First Test: 2005 KTM 250 SX-F Power House

Seeing the KTM 250 SX-F dominate in its debut year racing in Europe left us wondering how the production version would stack up against established models here in the United States. It didn't take long for factory-prepped orange bikes to startle the competition as Nathan Ramsey smoked everyone at the supercross season opener in Anaheim. During the following months, KTM was able to notch five 125cc-class main-event wins. With those, pressure began to build as KTM must have 400 production bikes on our shores ready for dealer release by June 1 to keep its AMA points under the production rule. Rumors were flying, and some of us weren't sure if the bike would be available for 2005; then the phone rang and we were off to test the highly anticipated KTM 250 SX-F.

Making Power

KTM is known for producing motorcycles with horsepower and has ruled the lightweight class's performance race with the 125 SX in past years, so we had high expectations for the new 250 SX-F. A first glance takes in the engine's unique look, but what's inside is the important difference. The cylinder head uses finger follower levers to allow smaller cam lobes as well as provide a quicker valve opening and a straighter, more-direct push on the valve. With this borrowed MotoGP technology, the cam lobes do not need to be super steep, so the SX-F can run a lighter valve spring. That allows the motor to rev higher and a bit more quickly than engines in which the cams ride on the valve buckets.

The cylinder head's construction uses a separate cam bridge support to mount the cams (rather than have it cast into the head as the Japanese 250s do), which allows an exceptionally rigid valve train, even as the head need not be replaced if the cam bearings (roller on one side and babbitt on the other) are damaged. The magnesium cam cover sits at an angle, easing valve-shim access—a true sign the design engineers have been around motorcycles for a long time. The cam sprockets are small and compact, which normally means the cam drive sprocket on the crankshaft would have to be even smaller; but the orange bike uses a drive gear on the crank instead of a sprocket. The gear drives an idler gear, and that idler drives the cam chain. The combination of the cam and cam-drive design means the top of the engine can be much more compact than other twin-cam layouts. A hydraulic cam tensioner automatically sets the cam-chain tension, as all auto-tensioners do, but the hydraulic tension can loosen or tighten the chain as needed; a mechanical tensioner has a one-way plunger that can only add tension. Finally, KTM mounted the crankshaft as low as possible in the engine cases to maintain a low center of gravity, but also mounted the crank bearings as close together as possible to minimize deflection at high rpm. Two oil pumps are used: One scavenges oil and air away from the crankshaft to reduce parasitic drag, and a second supplies pressurized oil to the top end.

On the track the motor has it all. Bottom-end power is instant and very usable. The power can be rolled on, or if you're a spaz, you can use the clutch to get the revs to come up more quickly; but in most cases the roll-on power gets the job done. Midrange power pulls long before rolling into great top-end with an amazing amount of high-revving pull and overrev. Most bikes hit the rev-limiter, fall flat on their face and don't make power. The KTM doesn't use a rev-limiter, and the ignition doesn't cut out at high rpm; it allows the rpm to stay steady, slowly signing off. After 13,500 rpm, the ignition timing retards, gradually dropping the revs. The insane top-end really allows you to get every ounce of juice out of the motor, and more important, it gives tons of confidence when you need it the most. We did have a few problems with the Keihin carburetor; it had a small hiccup off the bottom but nothing some fine-tuning couldn't cure. Basically, the carburetor was a bit lean, so we advanced the accelerator pump and richened the fuel screw.

The closely spaced six-speed transmission shifts flawlessly and effortlessly. We rarely used first gear as second gear worked great out of tight corners. The Magura hydraulic clutch worked well; the pull stayed very consistent, and the clutch plate life is long. After riding the KTM at several tracks, we thought the motor felt similar to a big-bore cheater. Overall, the engine package is strong yet inviting for riders of all abilities. Beginners will love the roll-on power while intermediate and pro-level riders will praise the mighty, high-revving top-end.

Meeting an Old Friend

Getting used to the KTM 250 SX-F is simple. In past years some of our test riders have complained about the bike not feeling like any of its Japanese competition. Yes, the KTM offers a unique feel, but the new-generation frame seems nimble and forgiving. The WP suspension has also come a long way. Although the 250 SX-F basically has the same WP suspension as the 250 SX, it feels well balanced and the fork is very controlled and progressive. At the top of its stroke, the fork is soft and very speed sensitive, but the harder you ride the better it reacts. The shock is a tad finicky yet performed well and balanced evenly with the front of the bike. We did have a few instances in which the shock blew through the stroke, sometimes upsetting the chassis. Making compression adjustments can create a big difference in the way the shock works, and setting the sag is a must; we ran it between 108mm and 112mm. Dialing in the shock really helped the bike to settle under braking and over mid-corner bumps. We noticed that the WP suspension responds to any adjustments; it just takes a bit of time to dial it in to your liking.

Weighing in at 220 pounds, the orange machine feels super light. It turns on a dime and can be slammed into any line on the track. In tight rutted corners, the front end stays planted and has very consistent follow-through. The center of gravity feels perfect, allowing for awesome midair antics. All of our testers praised the seat and tank area as both are very narrow, which allow the rider's knees to grip and is one reason the bike feels so nimble. The controls are easy to use and all have a light feel. Bold Brembo brakes are the most-powerful in the class and required a few laps for us to get a feel for them, as they produce strong, somewhat sudden power with one finger. We had mixed feelings about the handlebar bend; some of our test riders loved it and some thought it a bit high. As a whole, the KTM is easy to ride, and once the suspension is dialed in, the bike inspires confidence. Acclimating to the ergonomics is easy, and the riding position feels spacious.

The Real Deal

Although we received the KTM 250 SX-F late in the season so it missed our shootout, we truly feel it is more than a contender. The motor flat-out rips, and it has great characteristics. We were able to put 12 hard pro- and intermediate-level hours on our test mule and haven't experienced any major problems as can sometimes happen with a first-generation bike. The new orange machine was able to win some new KTM fans. Several of our test riders want the KTM when it comes time to roll up at the starting line. At the National level, the 250 SX-F has proved itself; both Ramsey and Josh Hansen are having great seasons and both were new to the bike and the brand at the beginning of the year. Now we just have to put more time on our new scoot, watch the hourmeter and determine what kind of durability the bike offers. The big question is, who's going to get to keep it? It looks as if we will be rolling the dice once again!

Opinions

I took the new KTM 250 SX-F straight to a race without riding it first. After about eight laps of practice, I went to the starting line in the Vet Intermediate class at Cahuilla Creek. I adapted to the bike right away because it has good ergos that are not at all unusual. As with other KTMs, the hydraulic clutch is magic, and the Brembo brakes are the best out there. This bike has the feel of a purpose-built motocross race bike with a snappy motor that has a light flywheel sensation. I did not get to do back-to-back riding with other 250Fs on this day but it seems to be the fastest 250 four-stroke on the showroom floor. The bike will pull third gear through turns like no other 250F I have ever ridden. The chassis is pretty stable and turned well. My only complaint was that the WP suspension is just not as compliant as the Showa or KYB unit found on the competition. If you can get that dialed in, this will be a great race bike.
Sean Finley - 5'1O"/165 lb/Vet Intermediate

I'm never surprised that a KTM is tops in power, especially smaller-bore sizes. And this 250cc thumper rips, even if the midrange feels a little flat packed between the snappy yet torquey bottom bounce and a screaming surge on top. What surprised me is the chassis and suspension package rounding out the deal. This is the best-handling KTM I've ridden—it is almost a front-end–turning bike. I say almost because if I charged into turns and compressed the rear suspension too much, I had trouble keeping the front planted, with no help from the power keeping the front wheel in the air! You could also say I'm a bit heavy for the bike, too. The clickers are sensitive and do a good job of dialing the ride, a sign the chassis is tuned. For a first-year bike, late or whatever, it is really impressive. This could be the first "no excuses" KTM motocross bike.
Jimmy Lewis - 5'1O"/18O lb/Vet Pro

Seeing how well the KTM 250 SX-F was doing in supercross this year really shocked me, and it left me thinking the bike has to be good. I was quickly convinced after completing my first day of testing, and the bike only got better from there. I absolutely love the motor; it works great in tight technical sections and rails in the wide-open ones. It's really fast. For the first time ever on a KTM, I really liked the stock suspension settings. The bike is well balanced and handles superbly. Starting the bike is easy; it usually fires up quickly, cold or hot. I hate the seat; it's too hard and actually left me with a sore tailbone, but that's an easy fix. The ergonomics are roomy and easy to get used to. My hat is off to KTM; I love riding this bike and can't wait to see how it will stack up in our 2006 shootout.
Corey Neuer - 5'11"/168 lb/Intermediate