The duo surprised the industry this month by unveiling their cheapest models globally in the largest motorbike market by sales, where their expensive imports have long struggled for market share.
This time, they are making the bikes in India with domestic partners to bring prices below 233,000 rupees (around RM13,000).
"These are aspirational brands," said Kotak Securities auto analyst Rishi Vora. "For people who were thinking of buying a Harley or Triumph earlier, the price points weren't accessible. Now, they are."
The similar, near-simultaneous change in approach by two of the industry's most storied brands represents one of the biggest challenges to Royal Enfield's virtual monopoly in high-end motorcycles, coming at a time of rising spending in India in premium segments across categories as varied as mobile phones and cars.
Such is the threat, the back-to-back launches pushed Royal Enfield maker Eicher Motors' stock price down as much as 12.5% and prompted brokerages to flag earnings risk for at least two years - even though Harley-Davidson and Triumph sales currently pale in comparison to those of Royal Enfield.
The pricing and brand cachet of the Harley-Davidson X440 and Triumph Speed 400 could cut Royal Enfield's share of India's 250 cc-plus segment to 75% from over 90%, Kotak said. Royal Enfield's nearest model is the Classic 350 starting at 193,000 rupees (RM10,737).
Eicher declined to comment ahead of its quarterly earnings announcement. Harley-Davidson did not respond to a request for comment. Triumph said it would significantly increase its dealer network to around 100 dealers over the next 12 months.
Royal challenge
The new models mark a return to India for Harley-Davidson and a huge step up for Triumph, but they are up against Royal Enfield's large number of showrooms, strong after-sales service network and entrenched fan base for a 100-plus-year-old brand.
"Is there going to be a challenge to Royal Enfield? Yes. Is it going to be a major one? It can't be immediately," said Shubhabrata Marmar, co-founder of automotive content platform MotorInc.
"Royal Enfield built the community, and have been iterating their showrooms to be ever classier places that have the feel of an international, retro, cool, chic brand."
Rival heritage brands have made little inroads against Royal Enfield, such as Mahindra & Mahindra's Yezdi and Jawa or BMW's eponymous brand that the German automaker manufactures with local partner TVS Motor.
"Once you buy the vehicle, everything else disappears. The pricing and the showroom disappear. It's you, your motorcycle and those trips to the service centre," said Varun Painter, editor of motorcycle content at PowerDrift.
Harley-Davidson spent a decade importing its ultra-premium motorcycles before exiting the market and shuttering most of its dealer network in 2020.
It sold fewer than 30,000 motorcycles - less than the number of bikes Royal Enfield sells each month.
It then partnered Hero MotoCorp, the world's largest motorcycle maker, to develop and sell a range of Harley-Davidson branded bikes in India, starting with the X440.
