How to Fit Universal Rally Mudflaps: Cutting, Marking and Mounting Guide
Universal rally mudflap panels are straightforward to fit. Unlike precision-fit rally style mudflaps, which come pre-shaped for a specific vehicle, universal panels are rectangular sheets that you cut and mount to suit your specific arch profile. Depending on your vehicle, they fit straight on without cutting if your arch is open enough to accommodate the standard panel sizes. This guide covers the full process from measuring to mounting.
Do you need to cut the panels?
Not always. On older rally cars, off-roaders, and vans with open arch profiles, a standard 500mm x 300mm panel often fits without any trimming at all. If your arch is large and unobstructed, hold the panel up against the arch before reaching for a blade – you may be able to bolt it straight on.
Cutting is needed when the arch profile is tighter, when surrounding bodywork or plastic trim would be obscured by a full-size panel, or when you want the mudflap to sit cleanly within a specific area of the arch. Modern cars with complex arch liner profiles and plastic trim are more likely to need trimming than older or simpler vehicles.
If you’re unsure whether you need to cut, fit the panel temporarily without fixings first and check the fit from the front and rear of the vehicle. That tells you immediately whether trimming is needed and where.
What’s in the kit
PolyWard universal rally mudflap kits are available with or without brackets and clips, depending on what you order. Check your order before starting. If you’ve ordered brackets and fir tree clips, they’ll be included in the package. If not, you’ll need to source your own fixings before fitting.
If you need to add brackets or clips, see the universal rally mudflap kits page for the available options, or pick up fir tree clips and hardware separately here.
Tools and materials you’ll need
- A steel ruler or straight edge
- A sharp Stanley knife with a fresh blade – a blunt blade drags rather than cuts and produces a ragged edge
- A cutting mat or piece of scrap wood to cut on
- Masking tape or a white marker pen for marking cut lines
- A drill with a bit sized to your chosen fixings; 6mm, 7mm or 8mm, depending on the fir tree clips you’re using
- [Optional] A second person to hold the panel in position while you mark it, if cutting to fit a specific arch profile
Step 1: Measure before you cut
The most common fitting mistake is skipping this step. Before marking or cutting anything, measure the area where the mudflap will sit.
For arch-mounted mudflaps, measure the width of the arch opening at the point where the mudflap will hang. This gives you the maximum width the panel can be without overlapping surrounding bodywork or trim. Also measure the height; how far down from the arch you want the panel to hang.
Write the measurements down. Check them twice before marking the panel.
Step 2: Mark the cut line
Use masking tape applied along the cut line on the mudflap’s surface, or mark directly on the panel with a white marker pen. Masking tape is slightly preferable. This gives the blade a clean edge to run against and protects the panel surface from scratches during marking.
For a straight cut, use a steel ruler as a guide. For a shaped cut following an arch profile, use the arch liner or the existing mudguard as a template, hold it against the panel and trace the profile with a white marker.
Take your time on this step. A rushed or inaccurate mark produces an inaccurate cut.
Step 3: Cut the panel
Use a sharp Stanley knife with a fresh blade. Score along the marked line with moderate pressure in a single clean pass. Do not try to cut through the full 4mm thickness in one stroke. Make several passes along the same line, increasing pressure slightly with each pass until the panel cuts through cleanly.
Keep the blade running against a steel ruler for straight cuts. Do not use scissors; they compress the PVC and produce a slightly crushed edge rather than a clean cut.
After cutting, run your finger along the cut edge. If it feels rough or has a slight burr, a quick pass with fine sandpaper or a craft knife at a shallow angle cleans it up.
Step 4: Mark and drill the mounting holes
With the panel cut to size, hold it in the position it will be mounted and mark the hole positions with a white marker or a sharp punch. Check the position from a distance; the panel should hang straight and sit evenly within the arch before you commit to drilling.
Drill the mounting holes with a bit sized to your fixings. For fir tree clips, use a 6mm, 7mm or 8mm bit, depending on the clip size — check and measure the clip dimensions before drilling. For self-tapping screws, use a bit slightly smaller than the screw diameter.
Drill through the PVC panel only at this stage, not into the vehicle. The vehicle mounting holes come next.
Step 5: Mount the panel
Using fir tree clips: push the clip through the hole in the mudflap panel and into the corresponding hole in the arch liner or bracket. The clip should push through firmly and grip the liner behind it. A correctly seated fir tree clip sits flush with the panel surface. If the head is sitting proud, the clip has not gone fully home.
Using universal brackets: position the bracket against the arch, mark the bracket mounting holes on the arch liner, drill and fix the bracket to the arch first, then attach the mudflap panel to the bracket using the supplied bolts or clips. The bracket approach gives the panel more rigidity and is preferable on vehicles where the arch liner alone is too flexible to hold the panel securely.
Using self-tapping screws: screw directly through the panel and into the arch liner plastic. This is the quickest method, but it gives less adjustability than fir tree clips once the screw is seated.
Step 6: Check alignment before fully securing
Once the panel is in position with fixings loosely in place, check the alignment from the front and rear of the vehicle. The panel should hang straight, sit evenly within the arch, and not foul the tyre at any point in the steering or suspension travel.
On a vehicle that’s been lowered, check the clearance between the bottom edge of the panel and the road surface. A panel that sits too low will scrape on speed bumps or catch on kerbs. Trim the bottom edge if needed before fully tightening the fixings.
Once you’re satisfied with the position, fully seat all fixings. Fir tree clips should be flush with the panel surface. Brackets should be tight against the arch liner with no movement.
A note on thickness – 3mm vs 4mm
PolyWard universal rally mudflaps are available in both 3mm and 4mm PVC. For Motorsport UK sanctioned events, 4mm is the minimum thickness requirement. For road use, off-road use, and non-competition fitting, 3mm is often adequate and slightly easier to cut and shape. If you’re unsure which to choose, see our guide to 3mm vs 4mm rally mudflap thickness here.
Frequently asked questions
Do I need to remove the wheel to fit universal mudflaps?
Not always. It depends on the vehicle and where the mounting points are. On simpler arch profiles with accessible mounting points, fitting mudflaps with the wheel on is manageable. On modern cars with tight arch liners and recessed mounting points, removing the wheel gives significantly better access. If you’re struggling to reach the mounting position, removing the wheel is faster than persisting with it on.
My panel is slightly too wide — can I trim it after fitting?
Yes, but it’s easier to trim before fitting. Remove the panel, mark the trim line, and cut with a Stanley knife as described above. Trying to trim in situ with the mudflap panel mounted produces less accurate cuts.
The fir tree clip won’t push home fully — what’s wrong?
The hole is likely slightly too small. Remove the clip, redrill the hole with the next size up drill bit, and try again. A correctly sized hole allows the clip to push through with firm hand pressure and seat flush.
Can I use universal mudflaps on a competition car?
Yes, that’s one of the primary use cases. For Motorsport UK sanctioned events, use the 4mm panels and ensure the fitted size meets the minimum coverage requirements for your event. Check the specific regulations for your series before fitting, as requirements can vary. For full details on Motorsport UK mudflap regulations, see our Motorsport UK mudflap regulations guide.
How do I get a clean cut on 4mm PVC?
A fresh, sharp Stanley knife blade and a steel ruler. Multiple light passes rather than one heavy cut. Score the line first with light pressure, then increase pressure on subsequent passes. Do not use scissors. A blunt blade is the most common cause of a ragged edge. Change the blade before cutting if there’s any doubt.
See the full range of PolyWard universal rally mudflap kits — available in 3mm and 4mm, black, red, white and blue, with optional brackets and fir tree clips.