Ninety Side Bites Fins Set - ST Box

For whom?

This is an ideal side bite for surfers who want to make their board more lively, more radical and more modern.

It suits an intermediate to advanced level. Ideal for those who like tight turns, vertical surfing and chaining fast manoeuvres. It requires an active and precise surfing style. 

What for?

The Ninety works particularly well when you want to bring a 2+1 setup closer to a thruster-like behaviour. It adds grip at the point of engagement while maintaining a feeling of freedom, allowing you to attack sections with more confidence and precision.

It is especially suited to fast waves, beach breaks and technical sections where responsiveness is essential. 

It is designed for modern longboards and mid-lengths that you want to make highly reactive and dynamic. 

What size?

In a 2+1 setup, the center fin and side bites work together. Their relative size directly determines the balance between glide, stability and manoeuvrability.

The center fin remains the dominant element of the setup: it defines the line, stability and overall behaviour of the board. The side bites complement this by adding grip when the board is on rail, allowing deeper engagement in turns.

The balance between these two elements is essential.

This guide focuses on two side bite sizes: 3.5” and 4”, the most common sizes covering all longboard and mid-length uses.

3.5” side bites remain discreet. They preserve a single-fin-like behaviour, with lots of glide, long lines and a very fluid board. In contrast, 4” side bites add more grip and responsiveness. The board becomes more dynamic, easier to turn and more modern in behaviour.

The fundamental rule remains simple:

The larger the side bites, the smaller the center fin should be.

And conversely, the smaller the side bites, the larger the center fin can be.

However, in practice there is an important limit: once the center fin exceeds 6.5”, only 3.5” side bites are recommended.

Why?

Because a large center fin already generates significant control and stability. Adding oversized side bites would unbalance the setup, making the board too stiff, less fluid and less enjoyable to surf.

Thus:

• a center fin of 7”, 7.5”, 8” works ideally with 3.5” side bites
• 4” side bites are reserved for smaller center fins, generally 6.5” or less, to add dynamism without excess.

When the center fin is large and side bites are small, the board behaves closer to a single fin: smooth glide, stable line and wider turns. This setup is ideal for semi-retro longboards, soft waves and noseriding.

Conversely, when the center fin is smaller and paired with 4” side bites, the board becomes more responsive. Rail-to-rail transitions are faster, turns are tighter and surfing feels more modern. This setup suits modern longboards, mid-lengths and faster waves.

Finally, note that total fin surface should increase as board size increases. 

2+1 setup examples by board type

The set consists of two side fins (right and left).

It comes with a fin key for installation.