You have four boxes in your board and a wall of sets in front of you, nearly all at the same price and described in the same handful of words.

Almost none of the differences between them are the ones the packaging talks about.

What removing the center fin actually did

The marketing line is that four fins give you the speed of a twin with the hold of a thruster. That describes the outcome and skips the mechanism, and the mechanism is what tells you which set to buy.

A thruster's center fin sits directly in the turbulent wake coming off the stringer. It is catching disturbed water at a bad angle — drag generated in the most expensive spot on the board. Take it out and that specific cost disappears. That is where the speed comes from.

What the marketing line leaves out: four fins produce more total drag than three. More surface, more skin friction, more induced drag. The center-fin position is simply so costly that removing it more than pays for the fourth fin in most conditions. Faster board, different reason.

Drive changes too. On a thruster you pressure one rail fin at a time and pivot around the center. On a quad the inside pair loads together — front generating lift, rear providing bite — so the turn is a wider, drawn-out arc you carry speed through rather than pivot out of.

Surfers who love quads love exactly that feeling. Surfers who hate quads hate exactly that feeling. It is the same sentence.

The hold argument, settled

Ask ten surfers whether quads hold and half will say better than a thruster, half will say skatey and unreliable. They are both right, and they are describing different axes.

Lateral hold — resisting being pushed sideways by the face — is where quads win. Two fins on the engaged rail is redundancy. In a barrel, on a steep open face, both are locked in. That is why "quads are for tubes" is mechanically true rather than just repeated.

Vertical hold — grip through a top turn or a snap, anywhere you redirect vertically — is where they struggle. A thruster's center fin is the anchor for that move. Remove it and the tail has nothing holding it through a sharp vertical change. It slides. That is real, not a technique problem.

So: better laterally, worse vertically. People who love quads surf hollow, powerful waves where lateral hold is the thing. People who find them unreliable surf beach breaks where the pocket turn is the thing.

Which axis you need is the first question, and it decides more than any template does.

The one number that separates the sets

Divide front fin area by rear fin area. We work it out; nobody hands it to you.

Equal fronts and rears mean both fins keep driving and nothing lets go. A big gap means the fronts hold and the rears only guide — push hard enough and the tail releases, which is a feature if you wanted it.

Across the True Ames line that ratio runs from about 1.0 to nearly 2.4. That is not a range of nuance. That is two different ways of riding a wave, sold at one price.

Everything else is narrower than it looks. Fourteen of the seventeen designs with published dimensions have essentially the same outline proportions, so outline is not what you are choosing on. Total area is a gross scale control — more for a heavier rider or heavier surf, less for weak waves. Rear foil is worth one glance: an 80/20 rear is drawn to sit out near the rail, a 50/50 rear is drawn to sit inboard near the stringer.

The three things you cannot buy

Where your rear boxes are. They are routed at a fixed distance from the rail and the tail, and no fin moves them. Your board was drawn around the placement it has. This is why a set that transformed somebody else's board can do nothing for yours.

Cant and toe. Both are cut into the boxes by your shaper. A fin cannot have them.

Colour, construction and system. System is the box in your board — buy what it takes. Colour is colour. Construction changes feel, not geometry: solid fiberglass is stiffer and heavier, Hexcore lighter with more give, plywood buoyant. Price is not a signal either — nearly every full set here sits at the same number.

That leaves the ratio, the scale, and which axis you need. Three things, and you already know the third.

Which one is yours

First quad, or you genuinely don't know. The TA Quad at $148.50, or the Mandala AK4 or Album at the same price. Middle of the range on every axis. Ride one a full season before deciding it is wrong — a quad takes longer to read than a thruster does, because the thing it does well happens on waves you do not get every week.

Coming off a thruster and you want to keep snapping. Timmy Patterson in solid fiberglass at $148.50. The lowest ratio in the line and the biggest rear — the set that keeps holding through a vertical redirect, which is the exact thing you are about to miss. In Hexcore at $138.50 if you are light or the waves are soft.

Performance shortboard, good waves, and you want the tail available. McCallum at $148.50 — area loaded forward, so the fronts do the holding and the rears let you break it when you ask. The opposite end of the ratio from the Patterson.

Fish or fish-hybrid. Three different answers depending on where you are coming from. From keels, the Pavel Speed Dialer at $148.50 — fronts and rears near enough the same size, so nothing lets go. From twins, the Lovelace Piggyback. On a wide tail where you want drive, the Mackie — the most fin in the line and the only one drawn low and long rather than square.

Mid-length, egg, or something with hull in the bottom. Ellis Ericson Feathers at $148.50 — the most upright outline here and the genuinely different one. Give it a month before you judge it. If the board is 7' or over and what you want is a tighter arc rather than more glide, John Simon Type II instead.

Small, weak, gutless. Lovelace Quad at $148.50 — the least fin in the water, and the most speed made out of nothing.

Rail-to-rail feels abrupt on the quad you already have. Pavel Quad at $148.50 — same size class as what you are on, double-foiled front and rear, noticeably freer through the transition.

Your rear boxes sit well inboard, near the stringer. Valaric at $148.50 — 50/50 rears, drawn for exactly that placement, and the highest ratio in the line.

You like your fronts and only want to change the back. The 6-4 Rear Quad in solid fiberglass at $73.75, or Hexcore at $69.00. Changing rears alone moves the ratio, which is the number that matters — for half the price of a set.

Whatever you land on: give it a season, and pay attention to where it disappoints you. A quad that feels loose off the top is telling you to go down in ratio. One that will not let go is telling you to go up. That is a more useful answer than the next set is.

Bring the board in and we'll look at where your rear boxes actually sit.

One thing you will read that is wrong

Plenty of quad guides say water "accelerates between the fins via the Venturi effect." It sounds scientific and it is not right.

The Venturi effect describes fluid forced through a constriction in a closed channel — a pipe, a nozzle. Quad fins in the ocean are open on every side. Water goes around them, over them, or not between them at all. There is no constriction, so nothing accelerates, any more than wind accelerates between two trees.

The speed is real. It comes from deleting the center fin's drag. This matters because the Venturi story sends people hunting for the right gap between front and rear, when what they should be reading is rear size, placement and foil.

Sources

All dimensions and foils from True Ames product pages, retrieved 2 August 2026. Prices from our own catalog, 7 August 2026. Ratios, totals and aspect figures are computed from those published areas; the full table, including the designs True Ames publishes no dimensions for, is on file. The drag comparison between three- and four-fin configurations is from published CFD work on surfboard fin clusters, cited in the same file.

Putting Two and Two Together: How Quads Work and Which Set Is Yours