Stroke vs 4 Stroke Dirt Bikes: 21 Pros and Cons You Should Know
As an Amazon Associate DirtBikePlanet.com earns from qualifying purchases. It’s a debate as old as time: 2 stroke dirt bikes versus 4 strokes. (Ok, maybe not as old as time. But it’s still a huge debate that’s been going on forever.) All over the world, dirt bike riders argue about whether 2 strokes versus 4 strokes are the better engine for dirt bikes. A stroke is a motion of a piston, meaning a two-stroke dirt bike has 2 different motions of the piston, while a four-stroke has 4. 2 Strokes are generally more unstable and accelerate faster, while a 4 stroke is more consistent and has a higher top speed. But this debate goes so much deeper than the simple question, “which is better?”. What should really be considered in the 2 stroke versus 4 stroke dirt bike debate is what is good and bad about each of them as well as how both of them work in different situations, settings, and riding styles.
Before we get going, I’m going to touch over a few examples of two-stroke engines, and four-stroke engines. Once we know the contrasts between the two, it will be easier to understand the different kinds of pros and cons that exist between the different engine builds.
What even is a “stroke”?
Prior to my life of dirt biking, stroke meant one of two things. Either something horrible was happening to your health OR you had just had the best idea in the history of best ideas. However, when it comes to dirt bikes, we’re talking about something entirely different, that has nothing to do with hospital visits or sudden flashes of inspiration. So, when it comes to your dirt bike, what exactly is a stroke? A stroke is the movement of a piston in the dirt bike’s engine. To put it simply, a stroke is a step in the process to get the dirt bike’s engine going. Following the trail of common sense, two-stroke engines use two “movements”, or strokes, to complete a full “engine cycle”, while four-stroke engines use four strokes of the piston to accomplish the same thing. Easy enough? Good. Now let’s get to the good stuff: what’s the difference between two-stroke dirt bikes and four stroke dirt bikes? Keep on reading to find out!
Two Stroke Dirt Bike
Two stroke engines are the much less complicated option out of the two engines. They are designed to complete their engine cycle in two piston movements, instead of four, like the four-stroke. The two-stroke engine begins its cycle with a power stroke. The ignited air, fuel, and oil mixture force the piston down until the mixture reaches the exhaust port, an opening on the side of the cylinder. The piston travels downward, and it pressurizes the air, fuel and oil mixture that was previously drawn into an attachment on the side called a “crankcase”. The mixture was pulled into the crankcase during the most recent compression stroke, the one prior to the current power stroke that hasn’t completed yet. An exposed intake transfer port lets the next air and fuel mixture into the cylinder, right as the crankshaft begins its next rotation, pushing the piston back up. This action blocks off the exhaust and intake ports, enabling the piston to compress the fuel and air mixture. The upward action of the piston pulls in the next fuel and air mixture from the carburetors and keeps it underneath the piston. The currently compressed air and fuel “charge” above the piston is ignited by a spark plug, and the whole thing repeats itself, over and over again. This operation produces less waste than a four-stroke engine of similar or equal power output. They have a more efficient build, enabling them to be assembled and maintained using thirty to fifty percent fewer moving parts than a four stroke. Two strokes are the easiest of the two types of engines to clean. They do, however, have elevated fuel consumption, and because of the way the stroke of the engine works with the openings in the chamber, it produces more emissions. Due to the intake and exhaust ports being open at the same time, with each piston rotation a portion of the air and fuel mixture escapes out the exhaust port without being used to power the engine. That being said, direct injection and catalytic converters are the exceptions to those rules and will reduce the number of unburned hydrocarbons in your emissions. Due to the way they’re assembled, they require a mixture of fuel and oil. Two-stroke engines generally require more maintenance, but the parts are cheaper. Bikes with two-stroke engines are generally lighter and faster, with more of an initial kick to the “get up and go”. While they require half the strokes to accomplish the same purpose as a four-stroke engine, they do make twice as much noise. Two-stroke engines will give you more torque at a higher RPM. Two-stroke engines basically combine a handful of steps and complete them in just two movements. So efficient! Dirt bikes with a two-stroke engine are generally lighter, produce a higher pitched noise, and are cheaper than dirt bikes with 4 stroke engines. Here’s a handy-dandy video that shows you exactly how two-stroke engines work, in addition to the parts they have:
How are they Similar?
Regardless of the engine built, both two strokes and the four strokes are great engines that make great dirt bikes. However, two strokes work better on some terrains and are more efficient on different types of dirt biking than four-stroke engines are, and vice versa.
Yet another similarity between two-stroke engines and four-stroke engines on dirt bikes is that they both have pros and cons. Keep reading to find out all of the good, the bad, and the ugly things about two-stroke engines and four-stroke engines. (Ok, not the ugly. But we’re gonna talk about the good and the bad.)
Two Stroke Dirt Bike
Two stroke dirt bike engines have a lot of really awesome things going for them. But they also fall short in a few areas.
As you read the pros and cons for two-stroke dirt bike engines, keep in mind the kind of dirt biker that you are. Where you ride and how you ride your dirt bike is honestly what should determine whether a two-stroke dirt bike engine is a good choice for you.
Because two stroke dirt bike engines are simpler, condensing four steps into two movements, they are smaller and lighter than four-stroke engines. Having a lightweight dirt bike can be a good thing for a number of reasons.
For example, they have faster acceleration and are capable of decelerating more quickly, which enables you to make split-second decisions that your bike can actually react to. Why? The reason is simple: weight slows you down.
Think about it with a childhood memory: running with your backpack on. If all you had in your backpack was a folder and maybe a notebook, running was no issue at all. You could get going without much effort, and slowing down was only as hard as slowing down is when you’re a kid. BUT if you had two or three workbooks, your lunchbox, and a water bottle in your backpack plus the folder and the notebook, getting started running was a little bit more challenging because you had extra weight to move. Slowing down was harder because the extra weight was pushing you forward.
Get the picture? It’s the same with engine weight. If your engine is lightweight, you can get started and slow down with ease.
Having a lightweight dirt bike is also good for smaller people like myself (or regular-sized children). I’ve said this in previous posts, but it’s really important that the size and skill of the person riding the dirt bike are balanced by the size and power of the bike. If this is weight ratio is not balanced, riding a dirt bike is going to be pretty darn challenging. Lightweight dirt bike engines can also good for trail riding at times. If there’s an obstacle that you don’t feel comfortable jumping or riding over, you can easily pick up your dirt bike and lift it over.
Now, I know it’s not that much of a weight difference for the overall dirt bike if you have a two-stroke instead of a four-stroke, but every pound counts in dirt biking. (At least, it does in my opinion.)
If you’ve read anything else I’ve written, you know that I am big on cost-effectiveness. So, of course, I had to include this in the pros of two-stroke dirt bike engines!
Brand new two-stroke dirt bikes cheaper upfront than four strokes are. If you buy a used two-stroke, though, you’re gonna save even more money. Who doesn’t love that?
Not only is the initial cost of a two-stroke dirt bike cheaper, but upkeep is also generally cheaper on these engines. Because these engines are simple machines that only need two piston movements to complete their process, the necessary maintenance is not only cheaper but easier to complete.
Two stroke engines are typically cheaper also because they have fewer parts than four-stroke engines. Less material means less money. This comes in handy when you have to rebuild your two-stroke engine.
They’re easy to clean.
Two stroke engines are assembled using fewer parts than the four-stroke, which is definitely the more complicated counterpart. In this case, the fewer parts and lack of complicated operation make cleaning the engine a piece of cake.
Because the two-stroke dirt bike engine operates on just two strokes to complete an engine cycle, it produces more power per stroke. While this does provide for things like quicker initial acceleration, it does have some downsides. For example, it can’t “hover” in a gear as well as a four stroke dirt bike can. This means that you’ll have to be shifting more often, as the threshold for variability in different gears is comparatively smaller with the two-stroke engine when compared to a dirt bike with a four-stroke engine.
While having a more simple engine is an absolute dream when it comes to doing your own repairs, there are some definite downsides to the two-stroke engine.
Is it easier and cheaper to maintain and repair? Absolutely! Unfortunately, since there are fewer parts, each of the parts does more work, and are subject to more wear on average. This means that, while maintenance and repair are easier and cheaper, you’re also going to have to perform more maintenance in general.
As long as you’re prepared to be heavily involved in the maintenance, upkeep, and rebuild of your engine, this could still be a good choice!
They’re not so great for the environment.
Because a two-stroke engine works at twice the speed of a four-stroke engine, they have higher fuel consumption. Two stroke dirt bikes also tend to “smoke” during startup. Burnt oil gets released into the air as well with the exhaust. These things put out a lot of emissions into the air, which hurts the environment.
The Yamaha YZ250 has an impressive track record in motocross and supercross. If you are in the market for explosive performance, this bike will not disappoint.
It is powered by a 249 liquid-cooled two-stroke motor. This compact engine is characterized by a wide and hard-hitting powerband. The bike features a lightweight aluminum chassis to keep the weight at 103kg for optimum agility.
The Yamaha YZ250 provides 5-speed transmission, and shifting will be incredibly smooth thanks to the multi-plate clutch.
The Speed-Sensitive System has been fitted on the bike’s 48mm forks to separate the air/oil function. Air will, therefore, not enter the cartridge, and the bike will have more stable damping.
The suspension system of the YZ250 consists of a swingarm, shock, and linkage borrowed from the YZ-F 4-stroke bikes. You can expect excellent traction and shock absorption while riding the bike.
To make the YZ250 more modern, Yamaha has introduced bolder graphics and sharper bodyworks on the bike. Riders can also enjoy wider footrests and an advanced clutch adjuster.
The golden years for the Suzuki RM250 was between 2003 and 2008 when Suzuki and Yamaha were locked in a competition for the best two-stroke. The bike may have been discontinued in 2008, but it still offers the 2-stroke appeal.
The RM250 is praised for its fast and reliable motor and its capable suspension system. Pre-2003 models were hard to jet, which is why you should opt for more recent ones.
Still, parts availability for the RM250 is excellent, and you can get it for a good bargain.
The Honda CR250R is a prized commodity in the dirt bike market, and it has a celebrated history in amateur and professional races.
The model’s production run began in 1978 and ended in 2007. During this time, it went through multiple makeovers that changed its identity many times.
Some riders covet a 1996 Honda CR250R since it had accumulated several significant upgrades. The models between 2000 to 2001 are also in high demand.
In 2000, for example, the dirt bike was fitted with a second-generation aluminum chassis that made it incredibly light and fast. The CR250R received an electronic power valve in 2002, but it turned out that it was driven by an underpowered motor.
The bike is readily available today, and you can get a good bargain on it.
Little screamers | Two-stroke icons punching above their power-to-weight ratio
Few expected to be saying the words ‘new’ and ‘two-stroke’ in the same breath in 2021, but the arrival the British designed, two-stroke engined Langen. which made its public debut at the Goodwood Festival of Speed last weekend. has given us all the nostalgic vibes.
Naturally, the signature traits that prompted a shift away from two-strokes in the first place – the explosive power bands, the shrieking exhausts, the distinctive aroma of blue smoke. have been given a modern makeover for 2021 on the Langen.
But that hasn’t stopped us thinking back to a time when emissions controls were the future’s problem and the shrill sounds were associated with fun rather than being a nuisance.
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No category of motorcycling was more synonymous with two-strokes than the 125-250 class, where lightweight chassis’ and screaming rev-hungry engines made them a riot to ride. After all, who needs power when you have the ultimate power-to-weight ratio?
But which do we remember most fondly? We’ve set the upper bar at 250cc and believe us, it wasn’t easy whittling it down to a mere 10…
Yamaha RD250 (1972-1979)
Of all the Japanese marques none is more closely associated with smaller two-strokes – and usually twins – than Yamaha. And arguably none of the Japanese marque’s two-stroke road bikes have been more significant than the 1970s RD250.
Launched alongside the larger RD350 in 1972, its ‘RD’ designation standing for Race Developed (which, considering its TZ lineage was completely true), the learner-legal 250, with a class-leading 30bhp was simply the fastest, most desirable 250 of the decade.
Originally with rather drab, curvy styling it was restyled into its classic, angular, ‘coffin-tanked’ form with the RD250C of 1976 from when it symbolised the 1970s alongside the Ford Capri, Oxford bags and The Rubettes.
Then it got better yet. The 1977 250D got (optional) cast wheels in place of the C’s wires, a disc not drum rear and a new seat/tailpiece, while the 1978 E got electronic ignition and optional red alloys and the final 1979 F got dog-leg levers. All were fabulous, especially in jazzy Kenny Roberts-inspired yellow/black speed-block or traditional Yamaha white/red.
Yamaha RD250LC (1980-1982)
Yes, it’s a story that’s been told many times before, but the 250 stroker that was so bad and brilliant it killed off the 250 learner law is a certainty to be included here.
The successor to the RD250, the LC was intended to claim its performance crown back from Suzuki’s 1978 lightweight, ‘ton-up’ GT250X7.
Tightening Californian emissions regs dictated the new bike was targeted primarily at Europe, instigated the involvement of Yamaha Europe in Amsterdam and with it Brits such as product planner Paul Butler (later Kenny Roberts team manager), test rider Dave Bean and stylish Mike Ofield.
A brief to create a ‘TZ for the street’ led to the pioneering introduction of liquid cooling (hence LC), cantilever monoshock rear suspension and blacked out styling (in place of ‘70s chrome).
Together with its dominance of 250 production racing, a sister RD350LC that had a starring role in ITV World of Sport televised ‘ProAm Challenge’ and the publicity generated by Roberts and Barry Sheene, the Yamaha RD250LC was the media darling of its time.
No 250 before or since has caused such a sensation.
Suzuki RG250 Gamma (1983-1987)
Suzuki almost created as big a sensation with its response to the RD250LC – almost, but not quite.
The successor to the GT250 X7 gained the Gamma tag in reference to Suzuki’s then world championship-winning RG500 Gammas and was, in most respects, the first true racer replica and a seismic advance over the 250LC.
Its liquid-cooled 247cc twin produced an LC-whopping 45bhp, its ultralight, box-section aluminium frame and Full Floater rear suspension were both firsts, it had disc brakes front and rear and, perhaps most importantly of all, it had swooping, GP inspired bodywork including a sporty, frame-mounted fairing.
Unfortunately, however, from 1983 a law change meant leaners were now restricted to 125s and the Gamma was also pretty pricey, but it and its successors certainly ushered in a new era of GP-alike 250 street two-strokes.
Kawasaki KDX200 (1983-2006)
We just had to include a two-stroke dirt bike – but which?
Being road legal ruled out full bore mental motocrossers such as Yamaha’s YZ465 or Honda’s landmark CR500. Softer trail bikes, particularly those from the 1970s and early ‘80s such as Yamaha’s DT175MX or Suzuki’s TS250ER were tempting. We even gave consideration to those classic trials strokers from the ‘70s, bikes like OSSA’s Mick Andrews Replica (MAR) or the legendary Montesa 247 Cota.
Ultimately, however, we went for Kawa’s long-loved, road-legal enduro that managed that rare trick of being both novice friendly yet also good enough for expert competition success.
Its 198cc stroker single delivered the perfect blend of flexibility and performance; it was light and didn’t intimidate yet grown-up, effective, simple and affordable.
In fact it was so good we dearly wish they were still available today…
Yamaha SDR200 (1987-1992)
The Yamaha SDR200 is proof that that less can be more.
Performance two-strokes have always been about maximising power but minimising weight and Yamaha’s featherweight, ultra-slim SDR – so much so that it gained the nickname ‘The Whippet’ – is surely the ultimate example.
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Unveiled as a prototype at the Milan Show in 1989, the CX is a bike so bonkers few expected it would ever enter production – but it did. Designed by Federico Martini (who in a previous life came up with the equally radical Bimota DB1) it stands out – quite literally – for its radical single-sided arm suspension front and rear which, from the right hand side, gives the impression the wheels aren’t attached at all.
They are, of course, to a state of the art liquid-cooled, 125cc two-stroke screaming out 30bhp and twin spar chassis all dressed in space age bodywork.
Unfortunately, the CX was also relatively heavy (compared to more conventional rivals such as the Aprilia AF1) so lacked their performance and was pricey, too, limited its commercial success.
But for a brief, fleeting moment in the early 1990s, it seemed like the space age had come…
Aprilia AF1 125 Sport Pro (1992-1993)
Gilera’s CX125 may have gained its inclusion here on the basis of its radical looks and suspension, but the early 1990s was actually rammed with equally deserving Italian 125cc sports strokers.
Gilera also had its GP-01, Cagiva its legendary, gorgeous Ducati 916-aping Mito (some of which even had seven gears so must have been faster) but best of all, in our book, was the exquisite Aprilia AF1 in 1992’s top spec ‘Sport Pro’ guise.
Simply, it had it all. It’s screaming liquid-cooled stroker single produced a whopping 33bhp in a knife-edge powerband. It had an aluminium twin spar chassis, RC30-alike single sided swing arm, inverted forks, Brembo brakes, fat tyres and GP-alike bodywork. I
In short, if you wanted the most GP-alike bike in 1992 you wanted this Aprilia 125, not a big lumbering four-stroke. It even had an electric starter. It handled, steered and stopped as well as it looked, too. Exquisite.
1992-1999 Cagiva Super City 125
We may have ranked Cagiva Mito 125 behind the Aprilia AF1 in terms of sports stroker 125s but the screaming little rocket did have a sister bike that’s worthy of inclusion.
The Super City 125 of 1992 was effectively a 125cc, single cylinder version of Yamaha’s TDR250 of four years earlier but being an upright 125 to make it appeal to learners, was drenched in Italian exotica and. in our eyes. was better looking.
In many ways it was the ultimate learner 125 boasting all the performance of the Mito. 30bhp unrestricted, 15 if you were being legal-ish. and with just as high spec cycle parts, yet came in an upright, street scratching form.
Of course it wasn’t sensible at all, a bit dinky for larger riders and expensive, too, but if I was 17 again and it was 1992 once more, the Super City would be the poster bike on my bedroom wall…
Honda NSR250 [MC28] (1996)
Two-strokes brought us a whole generation of twin cylinder, GP-replica sportsters first inspired by the Suzuki 1983 RG250 that filled roads and race tracks for the next dozen years or so with screaming exhausts, hooligan handling and reputations for big thrills on low budgets
It also gave rise to the so-called ‘grey import’ that saw the Suzuki RGV250, Kawasaki KR-1S and Yamaha’s TZR250 find their way onto UK streets.
However, the pick of the bunch was Honda’s simply astonishing NSR, particularly the mouth-watering incarnation of Honda’s V-twin.
The original NS250R (with the internal reference of MC11) debuted in 1985 as a junior version of the NS400 – but things quickly progressed. The all-new NSR250R (MC16) came in 1987 with new alloy twin spar frame and cassette gearbox.
The completely new MC18-I followed just a year later with computer-controlled induction; the face-lifted MC18-II with more upswept exhausts came in 1989 and the exquisite MC21, now with ‘gullarm’ rear suspension and further updated styling came in 1990.
But the most glorious of all was surely the 1994 MC28 with single-side Pro-Arm suspension, Smart Card ignition and the world’s first digital display. Throughout its life SE and SP versions, often with magnesium wheels, dry clutches and Rothmans replica paint, were offered throughout.
To us the Honda NSR250 SP MC28 in Rothmans replica paint is not just the most desirable NSR but one of the most desirable machines of its generation that brings back some very fond memories today.
Why are 2-Stroke Engines Banned?
Actually, 2-stroke dirt bikes are not banned. Some companies are still manufacturing 2-stroke bikes and are leaders in their field of innovation and more complex 2-stroke engines that are on par with 4-stroke sustainability. Yamaha is one of these companies, using reed valves to avoid emitting further fumes into the environment.
Although 2-strokes aren’t banned, and some brands are still manufacturing them, there are more 4-stroke bikes on the market today.
We’re huge fans of the environment at Risk Racing and we are all about keeping the planet clean and making it a safe place for our present and our future. Especially if that means we can keep riding our beloved bikes.
When the Environmental Protection Agency (EPA) brought in new and stricter laws to reduce pollution from vehicles and engines, 2-strokes came under fire.
With the mechanical ability to only use one power cycle and two strokes of the piston, the 2-stroke dirt bikes have higher vehicle exhaust emissions. The burnt oil in the engine gets released into the air through the exhaust and is released into the air which is bad for the environment.
You can read the EPA’s advice here on how to minimize your pollution from vehicles and engines.
Here’s why 2-strokes aren’t great for the environment unless the manufacturer has made some alterations to make them more environmentally sustainable:
- Higher fuel consumption.
- Burnt oil fumes.
- Releases emissions into the air.
- Causes greenhouse gasses which cause climate change.
What exactly do emissions do to our environment?
It’s not just our environment that we should be wary of with emissions. These pollutants in the air, caused by emissions, can exacerbate respiratory diseases, and also cause harmful pollutants to enter your lungs.
The EPA and other environmental agencies are doing what they can to reduce these emissions to create a safer world for humankind.
The pollution caused by, but not limited to, exhaust fumes, emits greenhouse gasses that cause climate change. But that’s a whole other issue we’re not going to delve into right now. For now, just know that 2-strokes aren’t banned, so you can calm down.
It doesn’t mean we, as avid and enthusiastic dirt bike riders, have to stop riding. It just means we need to be more aware of the situation and help where we can. So, the dirt bike industry started to faze out 2-strokes and marginally manufacture 4-strokes more.
Modern-day 2-strokes live up to the EPA’s standards and are currently still on the market. Check out Yamaha’s latest 2-stroke beauty here if you don’t believe me.
We’ve put together a little comparison table so you can quickly see what the main differences between 2-stroke and 4-stroke dirt bikes are.
There you have it, the differences, disadvantages, and advantages of both the 2-stroke and 4-stroke dirt bikes. I can’t tell you which is better because they’re both different and have their own style. Which one you choose to be loyal to is entirely up to you but maybe trying them both out before you choose is a good way to start.
You may not be able to change the mind of someone riding something different to you, but at least you’ll know everything there is to know about both kinds. Happy riding and stay safe on the tracks.