The Science Of Two-Stroke Exhaust Smell

The magic of the two-stroke’s distinct scent is just physiological

The science (and romance) of two-stroke exhaust smell.
The science (and romance) of two-stroke exhaust smell.Rich Lee

All it takes is one whiff. It could be an old dirt bike starting up fresh out of storage or a vintage scooter trundling past. No matter. As soon as two-stroke exhaust hits your nose, it splits your face into a big, toothy smile. The stuff literally gets under your skin.

But what are you actually smelling? And why is it so evocative?

From a physiological standpoint, the answer is straightforward. Olfaction, the process of smelling, is closely tied to emotion and associative learning. And, unlike our other senses, it’s wired directly into the limbic system; before you even identify a smell, the olfactory bulb has already triggered a memory and the feeling attached to it, a true primal reaction. So, if you grew up around motorcycles, your brain might associate two-stroke with the warmth of family, the pride of winning a race, or the satisfaction of tuning a carb. Getting a snoutful of the stuff can be comforting on a neural level.

But there might be more to the magic of two-stroke’s distinct scent. So says Kelly Jones, the New York-based perfumer behind Kelly + Jones, an experimental fragrance line stocked at stores including Urban Outfitters and Garmentory. Asked to analyze burning synthetic two-stroke for Motorcyclist, her trained nose picked up an array of smells, including benzoin and balsam (tree resins), cade oil (a species of juniper), and a hint of patchouli (yes, patchouli). To Jones, the underlying character here was revealing. She notes that tree resins represented the very first perfumes, tracing back to ancient civilizations. Benzoins and balsams have long been used to make incense, and cade oil is a known antiseptic.

Altogether, she describes the two-stroke fragrance profile as ancestral, ritualistic, ceremonial, and medicinal.

“In a way, this scent is actually very human,” she says. “There’s a term we use in perfumery, animalic, to describe musk. And this one’s a little dirty, isn’t it? There’s an element of the forbidden. That’s sexy. People have always been attracted to those smells. They always will be.”