Technical How much load is on wheelie bars?

There is some support for side loads, the mount is almost 3" wide, it sits in the old spring shackle bushing hole. Here's the peek a boo picture (yes the nut is loose in this picture)

 

Nice! That's a pretty clever design. What did you use for the piston/receiver portions? What size tubes?

 

The inner tube is 1.375, the outer is 2.00, wall thickness of both is around .10 there's a couple rings of 1.625" tube around the inner one to keep it in place, and the washer between the spring and upper tube has a nice loose fit on the OD of the lower tube. Hard to describe...and it took a while to figure out how to do it. It seems plenty stout.

 

Why do I think adding a shock absorber to that set-up would be a good thing?

 

I don't know...maybe you've watched cars bounce off the starting line?

 

I like the idea of slowing the momentum early on before it gets to moving at top speed and aggresively hitting the bars. I'm going to run longer bars than what you normally see on a vintage style build and also have them set pretty low. I have some ideas on how to keep them looking period correct. I also have no interest in big wheelstands either. Looking for a nice controlled launch. It's a ways down the road for me but I'll post mine once they are done.


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Are you sure that will hold up in a slightly side loaded launch? Maybe a very sturdy free castering mounting of those wheels would help along with a connecting bar between the legs. I agree about the shocks idea too.

 

Apparently it's not a big deal....






ran 10.58 in Tucson.

 

Squirrel
That was fun! You should have charged admission.

 

That is the key to all of this. I am a dragster guy and we run our wheel with as little as 1" of clearance to the ground. We run a long (6 feet or so) flexible bar so our package is a little different but the key is to slow the rotation of the car early so that it does not hit the wheelie bar wheel with too much inertia already built up. On an ideal run the car will carry the front wheels for a bit at the hit with the wheelie bar on the ground for about 3 or 4 feet until the car gets up on the tire. In our case the bar is set so that we also get a little wheel speed at the launch as the car will shake the tires if it dead hooks.
A number of the "big show" nitro cars have/do run load cells in the wheelie bar upper leg so once they get past the current four race back to back to back deal I will see if I can get any actual numbers from some of my mates that do that stuff.

Roo

 

I have no idea what the answer is. I just want to see you do it. Yes, I'm selfish.

 

Looks like a nice traditional setup. But looks like your tires/suspension handle the launch without worrying about big wheelies.

 

yeah, if I had some more stall....but then I'd probably need to do all the 9 second safety stuff, too, at least at other tracks I plan to run at.

 

What a nice launch! That looks to just hit and go!

That looks so nice going down the track.


jerry

 

You can do a back yard approximation by using some 2" x 2" square tubing lengths and u bolt attach each to the rear frame rails trailing rearward at a length that you are experimenting with. At the rear portion of each of the bars install a 500lb+ value bathroom scale and add a spacer to take up the arm to scale clearance so the scales will now read. Place a floor jack under the front crossmember and jack the car up to your desired lift height and read each of the scale readings to determine load transfer. Total will be determined by adding the sum together. At 2" lift you will have a number , at 6" lift you will have another number and you can increase or decrease the lift and make a graph of load from scale readings

 

..only if you can jack the front up at about 2 feet per 0.10 seconds.
This model will not account for rotational force and momentum only leverage.
I respect your effort though!


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That's the thing, I was mainly interested in the dynamics of it.

 

Just as a point of reference, we have a load cell on the passenger side wheelie bar of a 2425# door car that has over 2000 certified hp car and we get around 1400 psi off this load cell at the launch.

 

One thing to keep in mind is that you already have structure you are assuming can stand up to the loads being applied. You could back-solve for what forces it would take to bend your frame (on the way up) and then balance that load using the wheelie bars. Then you would essentially have a weak link in a part you know to be strong enough.

It also doesn't have to be something as stout as the frame. It can be the weakest part in the system that you'd expect to survive.

That being said,I have not run any numbers and doing so may give you a gigantic load on the bars.

 

Finally someone with a real world answer!

 

I bet those are some long ass bars too! Hit would even be harder closer to the axle. Thanks for the good info.

...2800 lbs total for both sides...long bars...I think I was pretty close after all

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Yup, it's a real world answer! Neat. Although a stress of 1400 psi doesn't tell me what the load is, without knowing the cross sectional area of the part the stress was measured in. And the car it was measured in is quite different than mine, having three times the power. But it's good to see a real number.

 

As they say, one test result is worth a thousand theories. Thanks for sharing that!

 

Load cells on both sides connected to a Racepak will give you the numbers you are looking for.
http://www.racepak.com/

 

Unfortunately I can't put any kind of useful modern instrumentation on this car. Oh...I lied, I put a gopro camera in it. I could stick it on the back of the car, and get video of what happens. The deflection of the springs will tell me exactly how much load is on the bars, as long as I can measure the deflection accurately. Since I know the spring rate.

 

That 1400# number I gave is the reading off our Racepak. The right bar (passenger side) hits first and we feel having a load cell on the drivers side doesn't serve a real purpose. Our bars are Titanium that are 60'' long and the upper bar on the passenger side is a larger diameter since that side of the car drops first at the hit and needs to be the stronger of the two because of engine rotation. It's also adjusted around 3/4'' lower to hit the ground first. We use the wheelie bar to maintain the front/back balance of the car and not as a Band-Aid for not having a good working suspension.

 

Sounds good. The number needs some translation...without knowing exactly what it represents, it doesn't tell me a whole lot, unfortunately.

Anyways, my set up is built and I think it will work fine, so I'll move on to the next part of the project. Getting the hood cut, braced, and doing the bodywork on it.

 

Couple of things to consider regarding Andamo's numbers and what I came up with.

They have longer bars so a softer hit
The car they are running is set up to use the chassis and not the bars to absorb the hit so even having 2000 hp the hit will be softer than the car I used for an example.
I also calculated the hit with the wheels at 2 ft above the ground which allows a good deal of energy to be created
Lastly, I did not have slo-mo to properly time the car rising which could totally skew the results.
Anyway..it's a helluva lot of force.


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The use of wheelie bars in each class and chassis is different and there's not a one size fits all application. Just make sure they don't unload the chassis when they hit.