Diesel power is a rarity in the motorcycle world. There have been only a couple of mass-market diesel motorcycles in history, and the chances of seeing a new diesel today are even lower as the world converts to electric propulsion. One startup wants to change that. Axiom Diesel Cycles wants to take everything America loves about gigantic, expensive Harley-Davidsons and fuel it with a tiny three-cylinder turbo diesel engine that gets a whopping 70 mpg or better.
I’ve been obsessed with diesel-powered motorcycles for longer than I’ve been writing professionally. I suppose it just goes with my character of loving everything about Rudolf Diesel’s invention. Yet, even I have to admit that, historically, the words “diesel” and “motorcycle” have not been complimentary to each other.
How rare are diesel motorcycles? Well, there are really only two models that could be classified as mass-production diesel motorcycles. One of these was the Royal Enfield Diesel, also known as the Taurus. The entire purpose of the Enfield Diesel was to save money. The engine in the Royal Enfield was known to get up to 200 mpg, and when the bikes were sold new in the 1980s and 1990s, diesel fuel was cheaper than gasoline in India. But the Royal Enfield Diesel wasn’t known for its fun ride with its 370-pound weight, unrefined 325cc Greaves Lombardini single cylinder engine, just 6.5 HP on tap, and top speed of around 49 mph. However, motorcycles were basically commuter cars in India, and Royal Enfield sold tons of these bikes to thrifty locals.
Then there’s the Hayes Diversified Technologies M1030M1 combat motorcycle. This motorcycle is more or less a Kawasaki KLR 650 with a multi-fuel engine that runs on JP-8, diesel, or almost anything else that you can get to burn.
The HDT was also made for a practical reason rather than fun, as the military wanted to streamline its fueling strategy in the field. If all of your military vehicles run on the same JP-8 as the planes do, then bringing fuel into the field becomes so much easier. Yet, the HDT M1030M1 wasn’t a bad bike with its great off-road performance, up to 100 mpg fuel economy, and top speed of 86 mph.
Depending on who you ask, there are only around 440 HDT M1030M1s out there, and sellers want $15,000 for them right now. The other production diesels have been even rarer than that. Chances are you’ll never see the Volkswagen diesel-powered Star Twin Thunder Star 1200 TDI sportbike, the Smart Fortwo diesel-powered EVA Track T-800CDI adventure bike, the Sommer Diesel 462 standard, or the Boccardo Aero 97 diesel commuter. All of these projects failed. Even Royal Enfield had to kill its diesel program when its bikes couldn’t meet emissions standards. Diesel motorcycles seem even more cursed than Wankel rotaries.
That’s what makes Axiom Diesel Cycles honestly surprising. Matthew Lach believes that there is a future in diesel motorcycles.
Cruisin’ Diesel
As Matthew explains, he got into the classic American cruiser, but found out that nobody made heavy cruisers with diesel engines. He wanted a big cruiser, but didn’t want to pay a lot for fuel or maintenance. A lot of folks get around 40 mpg or 50 mpg or so with Harley’s biggest cruisers, and Matthew wanted even more mpg than that. Matthew also loves the torque curve of diesel engines and wanted that on a motorcycle. In 2012, using his background in mathematics, Matthew decided to make his diesel cruiser a reality by building it himself.
This first Axiom motorcycle, named “Success,” was a proof of concept. It was constructed out of as many off-the-shelf components as Matthew was able to find. The engine in this motorcycle was a Yanmar V-twin (an engine more often found in generators and other equipment) that was good for 16 HP and 30.2 lb-ft of torque from the factory. Matthew added a turbo to it and on a dyno, it ran up to 27.2 HP and 42.68 lb-ft of torque at 2,500 RPM. This first bike had a frame, transmission, and bodywork from a Harley-Davidson. Matthew says that Success is actually pretty good on the open road, owing to the low-end torque.
That first motorcycle was put on the road, and Matthew found that there was real interest in the thing. During an interview with the Motorcycle Men Podcast, Matthew admits that there isn’t necessarily a need for diesel motorcycles, but perhaps a niche out there. Potential customers could be diesel freaks like me, people who want to save money, or RVers who want to run their bike on the same fuel their motorhome drinks.
Axiom Diesel Cycles
Matthew decided to evolve his concept into something that could be put into production. His concepts for his Axiom Diesel Cycles are the Paladin and the Knight, two heavyweight cruisers with the style of Harley-Davidson heavy cruiser models. The initial concepts, below, showed a diesel flavor of something like an Ultra Limited and the Road King, but the company’s website now suggests a style more like the Street Glide and Road Glide.
Despite the visual similarities, Matthew says that Axiom will build these motorcycles from the ground up with a frame of the company’s design. What parts Matthew can’t handle himself will be farmed out to suppliers. Matthew hopes to lean on the existing motorcycle aftermarket so that repairs and replacement parts can be obtained easily.
Power in what Matthew hopes to be the production Axioms will come from Doosan D10 engines connected to four-speed manual transmissions. Matthew says he’s chosen engines from the South Korean company because they’re sometimes used in Bobcat machinery. He hopes that when an Axiom motorcycle buyer runs into an issue on their bikes, they wouldn’t have to ship it to the company’s home base in Ohio. Instead, they’d be able to get parts from a Bobcat dealer and fix it themselves.
The Doosan D10 is a 1-liter, three-cylinder turbocharged power plant good for 24 HP and 45 lb-ft of torque. There’s no word on if the Axiom version will make more power like the hopped-up Yanmar build I talked about earlier. While these Doosan engines aren’t found in road vehicles, they are used in generators and other stationary industrial applications. Matthew hopes that a completed Axiom Diesel with this engine will achieve 70 mpg or better. The few data sheets I’ve found for the Doosan D10 do suggest that such fuel economy is possible. It will heavily depend on how much throttle is required for a Doosan-equipped Axiom to maintain highway speed.
Axiom Diesel Cycles is targeting the very high end of the cruiser market, basically Harley-Davidson’s bread and butter. The Paladin, the one that’s like a Harley Street Glide, is projected to start at $49,500. The huge price is in part because each bike will be built by hand, but also highly customized. Like Harley-Davidson, Axiom Diesel Cycles wants to offer an insanely huge catalog of accessories ranging from white wall tires and custom paint to air suspension and big stereos. Of course, that makes sense since Axiom wants to lean on the aftermarket for its parts to begin with.
The more expensive model is the $54,500 Paladin and that one is like a Road Glide. Like the aforementioned Harleys, the main difference between the Paladin and the Knight is how the fairing is mounted. The Paladin’s fairing is mounted to the bars while the Knight’s fairing is frame-mounted.
These very high prices would make an Axiom Diesel Cycle even more expensive than a Harley-Davidson CVO Street Glide and a CVO Road Glide. In other words, Matthew is targeting what sounds like a small market. An Axiom buyer is someone who can afford to spend more than the value of some of the most expensive Harleys, but wants to spend that money on a diesel bike with a generator engine.
The hardest part will just be getting the bikes in production. I’ve been following the Axiom story for years and noticed that Matthew stopped posting to his company’s social media accounts in 2022. Back then, Matthew said he was targeting a launch of spring 2023, but that rolled around without any news. I did find that Axiom filed documents with NHTSA in 2023, but that’s it. There have been no further updates anywhere. Yet, Axiom’s website is still up and is still asking for donations and reservations.
I reached out to Matthew, asking if he’s still working on the bike. His brother and CEO of Axiom, Joshua, responded with:
Yes, the motorcycles are still under development. It is a slow process and engineering is taking longer than expected. I am currently reassessing the market to decide what will work best: large cruiser, cafe racer, chopper, scrambler, etc. I will make sure to keep you informed as we progress.
Honestly, if the guys drop the price and put that Doosan into a scrambler or cafe racer, I think they’d have my money. I don’t have $50,000 to spend on a motorcycle, nor would I want to spend that much on a bike. But I could see spending somewhere in the mid- or high $10,000 range for a quirky diesel cafe racer. Janus Motorcycles seems to do well selling boutique bikes with similar prices.
Update: I also want to clarify that 70 mpg isn’t impressive by itself. My CFMoto Papio SS will do over 100 mpg all-day. Even my two-stroke Genuine Stella does 80 mpg. Axiom’s attempted hook here is that you’d be getting 70 mpg in something with the size and weight of a Harley touring cruiser.
Sadly, I don’t have any other news for now. But I do hope these guys make it. I love seeing weird ideas become reality and Axiom checks all of the boxes. Why yes, I’d love to buy a 70 mpg American turbodiesel bike!
Nope.