Will Kai Lenny's quad fins change your surfing? I tested a set
Updated 2026-09-19
A quad set with the rear fin bigger than the front, rather than the usual traditional layout, sounds like a gimmick until you actually ride one. I tracked down a set of the Maui Fin Company Kai XXL R2 quads, the setup Kai Lenny has been using, to find out whether the claim holds up on a normal-sized board rather than a big-wave gun.
What makes this quad setup different
A traditional quad runs a bigger front fin and a smaller back fin. This set flips that: the front fin is smaller and the rear fin is larger, closer to a twinzer layout than a standard quad. The fins were tight enough in the box that I had to sand down an edge to get a proper fit, and the front and rear fins are sized differently at the base, so swapping them front to back is not possible with a Futures or single-tab setup the way some owners on the manufacturer's own video suggested trying. FCS II owners may have more room to experiment there.
First test: a 7'6 semi gun
I took a 7'6 semi gun out on this set for a first look, catching a wave over 100 metres long in circa six-foot surf after a 15-minute paddle out. It felt smooth and fast. My guess, without being a hydrodynamics expert, is that the fins simply carry less surface area and less drag than a standard quad set, and I was concerned that would cost hold for a bigger rider. It did not. The board felt nimble and I was comfortable with it from the first wave.
Second test: an 8'2 triple stringer gun
The bigger test was an 8'2 triple stringer quad gun that normally runs standard-sized quad fins and feels stiff and reluctant to turn as a result. Smaller fins should loosen a board like this up, and I went in expecting enough hold simply because the same fins had already proven themselves on a big-wave board under a rider as capable as Kai Lenny. I have not logged a session on this pairing yet, but the theory holds up based on how the fins behaved on the first board.
Where I expect them not to work
A Firewire Seaside Volcanic, a small to medium wave board with a wide tail, is a different case. Traditionally that board runs a big front keel and a small rear fin, the opposite bias to these quads. The Machado fins I had previously used on that board were bad enough that I sold them and went back to standard quads, so I plan to try this set there too, but I expect either too little hold or too little drive, because this is not the type of board or wave range the fins were designed for. That board, an EPS quad at 6'1, logged a top speed of 22.7 km/h (14.1 mph) over a wave range of one to seven feet before it moved on, which is a fun, everyday number rather than the kind of speed these fins are built to reach.
What this says about matching a fin to a board rather than a name
The lesson across all three boards is the same one that keeps coming up in fin testing generally: a fin developed for one rider's conditions carries the bias of that rider's boards, not a universal setting. A smaller front and larger rear fin genuinely suited a semi gun and should help a stiff triple stringer gun loosen up, precisely because both boards already lean toward control over looseness. A board built the opposite way, with a big front keel doing most of the work, is fighting the fin's whole design rather than working with it.
Are they worth buying?
For me, yes, on the evidence of one strong first session on the 7'6 semi gun. Kai Lenny has clearly done real development work with the manufacturer, and if a set like this can hold a rider my size on a mid-sized board without sacrificing feel, it is worth the cost for anyone curious rather than only for someone chasing waves at Nazare or Jaws. Stock has been limited at times for the single-tab version, so availability is worth checking before ordering.
Questions people ask
What is different about the MFC Kai XXL R2 quad fin?
The rear fin is larger than the front, the reverse of a traditional quad setup, which gives a smoother, twinzer-like feel with less drag.
Do these fins fit straight into a standard quad box?
Not always. My set was tight enough in the front boxes that I had to sand an edge to get a proper fit before use.
Can you swap the front and rear fins to compare feel?
Not with Futures or single-tab fins, since the front and rear bases are different sizes. FCS II owners may have more flexibility there.
Do smaller quad fins work on any board?
No. They suited a 7'6 semi gun and should help loosen up a stiff triple stringer gun, but a small wave, wide-tail board built around a big front keel and small rear fin is likely the wrong match.
For the wider case on why fin choice changes a board this much, see do fins make a difference and quad fin sets. If you are deciding between quad, twin and thruster setups generally, twin, quad or thruster covers the decision, and fin size and rider weight explains why a bigger rider does not always need a bigger fin. Related fin tests on the same boards are in new Machado Too Fish keels.