Triumph’s New T-Plane Firing Order Explained

Do the math: 180 plus 270 and 270 add up to 720.

888cc three-cylinder engine with “T-Plane” crankshaft
New Euro-5-compliant 888cc three-cylinder engine with “T-Plane” crankshaft powers the 2020 Tiger 900, as well as the more off-road-capable Tiger 900 Rally and Rally Pro and street-biased GT and GT Pro.Triumph

I read in a Triumph press release that the engine used in the 2020 Tiger 900 adventure-model range has a “new unique 1-3-2 firing order for greater character and feel.”

This Tiger 900’s “T-Plane” crankshaft places crankpins one and three 180 degrees apart, with the number-two crankpin 90 degrees from the others, defining a “T.”

What does this mean? Traditional inline-triples have crankpins set at equal 120-degree spacing, giving a firing interval of 240 degrees; the four-stroke cycle requires two revolutions of the crank or 720 degrees. This Tiger 900’s “T-Plane” crankshaft places crankpins one and three 180 degrees apart, with the number-two crankpin 90 degrees from the others, defining a “T.” The new firing intervals are 180, 270, and 270, adding up to 720.

What is the purpose of this change? I suspect it was done mainly to make this engine’s exhaust sound stand out—in a word, “character.” It has certainly worked for Yamaha’s long-running YZF-R1 sportbike.

T-plane triple crank firing order chart
Triumph-supplied graphic illustrates 1-3-2 firing order for the Tiger 900 engine. Stated goals include lower-rpm “closer association to the throttle character, sound, and feel” of a twin and “feel and delivery” in the midrange and top-end of a triple.Triumph

Any time engine makers alter firing interval, we instantly think of the “big-bang effect.” In 1992, Honda found that by narrowing the firing angle of its two-stroke V-4 NSR500 Grand Prix roadracer from firing pairs of cylinders at 180-degree intervals to firing the two pairs only 68 degrees apart (this close firing of all four cylinders is the “big bang”), riders were able to begin throttle up earlier in corners and then accelerate harder. Why? The long quiet interval between big bangs—360 - 68 = 292 degrees—allowed the rear tire to roll forward a full footprint in lower gears, getting a fresh, unstressed grip on the pavement. Soon, every bike in the class was making the same deep 500cc-motocross sound. It worked.

But in the case of this Triumph, engineers increased the firing interval on two cylinders to 270 degrees by closing up the third interval to 180—not a big change, 12-1/2 percent. Yet without testing the result ourselves, who can say how much this change improves “feel”?

Ah, but doesn’t such a change require a balance shaft? Even-firing inline-triples already need a balance shaft to cancel what would otherwise be a substantial side-to-side rocking motion, so the only change needed is to reangle the eccentric weights on the already-existing shaft.