Building a light weight race car

Category: Innovation, Polycarbonate, Recycle, uses of plastic

If you’re interested in building your own race car this blog in conjunction with Chris Mohan Racing will show you how this can be an easily achievable project for someone with basic DIY skills. 

polycarbonate and aluminium composite was used to reduce weight in the Chris Mohan race car

With a combination of careful measuring and cutting you can reduce the weight of your race car:  weight being the enemy of any race car; reduce weight and you increase the BHP per ton of your vehicle.  Move weight around in your car, lower it, and you lower the centre of gravity and your car will handle better.   In the following project weight was removed from higher up in the car, hence lowering the car’s centre of gravity.

Weight Loss

At Chris Mohan Racing we decided it was time to replace our race car’s glass windows with something a little lighter, so we turned to The Plastic People for some help and advice.

We race a MkIV Golf GTi in the Maximum VAG trophy, so we have to abide by rules and guidelines.  A quick check found the following:

· The windscreen must remain standard glass

· The replacement material must be fire resistant

· The replacement material must be 4mm think minimum

· The driver’s window must have an opening

(If you would like to do this simple modification to your road/track day car, we recommend you follow the guidelines above. They are set for safety reasons after all!)

Instead of simply purchasing pre-cut window kits, we decided to make our own using polycarbonate from The Plastic People, who supplied us with the most suitable product:  Double sided UV protected Cut To Size, 4mm thick polycarbonate.

Racing in such a competitive championship, accidents tend to happen, so a little forethought was needed before we began.  With this in mind, we decided to bolt, rather than bond the new polycarbonate windows in. This makes removal quicker and easier, and we’d be less likely to damage the polycarbonate windows whilst removing them. We chose to create wooden templates, so if the need arises, we can quickly make a new polycarbonate window with little effort.

First – templates
We created paper templates by sticking them to the polycarbonate and drawing around the edges. Once cut to size, the paper templates were offered back up to the polycarbonate to confirm they were correct. Take time to be precise, this will benefit you later on!


The paper templates were laid on 4mm MDF sheet and the outline carefully transferred. With simple had tools, the templates were cut, taking care not to go inside the line.

Once satisfied with the shape, pay extra attention to the edges of the MDF templates, sanding them with fine sanding paper to get the smoothest of finishes without rounding the edges over. (This is important as a bearing guided router bit will run along this)

Once you are happy with the MDF templates, it’s time to start cutting the polycarbonate. There are many ways (and tools) to cut polycarbonate, but this is the method CMR used.

Note: at all times, keep the protective film on both sides of the polycarbonate sheets.

Place the MDF template on your polycarbonate sheet and roughly draw around it with a marker pen.  Remove the template and cover the outline with masking tape. Now place the template back over the polycarbonate and carefully redraw the outline around the template onto the masking tape with a permanent marker, making sure the template does not move.
Remove the MDF template, clamp the polycarbonate on a flat surface, with little over hang, and sandwich with a sheet of wood on top.

Now cut as close to the outline as you dare with a sharp universal hand saw. Keep the cuts straight; make multiple cuts to get around curves, always keeping a minimal overhang on your worktop. Do not go over the line!
Once you are happy with this, unclamp the polycarbonate and remove any large burrs with sand paper or a file.

Stick the MDF template to the polycarbonate with a good quality double sided tape. Now trim around the template in an anticlockwise direction, using a router with a straight flute bearing guided trimmer—at its lowest speed, use PTFE spay to prevent weld back on the cutter.

Remove the MDF template and carefully sand the edges of the polycarbonate by using 220 wet and dry. We progressively sanded all the edges from 220 to 800, gently rounding the edges, being very careful not to mark the face of the windows.  (You can heat the edges until they go crystal clear – but this is a little over the top in this case!)

Install the polycarbonate windows

Remove all the inner door covers, disconnecting all the locking mechanisms and electrics as you go. (We needed to loosen the window glass from its sliding mechanism clasps to do this) Remove the window and store it somewhere safe.

As we are working on a race car, we are not interested in any of the door furnishings or ancillaries, so the entire wiring loom was removed from the door.
The replacement polycarbonate windows were ‘offered’ in place and suitable fixing holes were drilled in the door. At CMR we devised our own way of doing this that means there are no visible screw heads on the outside of the car. Once both doors windows were fitted, we positioned and marked the driver’s side window slider for fitting.
The window was then removed, so we could cut the slider hole and its fixings. We fitted the slider with 5mm stainless countersunk screws, so care was needed when countersinking the polycarbonate. The polycarbonate window was repositioned into the car and the protective film removed.

With the front windows now fitted securely, attention now turned to the creation of lightweight door panels. Once new templates were made, we turned again to The Plastic People, who this time supplied us with some tough, yet lightweight aluminium composite sheet.
Again, masking tape and a permanent marker was used to mark the outline of the template onto the composite sheet, but this time a fine tooth blade in a jigsaw trimmed around the line. Once cut, we used different to remove any sharp edges and gain a smooth finish (draw file technique)

The new cards were offered up to the doors and fixing holes marked. We used 5mm nut inserts to create fixings within the car door shell itself, and 5mm stainless cap head Allen bolts attach the cards to the doors.

Home-made door pulls were fitted to the cards, whilst strategically drilled holes allowed the door pull cable to be presented through the front of the card, allowing it to be used as the door opener. (We don’t want anything unnecessary in the car!)

In keeping with the car, we decided to ‘vinyl wrap’ the panels in black. (The regulations also state the interior of the car should be of one colour)


The Rear

The rear side windows were carefully removed using a glass removal tool, and any excess bonding agent was removed with a sharp blade. The polycarbonate windows were offered in place and fitting holes were marked.

The polycarbonate window holes were drilled out using a 5.5mm bit and carefully countersunk. The corresponding holes in the body shell window frame were drilled using a 6.5mm drill bit. Self-adhesive foam tape was stuck around the window frame (to act as a water tight seal and vibration damper) and the poly window was fitted using 5mm stainless steel countersunk screws, washers and nylock nuts. A little clear silicone was squirted into the holes at the same time.

We used different size holes and screws to allow some ‘give’ as Polycarbonate and steel have different expansion rates – we don’t want any unsightly stress cracks!

The large rear screen was fitted in exactly the same way as above, but this time, we carefully heated and formed some curves in the poly screen  using an electric heat gun, so that when fitted it wasn’t under great torsion.
If heating the polycarbonate, remove the protective film.

Item Original Replacement
Front door glass 3.5Kg 1.5Kg
Rear side glass 2.5Kg 1kg
Rear screen 4Kg 1Kg
Door ancillaries 5.5Kg 1Kg
Total 15.5Kg 4.5Kg


NOTE: We had already removed the inner ‘plush’ door panels and speakers from the front doors and were running with the inner steel liners only. If all the original door components were included in the measurements, savings would at the very least double, if not triple.


Materials Tools
Paper (templates) Safety glasses & gloves
4mm MDF (templates) Rulers
Masking tape (templates) Hand saw
Marker pens Various clamps
Double sided tape (good quality) Various files
4mm Polycarbonate sheet Jig saw (fine blade)
3mm Aluminium Composite sheet ¼” router (at slowest speed possible)
Various grades Sandpaper, Wet & dry Drill
Socket Countersunk Screws A2 Stainless Steel M5 x16mm Drill bits
Socket Button Screws A2 Stainless Steel M5 x 16mm Countersunk piece
Nylon Lock Nuts A2 Stainless Steel M5 Electric heat gun
Flat Washers A2 Stainless Steel M5 Vice/workmate
Adhesive Waterproof Foam tape Nut insert tool
PTFE spray (used to prevent weld-back on the cutters) Hammer
Various screws/nuts Centre punch
Router bit the C006AX1/4TC to make slider opening
A straight flute bearing  trimmer
Windscreen removal tool
Retractable knife



Leave a Reply

Your email address will not be published. Required fields are marked *


You may use these HTML tags and attributes: <a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <strike> <strong>