MXA’S 2012 KTM 250SX TWO-STROKE MOTOCROSS TEST: THIS IS THE KING OF ALL SMOKERS

May 18, 2012
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2012 KTM 250SX: There was a time when the Yamaha YZ250 two-stroke could compete on equal terms with the KTM 250SX, but in the last two years the six-year-old YZ has been surpassed by KTM’s superior engineering.

Q: FIRST AND FOREMOST, IS THE 2012 KTM 250SX BETTER THAN THE 2011 KTM 250SX?

A: Yes and no. Yes, because it is new, has linkage and benefits from KTM’s yearly upgrades. No, because the 2011 KTM 250SX works virtually the same (and some MXA test riders preferred the ’11 to the ’12).

Q: WHAT IS THE BIGGEST CHANGE ON THE 2012 250SXF?

A: The big news revolves around the all-new rising-rate linkage rear suspension and new frame to go with it. KTM is quick to point out that they believe the linkage system, which debuted on the 250/350/450SXFs last year, works the same as the no-link PDS system. So, if it works the same, why did they go with it? KTM readily admits that they changed all of their motocross bikes to linkage systems in response to demands from the American market. Even though they may have changed from the no-link PDS system to the linkage system grudgingly, there were solid technical reasons why the links made sense to KTM.

(1) Breadth. KTM’s engineers admit that the linked rear suspension works on a wider range of track conditions with fewer clicks necessary to bring the suspension into line. On the PDS system, some conditions would require very large clicker adjustments (or even a spring change), while the linkage system can normally make the rider happy within seven clicks.

(2) Shock length. American-spec KTMs get shocks that are 4mm shorter than Euro-spec shocks. Also, KTM says that the American factory bikes run 10mm-shorter shocks. This presented a problem on the old PDS system, because it only had 108mm of stroke to work with. The new linkage system has 130mm of stroke. That means that the American-spec and factory shocks can now be shortened without seriously biting into available shock stroke.

(3) Linkages. One obvious advantage of the linkage bike over the no-link PDS bike is that both the suspension and handling can be altered with longer or shorter links. MXA prefers to run a 143.75mm shock linkage instead of the stock 142.50mm link. The extra 1.25mm not only lowers the rear of the bike, but it stiffens the initial part of the stroke to hold the suspension higher in its stroke for a more aggressive feel.

Q: WHAT OTHER CHANGES DID KTM MAKE TO THE 2012 250SX?

A: Last year, KTM redesigned the cylinder (with a lower exhaust port), reconfigured the power-valve flap spring (from a 2mm to a 1.8mm wire diameter), installed keystone rings (with a slight taper on the top side for better reliability), made a new exhaust pipe (targeting improved bottom end), outfitted the 250SX with a new silencer (2mm-larger core), developed a wraparound silencer mounting system (that allows more flex), and eliminated the silencer’s large star-shaped nut (that had the irritating habit of falling off). These 2011 changes negated the need for KTM to completely overhaul the 2012 model, but KTM did make four changes (apart from the switch to rising-rate linkage):

(1) Head stay. Ed Scheidler, the retired guru of Yamaha testing, proved to the MXA wrecking crew decades ago that handling could be changed by simply switching cylinder head stays. If you don’t believe us, test it yourself by removing the head stay and riding your bike (although don’t do this for too long). For 2012, KTM discovered what the “Field Marshall” knew years ago and designed a new head stay that reduces vibration and improves the chassis feel. KTM tested 20 different head stays, but eventually chose head stay number seven.

(2) Reed valve. Although KTMs have come stock with Moto Tassinari VForce reed blocks for years, for 2012, they will get the latest VForce3 reed block (the one with reed stops).

(3) Frame. The frame layout had to be modified with a shock tower and lower linkage brackets, but apart from these elements, it is still the same frame as last year in terms of geometry and front triangle.

(4) Swingarm. KTM’s engineers didn’t waste time with any busy work. The 2012 KTM 250SX uses the exact same swingarm as used on the linkage-equipped KTM four-strokes. KTM’s one-piece swingarm casting is a technological marvel. There are no welds, hot spots or stress risers in the design. It comes fully formed from a single casting.

(5) Rear fender. Last year’s fender flapped when it got loaded with mud. The 2012 fender is reinforced along its edges, which also makes it more comfortable for your hand when picking the bike up.

(6) Airbox. KTM redesigned the air boot and airbox to accommodate the new, more upright rear shock position. They took this opportunity to incorporate a design that enhances air velocity.

(7) Fork seals. KTM formed a strategic alliance with SKF to produce forks seals that greatly reduce stiction.

(8) Rear master cylinder. Previous KTMs suffered some wear issues with the rear brake seal. For 2012, they reengineered the master cylinder to integrate the bleed hole into the piston, which stops the seal from wearing against the hole.

(9) Tires. The American-spec tires of choice for 2012 will be Dunlop Geomax MX51s, but the Euro-spec 250SX gets Pirelli Mid-Soft tires.

(10) Bodywork. Last year’s two-stroke plastic was different from the four-stroke plastic in some areas. This year, they share the same plastic.


 
Q: HOW FAST IS THE 2012 KTM 250SX?

A: This is a very quick bike. It doesn’t have a torquey low-end throttle response, but it snaps to attention just before the midrange and has ample blast to impress any two-stroke aficionado. It is fast, as you would expect from a 250cc two-stroke that produces 50 horsepower.

Q: IS THE 2012 KTM 250SX FASTER THAN THE YAMAHA YZ250?

A: Yes. There is no real horsepower comparison. The KTM makes five horsepower more than the YZ250.

Q: CAN THE KTM 250SX POWERBAND BE ADJUSTED?

A: Yes. Not only does the 250SX have two ignition maps programmed into the ECU, which can be changed by plugging and unplugging one wire, but the preload on the power valve spring can be increased or decreased to change the power delivery between 5000 and 7500 rpm (one turn on the preload changes the actuation point by 200 rpm). On top of that, KTM includes two additional power valve accessory springs that further fine-tune the speed at which the power valve responds within its 2500 operating range.

The accessory spring come in three rates; red is the lightest spring (it allows the power valve to actuate the quickest for a harder hitting power delivery); yellow is the medium spring rate and is the stock spring; green is the stiffest spring and it produces a softer hit.


Contender: Not only does it pump out a legit 50 horsepower, but the small engine leaves room to access the parts.

Q: HOW IS THE 2012 KTM 250SX JETTING?
 

A: Most MXA test riders felt that the 2012 KTM 250SX was a little lean compared to last year (probably brought about by the improved air flow of the new airbox). Luckily, KTM includes optional needles and main jets in the toolkit. We installed the richer N1EH needle in place of the stock N1EI and richer 160 main.

Here are MXA‘s recommended jetting specs for the 36mm Keihin PWK carb (when changed, stock specs are in parentheses):
    Main: 160 (158)
    Pilot: 42
    Needle: N1EH needle (N1EI needle)
    Clip: 3rd clip from top
    Air screw: 1-1/2 turns out
    Notes: KTM has a fuel-injected two-stroke engine in the works, but surprisingly they claim that they will release it as an offroad model before putting it on the motocross models. Because of environmental regulations, the enduro line must run cleaner than closed-course motocross machines, which is why KTM fuel-injected the 2012 450EXC, but not the 450SXF.

Q: HOW DID THE 2012 KTM 250SX HANDLE?

A: If you are getting off a four-stroke, the first thing you’ll notice about the KTM 250SX is how light it feels. It feels like a feather, and that pays big dividends in the tough and tight stuff. This is a superb-handling bike (once you get the correct fork spring rate for your weight and speed). Every MXA test rider raved about how accurate it was in the corners. Test riders could go wherever they wanted?and places they could never get to on a four-stroke.

Q: DOES THE 2012 KTM 250SX HANDLE BETTER THAN THE YAMAHA YZ250?

A: Yes.

Q: WHAT WERE OUR BEST FORK SETTINGS?

A: In the crazy world of supplying bikes to every continent on the planet, KTM produces two suspension settings. (1) Euro-spec: Euro-spec bikes are set up with what KTM believes are the best settings for the average European track, riding style and rider. (2) American-spec: American-spec bikes get stiffer suspension and the previously mentioned shorter shock for the unique needs of American motocross. But, not every bike headed to America gets American-spec settings. KTM’s 2012 two-strokes come to the USA with Euro-spec spring rates. In our opinion, the stock 0.44 kg/mm fork springs are not stiff enough for most American riders. MXA test riders prefer to go up to 0.48 kg/mm springs (we raise or lower the fork oil height to fine-tune the midstroke).

For hardcore racing, we ran this setup on the 2012 KTM 250SX (stock clickers are in parentheses):
    Spring rate: 0.48 kg/mm (0.44 kg/mm)
    Oil height: 375cc (390cc)
    Compression: 7 clicks out (12 clicks out)
    Rebound: 12 clicks out
    Fork leg height: 5mm up (flush on a sandy track)
    Notes: The 0.44 kg/mm fork springs are too soft for serious racing. Smaller riders could get away with 0.46 springs, but anyone fast enough will want 0.48s.


 
Q: IS THE LINK REAR SUSPENSION BETTER THAN THE NO-LINK SUSPENSION?

A: Unlike the front forks, we felt that we could live with the 5.4 kg/mm Euro-Spec spring rate (because the 250SX is about 20 pounds lighter than the 450SXF). The big question is whether the linkage 250SX rear suspension is better than the no-link suspension from last year. Most MXA test riders would say no. The two systems feel comparable, but that is probably a byproduct of the fact that KTM used the same engineers and test riders who developed the no-link setup to finalize the settings on the linkage system. As has been proven year after year with virtually every brand, no matter what changes a company makes to the mechanical parts, the engineers get the suspension and handling characteristics that they prefer.

Q: WHAT WERE OUR BEST SHOCK SETTINGS?

A: For hardcore racing, we ran this setup on the 2012 KTM 250SX (stock clickers are in parentheses):
    Spring rate: 5.4 kg/mm
    Race sag: 105mm
    Hi-compression: 2 turns out
    Lo-compression: 15 clicks out
    Rebound: 12 clicks out
    Notes: We ran a 1.25mm-longer Pro Circuit shock linkage arm. Not only did it lower the rear of the bike by 10mm, but it stiffened up the initial part of the shock’s stroke to help widen the range of the stock 5.4 shock spring. Faster or heavier riders might need to go to the stiffer 5.6 kg/mm shock spring. If you are savvy, you will use free sag to make the decision for yourself.


European numbers: The WP forks need stiffer springs and a lower oil height to work to their full capability.

Q: HOW DID THE SUSPENSION WORK?

A: MXA test riders are not big fans of the Euro-spec suspension settings, especially in the forks. The soft fork springs allow the front to dive too much, which eats up usable travel before you have even encountered a bump. This low-rider setup requires the forks to ride on the compression damping hump, which makes them feel harsh in the midstroke. Unless you weigh under 165 pounds, you should switch to stiffer fork springs immediately (either 0.46 kg/mm or 0.48 kg/mm springs depending on your speed and weight). We opted for 0.48 springs. Once properly set up, the WP forks are decent?not on par with Kayaba’s SSS, but equal to most Showa units.

As for the shock, true to KTM’s promise, we could get the rear dialed in quicker and with less drama than on the PDS system (the no-link PDS system required the rider to swap shock springs to get the perfect rate for his speed and weight?this could be difficult to get right). Once in the ballpark, the rear suspension felt a lot like PDS suspension, which contrary to popular opinion was quite good over the last three years. We still felt that the rear was too high and dropped too quickly under acceleration, which is why we installed a longer link.

Q: HOW WAS THE GEARING?

A: In the past few years, test riders added a tooth to the rear sprocket to get more of a gun-and-run motocross power delivery. Stock gearing is 13/48. Some riders still chose to gear the 2012 KTM 250SX down with a 49-tooth sprocket, but the snappier power delivery of the new engine lessens the need to go lower.
 
Q: WHAT DID WE HATE?

A: The hate list:

(1) Handlebar height. Every test rider felt that the stock Renthal 672FatBars were too low. Depending on the test rider, we had three options. First, KTM offers a 5mm riser that is less expensive than new bars. Second, the Renthal 996 TwinWall, 604 FatBars and Renthal 997 FatBars are taller.
(2) Gas cap. Contrary to popular belief, the MXA wrecking crew likes KTM’s quarter-turn gas cap; we just don’t like the locking feature. It sticks, is hard to use and allows dirt to fall down into the lipless orifice. We cut the tangs off in a manner that allows the gas cap to click on, but does not require two hands to remove it. Yes, we could have just removed the locking device from the inside of the cap, but this would eliminate the click-on feel.
(3) Shock preload ring. We hate KTM’s nylon preload ring (hate is not really a strong enough word). We prefer to run Xtrig preload adjusters on our KTMs.


Envy: This is the best front brake in motocross. Thanks to an oversize rotor and Brembo power, it maximizes pucker power.

Q: WHAT DID WE LIKE?

A: The like list:

(1) Price. Expect to spend $2000 less for a 250SX than a 450SXF. The money saved will be magnified by the lower cost of maintaining a two-stroke.
(2) Ground clearance. The 250SX two-stroke has 14mm more ground clearance than the 450SXF. Thanks to the more compact two-stroke engine, the 250SX has a much improved roll rate and can get through rutted corners and whoops much easier.
(3) Weight. The switch to linkage added five pounds to the 2012 KTM 250SX (and MXA test riders insisted that they could feel the extra weight). Luckily, the 250SX is one of the few bikes that could gain five pounds and still weigh only 217 pounds.
(4) Brakes. KTM’s oversize Galfer/Brembo combo is impressive on a heavy four-stroke, so imagine what this combination feels like on a lightweight two-stroke.
(5) Noise. Two-strokes are much quieter than four-strokes?plus, four-stroke sound travels twice as far.
(6) Hydraulic clutch. We love KTM’s hydraulic clutch and wonder what the Japanese manufacturers are waiting for.
 
Q: WHAT DO WE REALLY THINK?

A: KTM plans to produce 56,000 offroad motorcycles in 2012. Read that again: 56,000. And, 14,000 of them will be two-strokes. This is the best 250cc two-stroke bike ever made, and you wouldn’t go wrong by pushing KTM’s sales figures up to 14,001.
 

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