REAL TESTS! 2010 MXA RACE TEST OF THE KTM 150SX:

Valuable lessons: It is a shame that most young riders will never experience the joy of racing a full-size two-stroke. The KTM 150SX teaches throttle control, energy management and how to race while giggling in joy.

Q: FIRST AND FOREMOST, IS THE 2010 KTM 150SX BETTER THAN THE 2009 150SX?

A: Yes, but not because it is a completely new machine or because the engineers found a spare five horsepower lying around. It’s better because KTM has always made yearly updates?not always big improvements, but changes that make a difference (and those changes add up).
 
Q: SHOULD I BUY A KTM 125SX OR A KTM 150SX?

Simplicty: No cams. Lots of power and very few moving parts.
 
Q: IS THE 2010 KTM 150SX AN ALL-NEW DESIGN OR JUST A “BNG” BIKE?

A: Neither. KTM has not forsaken their two-strokes, and while the 2010 150SX is not new from the ground up, it isn’t a “Bold New Graphics” model, either. KTM’s R&D department produced a healthy list of changes for the 2010 150SX.
 
Q: WHAT DID KTM CHANGE ON THE 150SX FOR 2010?

A: The first three changes listed are unique to the 150SX. The rest are general updates received by all of KTM’s motocross and cross-country models for 2010.

(1) Cylinder. The 150SX has a new cylinder. The castings have been improved and the porting is more precise with a better finish.

(2) Frame. The head angle has been steepened by half of a degree. That is a very significant geometry change for any race bike.

(3) First gear. KTM upgraded the strength of first gear in their unique six-speed gearbox. The gear ratios aren’t changed, but the durability was improved with a high-grade steel.

(4) Triple clamps. The triple clamps have been redesigned to improve flexibility?evidenced by the change from a two-bolt to a three-bolt bottom clamp. The fork offset has also changed. Last year’s clamps could be switched from 20mm to 18mm; the new clamps are fixed at 22mm.

(5) Suspension. The WP forks have new seals and bushings to reduce stiction (static friction) and sliding friction.

(6) Airbox. KTM has reshaped their airbox to reduce the likelihood of water splashing onto the filter. Additionally, Twin Air designed a new filter to go with the airbox (although the old one still works).

(7) Brake pads. KTM switched to Toyo brake pads on every 2010 model, save the 450SXF, to get a more progressive and less grabby feel.

(8) Miscellaneous. The goofy 2009 cartoon graphics have been replaced by a more sensible design, and the Renthal dual-compound grips are now a diamond pattern with a traditional half-waffle.

Q: WHAT ARE THE DIFFERENCES BETWEEN THE KTM 125SX AND KTM 150SX?

A: There are four significant differences between the 125SX and 150SX.

Bore and stroke: The KTM 125SX has a 54mm x 54.5mm bore and stroke. The 150SX is bored out 2mm and stroked 4mm (56mm x 58.4mm). The 150SX obviously has a different piston, rings, cylinder and crank.

Exhaust pipe: The only way the MXA wrecking crew could tell the 150SX from the 125SX in the pits was by looking at the exhaust pipe. The 150 and 125 share the same basic pipe, but the 150SX has a 1-1/2-inch extension added to the head pipe.

Gearing: The 125SX has a 13-tooth countershaft sprocket, while the 150SX uses a taller, 14-tooth countershaft (both have 50-tooth rear sprockets). What does that mean? The taller countershaft sprocket is the equivalent of running a 47- or 46-tooth rear sprocket. The 150SX’s taller gearing is designed to take advantage of its extra power and torque.
 
Q: WHAT DOES THE 2010 KTM 150SX ENGINE RUN LIKE?

Spring: The stock 6.3 kg/mm is well suited for most 150SX riders.

That said, the horsepower numbers favor the 150SX over the 125SX (and, amazingly, over the KTM 250SXF four-stroke also). The 2010 KTM 150SX tops 40 horsepower at peak (which is about two horsepower more than the 125SX’s and 250SXF’s peaks). Best of all, the 150SX makes as much as three horsepower more than the typical 125 in the meat of the powerband.

Q: HOW DOES THE KTM 150SX COMPARE TO THE KTM 250SXF?

A: Compared to the KTM 250SXF, the 150SX is incredibly quick-revving and peaky. On the 150SX you can either scream or just putt, but you can’t cruise around. To maximize speed on the 150SX, the rider has to learn exactly when to shift, what gear to be in and to have an itchy trigger finger on the clutch lever. In a wide-open drag race against 250Fs, the 150SX actually wins out and gains inches. But any time it’s not in the sweet spot, it’s getting pulled by the thumpers.

The 150SX makes more horsepower than the 250SXF, but it gives up a little torque (18.9 ft-lb to 19.2 ft-lb). The broader powerband of the four-stroke and the extra torque make it easier to ride, while the hard hit and extra power of the 150SX make it a potent weapon in the hands of a talented, go-for-broke rider.

Q: CAN THE KTM 150SX BEAT THE KTM 250SXF?

A: Yes. It is an underdog, but the truth is that it makes more horsepower (albeit a lot peakier than a four-stroke), weighs a lot less (it is more than 15 pounds lighter than the typical Japanese-built 250F), is eminently more flickable (so much so that riding a 150SX is completely different from riding a 250 four-stroke) and can be repaired for a quarter of the price (should anything go wrong). The caveat is that not just any ham-fisted novice will have the skill or know-how to dance on the edge of the KTM 150SX’s powerband.
 
Q: HOW WAS THE GEARING?

A: The six-speed transmission is a good idea for the 150SX, even if you never make it to sixth gear. Like last year, the 150SX comes with one more tooth on the countershaft sprocket than the 125SX. We didn’t like this gearing. KTM tends to over-gear their machines from the factory. Adding one tooth to the rear (from a 50-tooth rear sprocket to a 51) saves some clutch feathering and makes more sense for all but the fastest tracks and riders.

Q: HOW WERE THE BRAKES?

A: Realistically, the 260mm front brake on the 150SX is too powerful for the size of the bike (and that is with the less grabby Toyo pads installed). A light squeeze sent a big response through the forks and into the chassis. Half of the MXA test crew thought the front brake was too powerful, while the other half loved the ability to stop on a dime. Unless you have an educated right hand, it’s best to use caution until you get a feel for what a works brake feels like (and amazingly, if you put the pads from the KTM 450SXF into the 150’s caliper, it could be even more powerful).

The rear brake offers good performance unless you are a brake dragger?then it will start chirping after heavy use or abuse.

Q: WHAT ABOUT THE KTM 150SX JETTING?

Q: HOW GOOD WERE THE WP FORKS?

A: The 150SX is sprung for featherweight riders. Full-grown men and fast kids will need to go up to a 0.44 kg/mm or even higher spring rate. Our quick fix for the KTM 150SX forks was to go with stiffer fork springs. We didn’t lower the oil height to make the forks more supple in the midstroke (to go along with the stiffer fork springs). Why not? Because KTM lowered the oil height for us. Two years ago, the 150SX had 370cc of fork oil; this year it has 350cc.

If you are a small minicycle transplant, the stock fork setting will work well.
 
Q: WHAT ARE MXA’S RECOMMENDED FORK SETTINGS?

A: Here is what we ran in our 2010 KTM 150SX (stock settings in parentheses).
   Spring rate: 0.44 kg/mm (0.42 stock)
   Oil height: 350cc
   Compression: 6 clicks out (12 clicks out)
   Rebound: 10 clicks out (12 clicks out)
   Notes: The WP forks used to suffer from serious stiction, but starting in 2008 KTM began a program to pursue less drag with new seals and bushings. We had good luck with 2010’s new seals.

Q: WHAT WAS OUR BEST SHOCK SETTING?

A: KTM has been very proactive with their rear suspension. Two years ago, it came with a very wimpy 6.0 kg/mm shock spring. Now the 150SX has a much more versatile 6.3 spring. As with virtually every bike ever made, the lighter the bike, the better the suspension works?and the KTM 150SX is very light. Our best shock trick was to slow the rebound down a few clicks and increase the high-speed compression. Once dialed in, the shock offered stability through braking bumps and compliance on rough corner exits under a heavy load.
 
Q: WHAT ARE MXA’S RECOMMENDED SHOCK SETTINGS?
     
A: Here is what we ran in our 2010 KTM 150SX shock (stock settings in parentheses).
   Spring rate: 6.3 kg/mm
   Race sag: 105mm
   Hi-compression: 1-1/4 turns out (1-1/2 turns out)
   Compression: 10 clicks out (15 clicks out)
   Rebound: 14 clicks out (24 clicks out)
   Notes: Most MXA test riders feel that the 150SX shock is very spring-rate sensitive. The best tip is to check the free sag (after setting your race sag at 105mm). If the free sag is more than 35mm, consider changing the shock spring.
 
Q: HOW DID THE 150SX HANDLE?

A: KTM has long fought the stigma of building quirky, Euro-feeling bikes, but those were the old days. The 2010 KTM 150SX is very accurate, crisp and agile. KTM obviously put some serious effort into getting the handling up to date. The steeper head angle, more resilient triple clamps and decreased trail (thanks to 2mm more offset) resulted in a chassis that goes where you point it.

The frame is suspension sensitive in that the wrong springs will induce headshake with the new steeper head angle, but that is only a problem if you get the numbers wrong. Best of all, the KTM responds very well to slight geometry changes. When a test rider complained about understeer or oversteer, it was easily dialed out with fork height and race sag changes. This is a very tunable frame. The bike encouraged squaring out of ruts, carving berms and changing direction in general. The 150SX loves tight tracks.
 
Q: WHAT DID WE HATE?

A: The hate list:

(1) Gas cap. We take dykes and cut the locking tabs off KTM’s push-button gas cap so that it works with a twist of the wrist. Maybe it’s just us, but we have trouble getting the push-button lock to work.

(2) Black gas tank. With dark premix and a black gas tank, the only way to tell if the tank is full is when your feet get wet.

(3) Sprocket bolts. Don’t lose the supplied tool kit. Why not? You will need the Torx wrench to tighten the rear sprocket bolts. And you need to tighten them regularly. And while you are tightening the sprocket bolts, pay special attention to the bolts on the shift lever, kick-starter, top shock mount and large star nut on the muffler.

(4) Rear brake. It would start chirping late in a moto. Brake draggers can prevent overuse by adjusting the pedal lower.

(5) Lifting. It doesn’t weigh very much, but that doesn’t help if you can’t find anything to grab hold of when the time comes to pick it up.
 
Q: WHAT DID WE LIKE?

A: The like list:

(1) Smell. We love the aroma of two-stroke oil. Even though most of our testers know that premix only needs to be mixed once, we caught them shaking the gas can for old time’s sake.

(2) Clutch. Two-stroke riders are intimately familiar with their clutches, and it’s nice to have the hydraulically actuated Magura when trying to eke out every bit of power in the 150SX.

(3) Longevity. Thanks to in-molded graphics and quality coatings, KTMs still look good after a couple months of abuse. Thanks to a simple engine design, it’s easier and cheaper to keep the two-stroke running than a comparable four-stroke.

(4) Jumping. Sir Isaac Newton might think twice after hitting a tabletop on this flickable bike. It weighs just a hair over 200 pounds (with no fuel). That’s 15 pounds lighter than a typical 250 four-stroke.

(5) Graphics. Last year’s graphics were atrocious. The 2010 model has a vastly improved graphics scheme.

(6) Cool factor. Riding a two-stroke is the red badge of courage. With all the four-stroke sheep on the track, the KTM 150SX stands out.

Q: WHAT DO WE REALLY THINK?

A: We are sad to see the KTM 125SX slip from the American scene, but more than happy with its 143.6cc replacement. Thanks to its 125 roots, the KTM 150SX is light, nimble and quick. Not only is it a totally unique bike, but it is so much fun to ride that you’ll have trouble wiping the smile off your face.