Flagship of KTM's new four stroke racing series is the mighty 520 SX. At a mere 235.8 pounds, it's a no-holds-barred racing machine.

RIDING IMPRESSIONS ? 520 SX RACING

Don't even think about buying a 520 SX for a fun or play bike! This is not an easy bike to ride. It has snappy, sudden power ? and lots of it ? combined with an ultra-sharp steering chassis.

This means that things happen RIGHT NOW! No doubt, in the hands of a good Pro rider, this machine would be a great deal of fun. However, in the hands of a crusty old fat guy who used to be semi-quick, the KTM 520 SX is intimidating.

The bike feels light, slim, trim and tall. It's set up to turn sharply, with a near vertical 26.5 degrees fork rake angle. For a tight, twisty supercross track, it'll probably turn with (or under) anything else on the course. But on a normal outdoor MX track with higher speeds, the 520 SX becomes a hand full, demanding total attention to keep from getting pitched off.

It's only fair to say that the bike moves around a great deal in the process of going forward. As long as I anticipated the bumps, or hit them squarely, I was able to cope with the speeds the bike was capable of generating. But when I got tired and tried to ride lazy to save energy, the bike seemed to get a mind of its own and deflect way too easily for my limited reflexes.

To be utterly honest, this particular bike deserved some laps in the hands of a good Pro to truly evaluate its capabilities. Therefore, the stuff you read here is tainted from my own abilities, or lack thereof.

Power starts early and hard in the 520, with much more snap off the bottom than a YZ-400/426. Mid-range is positively brutal ? even stronger than the bigger 650 XR Honda. The bike also revs out well. The spread of power is so wide, that the four-speed tranny is not a handicap for a normal MX or Supercross track.

Engine response is clean, with no hitch or stumbling anywhere. Much of the response can be credited to the carb that's mapped to the variable curve ignition system.

KTM told us that swapping the four-speed box, for a six-speed set up, is simple. Just remove a clip and add the needed pieces. Shifting was excellent. It had the kind of touch and feel where you never even thought about shifting as you rode the bike, which is how it should be.

Clutch pull is hydraulic and very light. It's also adjustable.

The hydraulic clutch was smooth and light, but there was so much power available at all times, that you really never had to use it except for starting and shifting. And, if you choose to abuse the gearbox a bit, you can slam it into the next gear without using the clutch.

I felt that the suspension was too firm ? almost harsh ? but the way the bike is delivered, means that it has to be able to take the landing from one of those ball-busting launcher double jumps. Naturally, you'll be able to dial in compression and rebound at both ends to suit your style, bodyweight and skill level (or lack of) easily.

The 520 SX (as well as all the other bikes in the family) is very thin through the midsection, with nothing to snag boots, or get in the way of the rider. I'm 5 feet 8 1/2 inches short, and found the tall saddle height irritating. Much of this height stems from the fact that the bike has 15 inches of ground clearance.

For some reason, the saddle on all four of the bikes we tested was very hard, much like the seats of the KTMs from a decade ago.

Little things on the bike are great! Take the grips, for instance. Up until now, I've always thought the Honda grips (properly trimmed with a razor blade) were the best in the world. The Domino grips on the Katoom are just like the Honda grips already trimmed in the critical palm and thumb area.

Mugura Aluminum Handlebars.

Bars are tapered aluminum items that would cost you a bundle to add to your garden variety race bike. Like we said, nice stuff. And certainly one of the six available bar positions will fit your body just about right.

Attention to detail is so good that someone returning to the sport after a decade away, might think it was a show bike. The exhaust system is chrome-plated, aluminum parts are buffed out, nuts and bolts are high-quality pieces, welds are clean and even the graphics show a bit of classic restraint in an era of pop-art flash bikes.

Oh yes ? let's jabber a bit about starting. Most four-strokes are a real pain in the a ? uhhhh ? ankle. When the very first KTM four stroke was introduced to the market as a 504 powered by a Rotax engine, it was easy to start.

But when KTM brought out their own engine and dumped the Rotax, they acquired a reputation for hard starting that was certainly deserved. Those bikes had a mind of their own and would sometimes refuse to start, unless you bowed toward Mecca, lit three candles, said a rosary and burned some incense.

The new generation racing four-strokes put all this behind, as they start without mystery, and start consistently.

The bottom line?

If you want a true, pure-blooded, four stroke racer, this is it. Like we said, in less than stellar hands, it is not an easy bike to ride aggressively. Power is all you could ask for and more than most riders will ever need. In fact, the legendary "average" rider will probably go faster with less fatigue on ordinary, less powerful bikes.

It's a deadly serious machine and you better think long and hard before you get one. If your skill level isn't high enough, having a KTM 520 SX would be much like using an Indy car to make a beer run down to the local 7-11.

TECHNICAL SPECIFICATIONS

Engine;

Single Cyl. 4-Stroke, SOHC/4 Valve Head, Liquid Cooled, Automatic Decompression System

Cylinder;

Mahle Nikasil Coated

Exhaust;

Twin Head Pipe, Two Into One Collector

Silencer;

Aluminum Muffler

Bore/Stroke;

95.0mm X 72.0mm

Displacement;

5l0ccm

Trans;

4 Speed, SX Close Ratio

Gear Ratios;

1st -14:34, 2nd - 17:31, 3rd - 19:28, 4th - 22:26

Primary Drive;

30:81

Final Drive;

14 / 50, 520 chain

Trans Oil;

SAE 10W-40 wt.; Capacity 1200cc

SparkPlug;

NGK CR8 EK

Fuel;

Premium Fuel (92+Octane U.S. Octane)

Fuel Capacity;

7.5L/2.0 U.S. gallons

Carb;

Keihin MX-FCR 39

Jetting;

Main: 1 75 Idle: 48 Start: 85 Needle: OBDTM Slide: #1 5 Needle Position: #2 Mixture Screw: 1? Turns Out

Ignition;

Kokusan 4K3 Electronic, w/ Lighting Coil 12 v 110w

Timing;

5 degrees B.T.D.C. @ 1000 R.P.M.

Mainframe:

Chrome-Moly

Subframe;

Aluminum

Fork;

WP 43 USD, MA

Fork Travel;

295mm/11.6 inches

Fork Oil;

SAE 5 wt.

Rake Angle;

26.5°

Front Brake;

260 mm/10.2" Disc, Brembo Double Piston Caliper, Sintered Pads

Front Tire;

Bridgestone M77 80/100 X 21"

Shock;

WP PDS, External Adjust Compression/Rebound

Rear Wheel Travel;

320mm/12.6 inches

Rear Brake;

220mm/8.65" Disc, Brembo Single Piston Caliper, Organic Pads

Rear Tire;

Bridgestone M78 11 0/90 X 1 9"

Seat Height;

92 5mm/36.4 inches

Wheelbase;

1481 mm/57.3 inches

Ground Clearance;

380mm/15.0 inches

Weight;

107kg/235.8 lbs. (dry)