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TWO-STROKE VERSUS FOUR-STROKE: 2012 KTM 250SXF VS 2012 KTM 250SX

December 25, 2013
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And in this corner…the 2012 KTM 250SX two-stroke.

The MXA wrecking crew can make one promise with this shootout: a KTM is going to win. In truth, this is the best two-stroke versus four-stroke comparison possible. Why? Both the KTM 250SX two-stroke and KTM 250SXF are brand-new models. They have been updated every year for the past five years?and they aren’t apples and oranges. This is as clear-cut and as accurate a head-to-head comparison can get. These are both brand-new, modern, up-to-date machines…and are representative of their classes. True, we could have done a Yamaha YZ250F versus YZ250 shootout, but it would, in essence, be a test of seven-year-old technology?interesting, but not pertinent.

As it stands right now, the Yamaha YZ250 two-stroke is no match for the KTM 250SX two-stroke. The KTM is a vastly superior machine (with the exception of the suspension setup). The KTM is faster, more powerful, better handling, quicker stopping, significantly lighter and fresh off the drawing board. The Yamaha is, at best, 2006 technology.


And wearing the orange trucks……the 2012 KTM 250SXF four-stroke.

So, the MXA gang decided to do an all-new 250 shootout, comparing a two-stroke against a four-stroke. Since 2008, both bikes have been legal to race in any 250cc class at the local and regional level?250 Beginners (D), 250 Novices (C), 250 Intermediates (B) and 250 Experts (A). The choice between a 250 two-stroke and 250 four-stroke has significance for local racers from Punkin Center Raceway to Loretta Lynn’s. As you would expect, AMA Pro Racing does not allow two-strokes of equal size anywhere near its favored four-strokes in Supercross or the AMA Nationals.

The MXA wrecking crew has tons of two- and four-stroke experience, so it was only natural that we answer the question that every AMA Amateur should be asking. Which is better? A KTM 250SX two-stroke or KTM 250SXF four-stroke?


Valves and cams.

Q: WHAT DO THEY COST? WHICH ONE IS CHEAPER?

A: The manufacturer’s suggested retail price (MSRP) for a 2012 KTM 250SX two-stroke is $6899. MSRP for the 2012 KTM 250SXF is $7699. That makes the two-stroke $800 cheaper.
If you compared the KTM 250SX to a four-stroke of any brand, the dollar difference goes up another $500 in favor of the two-stroke.

Q: WHAT’S THE DIFFERENCE BETWEEN THE 2012 KTM 250SX AND THE 2012 KTM 250SXF?

A: One of the benefits of testing two bikes from the same brand is that it eliminates oddities, peccadilloes and aberrations. Both KTMs share the same basic suspension, frame geometry, shock linkages, brakes, wheels and overall design. However, the 250SX and 250SXF differ in two major areas. (1) Spring rates: The shock and fork spring rates are different on both bikes. Amazingly, this is a non-issue, since both bikes’ spring rates are wrong from the factory? making mods necessary on both machines. (2) Engine type: One bike has a 250cc two-stroke engine and one has a 250cc four-stroke engine. The four-stroke is fuel injected, has a six-speed gearbox and comes with an electric starter. The two-stroke has a Keihin PWK carb, five speeds and a kickstarter. Because of the difference in engine size and shape, the lower frame rails are specifically designed to arc around the engine’s cases, and the ground clearance is greater on the two-stroke.


Reeds and power valves.

Q: WHAT DO THEY WEIGH? WHICH ONE IS LIGHTER?

A: When the MXA wrecking crew tested the 2012 KTM 250SX two-stroke, we were shocked to discover that it weighed 217 pounds. Why? Because last year’s no-link, PDS equipped 2011 KTM 250SX hit the scales at 212 pounds. Where did the extra 5 pounds come from? It came from the longer shock, shock linkage, linkage bolts and reinforced shock tower.

We were depressed by the 5-pound weight gain, but it turns out that 5 pounds is nothing. The previously svelte KTM 250SXF four-stroke is a tub of lard. It hit MXA‘s scales at 231 pounds. This bike used to come in at under 220 pounds. No more! The addition of rising-rate linkage, fuel injection and electric starting piled on the pounds. The 2012 KTM 250SX two-stroke weighs 14 pounds less than the 2012 KTM 250 four-stroke. It helps a little to compare the KTM 250SX two-stroke against the Japanese 250 four-strokes, but it is still 7 pounds lighter than an RM-Z250 and KX250F, 5 pounds lighter than a CRF250 and 1 pound lighter than a YZ250F (the YZ250F is light because it still has a carburetor).

KTM 250SXF
: With the exception of the engine and exhaust, the KTM four-stroke shares the vast majority of its components with the KTM 250SX?including geometry.

Q: WHICH BIKE MAKES THE MOST HORSEPOWER?

A: No need to ask. The KTM 250SX two-stroke pumped out 49.77 horsepower in MXA‘s dyno runs. The KTM 250SXF could only produce a meager 35.5 horsepower. You don’t need us to do the math?but we will. The two-stroke makes 14 horsepower more.


KTM 250SX: Although the two-stroke makes more power, a quick glance at where the 250SX and 250SXF produce their power will reveal why they are about equal once in motion.

Q: WHAT DO THE TWO POWERBANDS LOOK LIKE ON THE DYNO CURVE?

A: To make the dyno numbers understandable, we will present them in rpm increments.

    5000 rpm:
At 5000 rpm, the 250SX two-stroke makes 21.61 horsepower, while the 250SXF four-stroke produces 12.85 horsepower.

    6000 rpm:
One thousand rpm later, the 250SX two-stroke is at 30.86 horsepower, while the 250SXF has climbed to 17.74 horsepower.

    7000 rpm: The KTM two-stroke cracks the 40-horse mark at 7000 rpm (40.03 horsepower). The four-stroke is still at 24.50 ponies.

    8000 rpm: The 250SX two-stroke is closing in on its peak horsepower. It makes 49.63 horsepower at 8000 rpm and peaks out at 49.77 horses at 8300 rpm. The four-stroke 250SXF is still 2000 rpm below its peak and produces 29.13 horsepower at eight grand.

    9000 rpm: Although the two-stroke is on the downside of its peak, it is still pumping out 43.87 horsepower compared to the four-stroke’s 32.46 horses.

    10,000 rpm:
The two-stroke signs off at 10 grand?and makes 19.25 horses before going to zero at 10,100 rpm. The 250SXF four-stroke is still 800 rpm below peak. It makes 33.93 horsepower at 10,000 rpm.

   11,000 rpm: The four-stroke’s peak is at 10,800 rpm (35.48), and at 11,000 rpm, it is in the meat of the powerband at 35.15. The 250SX two-stroke is not making any horsepower at this rpm

   12,000 rpm: The 250SXF is still meaty at 34.83 horsepower.

   13,000 rpm: With the rev limiter set at 13,500 rpm, the 250SXF is still making a healthy 33.41 horsepower at 13,000.

Q: WHICH BIKE MAKES THE MOST TORQUE?

A: There is an old saw that states that horsepower doesn’t matter as much as torque. It is assumed that since four-strokes typically produce a boatload of torque, they have an advantage over two-strokes. Guess again, Sherlock! A KTM 250SXF four-stroke is no slouch at 19.42 foot-pounds of torque at 8600 rpm. That is a healthy number, but it pales in comparison to the 250SX’s 31.93 foot-pounds of torque at 8000 rpm (very close to peak horsepower at 8300).

Q: WHICH BIKE HAS THE BEST POWERBAND?

A: Although the displacements of the KTM 250SX and SXF are the same, the powerbands are horses of different colors.

KTM 250SX two-stroke: The KTM 250SX has a very distinct powerband (as evidenced by its dyno numbers). It hits hard in the middle and pulls across a relatively wide range for a two-stroke. It tops 30 horsepower at 6000 rpm and stays above that until dropping below 30 ponies at 9800 rpm. By four-stroke standards, the power is peaky, snappy and explosive, but the two-stroke’s power is harnessed in a way that magnifies an all-out attack in the usable part of the powerband. It doesn’t rev past 10,000 rpm, but it doesn’t have to, because it gets the job done at an engine-saving 8300 rpm. From idle to 9400 rpm, the KTM two-stroke makes more power than the KTM 250 four-stroke. In fact, there are points along the 250SX’s dyno curve where it makes as much as 19 horsepower more than the four-stroke ever dreamed of producing. The 2012 KTM 250SX is the greatest two-stroke engine ever manufactured.

KTM 250SXF four-stroke:
Every test rider who got off the KTM 250SX two-stroke and on the KTM 250SXF four-stroke laughed out loud when comparing the power. “The two-stroke blows the four-stroke away” was the common refrain. In test starts, the two-stroke riders would let the four-stroke go before blasting past it in 100 feet. In back-to-back races against the KTM 250SX, the KTM 250SXF engine felt slow. It revved slower. It had less hit. It droned when the two-stroke went braaappp. But, and this is a big but, while the four-stroke’s hit was less pronounced, there was no wheelspin and no wiggle under acceleration. The slow feel of the KTM 250SXF was misleading. The lack of the sensation of speed wasn’t indicative of a lack of speed on the track. The 250SXF may have been down 10, 15 or 20 horsepower at various stages of the powerband, but after 10,000 rpm, the two-stroke was down 30 horsepower to the four-stroke. What the 250SXF lacked in ponies, it made up in rpm. The four-stroke revved 3000 rpm further than the two-stroke, and during those 3000 rpm, it was making broad, usable and tractable power. The 13,500 rpm rev limiter is 3500 rpm higher and wider than the two-stroke’s working spread.


No need to worry about stopping, KTM’s 260mm front brake is the best in the biz.

Q: WHICH ONE IS EASIER TO RIDE?

A: The four-stroke is much easier to ride?in the same way that the family station wagon is easier to drive to the store than John Force’s funny car. The two-stroke makes the rider work harder. It jerks, tugs, pulls and pries on the rider’s arms and chest. It demands action to get a reaction. The four-stroke doesn’t need to have its throat wrung out to generate speed. It is like the little engine that could. It just goes without much effort or thought.

Q: WHICH ONE IS FASTER?

A: There is a caveat that must be stated: going fast isn’t always about sheer horsepower. That said, in perfect conditions, horsepower will always win. In straight-line speed, the KTM 250SX two-stroke can run circles around the KTM 250SXF four-stroke.

But, motocross doesn’t take place in a straight line. It is not the same as drag racing?which is why John Force hasn’t won any AMA Nationals. In motocross, cumulative speed is worthy of note. The arrangement of corners, offcambers and tricky dirt conditions often favor the tortoise over the hare. Thus, while the two-stroke is faster in an empirical sense, it isn’t always faster over a given distance.


Expansion chamber.


Q: WHICH BIKE PRODUCES THE BEST LAP TIMES?

A: We’ve done this test before with a Yamaha YZ250 two-stroke and Yamaha YZ250F four-stroke. So, we had an inkling of what the results would be. We took three test riders (Pro, Intermediate and Vet) and examined their lap times on both bikes. We did not do practice laps or test laps. Instead, we did race laps with the times taken directly from transponders during actual competition. Why? Because we wanted the test riders to give it their all?without a chance to coast or look around.

We spent a couple race weekends swapping bikes and test riders to get enough laps to prove one undeniable fact: if a rider can turn in a 2:03 lap time on a 250 two-stroke, he can turn the same time on a 250 four-stroke. Motocross racers must have internal clocks, typically referred to as “talent,” that determine how fast they are capable of going. A faster bike didn’t necessarily make them faster.

The only statistically significant result was that all three test riders did their fastest laps on the 2012 KTM 250SX two-stroke. There were sections on every racetrack where an extra 14 horsepower could knock milliseconds off short straights and steep hills. That said, the slowest laps of all three test riders were also clocked on the two-stroke. Why? The two-stroke demands the rider’s attention. It was easy to get that 50-horsepower fire breather to spin its rear tire, get sideways or wheelie at inopportune moments. Every test rider knew which lap was his slow one, because he typically scared himself enough to burn it into his memory.

Q: WHICH BIKE PRODUCED THE BEST RACE RESULTS?

A: Every MXA test rider had preconceived notions before their races. They all assumed that on hard tracks with lots of corners that the four-stroke would win the races, while longer and loamier track would favor the two-stroke.

They weren’t wrong, but they failed to take one major factor into account: the start. Whether the track was hard or soft, long or short, the two-stroke almost always got a better start than the four-stroke. You don’t need to be Sherlock Holmes’ younger brother to figure out that you will win more races from the front than from the back.

On overall results, the two-stroke was better than the four-stroke. Sadly, the 250SX two-stroke did not turn a fifth-place rider into a winner, nor did the 250SXF four-stroke make him a loser. The only empirical data that comes from our tests is that across a wide spectrum of races, the same rider on a two-stroke finished higher than he did on the four-stroke?though not significantly higher. And, most of the advantage came from the start.


Head pipe.

Q: WHAT CONDITIONS FAVOR EACH BIKE?

A: In hardpack conditions, where traction was limited, the KTM 250SXF had the upper hand. The same was true in off-cambers and hard, smallish, close-together whoops. The steady throttle approach of the KTM 250SXF four-stroke made the bike hook up better in tricky situations. When the dirt was good, there was a lot of sand, the hills were steep and the whoops were big the KTM 250SX two-stroke was a vastly superior machine. It could explode out of the soft dirt that bogged down the four-stroke.

Q: WHICH BIKE HAS THE BEST HANDLING?

A: Most MXA test riders preferred the handling of the KTM 250SX two-stroke over that of the 250SXF four-stroke. It should be remembered that these bikes share the same head angle, wheelbase, suspension system and layout. The two-stroke gets the nod because it is significantly lighter and feels even lighter than it really is. Plus, the snappy response of its two-stroke powerband and the lack of decompression braking under deceleration make it more responsive to differing conditions. The two-stroke is more willing to make quick direction changes, go in deeper and switch lines on a whim.

Q: WHICH BIKE HAS THE BEST SUSPENSION?

A: Given that the suspension systems are identical?and the setup is identically wrong from the factory?the best suspension is on the bike that is 14 pounds lighter.

Q: WHAT’S THE FINAL WORD?

A: Without pulling any punches, every MXA tester thought that the 250SX two-stroke was a better race bike?lighter, faster, cheaper, better handling and easier to maintain. Yet, we would be the first to admit that a two-stroke isn’t for everyone. It takes, as Roger DeCoster noted, more talent to ride a two-stroke. It places greater demand on the rider’s reflexes, instincts and muscles. The two-stroke’s greatest strength isn’t in its obvious list of superlatives, but rather the simple fact that it heightens the intensity of racing more than the same displacement four-stroke.

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