

Thank you for helping confirm I'm not a nutter! Haha!


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Bean, Squirrel asks the best questions. One tough part about 'dynamics' motion based ****ysis, is the impact of brief time, and LARGE forces that result. Check what happens when it becomes only .3 seconds! Derivatives; yep, part of calculus, greatly increase a calculated value as well. They help find either peak loads or rates, of change. Rates: Velocity is ~ feet/sec, Accel ~ feet/sec/sec, Jerk (yep, no kidding, the third deriv. is called Jerk!) ~ feet/sec/sec/sec. The value IS the impact felt, depending upon how many milli-seconds you find (calc) it has, to deliver its hit. Start with a 16 penny spike, (V),
then (A) is a finish nail, finally (J) hits like a hypodermic needle! Things can break.

 

Danggg....now you have my head spinning! LOL! I felt like that value had to be a bit high because it was at an exact instant instead of being spread out a bit. It's that same reason why I had thought about using a dual rate spring (to slow the hit) but no sooner than I had THAT thought I realized that my math limitations were going to squash any hopes I had of being able to pull it off. I think I could get fairly close on paper but measuring all the springs an at different fulcrum points it just gets a bit outta hand...especially when there are some working bars out there. Like Squirrel though I enjoy thinking about these things.
Calculus huh?!...oh boy...I think I'll stop here...well maybe after I figure out the hit at 0.3 secs


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Unless wheelstanding is the desired effect, that car needs a properly set up 4-link. The ch***is needs to be doing the work.

 

Interesting...but I think there are some problems with your ****ysis. I should draw a free body diagram, and do the numbers, but I'm too dang tired right now.

 

I'll be around...

Keep in mind that number I came up with will be even higher as you move towards the axle. It's a confusing figure because it's not spread out over time but taken at an exact instant. I bet Pitman could help...nudge-nudge


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Squirrel and I will both fess...to having taken the engineer's pledge!

 

This is way outside my thought process, I got some 4" square 1/4" wall tubing, Think it will hold? LOL

 

Well damn if that's the case ain't this about like a dentist asking the guy that cuts his gr*** if he needs a root c****?!
I want my 2 hours of sleep back I lost last night. Jeezus..I think I need to keep my *** on my own thread.


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Any time you do the math (or just lay in bed thinking about the math), you're not wasting time....

 

Bottom line...steady state situation of stable accelerating car accelerating happily could be calculated, violent slam down with or without wheel stand would have to be ****yzed for 10 years by the GM tech center with 50 prototype cars destroyed to get an answer.
So, this requires the traditional Striped Wild *** Guess with all fudge factors on the "make it stronger" side.
If you collected any 50 HAMbers and extracted guesses, squirrel's would be the guess to bet on. He has experience, expertise, and good instincts.

 

Thanks Bruce...but in this case, I don't have any applicable experience, which is why I asked.

I plan to have the casters close to the ground, so there should not be a lot of slamming. Also with only a 3000 stall converter, and no trans brake, and 3.25 gears, it's not like it'll launch hard. No pro mod action here, folks.

I appreciate all the answers, there is a lot to think about. I ordered some parts, I'll work on building the bars and see what happens.

 

You might be an engineer if...
You have ever ***umed a horse was a sphere to make the math easier.....

Keep us posted on how the bars turn out.

 

Or if your response to the aftermath is "well it works on paper"....

 

Ahhh, the old "weightless, m***-less beam ****ysis!"
Who overfed that hoss?

 

wheelie bars are over rated , thats what back bumpers are for ! on my O/T superstock car I would have to replace the bumper cover atleast 2 x a year . as for figuring it out call at S&W race cars and he should be able to help you out . on my car when I took it out of cl*** into comp we used 1 1/8 4130 uppers and lowers and they were trianulated and allowed to flex a little so not to steer the car , short bars can steer a car if you get on them and the loads are not set evenly ,

for some reason I remember seeing the old Dodge SS bars ( the short ramchargers one that used the valve springs in the tubes under/behind the back of the bumper ) they listed and showed the design in the old Direct Connection Books of the late 70's and early 80's ( pre Mopar Performance issues which got rid of alot of the old info ) or it was in a Mopar magazine . but IIRC they were not built like a modern bar and only had 2 bottom tubes that bolted to the axle or body to triangulated it to keep it from being bent back or forward and the uprights in back had a rod in them that held them up off the track and slid up and down and preloaded the springs .. but it has been ages or someone elses car I saw them on . ..

 

That's the thing...I'm building the car as if it were ages ago. I'm trying to use all the old tricks, not the new tricks. It's challenging.

 

is this the type you want to build ??? looks like 1 5/8 tube

 

the DC book is 1960s stuff the ramchargers used they just booked it and handed it down . I made the mistake of letting my copy go when I changed brands , but still I remember some of the stuff that was in the bookand the magazines , Mopar guys stuck to the old stuff as it worked till someone proved they found a better rock . they liked the KIss methods

 

the post ramchargers stuff is the 4 point axle mounted stuff , which went on the O/T as for the amount of force it would see depended mostly on how close the triangulation was , the tighter the stiffer ( spring rate ) it was , and the flat spring lowers were very unpredictable as the springs would change rate over use by work hardening and the springs on the ends by the wheels caused unloading problems ( would steer the car )

 

I would over build them.... just incase
Godspeed
MrC.

 

....or, I could just not build a Pro Mod

 

Maybe not Pro-Mod, but you may re-think your satisfaction of performance when you dial that thing in and it gives you a repeatable 10.01 ET lol....
Myself, i'm thinking of combining a couple of the above suggestions on my 61 Falcon- I want to put the wheelie bar wheels sticking out through slots in the rear bumper -rick

 

Looked like a really soft landing from the wheelie. Pretty cool. Bean dip, I am the LAST guy on earth to question anyone's math, but you have feet and meters in your equations. is that kosher?

 

I didn't show all my math but I converted feet into meters. Thanks for taking the time to review my effort!

Now I should add that I only took one cl*** of physics and used just basic algebra in my attempt at helping. No trig let alone calculus. There are people reading this that can solve this question no sweat. My answer is close but only a partial answer. I just don't have the tools in my box to get the job done. I have had calculus but not about to attempt math I haven't used in over 20 years and wasn't that good at it then.

The problem is VERY solvable BUT the answer will vary depending on the car wheelbase and weight distribution,gear,track bite,bar length, when you want the hit etc etc...

I "think" my answer appears outlandish because it is the force required to stop the upward movement of that 56 INSTANTLY at 2 feet off the ground...which really doesn't answer the original question but the thought process is in the right direction so far as figuring out rotational force around rear axle.

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That would probably be the reason the number is so high. I plan to prevent my car getting two feet in the air, in the first place, and the springs are there to give it some time to absorb the engergy.

The springs are 100 lb/in each, and have 3" travel, although they start with half an inch of compression.
There isn't much adjustability in the system, although I do have some softer springs I can try.

 

I probably don't have that much to add and no where near as valualble as already posted. I would think with so many different variables in a wheelie (height, lean left, right, speed) that any one conclusion would be hard to build to. So I would take the highest and build to that. I would probably spend alot of time on the shear ratings of welds, bolts and material used

 

If it bends the 3/8" grade 8 axle, then I'll know the load was higher than I thought it would be!

 

I like it. The whole build is super sanitary. Can we get an ******* picture of the whole wheelie bar set up? Is that spring free standing with no other support to keep the wheel from skewing if there's any side load or if the leaf twists or bends horizontaly? -rick