Two-Stroke vs Four-Stroke: The Truth
Two-stroke vs Four-stroke : The Truth… It’s the question that goes round and round in circles. In clubs and paddocks across the world, proponents from both camps argue their corners passionately; each convinced that they are right. But what’s the real truth? Can you definitely say which makes the better dirt bike – two-stroke or four-stroke? Ride Expeditions decided to investigate…
2 Stroke Vs 4 Stroke
BACK IN THE DAY
If you go back into the archives in search of an answer, then you’ll be looking a long time. When motocross was in its infancy in the UK, riders used stripped back versions of the current road bikes on the track. At that time that usually meant the big four-strokes like BSA, AJS and Triumph but there was still a sizeable contingent that favoured the less bulky two-strokes such as Greeves and Cotton. A look at the world championship winners from that time and it’s evident that from between the late fifties right up to 1969 there was little to split the wins between the big British thumpers and the European strokers.
But once Suzuki entered the ring in the late sixties, the death knell appeared to have rung for the four-strokes, and for decades the world championships were dominated with the smell of two-stroke oil. But Jacky Martens had a different idea when he took the 500cc world championship with his four-stroke Husqvarna in 1993. Few could have predicted that this victory would mark the beginning of the end for the strokers.
But for professional motocross that was indeed the case. From the mid 2000’s the bike manufacturers – lead very much by the Japanese brands – threw their development budgets into all things four-stroke, leaving the strokers largely undeveloped and in most cases, entirely dropped. The resultant landscape within motocross is now entirely four-stroke with MX1 and MX2 riders only able to be competitive on these bikes, a change largely artificially engineered by the increased capacities permitted for the four-strokes. The two-strokes may still dominate the junior classes and various niche race series, but for the time being, their day is done.
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A LEVEL PLAYING FIELD?
But while the market has polarised in terms of motocross, for enduro and off-road the playing field is entirely different. Thanks largely to the persistence of KTM, the two-strokes continued to be relevant and competitive throughout the darker years. Once the firm was rebranded and relaunched back in the late 1990s, the Austrian firm’s dogged determination and racing success with both their two-stroke and four-stroke ranges within enduro and motocross has meant that they have continued to produce and develop both. OK so for the strokers the leaps in technology have not been as marked as their siblings, but KTM still offer the widest and most comprehensive range of off-road bikes on the market by far.
And the parallel success of both engine types within the off road sector has encouraged other brands, most noticeably the European companies. While the Japanese firms are decidedly cool on the off-road market – with Honda and Yamaha only fielding two bikes each to the sector and Suzuki and Kawasaki all but opted out, the Euro boys are having a field day.
If you are in the market for an off-road bike, buyers in 2016 now have an astoundingly good selection to choose from – KTM, Husqvarna, Gas Gas, Beta and Sherco all produce a wide range of capacities and engine configurations. Factor in the Yamaha WRFs and the Honda CFRXs and it’s a great position for dirt bike lovers.
BUT WHICH IS BETTER
TWO STROKE OR FOUR STROKE?
WE BREAK IT DOWN
OK so most rider’s initial reaction would be to say that the thumpers are heavier. But is that actually true? If you look at the data for the 2017 KTM EXC250 and EXCF 250, the four-stroke is a mere 3 kg heavier, which in the grand scheme of things is not vast. And in terms of the top capacities in each engine type, the EXC300 is only 6.5 kg lighter than the 500. Whatever might have been the case in the past, the weight differences are nothing like as marked as they used to be
But it’s not as simple as that. Four-stroke engines are taller than their equivalent two-stroke counterparts. And the further away from the centre of gravity that weight sits, the more noticeable it becomes meaning that the big 500 KTM will feel substantially heavier than the 300 than those 6.5 kg would suggest. It’s just physics. Yamaha have countered that issue to some extent by their rear-slanting engine that takes the weight closer in to the centre of gravity of the machine, which works well. The WRF450 wears its weight well.
The handling on any bike can sometimes appear quite subjective, and what works for one rider will not be the same for another. But that’s largely because so many riders simply run their bikes as the factory set them. The manufacturers allow us endless adjustment of sag, rebound and compression damping and options on springs rate as part of their marketing push each year. But having shelled out nearly £8k on the machine that is capable of winning Romaniacs, what do we spend our aftermarket cash on? Having the suspension properly set up for our weight, ability and preferred riding style? No – we buy a replacement end-can that makes more noise and marginally more power, even before we know whether we actually need more power …
OK so this aside, let’s assume that we’ve actually got properly dialled suspension. Which will handle better – two or four-stroke? The answer is again about physics and the lighter bike will always come out on top in a straight fight. If you factor in the ‘perceived weight’ of the bangers taller engine then it’s a hand’s down win for the stroker. Look how the 300cc two-strokes dominate the top end of extreme enduro – those boys know a thing or two about a bike’s handling. Strokers turn quicker, push less and are easier to control.
For less extreme riding then, in reality the handling between the two will be less marked, and for trail riding – almost unnoticeable. Because the four-strokes are easier to ride thanks to their power delivery – see below – the guy on the thumper is not going to feel as beat up at the end of your average day. But when the going turns really wet and snotty, the stroker riders will be the last man standing.
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Now as we said in the intro, the reason that the four-strokes have won out in motocross is that the authorities allowed them to be twice the size of the two-strokes. Hardly surprising that they won the day really. But if you compare like with like at a given capacity, a two stroke will always be more powerful than a four stroke – it has twice the amount of firing strokes! Although KTM don’t quote power on their spec sheets, the 250SX makes nearly 50 bhp, compared to the SXF that generates somewhere near the high thirties.
Before the advent of power valves, the power delivery on the strokers was brutal. They’d have no power for ages and then the hit would come in like a sledgehammer to the back of your head. If you ever get the chance to ride a Kawasaki KX500 you will know exactly what we mean – hit the power band and the landscape just blurs. But the power valves made this power far more manageable and tuneable and modern two-strokes are very sophisticated machines, delivering power through the rev range while still maintaining that top end hit that owners love. Add in the ability to adjust the delivery by changing the springing and opening point of the power valve and variable ignition mapping and the two-strokes are a different prospect than those arm-wrenching animals of the 80s.
But the four-strokes have changed remarkably too. Gone are the pistons as big as bean cans and now modern thumpers have slim line pistons that are barely a centimetre deep, capable of moving at up to 12,000 rpm – that’s an astonishing 200 times a second! Faced with technology that seems more at home on Formula 1 cars, if you ride a 2017 four-stroke, the flexibility and response from the engine is staggering. From tick over to red line, the new breeds of four-strokes deliver a progressive and linear power curve that would have been unimaginable twenty years ago. And that is the secret to their success.
Four-strokes are incredibly easy to ride whether you are a novice or an expert. Gear selection is far less critical when the bike will pull almost any gear from almost any speed. While the two-stroke pilots will be dancing up and down the gearbox, the thumper boys are pretty much twist and go. On hardpack and slippery surfaces, the way the four-stroke puts down the power is easier to manage, but that’s also tied in to the rider’s ability – a poor rider is still a poor rider, they’ll just get into less problems on a thumper.
If you ask which is faster, the answer will be the stroker in a straight drag race. But off-road riding is not a drag race and there’s an element of tortoise and hare here. And we all know who won that one.
EASE OF USE
Put back to back, the thumpers are going to win this one hands down. They are easier to ride thanks to a broad spread of linear power that anyone should be able to master, compared to the slightly more involving riding style needed for the stroker.
In terms of trail riding, the four-strokes tend to be vastly more comfortable to run long distances on the black top than the equivalent two-stroke. They will also get through much less fuel, which is pretty important in terrain where there isn’t a petrol station round the corner. On top of this, riders don’t have to remember to take enough two-stroke oil with them on every single trip, or spend time measuring out oil and shaking the bike like a loon on the forecourt when you’ve filled up. OK so some manufacturers are bringing oil injection back in, but you still need to remember to top it up!
OK so we have to define how you are using the bike. This blog isn’t really aimed at all out racers, so lets assume an active hobby rider. In terms of what you get through week to week, it will be two-stroke oil on the stroker and engine oil and oil filters on the thumper. Strokers don’t seem to care too much about what’s in the sump and how meticulous you are about changes, but if you want to get the best out of your modern four-stroke you need to give it some regular love on the oil side of things. Not excessively as the owners manual might suggest as that assumes you are an enduro god, but just regularly to keep things sweet.
Other than that, the other consumables will be largely comparable. Wring the throttle and you will get through tyres and drive train components just as fast on whichever you chose. Similarly, suspension, bearings and things like that will depend on how much you ride, where you ride and how hard you ride. It’s not rocket science!
OK so this is the one that frightens many riders off the four-strokes. The prospect of replacing all those moving parts at the top end of a thumper is enough to make most go pale. And undoubtedly this is true – if you trash the top end of your Husky FE450 it will be vastly more expensive than the same operation on a TE300. On top of that, while most riders will still not worry too much about stripping down a two-stroke top end, the same guys may be more nervous about replacing the piston on a thumper, so then you also have to factor in somebody else doing the job on top of the parts. It gets expensive.
But let’s rewind a little – this whole scenario is based on two assumptions:
a) that four-strokes are somehow unreliable and prone to self-destruction
b) we are professional racers running the bike at the ragged edge for lap after lap
While a) might have been the case fifteen years ago, it’s simply not true now, and as for b) we are definitely not pro racers!
Buy yourself any of the 2018 models for trail riding and general off-road use and it will go on for years if you look after it. Yes you might need a new piston every so often and need to check the valve clearances occasionally but that’s going to be it.
Choose the stroker route and although the costs are less, you are a lot more tied into slightly more regular freshen ups. As a rule of thumb, we will look to replace the piston on the Ride Expeditions EXC250 after around 120 hours to keep it fresh and on the pipe, much more frequently than we’d need on an equivalent four stroke.
Just a tip here – the Power Parts Piston kit for this bike includes a piston, rings, gudgeon pin, circlips and all gaskets and costs less than the piston on it’s own!
Again this is a difficult one to really quantify because it assumes that a potential buyer is looking at two bikes of the same capacity, which is maybe unlikely. If this is the case the stroker is always cheaper – commonly by about £500 if buying new in the UK. If you look at a more realistic comparison of a buyer considering a 450 four-stroke over a 300 two-stroke from a dealership, the difference is around £550.
In terms of the second-hand market, the strokers come out on top too – but only if you are selling! Buyers are generally more comfortable buying a used two-stroke, given that they are unlucky enough to buy a wrong ‘un, fixing it will be vastly less costly. Consequently, residual values sink slower on the oil-burners, so proportionally you’ll be paying more for a used two-stroke than a ‘pre-loved’ four-stroke.
2T vs 4T – THE VERDICT
OK so if we add up the scores, it’s a straight tie on points. Where the stroker gains in terms of weight, the thumper wins out with ease of use. Where the one with the valves is more cheaper to buy initially, you’ll need to find more cash for a used oil burner. And the result is no surprise if you have owned and ridden both. Gone are the days of fragile four-strokes that lunch themselves after six months, as are the hair – trigger throttle two-strokes of the past. If you haven’t upgraded your bike since 2005, then you will be truly astounded as to how much better the new crop of bikes really are. Get yourself to a try-out-day at the very least and give them a go – and then get yourself a bank loan.
But as to which you actually choose, the buying decision may be far more about where you live and where you ride rather more than any of the considerations above.
Tell a Western Australian that he needs a 250 two-stroker for his trail riding and you’ll get a two word answer. These boys cover big distances flat-out on sandy trails, so a 450 thumper is the obvious tool for the job. But try to convince a British trail rider that the same bike works well on snotty, stony and tight trails in North Devon and you’ll be banging your head against a brick wall. The phrase ‘Horses for Courses’ comes to mind…
So what do you think? Have you owned both the strokers and the thumpers and do you think one is better than the other? Please let us know your comments below.
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