Transmoto Exclusive – 2013 KTM 250SX vs 2013 KTM 250SX-F

_iKapture Images

With KTM releasing their 2014 model range last month, we decided that now would be the perfect time to reflect on this test we published in Transmoto Issue #25. Race results and sales figures confirm that KTM’s 250SX is back on racers’ radars. But could a two-stroke really upstage KTM’s high-tech 250SX-F on the track? We put KTM’s two 2013-model Lites-class options back-to-back to find out.

If someone wandered up to you back in 2007 and ‘projected’ that 250cc two-stroke motocross bikes would be selling like hotcakes in 2012, you’d have laughed in their face, right? In fact, you’d have reminded the buffoon that the Big Four had turned their backs on two-stroke R&D several years prior, and focused their attention on the four-stroke technology that had overrun motocross paddocks ever since.

But, with the benefit of hindsight, who’s the buffoon? Admittedly, Japan’s premix-burners have been stuck a in time warp for many years, and Honda ceased production of their two-strokes altogether in 2007. But what about KTM, who’ve maintained that the very future of the sport would depend on the survival of these cost-effective machines? Yep, while everyone else’s two-strokes have received little more than cosmetic tweaks over the past five or six years, KTM has forged ahead with substantial upgrades to their SX models – not least of which was the fitment of a market-pleasing rising-rate linkage. At the same time, KTM’s brass lobbied the sport’s administrators to relax class-eligibility rules, and make the low-maintenance two-strokes a much more attractive proposition for racers. And that’s exactly how things have played out – in Europe, America, New Zealand and Australia.

The 250cc two-strokes have been entitled to race in the same class as 250cc four-strokes in Australian motocross for two seasons now (and three years in the Under 19 class). And given that they’re lighter, more powerful, and substantially cheaper to modify and maintain than the average 250F, their sales have surged – KTM’s in particular. KTM Australia imported 225 250SXs for 2013. “That’s 75 units up on 2012 because we sold out of last year’s 250SX shipment within the first few months,” explains KTM’s Marketing Manager, Greg Chambers. “It’s a similar story for KTM in many other countries, too.” Sure, 225 units is less than half of the 500 250SX-Fs that KTM Australia plan to bring in for 2013, but it’s still way ahead of what anyone would have predicted several years back. And the bike’s recent success on the racetrack won’t hurt numbers, either. In the hands of Kayne Lamont, KTM’s 250SX won the MX Development class (formerly Under 19s) at the 2012 MX Nats, while more and more Lites-class riders – at club, state and national level – are now campaigning a two-banger. In fact, demand for two-stroke racing has become so strong that a “KTM 2-Stroke Cup” was incorporated into the 2012 MX Nats calendar; a class that’s expected to run over three rounds in 2013.

But what is KTM’s 2013-model 250SX actually like to ride? Flighty and brutal? Or a more refined and user-friendly animal? To get a handle on how this new-generation two-stroke motocrosser compares with its much-updated cousin, the 2013 250SX-F, we took the two machines to Conondale’s Green Park motocross track in Queensland and let the them loose in the hands of a range of testers: three-time AORC champ, AJ Roberts; MX2-class Pro racer, Brock Winston; and Vet, iKapture Images’ Greg Super-Smith.

2013 KTM 250SX – $10,295

Aside from sweeping changes to bodywork and suspension, the two-stroke’s powerplant gets the new DDS clutch and V-Force reed block for 2013. The SX is light and powerful, but can everyone ride it fast?

2013 KTM 250SX-F – $10,495

KTM’s quarter-litre four-stroke gets a swag of fresh technology for 2013 and sees big power gains on the 2012 machine. But has it retained that user-friendly advantage over its lighter two-stroke stablemate?

In The Saddle

To sit on the bikes with your eyes closed, you literally wouldn’t know the difference between the two- and four-stroke. With the same rolling chassis, bars, controls, seat, fuel tank and bodywork, the seat/bar/peg triangulation is identical and there’s no discernible difference in the width of their engine cases. Open your eyes and the 250SX’s nickel-plated expansion chamber is the only telltale sign that you’re not aboard the four-stroke. Well, that and the fact the SX’s handlebars have one less red button (no electric leg!). The ergos are superb on both machines – there’s nothing to snag your boots, burn your gear or impede your movement back
and forth in the cockpit.

Start these two race weapons, however, and you can hear, feel and smell the difference. Aside from the two-stroke’s distinctive exhaust note, it also produces noticeably more vibration through the bars and balls … of your feet. And it doesn’t like to hang around idling in the pits. According to Greg Smith, “It’s kind of like the porn star versus the girl-next-door – these two bikes may look the same, but they turn into very different animals when they get started!” Colourful, Greg. To ‘get started’, the 250SX needs two things the SX-F doesn’t: a swift kick and a handful of throttle. It’s an upfront reminder that you’re aboard a no-compromise, lightweight race weapon that’s equipped only with the hardware required to go fast, and no creature comforts. Starting the 250SX-F with a button – rather than a boot – is so effortless, you almost feel guilty. All you have to focus on is not touching the throttle. As you let the clutch out and ride away, it immediately becomes apparent that these two machines have very different character, despite the fact they share the same rolling chassis. Even at low speed, the 6.5kg lighter SX has noticeably less tip-weight and feels more agile. But it also gives you the distinct impression that it’s time to have your wits about you!

Power Delivery

Even five years ago, you would have been mad to race a 250F against a 250cc two-stroke. With just 35 horsepower at your disposal, you’d be giving away some 8hp and wouldn’t stand a chance in a head-to-head. In the years since, however, 250Fs have come a long way – both in terms of outright power and engine durability. KTM’s 250SX-F now puts out 40hp at the rear wheel, and yet it’s easier to ride at the limit than ever before. Meanwhile, the 250SX delivers similar peak power to its predecessors, and it’s only slightly more refined and user-friendly – thanks largely to the new reed block and rubber-damped DDS clutch for 2013. Yep, it’s clear that the gap between the two bikes’ engines has narrowed substantially. The much-revised powerplant in the 2013 250SX-F is noticeably stronger than the 2012’s, particularly from the perky mid-range through to its prodigious 14,000rpm rev limiter.

Granted, there’s nothing’s more exciting than a free-revving two-banger, but when you’re trying to put the power to the ground on the hardpack of Conondale’s Green Park, it’s all about taming the beast within, because the SX still has a mid-range hit and launches like a crazed baboon if you feed it an ill-considered handful. Our test track’s slick conditions reinforced the fact you still need to be much more precise with throttle inputs on the two-stroke. Which is fine if you’re an experienced rider. But if you’re not, or if you start to fatigue, the SX’s explosive delivery is much harder to dial on smoothly … and much more inclined to bite you. The two-stroke definitely requires you to adapt your riding style. You need to move your body weight around on the bike more, always have a finger poised over the clutch to help control power delivery, and focus on short-shifting the engine for those slick sections of track. If there’s one area the 250SX has made gains in recent years, it’s in the torque and throttle response at lower revs. Admittedly, you need to keep the SX’s revs in that narrow 4000 to 8000rpm range to keep it on-song. But with almost twice the torque of the 250SX-F, the SX is much less inclined to fall off the power if you short-shift or prematurely pull a taller gear in power-sapping sand. Which is exactly why the SX can get away with a five-speed transmission and 48-tooth rear sprocket compared with the SX-F’s six-speed box with a 50-tooth sprocket.

After repeated starts, we can confirm that neither machine has a clear advantage. The four-stroke might get the initial jump out of the gates, but the SX tends to peg it back by the time you click fourth. That said, you do need to be more mindful of timing your shifts right on the SX – if you hold a gear beyond 8000rpm, you go backwards fast. The endless overrev of the 250SX-F, on the other hand, means you get plenty of warning before you really need to upshift. And with useable power across a much broader rev range, the four-stroke’s engine is easier to use for a wider range of riders. Its linear power makes it easier to draw smooth power-slide arcs on slick terrain, but in grippy conditions you do need to be busy with gearshifts if you want to keep it in the meat of its power.

Handling Character

The design mantra for KTM’s new-generation 250SX-F was to minimise oscillating mass and its impact on handling. And they’ve certainly achieved that. But in comparison to the two-stroke, the SX-F’s additional rotating mass is still substantial. Those gyroscopic forces change the way the chassis and suspension reacts to bumps, and it’s most noticeable in the front-end. Even though the fork springs on the 250SX are softer (4.4N/mm), you’d swear they were the same, or even firmer, than the 250SX-F’s 4.6N/mm coils. This is partly because the SX is lighter and partly because its lack of engine braking. But it’s also due to the four-stroke’s oscillating mass, which gives the slightly heavier SX-F a much more planted feel in the front-end and noticeably more grip. It sits down into its stroke more and ploughs through the bumps rather than skimming over them. This is exactly why the two-stroke didn’t get the stiffer frame that was introduced to the SX-F range for 2013, mainly via a reinforced headstock. If it had, the already livelier temperament of the two-stroke’s front-end would have been exacerbated.

Compared with the SX-F’s ultra-predictable front-end traction – especially on skatey hardpack – there’s something about the SX’s lighter front-end that needs to be learned. You have to guide the SX around the entire turn if you want to keep the front tyre biting and hold a tight line, and you can’t afford to let your attention wander for a second. For the average rider, the SX-F’s ride is more reassuring because you can relax in the saddle and not have to constantly adjust your body weight. Its engine braking helps anchor the chassis and re-connects both ends of the bike on the way into turns, and that gives you the confidence push harder or change lines at the last moment. The lightweight SX is fantastic under brakes as it sits up higher in the fork’s stroke compared with the four-stroke. Its lower tip-weight helps you change lines mid-corner with less rider input, but it’s not as confidence-inspiring if you come into a turn too hot and try to make the inside rut. Put simply, it’s easier to wash the front tyre on the SX if you’re not sitting right over the front in slippery conditions.

The chassis and suspension set-up on both machines produces an excellent front-to-rear balance and predictable steering, and both shock absorbers (each with a 54N/mm spring) have a very similar action. But in hardpack conditions when traction is at a premium, the SX-F owns flat turns because both ends of the bike behave more predictably and, unlike the SX, it doesn’t need berms to turn off. But in loamy conditions, the two-stroke starts to shine. Its lightweight chassis makes short work of sandy whoops and big braking bumps. Similarly, it’s easy to pull back into line if you cross-rut an upramp and get the thing sideways in the air. But when the rolling bumps turn into nasty, square-edged specimens, the SX’s rear-end is more difficult to keep tracking straight for less experienced riders – which has more to do with the explosive power than the shock’s performance.

Swapping Seats

There’s no doubt that it’s much easier to jump from the SX to the SX-F, mainly because the four-stroke’s inherent stability gives you the confidence to just climb aboard and pin the thing. Going from four-stroke to two-stroke, however, requires a more methodical process because the two-stroke has a livelier engine and chassis … that ‘flighty’ feeling people often refer to with two-strokes. With the new-generation chassis, much-improved WP twin-chamber 48mm fork and shock linkage, the 250SX is well balanced and nowhere near as nose-down and nervous as it once was, but its front-end still doesn’t have that sure-footed, unflappable feel of the SX-F. While all three riders clocked very similar lap times aboard each machine, the four-stroke let them do it more effortlessly and for longer. With more feedback back through the SX’s bars and more clutch control needed to handle the power on the skatey hardpack, there’s a lot to think about to cut a fast lap on the two-stroke. That said, with ruts and berms to turn off or with a bit more loam to rip into, the SX starts to gobble up the SX-F pretty quickly. We’d like to repeat the lap time comparo at a sandy track.

Taking Stock

The mere fact that KTM has priced these two 2013-model 250s within $200 of each other demonstrates how confident they are there’s a market for both. And with the resurgence in two-stroke sales, the 250SX is sitting pretty against the five- and six-year-old technology found on its rivals’ two-stroke motocross bikes. But, as much as the new-generation chassis, suspension, bodywork and engine mods make the 2013 250SX more refined than its predecessors, the machine is still much more suited to the serious racer than the practice-track punter. For average riders, the SX simply can’t match the forgiving engine and chassis package that comes on the 2013 250SX-F, and the confidence that instantly inspires on a range of terrain types. Of course, we make those comments solely from a performance perspective. When you introduce modification and maintenance costs into the equation, the two-stroke starts to make a very compelling argument for itself. For the cost of seriously campaigning a 250SX-F over a season, you could buy and competitively race two 250SXs! So, yes, it is possible we’re heading back to the premix future in the motocross market.

You’d Buy The SX-F Because…

• It’s easier for more guys to ride confidently across a broader range of track conditions.
• It’s forgiving engine and chassis is less likely to spit you off.
• The electric start is not only convenient; it also saves energy when trying to re-start the bike mid-race.



You’d Buy The SX Because…

• You’re getting a little too heavy for a 250F.
• It’s cheaper to modify and maintain, and you can perform more of the work yourself.
• That explosive power offers a better stepping-stone en route to the 450cc class.
• It’s lightweight, nimble chassis takes less of a toll on the body on bumpy tracks.



Maintenance

With KTM’s ever increasing sharing of components across its off-road range, maintenance differences between these two machines are mostly engine-related. But is two-stroke technology still being advanced in this era of four-stroke dominance, and have the smaller four-dungers finally lain to rest their early hand-grenade reputation? KTM Australia’s Rob Twyerould helps us sorts the facts from the fiction…

Transmoto: Rob, let’s cut to the chase: how far removed are today’s 250cc four-stroke engines from those fragile motors of five or six years ago?
RT: Back when all the major manufacturers first brought their 250cc four-stroke bikes to the market, there were failures on some engines due largely to the piston dimensions and valve-train instability. A small four-stroke effectively uses a wide bore in comparison to its stroke, and the piston has a very shallow skirt. So the high revs needed to produce enough power could see the piston try to turn within the bore. Also, the valve-train could have movement within its components, and that’s not a plus on such a high-revving engine. But due to advancements in materials, technology, design and maintenance schedules, those very early failure rates have dropped dramatically. The pistons have become stronger and the valve-trains more stable.

Transmoto: So has any of this advancement filtered down to KTM’s SX models?
RT: There has been cross-pollination between the engine types. As four-stroke engines get more compact and stronger, so do the two-strokes’. The 250SX has seen constant development to many areas of the engine in the last few seasons. Crankcases now are thinner but stronger, while the cylinder heads now feature removable inserts (for customisation of the combustion chamber). The 2013 250SX now rides with some of the characteristics of a four-stroke; namely torque at lower revs and engine smoothness.

Transmoto: And what of the on-going DIY maintenance debate between the two- and four-strokes?
RT: It’s true that the two-stroke is as easy to work on as ever. Most mechanically minded riders can replace the piston rings the night before a ride without loosing any sleep. The four-stroke still remains a more complex beast and does require special tools and a more advanced skill set to carry out tasks such as valve-shim checking and replacement. That still involves camshaft and tensioner removal and re-timing of the engine. But in saying that, the advances in technology and material means that changing the valves’ shims is a process very rarely called for now.

Transmoto: What effect do the different engines have on the chassis components?
RT: The frame is subject to different vibrations from the two types of engine. This makes it very important for engine mounts to be in good condition and torqued to their correct values. Other than that, there’s no real difference between the two in terms of the engine’s effect on the running gear.



KTM Australia’s Rob Twyerould…

Rider Feedback

Pro, Brock Winston – 24, 77kg, 175cm
“For a privateer to be competitive against the factory riders on their trick four-strokes, the KTM’s 250SX is a really cost-effective option. It’s cheaper and easier to maintain and much cheaper to throw performance mods at, and it gets out of the start gates quickly – which is half the battle in motocross. But if I had the option between a factory two-stroke and a factory four-stroke – and I thought purely in terms of overall performance – I’d certainly consider the four-stroke. It’s definitely easier to get on and instantly feel comfortable on the SX-F, and I find that it holds it line much better through corners. And that can help save energy.”

Off-Road Pro, AJ Roberts – 29, 70kg, 170cm
“Our lap time comparison revealed that the 250SX-F isn’t actually as fast as it feels to ride, and even though the conditions at the test track suited the four-stroke better, lap times were very similar between the SX and SX-F. I think the SX would be faster on prepared tracks and loamy or sandy conditions. But if you’re a privateer, why not have both – a cheap, low-maintenance two-stroke for practice, and a four-stroke to race … as it’s easier to jump from the two- to four-stroke. Then for sandy race race tracks, just whack a fresh top-end in the two-stroke and you’re ready to cut loose.”

Clubman, Greg Smith – 43, 88kg, 182cm
“I can see why people are gravitating back to KTM’s two-stroke. You can be just as fast – if not faster – aboard the SX, but you do need to take the time to adapt your style to get the most from it. Fit riders would be faster for longer on the 250SX, simply because of its better power-to-weight ratio. Personally, I’d take the four-stroke as its power-delivery is smoother and less physically demanding. It’s a double-edged sword – the average guy who’s looking to save money on maintenance will want the SX, but he probably won’t have the time to get fit enough to ride the two-stroke to its full potential.”

—

For a few extra details, purchase a print or digital edition of Transmoto Issue #25 where this feature originally appeared. Don’t forget to check out our online image gallery from this test, too.