Technical How much load is on wheelie bars?

Several yrs ago I did a wheelie much like the 57 chevy in the earlier post. Luckily the only thing that bent was the front end mounting points and the wheelie bar (84" dual wheel pro stock style) which afterward looked like a rocker off a rocking chair. One thing I learned is that the bar must be low enough to partially unload the rear tires, allowing them to spin a little (re. the term early wheel speed). The darn wheelie bar needs to be strong because I'm betting you're gonna be abusing it. Cheers, Allan

 

what is this "launch rpm chip" thing you speak of? There's nothing electronic on this car...it just has a foot brake, dual point distributor, etc. I might put a line lock on it, or I might not.

 

Pretty sure the Motown Missile pro stock car ran a similar setup to what you're planning back in the day,using old valve springs in the risers to vision the shock when they loaded up suddenly on a hard launch...It would be cost effective,anyway...!

Scott


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Im with ThorL using the words mild blown 427 and I plan to go 10's in the same sentence
made me go I wanna see this thing leave the Line
Im thinking this thing is gonna hook like a shark! and the wheelie bars are NOT going to be for show!

 

It's a mild engine. Old Chevy heads, mild cam, not much boost, not much stall speed, not much gear. It's lazy. Pretty much the same setup as in my 55, and it had 60' times in the 1.70s. Just less weight to get moving.

 

MSD sels them by the bag. They have "wavy" and "crispy". Really good with French onion Hella Dip!

 

Watching here, hope I need 'em, too. The "mild blown 427'' line was my 1st chuckle this father's day morning!

 

I find this thread really interesting because I almost started the same one about a month ago! I had a bit of physics but that was some time ago, but I will share with you how I had thought if approaching this question. I was going to watch videos of car I knew were very similar to my own which in my case is a 56 Chevy with 10% engine set back and ladder bars. I was going to roughly calculate the rate of rise of the front wheels by watching the elapsed time frame to frame (for example it took 0.5 seconds for the wheels to come up 1.5 feet. ) the wheel base on the cars would be the same so using the rear wheel as the pivot point I could then figure out how quickly the rear bumper came down. Assuming similar weights of the cars I could get real close to how much force was placed on the rear bumper and could just vary the equation depending on the length of bars I wanted. That's the thought anyway..


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"Everything should be made as simple as possible, but not simpler"

Albert Einstien

Sir Henry Royce said something similar about complicating the simplest of ideas. I hope the point wasn't offensive to you or anyone else reading this topic.

 

I think the key to them holding up, and not having exteme pressure on them is how low they sit. If they're short and the car gets a good vertical launch, they'll really get hammered. But if they're down around 8"-10" off the ground they'll most likely handle the wheelie btter, and not get hammered as hard.
Something like this pic I found, only with a short spring inside the upright to cushion the hit:
http://img21.imageshack.us/img21/25/013jw.jpg

 

Or Ohio George's extremely beefy setup!
http://www.reliableresin.com/images/products/rr_gasser_wheelie.jpg

 

Not to me at all. I totally agree and that's why I decided to simply mimic what I have seen that works.


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quote of the day

 

Yep! That's the true spirit of hotrodding!

 

I suggest asking Quain Stott, he will give you the correct advice.
Glenn

 

There you go. Quain Stott!

 

Here is a question for you..what are you going to do with that information once you have it? Lets say I tell you there is 500 lbs of force applied 40" behind your rear axle....then what? Do you want to exceed that amout..I would hope so...by how much? Do you want it to give? Would you like a dual rate spring? Do you want tire slippage? It actually gets much more complicated than the original question. The more you look at it the more you spin your gears.
I had considered using leaf springs with valve spring sandwiched between them and the fulcrum point to make a dual rate spring. After spending a good amount of time I ended up just deciding to look at the thousands of options already out there and choosing an idea which fits my application...or you can reinvent the wheel.
I like to do that sometimes too. I plan on running my wheelie bars from a bracket instead of the axle housing because I believe it has to shock the wheels when the wheelie bars touch down in the conventional setting. To each his own.


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I'm looking for a ballpark number to help me size the various parts, and to guesstimate spring rates.

 

I THINK I could get a ballpark estimate of the force and I'm pretty curious too so I may just take on the project one night. Rear gear ratio will alter the results between similar cars.
It's funny that Quain was brought up because I have spoken to him about wheelie bars too..in fact I had discussed him making me a set like his but now feel confident enough to do my own. Quain is about the nicest guy you will ever talk to..and obviously very knowledgeable.


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Hey squirrel, I hope all is well and it sounds like you're having a good time. I'd like to throw out a thing or 2..or 3, 5, etc The force may never be the same, even on the same track on the same day. You may not even get high enough to worry about it if the motor is really as mild as you say (however I think it might be mild to you!). Somewhere along the line the actual safety required for such a thing will have to be considered, regardless of how correct or period perfect you'd like it to be. I couldn't raise a rt hand as to when the conventional "bracket racer" wheelie bars came along, but it was quite a while back and they work. You could hit the books and find something close, you could find a used set and simply paint em black so they tend to "go away" and not disturb the vibe. At least you'd have the strength, adaptability, and most important, the safety that such devices have the potential to offer. In my business there's very few concessions we can make regarding authenticity so I feel your angst, but like the other requirements you followed to stay within the sanctioning body rules for safety...?

Just sayin bud, and good luck with it.

 

Cool thread here. Good info alot of it is over my head but good.

 

It would seem to me that at some point that dude with the 57 has to have the full weight of the car, plus inertia on his bars. I think 500 lbs might be a low estimate, although in theory, the less weight they see, the faster you will go.

 

Squirrel's teasing us here. Which component do you want to buckle,
or shear? (I'd use the shear-pin analogy). And live with the likely outcome. Hate to see
that properly-powered little Nova on it's backside, like a turtle having a bad day.
If the bars and mounts are stronger, the frame is next up, yes? Peak loads are tricky stuff to estimate.

 

I think 500 is light too.. I was just throwing a number out for discussion. I think I am going to play with it tonight after work. I am not a math expert by any stretch but I think I can get pretty close. It will be fun to try anyway.


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I've built a few sets from supplied kits from companies like Chris Alston and did one set for a customer that wanted the lower leaf spring type without the coil spring arrangement. Never calculated the load out but then I never saw any of them give up either. Usually made from 3/4 or 7/8" chromemolly tube.

I would think that there is a fairly light load considering the types of wheels being used except for the rare instance where things go awry.

 

Just kicking it around in my head in the shower I think since the full weight of the car is actually on the rear wheels and not on the wheelie bars...you only have to figure out the momentum of the car rotating on that axis......simple right??!......hmmmm


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Yep. Take the rear axle as a center of rotation, and calc the moments around it, at the point when
the load goes entirely onto the wheelie bars, would be one "statics" method. M = F X R
Mind you, dynamics makes it far more complex, and a fraction of a second, (T) is involved.
Jim, the first 'drive' on the build thread is a great clip! Thanks for this.

 

Hey squirrel, I havent got a clue about formulas or measures of force on this matter but hopefully I can shead light on the subject.
In the avatior is the first set of bars I made for my ride. They were 12'' beond the bumper and rigged (no spring). Worked well at first but as I made more power the car would get more and more air untill I started bending the front axle. The new bars are moly and about 32"" beond the bumper, I also installed shock springs to stop unloading the tire (mounted them under the car). These work well but the things I dont like are I have to set them almost to the pavement (they have about 12"" travel) and at the hit the tire squat alone will put the casters on the ground. After the pass the casters are still going strong. The good points are the car will wheelie great and do not unload the tire (clutch car of corse). My photobucket took a dive on me or Id post picts.
If Quain see's your bars as long as mine he would call them pro mod bars as he calls mine, however he dosnt have to replace the front axle, I do
Wish I could post picts but its outta ny control. By the way......NICE hot rod you got there, my kinda style...........COOL John

 

Lemme jus say..."This sucked". Not at all fun to figure out...however the results are very surprising..at least to me. Squirrel, I don't think this is going to help you a lick, but here goes. I used Mike Bilina's 56 Chevy for my example because it's a wheel standing sumbitch and it's the same car as mine (hey I did the work after all!) I used the following video to base my calculations on.

This is the really tough part because I couldn't watch this in slow motion..I actually sat with a stop watch and did my very best to figure out how long it took the front wheels to lift 2 foot in the air. I chose 2 feet because any higher and you're going to have to figure in the force of air on the car, rear wheels trying to drive under car instead of through it, and a whole bunch of other shit I didn't want to mess with...also that's about as high as you want to go with wheelie bars. I figure at 2 feet there totally maxed out.

I also had to do some guessing so far as total weight of car, weight distribution, and weight of driver. I went with 2800 lb car, 200 lb driver and 50/50 weight distribution on the wheels.
To the best of my ability with my crude methods I measured the car lifting the front wheels 2 foot in the air in about 0.1 seconds. It's an important piece of data and if anyone can do better please do. Based on that I calculated (2 different ways) that there is a total of 22,400 lbs on the wheelie bars in a given instant...or 11,200 on each wheel!!! Nuts huh?...well you do the math...here is mine...

 

...and on that note I am going to bed.


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