As title really.

Would like to knock up an undertray connecting to the front and rear bumpers and the skirts, so all four corners, ideally incorperating a front splitter and rear diffuser.

The question is, HOW do you attach it to the car (bearing in mind the bottoms of all of those parts are lower than the lowest part of the chassis) so its firmly attached and doesnt rip off at 500000mph?
I know from experience how effective a proper front splitter can be at creating downforce, to the extent that even what I thought was OTT fixings succumbed to aerodynamics even at 70mph and pulled the splitter off downwards and under the wheels of the car on its first run, so it needs to all be on properly!

Also, the basics, bumpers and skirts- Whats the best way to hold them on so they stay on at speed? Im used to drifting so they are all on with cable ties, but at big speeds that doesnt seem a good call.

Any experienced racers please chime in, and if you got pics of how your aero stuff is held on, please post

 

This is not an easy answer. If you are using generic GRP parts then I tend to use nutplates and appropriately sized and number of bolts, keeping in mind that you will need to use some form of stress plate- usually alloy- to keep the bolts from simply pulling through the GRP. GOOD aero parts have hard points molded into them, either hardwood (prefered) or alloy, and make it easier to hang them on the car.

Some applications allow a mixture of DZUS or CAMLOC fasteners and bolts. DZUS buttons are a little cheaper and easier for the average mug to use, CAMLOC's are more expensive and require specific tools and a fair amount of measuring to get them right.

I have also used pin-and-socket assemblies to hold on aero bits, but this requires a good bit of careful thought as to how to properly mount whatever it is your mounting.

If your not confused enough already feel free to post up pics of what it is your mounting and I could maybe help with more accurate guesses as to how to do it.

 

the issue with dzus or camloc fasteners is that they require a decent amount of force to collapse the springs and create positive lock. it doesn't work to well on a fender where the amount of force required to collapse the spring exceeds the amount of force required to collapse the fender!!

What I use on my road racer is furniture bolts. They are low profile allen heads that have a large surface area under the head. they are fully threaded 1/4" N/C and use nylon locking nuts to secure them. My car has seen speeds >140mph on the back straits and my cheap knockoff body kit doesn't have any spider cracking yet!! ****knocking on wood****

I use them to hold on my front valence, side skirts, rear valence and spoiler. All but the spoiler needs to be removed prior to loading on the trailer. Sometimes it can be tedious, but it works!

The bolts i'm referring to are similar to these:

 

Pretty much the entire body- front and rear fenders, front and rear bumpers, and side sills of this Porsche is held on with Camlocs

 

Cam locks are good, quick release fasteners like the one I posted below also work. but when it comes to front splitters we usually have them bolted on with tension bars.

 

Those are DZUS fasteners (also called 1/4 turn fasteners), work perfect depending on how they are used.

 

My whole FC2000 front end is held on with 7 Dzus fasteners. Primo!