2015 KTM 250 XC-F vs. Yamaha YZ250FX

Adam Booth | March 3, 2015
Until recently, KTM lived alone in the category of closed course off-road race bikes, and that makes it pretty easy to dominate. The idea isn’t rocket science, take a motocross bike and slightly tweak it to handle the rigors of off-road racing. Picture GNCC-style race courses that favor a motocross machine more than a trail bike. The KTM XC line is all about producing bikes that can handle a wide range of terrain and the Austrian marque does it well. Now Yamaha has thrown its blue hat into the KTM-ish world of closed course off-road race bikes with the all-new YZ250FX, providing a bike that can do it all – from trail riding to motocross. If a 250 four-stroke bike that can enjoy a day trail riding, compete in GNCC style off-road racing and then rip up a motocross track is on your radar, you now have two excellent choices.

KTM 250 XC-F

The 2015 KTM 250XC-F does not come with a spark arrestor so we used an FMF 4.1 slip on with spark arrestor to legally ride public lands.
The 2015 YZ250FX does not come stock with a spark arrestor but the use of an FMF slip on Power Core with a removable spark arrestor adds some power down low and makes riding on public lands legal.
(Above) The 2015 KTM 250XC-F does not come with a spark arrestor so we used an FMF 4.1 slip on with spark arrestor to legally ride public lands. (Below) The 2015 YZ250FX does not come stock with a spark arrestor but the use of an FMF slip on Power Core with a removable spark arrestor adds some power down low and makes riding on public lands legal.

The XC in KTM model names signifies cross country, and KTM sells an XC version of nearly every SX model it makes – both two-stroke and four-stroke. This means the 2015 250 XC-F is virtually a 250SX-F and the differences between the two models are minimal. The 250 XC-F is equipped with different ignition mapping, an 18-inch rear wheel, off-road suspension valving and one fork rate softer fork springs. The XC-F uses a six-speed transmission with first gear the same as the 250SX-F, while second, third and fourth are more spaced out. Fifth gear is the same as the 250SX-F, while sixth gear isn’t even equipped on the SX-F. Everything else, including the exhaust, is identical on both bikes. KTM doesn’t have to worry about adding electric start to the XC, as the 250SX-F already has it. KTM has always been the leader when it comes to equipping both off-road and motocross bikes with electric start.

YZ250FX

Similar to its KTM rival, the new Yamaha YZ250FX is a virtual clone of its motocross analog – the YZ250F. However, Yamaha did have to add a few key features, like electric start. Yamaha integrated the starter into the side case and tucked it in front of the cylinder, keeping it out of harm’s way. Tweaks to the motocross suspension come in the way of off-road valving and softer fork springs. The shock spring rate stays the same as the YZ250F. As you would expect, the YZ250FX uses an 18-inch rear wheel,

The 2015 YZ250FX doesnt rev as high as the KTM 250XC-F but delivers great off idle torque.
The 2015 KTM 250XC-F has a very strong but smooth power output.
(Above) The 2015 YZ250FX doesn’t rev as high as the KTM 250XC-F but delivers great off idle torque. (Below) The 2015 KTM 250XC-F has a very strong but smooth power output.

powered through a six-speed transmission. The six-speed transmission is not just the YZ transmission with a sixth gear, first and second gears are shorter than YZF and fourth and fifth are longer. Sixth is an overdrive gear for high-speed hauling. The ECU has been revised to smooth the motocross engine slightly. A Euro spec MX muffler is slightly quieter than the full-on US moto unit that comes on the YZ250F, unlike KTM which uses the moto exhaust from the 250SX-F. In California these bikes are not green sticker machines and neither bike comes with a spark arrestor.

Keeping It Legal

Getting stopped without a spark arrestor in a public riding area in California will set you back almost $1000. We weren’t about to take that chance so we installed FMF slip on mufflers with spark arrestors on both bikes. We used an FMF Aluminum Factory 4.1 RCT ($374) on the KTM and a Powercore 4 Hex ($329) on the Yamaha. We did a day testing at a motocross track with stock mufflers and did the rest of the comparison using the FMF slip-on mufflers. We ran the bikes on the MotoUSA dyno in stock trim with the stock mufflers and then with FMF mufflers.

In stock form the KTM produces more horsepower and torque throughout the curve. The biggest difference between the two bikes is when they hit the rev limiter. The Yamaha power peaks around 11,500 rpm, producing 35 horsepower while the KTM pumps out 38.5 at the same rpm. Then while the YZ250FX is signing off, the KTM keeps pulling and building horsepower all the way to 13,500 rev limiter, maxing out at 40 horsepower – five more peak ponies than the Yamaha.

Once stock testing was complete it was time for the FMF spark arrested slip-on mufflers. With the FMF Aluminum Factory 4.1 RCT installed (with spark arrestor) on the KTM we found it mimicked stock within a quarter of a horsepower all the way through the power curve. We were happy to find the FMF Powercore 4 woke the power up right off idle on the YZ250FX and also gave it a little more pulling power up high in the rpms.

Adam Booth

Off-road Editor | Articles | Enjoying single track in the mountains, hitting the motocross track or battling an EnduroCross track, if it's on two wheels Boothy will have a smile on his face. Adam has served a mega ton of years in the off-road industry as a photographer, writer and popper of wheelies.