4D and 3D plates on a motorbike: what is actually road legal
Raised-character plates are popular on bikes, and there is a lot of confusion about whether they are allowed. The short version: raised is fine, coloured is not.
What BS AU 145e requires
Since 1 September 2021, plates fitted to a vehicle must meet BS AU 145e. The change that matters here is that characters must be a single shade of black. That rules out two-tone effects, carbon-look finishes and any coloured raised character, regardless of how it is made.
It does not rule out raised characters as such. A plate with black, laser-cut acrylic characters bonded to a compliant plate still meets the standard, because the characters are still single-shade black and still the correct size, stroke and spacing.
4D laser-cut
4D plates have solid acrylic characters cut by laser and bonded onto a plate that is already fully legal underneath. Ours are 3mm deep, which we find is the sweet spot: enough depth for the side-on look people want, without the cleaning difficulties and snagging of 5mm.
Because the characters sit on top of a compliant plate, a damaged or missing raised character still leaves a readable, legal registration underneath. That is a genuine practical advantage, and not every supplier builds them that way.
3D gel
3D gel takes a different route to the same idea. A clear polyurethane resin dome is applied over each printed character and cured, giving a raised, rounded, high-gloss finish rather than the square-edged look of laser-cut acrylic.
It is road legal on the same terms: single shade of black, correct size and spacing, made to BS AU 145e. Coloured and carbon-effect gel is where people come unstuck, because the standard requires single-shade black characters. A carbon-look gel plate is a show plate, whatever the seller calls it.
We sell both. 3D Gel and 4D Plate are two of the three text styles in our builder, alongside Printed, and either can be built as a legal plate.
Show plates are a separate thing
Show plates have no legal markings and are not road legal. They exist for display, off-road use, track days and photography. There is nothing wrong with buying one, as long as you know what it is for. Our builder asks whether you want a legal plate or a show plate before anything else, because the two are made differently from the start.
If you fit a show plate to a bike on the road, you risk a fine of up to £1,000, an MOT failure, and potentially losing the registration.
The rule of thumb
If the characters are black, the right size and spacing, on a reflective yellow background, on two lines, and the plate carries BS AU 145e with supplier details, it is road legal. Raised or flat does not change that. Colour does.