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Lightweight Race Car

If you’re interested in building your own race car this Customer Story 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 (Brake Horse Power) per tonne of your vehicle.  In the following project weight was removed from higher up in the car, hence lowering the car’s centre of gravity.

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 Group.net VAG trophy, so we must 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 minimum thickness

· The driver’s window must have an opening

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 solid templates, so if the need arises, we can quickly make a new polycarbonate window with little effort.

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.

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

Once satisfied with the shape, we sanded them with fine sanding paper to get the smoothest of finishes without rounding the edges over.

Once happy with the MDF templates, it was time to start cutting the polycarbonate.

Keeping the protective film on both sides of the polycarbonate sheets we placed the MDF template onto the polycarbonate sheet and roughly drew around it with a marker pen. We then removed the template and covered the outline with masking tape. We placed the template back over the polycarbonate and carefully drew an accurate outline around the template onto the masking tape with a permanent marker.

We removed the MDF template and clamped the polycarbonate onto a flat surface with little over hang, and sandwiched with a sheet of wood on top.

We then cut as close to the outline as we dare with a sharp universal hand saw. Keeping the cuts straight and making multiple cuts to get around curves we were careful not to go over the line.

Once happy with this, we unclamped the polycarbonate and removed any large burrs with sand paper.
We stuck the MDF template to the polycarbonate with a good quality double sided tape and trimmed around the template in an anticlockwise direction, using a router with a straight flute bearing guided trimmer at it's lowest speed. We used PTFE spray to prevent weld back on the cutter.

After the MDF template was removed we carefully sanded 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

To fit the windows we removed all the inner door covers, disconnecting all the locking mechanisms and electrics. We then removed the window and stored 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 files 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 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 polycarbonate 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 polycarbonate screen using an electric heat gun, so that when fitted it wasn’t under great torsion.

If heating the polycarbonate, remove the protective film.




Front door glass   



Rear side glass   



Rear screen   



Door ancillaries   



Total Weight Loss - 11kg

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.

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Here polycarbonate is being used as an alternative to glass for the car windows.  Polycarbonate has been cut to the shapes needed to fit where the original glass windows were.  As polycarbonate is 200 x stronger than glass, these windows won't need replacing anytime soon.

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If you want to try your own project and you need any advice, please do not hesitate to get in touch with our friendly customer service team.

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