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I can only assume it's to make it easier to weld. Not particularly good practise though.

I saw this on various builds, even some really hi cost ones, and am always amazed at why people do such an obvious mistake.. Getting all the tubes right into the node together is sometimes a problem but well worth it...


Sometimes, at real work , I use 1 inch aluminum tubing to hang cameras from high speed vehicles.. such as:


getting them all connected to a point makes a huge difference in the stiffness of the whole structure..

Work out your ratios before chopping length off the pedal arms to make the assembly fit. A shorter throttle pedal will likely make it more sensitive. Mount the assembly as high as necessary.

a.moore, Benonymous, and kikiturbo - I brought this concern up to my cage guy after it was pointed out and he stated that the vertical bar is support for the horizontal and the angle pieces are there to help hold it square. Only experience I can go off of is when we built trusses in 7th grade and the design of the truss would determine the load the roof could take. I know that he is not doing this out of laziness or difficulty of a weld.

Miatav8,MstrASE,A&P,F - Thank you for pointing this out, it will be addressed at that point of the build. I had assumed it would be the same "throw" but I see what you mean.

More pictures of the build -

I do not want to "piss on your parade" but there is a lot of tubes here going into an unsupported joint.. the worst offenders are the upper two curved tubes connecting the front clip to the main frame.. you are going to have a problem with stiffness in pure bending.. not to speak of crash worthiness..

Who said anything about crashing?

I can see your point, the steering box is just "floating" out in front with not much holding it to the chassis. I will bring that up. I don't consider any opinions/suggestions as "pissing on parades" either. I welcome any feedback, that is part of the reason that there is a build thread on this project.

Um, interesting frame design...
Not designed by a chassis engineer.
It will work fine for the speed you are likely going to be going and the very light weight and (relatively) low torque engine of your car, but it is not an ideal design.
It is not terrible though so don't pull your hair out.
It is just not as strong and as stiff as it could be for the same number of tubes.
When we look at the common race car frames of the past (the Cobra comes to mind) your frame is light years ahead in strength and safety so no worries there mate!

For fun, build a scale model (1"=1') out of 1/8" square balsa wood with superglue joints to the tube layout as built, and build another model with the tubes all intersecting at the nodes (control points) and then twist them to see the difference. Model building is fun, fast, and very educational. The strongest structure for the weight is a pyramid, triangulated triangles. That is why we "usually" have the tubes all meet whenever possible but there are times when that is not workable.

So, for your next car...

I didn't want to push the issue without running some numbers in case the stiffness loss was negligible. All elements have been set to beam (ends can carry bending load) and the material is 1" x 0.065" round steel. A 1000 lbs load was applied to node 4, fixed node 1 in the X,Y,Z, and node 3 in the X,Z.

The first test was with no diagonal and it is bad:

Node 4 moved about 1.9" down.

Next the diagonal was added but it was located 3" away from the nodes:

Its much better than before since node 4 only moved 0.094".

Finally run the diagonal node to node:

Node 4 only moved 0.0165".

By running the diagonal the way he has, it is only about 1/6 as stiff as running it to the node for that load scenario but it is still about 20x stiffer than having nothing. It would take a lot more work to determine its effect on the overall frame stiffness but you get the idea that it does matter. With that said the book Locost frames are not the best from a chassis engineering standpoint and they do fine.

Andrew - that is an awesome program. I am at the mercy of my cage builder, I wanted to do all the welding with my brother but my dad did not want the car to "come apart" as I was driving it and cause injury to myself or others. (I have zero welding experience and my brother is teaching himself) I am really just going to have this be a sunday driver and will not be putting much strain on it anyway.

I believe in carrying it to the node and using gussets in areas. There is always next time...

I suggest, when your cage builder is done, to measure the torsional stiffness of the frame...Then you'll see if you really need to do some additional work or not... (although you will surely be at the low end of stiffness vs weight ratio)....

however, If I were in your place, I'd add a couple of tubes, to tie in the front end better.... can't hurt..

Had a talk with my cage guy and we are going to add more to the front once we see where the tire clearance needs to be. Updates on that when we get to that point on the build.

Engine is mounted and work on the suspension will begin. It is awesome to see the car on the ground with wheels. There will be another support on the upper engine mount that continues to the bottom cross bar for extra support.

I just had an interesting thought about those funny bent bars up front, they might give you a bit of a crumple or energy absorption zone in an impact.

You are NOT at the mercy of your cage builder! If he won't build it the way you want it built, find someone that will! Those diagonals NEED to extend to the node, not just for torsional rigidity, but for safety in a crash! Loads need to be carried from one tube to the next, he's designing in a lot of dead nodes because it's easier to get the tube in there. Built properly, the tubes are an absolute PITA to get in place, but must be done.

Russellmn - valid point, I am using this as a learning experience and I am excited to see what I can produce on my first try. We are hoping to have a rolling chassis in about a week.

It's faulty in a lot of areas from an engineering perpective but if it's just a fun street car then go for it and have fun, it's not going to fall apart on you.