TWO-STROKE TUESDAY | 2005 KTM 250SX | GOOD ENGINE, BAD SUSPENSION
The 2005 KTM 250SX was a handful to ride. It was fast, but as we all know the WP PDS rear suspension was only good if you knew its secrets.
KTM’s design philosophy used to be quite mysterious, and sometimes still is. Over the last decade, the Austrian powerhouse has adapted to our American needs. Back in KTM’s growing pain years they still produced awesome engines, although they were known for neutering them the following production year. Back in 2002, the KTM 250SX pumped out 50 horsepower. This was a number only reached by works bikes back then. In 2003, instead of building on that base, they produced an over-geared, light flywheel, richly jetted powerplant that could barely get out of its own way. And, to make matters worse for 2004 they mellowed it down to the 46 horsepower range. They went from the top of the heap (at least in peak horsepower) to also-ran for no discernible reason. It was mysterious to say the least.
Then, in 2005, they were back on top again. Their new engine was marvelous. The real questions revolved around the rest of the package.
Q: WAS THE ‘05 ENGINE FASTER THAN THE ‘04?
A: Yes. Mucho faster. Mucho broader. Mucho easier to use. If you compared powerbands from the 2005 250SX and 2004, you’ll find that the curves are similar, but that the ’05 models make more power at every point on the chart (to the tune of two ponies more from 6500 rpm all the way to 10,000 rpm). In the real world, power is not as important as placement, but if two engines have the exact same powerbands and one makes more bottom, more middle, more top and more overrev you don’t need a degree in mechanical engineering to guess which one is best.
At peak horsepower the KTM 250SX made more horsepower than its Japanese competitors.
Q: WAS THE 2005 KTM 250SX ENGINE ALL-NEW?
A: No. Mechanically it is a kissing cousin to last year’s mill, but the few changes the Austrians did make paid big dividends. Here’s the list: (1) Crankshaft. Although it weighs the same as the 2004 cranks, the weight was moved farther out on the crank halves. This increased flywheel inertia and made the power more tractable. (2) Compression. Engine compression was increased by three divergent methods. First, the combustion chamber had less volume for a slightly higher compression ratio. Secondly, the single-ring piston had been replaced by a dual-ring piston. The dual rings seal better at higher rpm and decrease fractional compression loss. (3) Finally, the larger crank halves double as engine stuffers to increase cranking pressure in the lower end.
Q: WHAT ABOUT THE 2005 250SX GEARING?
A: The MXA test crew has hated most of KTM’s gearbox iterations. In 2003 we dropped one tooth on the countershaft sprocket and one tooth on the rear sprocket (13/49). For 2004, KTM copied our gearing, with the notable exception of a 50-tooth gear in place of our favored 49-tooth rear. For 2004, we simply reinstalled the 49 on our race bikes.
For 2005 KTM dropped the 50 and mounted a 48. If it seems that they are dancing around MXA’s gearing, they are. But, it isn’t that they didn’t want to run MXA’s 13/49, it’s just that the bean counters at the KTM factory only spec’ed even-numbered rear sprockets. Thus the 48! No sweat. Most Novice and Intermediate riders will want to run a 49, but Pros love the 48.
Q: WAS THE 2005 250SX FASTER THAN ITS JAPANESE COMPETITION?
A: Yes. At peak horsepower, the KTM 250SX made more horsepower than its Japanese competitors. Best of all, it had a very broad powerband. It cracked the 30 horsepower mark at a low 5800 rpm, peaked out at 48.1 horsepower at 8400 rpm and didn’t give up the ghost (defined as dropping back below 30 horsepower) until 9800 rpm. That is a 4000 rpm wide period of time in which the KTM made over 30 horsepower. Only the YZ250 had a broader powerband, but it did it by cracking 30 ponies at a very low 5500 rpm.
If you raised the powerband indicators to 40 horsepower, the KTM had no peers, it made more than 40 horsepower for over a 3000 rpm range. No other bike came close to this mixture of breadth and horsepower.
For 2005 KTM dropped the 50-tooth rear sprocket and mounted a 48. Faster riders liked the bigger 49 tooth, but KTM only made even tooth sprockets in 2005 to save money.
Q: WAS THE 2005 KTM 250SX A FIRE BREATHER?
A: No, far from it. It was very easy to ride. It gave up a little roll-on power to the YZ250, but had manageable throttle response, excellent acceleration and good pull. It didn’t have the torquey low-end of the YZ250 or the snappy midrange of the RM250, but it covered all the bases with an engine that was a jack-of-all-trades. Every MXA test rider liked the engine. It was a joy to ride.
Q: WHAT WAS THE PROBLEM WITH KTM’S SUSPENSION?
A: ”The worst business decision that KTM ever made was to buy the Dutch-based WP suspension company.” In-house ownership of their own suspension components killed the initiative. Since WP couldn’t lose the KTM contract, they didn’t have to try as hard as a company whose very life depended upon satisfying a picky customer. Thus, KTM racers have been cursed with a series of halfhearted suspension set-ups, soft spring rates, harsh shocks and do-nothing fixes. In our opinion, KTM’s designers were stymied by lethargy at WP. For 2005 they must have kicked out the jams, because for the first time since the PDS system was introduced, the KTM suspension system had taken a step forward.
Q: HOW DID THE 2005 KTM 250SX FORKS WORK?
A: We’d have to say that the 2005 suspension was the best stuff we have seen from KTM since the Marzocchi days. The WP forks had totally new tapers to lessen bow-induced stiction and thinner chromoly fork tubes (to regulate flex). A lot of effort went into eliminating bottoming and midstroke harshness. As for settings, we ran the fork caps flush with the triple clamps, the compression 18 clicks out and the rebound on 18 clicks.
For 2005 KTM put a lot of effort into eliminating bottoming and midstroke harshness on the forks.
Q: WHAT ABOUT THE KTM’S WP/OHLINS PDS SHOCK?
A: In the past, we could write a test report on KTM’s rear suspension woes with our eyes closed. It went like this, “When the rear shock works over small bumps, it bottoms over big jumps. When it is stiff enough not to bottom over big jumps, it beats you senseless in the little stuff.” If that wasn’t bad enough, KTM didn’t seem to know what to do to fix it. The poor taper rod inside the PDS shock was shortened, lengthen, trimmed, clipped and spade like the yearly return of the swallows to Capistrano. All to no avail.
It’s a shame because the Ohlins-licensed technology inside the WP shock is cutting edge. One piston was speed-sensitive (responsive to shock shaft movement and oil flow) and the other was position-sensitive (activated when the shock compresses a predetermined amount). Theoretically, a twin-piston shock should have been supple in the small bumps (thanks to its speed-sensitive valving) and ultra-stiff for the big hits because the second piston’s valving backs up the first piston. Why it wasn’t was a mystery.
KTM must have hired Sherlock Holmes as a test rider for 2005 because they finally got a clue. By making the rear of the frame 30 percent stiffer (mostly at the swingarm pivot), stiffening the shock tower (with a full-on forging) and increasing the independence of both pistons, the rear of the KTM actually worked. The MXA test crew’s main goal was to balance both ends (which translated into lowering the rear and raising the front). The rear shock worked best with 105mm of sag, 17 out on low-speed, 2 out on high-speed and 26 out on rebound.
Q: HOW DID THE 2005 KTM 250SX HANDLE?
A: MXA test riders have scourged KTM handling from day one. For years KTMs have displayed sluggish handling traits. They understeered to the point of washing out. Our backyard fixes have always involved changing the fork’s offset from 20mm to 18mm (and 16mm on the four-strokes). For 2005 KTM outfitted every bike with adjustable offset. The stock triple clamps could be changed from 20mm to 18mm. Since the bikes rolled off the assembly line with triple clamps set at 20mm, you would have to press the stem out and rotate it 180 degrees by yourself. We heartily recommend 18mm offset.
So, how did it handle? It is sharper than it was. The biggest improvement was at turn-in. This was where previous models of KTM would give up the ghost and start to push. Not so with the 2005 KTM 250SX. It tracked with considerable authority at turn-in. The first action gets a reaction out of the KTM chassis. This came as a revelation to KTM owners because they were used to a bike that ignored most rider input.
Was it great? No. Turn-in was the most noticeable improvement. The front end was still vague in the middle of the corner (although better with the 18mm clamps than with the 20s). Finishing off the turn revived the newfound accuracy. It bit on the entrance, slipped a little in the center of the corner and tracked out straight. It is much better than it was. Much better than the Kawasaki KX250s. But not nearly as predictable as the YZ or agile as the RM. We’d give it a B (in a world where the RM250 got an A+, the YZ250 got an A and the KX250 got a D).
We gave the 2005 KTM 250SX’s handling a B (in a world where the RM250 got an A+, the YZ250 got an A and the KX250 got a D).
Q: WHAT DID WE HATE?
A: The hate list:
(1) Side panels: Don’t they run numbers on their bikes in Austria? If they did, where did they put them? The trapezoid-shaped side panels will only accepted minicycle numbers.
(2) Triple clamps: We loved the billet triple clamps, but why not swap the stem at the factory so that American owners could get 18mm offset straight off the showroom floor.
(3) Front fender: Aesthetically, it’s ugly. Functionally, it would hit against the front tire if it wasn’t for the fender brace. Philosophically, you have to ask why KTM didn’t do something about this albatross of a fender long ago.
(4) Radiator wings: KTM added new rain gutters around the top of the radiator wings to keep the rider from catching on them.
Q: WHAT DID WE LIKE?
A: The like list:
(1) Handlebars: We appreciated the oversize Renthal FatBars.
(2) Triple clamps: All-new, CNC-machined and blessed with four-position bar mounts. When you add in the adjustable offset, these were awesome triple clamps.
(3) Clutch: Magura’s hydraulic clutch was and still is the best in the biz.
(4) Sneakers: According to KTM sources, they had a special run of old-school Bridgestone M70 rear tires run for their bikes. The M70 was a soft terrain tire but worked better than the new-school Bridgestone stuff.
(4) Pipe: On a whim, we tried Pro Circuit’s Jeremy McGrath pipe on our 2005 KTM 250SX. It was a long shot, but the smartest thing we ever did. It was worth three horsepower. That pushed the ’05 KTM over 51 horsepower.
KTM’s standard hydraulic clutch has been a staple for many years. We loved it then and we love it now.
Q: WHAT DID WE REALLY THINK?
A: A year ago we said that the 2004 KTM 250SX was a better KTM for KTM aficionados. That was a left-handed compliment—sort of like saying that cauliflower is better tasting than asparagus. A year later, we think that the 2005 KTM 250SX is the best KTM we had ever ridden. It is faster, easier to ride and more manageable than most of its competition. It was a serious contender—and not just against the other vegetables.