Old 03-16-2017, 12:34 PM
Join Date: Oct 2012
Posts: 82
Default How to DIY under tray on the cheap

After a garage remodel I ended up with a ” 4X4* sheet of Lexan. Contemplating on buying an SSP under tray but being unable to cough up the over $400.00 for it, I decided to make my own.

Now I know ” might seem a little overkill in thickness, but it’s what I had and if you were thinking a 4X4 sheet would be a little short, it is. I made it work for me though.

*The ideal sheet would be either a 4X5 or a 4X6 in a 1/8” thickness if using Lexan. Feel free to use whatever material your little heart desires.
My car is a commuter and sees mostly city driving, therefore Lexan.

Stuff needed:
Lexan sheet, Cardboard, Sharpie
Drill, Jigsaw, Jack with 4 stands, measuring tape
25 M6-1.0 16mm bolts and washers
Salvaged bolts and u-clips from your under-tray
Rivnut tool and Rivnuts (if you wanna get fancy)

So this is how it went down:
I started by removing the under tray (all of it)
I traced it on a piece of cardboard I had lying around, making sure to mark all original mounting points. This was a little tough considering the OEM under tray isn’t exactly flat, so take your time marking and tracing.

Once I was happy with the markings on my template I went ahead and proceeded to cut. I went ahead and cut slightly away from my markings just in case if I had any fitment issues I could go back and trim as I go.

I went ahead and jacked up the car placed it on 2 jack stands, then I used my additional jack stands and jack to help me support the template under the car while I did the fitting.

Once I was happy with the fit and finish I went ahead and salvaged the U-Clips and bolts from my OEM under tray. This included the 10mm bolts in front, and all the other 10mm bolts and U-clips from the oil filter cover and oil drain plug cover.

Since I was using a 1/4” sheet of Lexan the bolts from the pans were too short, so I went ahead purchased about 25 M6-1.0 16mm bolts and washers, the bolts are the OEM thickness and are compatible with the U-clips I salvaged.

Now that I had my hardware I proceeded to trim the inner splash guards just enough so that the u-clips fit in the original holes, you can use shears for this.
I did the same and trimmed the corner mounting points on my bumper so I could add U-clips. These originally had the push clips, I won’t be reusing those

Once my mounting points on the car were set I traced the template on to the Lexan marking everything. To cut the Lexan I used a jig saw with the metal cutting blade (a lot of tiny teeth). I was surprisingly easy to cut. I sanded the rough edges and went on to test fit.

Being that the Lexan used was clear it made it a lot easier to mark and line up the holes for mounting points, and service cut outs. Once I was happy I proceeded to drill the holes.

There’s a brace with a hole on it, I deburred it and inserted a #10-24 corse thread rivnut. Doing this will give the sheet extra support in the center. When using rivnuts always make sure to deburr the hole for a secure, spin free fit.

There’s a brace with a M8-1.25 bolt in place. I used that along with a washer to secure the rear part of sheet to the car.

While looking at the OEM under tray I noticed there’s a duct directing air to the front differential, I measured the location and cut a 5x6” hole on my Lexan tray in the meantime, in the future I plan add a Lexan NACA duct for cooling of the diff. I also cut some gills for cooling and used a heat gun and a wooden ruler in between the gills to bend the Lexan.

I secured the plate to my bumper and splash shields using my new 16mm M6 bolts and washers and for the rivnut I inserted in the center brace I used a #10-24 45mm coarse head hex screw with washer and voila!

Total spent: $15 in bolts and washers and a brace
(since my plate is 2pc I had to use a brace and rivets to hold the pieces together)
Approx. $40 worth Lexan (from a left over project)

Let your creativity juices flow: you could cut holes and make covers for the oil filter and drain plug, or for jacking up the car.
In the end it beats the craptastic OEM plastic under tray.

I want to thank clubralliart members Jackal since I got the DIY idea from his build thread and also thanks to Markspd6 for pitching in the use of Lexan as an under tray in MTZL’s Aluminum under panel thread.

For those not familiar with Lexan here is a vid showing a strength test of a 1/4" LEXAN sheet

Last edited by HENRYBEAST; 03-16-2017 at 01:10 PM.
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Old 04-11-2017, 10:12 AM
TrailBrake TrailBrake is offline
Senior Member
Join Date: Mar 2011
Location: At the apex
Posts: 1,007

Sounds interesting

Any pictures?
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Old 04-20-2017, 03:51 PM
Join Date: Oct 2012
Posts: 82

Pics are in the works, kinda hard to take good pics with the plate on the car. Here is one with the plate off, not the best pic but just to get an idea. I'll be changing the tranny oil next month I'll take very detailed pics then and follow up on how great it's held up
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