I think welding is a great option, but I just don't want to do it for a few reasons right now. I'm quite sure a bolt-on flush mount design is achievable. Will share my design once complete.

I was referring to what Moti did; we have done a bunch of it in FSAE at the past. Easy if you have access to the lathe, hence I am not aware of market-available solutions, although the McMaster one posted seems close enough. We also used low profile socket hex bolts, as we did not like countersunk hardware at all (even though it would make no difference with the loads of the undertray)

I was going to suggest the elevator bolts as well. Works just like carriage bolts but you can draw them up almost flush.

After reviewing it again I can only find it in the GTA rulebook. Nothing about barge boards in the GL rulebook although most of the classes are identical concerning aero.

Adam (GridLife) told me last off-season that barge boards would be considered an aero element and allowed 5" protrusion from the body for GL but GTA limits to 3".

Also had a thought, what if the mounting brackets for the barge board extended inwards towards the frame rail but the barge board itself doesn't. Then that's technically abiding by the spirit of the rule I'd think.

Looks like Alumalite will be the way to go instead of PVC trim board. Support the outboard edge with a 1/2" x1/2" x 1/16" aluminum angle as well.

Here's the link I intended to have come through: https://www.mcmaster.com/98007a029

3" viewed from the top is quite a bit.

Thats what she said.

Well I must admit I was in this for the aerodynamic discussion but seeing and reading the mountings have given me a bit of a DIY boner.
Have to ask my friendly MOT tester about allowances

My ever changing barge board design from edge to edge total width is 67" which matches off with the width of my splitter and front spats that were designed around covering my 10" wheels. Don't see a reason to go wider regardless if rules allow.

Been looking into materials for this and alumalite in the size required is roughly $200 then when researching weight the 6mm alumalite was roughly 7.65lbs and a using the same shape and made out of 3/8" birch play the weight comes in a 9lbs or 6lbs for 1/4"


Where are you guys getting alumalite? would birch suffice or is it worth the price bump? What other materials could we use? Has anyone tried dibond, its like alumalite but with a solid core.


Also from outside of frame rail to outside of widest body point on car in multiple spots along the side is 15.5" as a reference point if anyone cares.

Most of the stiffness of Alumalite and Dibond comes from the face panels, as with any composite sandwich panel. 6mm Alumalite and 6mm Dibond have the same aluminum skin thickness (.012"), so they are comparable in stiffness. Alumalite is actually slightly stiffer, as it uses a slightly stiffer core material and maintains a decently thick layer of this material at the outside of the corrugations.

On the other hand, 6mm Dibond / Omega-Bond (another brand of the same thing) is approximately twice as heavy as Alumalite (50lbs vs 25lbs for a 4x8' panel). Therefore, I would avoid using Dibond / Omega-Bond in any application where you care about weight.

You could try looking for "Econolite," which leaves one side bare mill finish aluminum instead of paint. In practice, what really matters is what's available locally, so Alumalite might still be cheaper.

Makes sense. So what is the general consensus on using 3/8 birch ply instead. (36lbs for a 4x8'sheet) My materials class was seriously lacking when i went to school.

Fortunately, good intuition about statics matters at least as much as knowing anything about materials. What you actually care about is overall stiffness, not modulus, so geometric stiffness from thickness is an excellent way to reduce stress when applying bending load to the panels.

That being said, $200 on a panel looks pretty good when you think about the money you save going DIY. Alumalite is geometrically optimal for the application and resists weather and chemicals very well.

Can some throw up some details for a 4x8 alumalite sheet? So I can add it to my spreadsheet.

We don't have it here (ironically a company that makes a similar product is multipaneluk but they don't stock it just ship it to the US).

Have you found alumalite kind of panels in Europe? The closest I got was Aluben by Bencore, but it's 20mm thick, and Alucore 6mm, which ist stiffer than 4mm Dibond but weighs the same. The price? Astronomical.

All I ever seem to find at a reasonable rate is Dibond, but I want something lighter

Yes. As I said MultiPanelUK are the only ACP manufacturer in the UK and make AluFlute which is Alumalite in all except name (so it may just be renamed in the US).
They simply make it in bulk and ship to the US they do not distribute it in the UK at all.

I got as far as having contact with an account manager at two sellers and an account manager at MPUK.
I said what I wanted and the MPUK AM pointed me to the sellers.
The sellers then said AluFlute was a special batch and I'd have to order a production run.
I asked how much that would be (after all I'd need probably4-5 to aero the entire car).
Was told 800 sheets which at 8x4 would mean a shit ton of money and I'd never be able to shift all that if i gave it away to everyone active on this forum regardless of location

As described in my materials spreadsheet you can put together a DIY variant with aluminium and correx for about the same price.

Not helpful to our friends in the UK but if you are in the Washington area Denco sales in Kent WA has 4'x8' sheets of 6mm alumalite for $124 in stock everyday.

@matrussell122 How much does that weigh?
Has anyone got a modulus for alumalite too?

It's a sandwich panel. Aluminum has an elastic modulus. Polypropylene has an elastic modulus. You do not actually care about the elastic modulus. Modulus is analogous to density; it does not account for geometry. You care about the bending stiffness, which comes largely from spacing the aluminum apart.

A sheet of steel that is one thousandth of an inch thick has a much higher elastic modulus than 10mm Alumalite. It is also much less stiff in any way you'd care about.

Good napkin estimates of the bending stiffness of Alumalite can be obtained by modeling it as an "air core," where you only have to analyze the face panels. It depends on the loading, though, so you should figure out what parameters of deflection you actually care about.

About 25lbs a sheet
https://cimg6.ibsrv.net/gimg/www.mia...e0ba24f53a.jpg