Q: IS THE 2015 YAMAHA YZ250FX BETTER THAN THE 2014 YZ250FX?

A: Of course it is, because there has never been a YZ250FX before. The “FX” is Yamaha’s attempt to compete against offroad juggernaut KTM for the offroad market. As the Japanese manufacturers lost interest in two-strokes and enduro bikes, KTM cleaned house, ran the table and swabbed the decks with their amazing lineup of offroad machinery. It was no contest against the typical Japanese version of an offroad bike, which was normally a porcine beast that wasn’t ready for serious offroad racing. The 2015 Yamaha YZ250FX is fluff-free.

Q: WHY IS MXA TESTING AN OFFROAD BIKE?

A: Two reasons:

(1) We wanted to.

(2) We really wanted to.

Yamaha’s FX, much like KTM’s XC, should appeal to every hardcore motorcycle racer. It is a bike that can be ridden in the desert, woods, enduros and on trails. And, as the MXA wrecking crew hoped to prove, it could be raced in motocross as well (with minimal modifications).

Q: ISN’T THIS JUST ANOTHER OVERWEIGHT JAPANESE ENDURO BIKE?

A: No. It is true that in the past the “Big Four” have overloaded their enduro bikes with more tonnage than a freight train. If you remember the IT, WR, XT, DT, RS, RMX, DR, PE, KDX, KLX, XR, MR, XL and CRF-X machines, you can easily pick out a small handful of winners (led by the Kawasaki KDX200 and the Honda XR400) in a slew of losers. Where the Big Four flopped, KTM succeeded. Why? Because KTM didn’t reinvent the wheel. KTM took its motocross bikes and added just enough offroad paraphernalia to make them lean and mean. Yamaha followed KTM’s lead with the YZ250FX. The FX is essentially a YZ250F motocross bike with softer suspension, a six-speed gearbox, kickstand and electric start. No fluff, just real stuff.

Q: HOW DOES THE 2015 YAMAHA YZ250FX DIFFER FROM ITS WR250F BROTHER?

A: First, this is closed-course race bike. The previous and current WR250F enduro bikes have been EPA- and CARB-approved. That is pretty much the death knell to racing the bikes. The WRs have intake baffles, restrictive mufflers, unprogrammable black boxes, throttle stops and weigh 9 pounds more than the YZ250FX. Additionally, the WR is very mildly tuned. It is softer, quieter and slower than the YZ250FX (and a lot slower than the motocross-bred YZ250F).

Q: IF IT’S SO GREAT, WHY IS MXA MODIFYING IT?

A: That’s simple. We are motocross racers. Week in and week out, we spend the majority of our time testing, racing and riding on hardcore motocross tracks. Thus, our primary focus is not on offroad, woods, enduro or dual-sport bikes—unless we can race them in motocross also. The MXA wrecking crew does a lot of offroad riding in the hills, deserts and mountains of our SoCal base; it’s just that we don’t need to spend $7890 on a bike that can only do that.

Q: HOW FAST IS THE YAMAHA YZ250FX?

A: It is faster than the 2015 WR250F but not as fast as the YZ250F. No matter what anyone tells you, the YZ250F is faster, quicker and revs higher. Where the YZ250FX shines is in low-to-mid throttle response. It is very lively and accelerates at a brisk pace. It pulls strongly into the midrange and then goes flat. This is where the YZ250F motocross bike really has a major advantage.

You didn’t really think that it was going to be as fast as a YZ250F, did you? It has a mellower ECU map (with retarded ignition timing and lean fuel settings). When you add in the Euro-spec muffler (with its restrictive baffle), lack of high-rpm over-rev and wide-ratio gearbox, you have a very usable powerband that is spread over a broad set of gear ratios.

Q: COULD YOU RACE CROSS-COUNTRY AND A MOTOCROSS RACE ON THE STOCK 2015 YAMAHA YZ250FX?

A: Yes. Beyond a shadow of a doubt. And, to prove it, we did just that.

Offroad: As an offroad racer, the FX is almost perfect. Its perky low-to-mid powerband was perfect for picking our way up rocky uphills. Thanks to its very low first gear and very high sixth gear, we could plonk over rooted trails or run at 80 mph on fast fire roads. The electric starter helped us get out of steep ravines when we stalled, and there was a handy kickstarter just in case we ripped the battery terminals off in a crash. It had amazingly plush suspension; although we bottomed it on occasion, it never felt like it bottomed.

Motocross: We assigned three MXA test riders to race the 2015 Yamaha YZ250FX. We thought they would revolt, but instead they loved the challenge. And when they finished their assignments, they all had minor quibbles, but each rider admitted that it was raceable in stock form—maybe not Supercross-ready, but perfect for natural-terrain motocross.

After the offroad and motocross portions of our test, we asked each test rider what he liked and what he disliked. Then we set out to fix the flaws. Remember, our goal was not to ruin the offroad, trail-riding and GNCC-style racing capabilities of the FX, but to enhance the overall package with an eye toward motocross. Here is what we did and why.

Q: WHY DID WE CHANGE THE REAR WHEEL?

A: The YZ250FX comes with an 18-inch rear wheel shod with a Dunlop AT-81 tire. We wanted to switch to a 19-inch rear wheel—not because the 18-inch won’t work on a motocross track, but because we place our trust in the tires we know best. Most test riders wanted the 19-inch Bridgestone 403/404 tires that come stock on the YZ250F.

There are tricks to swapping to a 19-inch rear wheel. First, it is possible to transplant the complete rear wheel, axle, wheel spacers, brake carrier and axle blocks off of the YZ250F onto the FX; however, if you don’t have a donor YZ250F, this will be very expensive. Since the YZ250FX has a 22mm rear axle and the YZ250F has a 25mm axle, you can’t make a tit-for-tat swap (without buying an axle, axle blocks, wheel spacers and rear brake disc carrier). The best solution is to buy a 19-inch rim, longer spokes (YZ250 two-stroke spokes work) and have the big hoop laced onto the stock FX rear hub.

Q: WHAT DID WE DO WITH THE GEARING?

A: The MXA wrecking crew has turned several KTM 300XC bikes into 300SX motocross bikes, and the wide-ratio, six-speed gearbox was always a problem, which is why we always say that it’s best to start with a 250SX and bolt the 300cc engine kit on it. Motocross demands a close-ratio, slam-bam-thank-you-ma’am set of gears. It is hard to get six wide gears to mimic five narrow gears, and the 2015 Yamaha YZ250FX’s six-speeder was no different.

First, second and third gears are much lower than on the YZ250F, while fourth, fifth and sixth are higher. In offroad riding, this provides a decent balance between the need to go slow in the tight stuff and fast over open ground; however, when racing the YZ250FX in motocross, first gear was useless. Second gear was lower than optimum and very short. Third was the best all-around gear, while fourth was a big reach, and the FX tended to fall off the pipe on the upshift. If you could pull fourth, then you could pull fifth. The only American motocross track that could feasibly need the FX’s sixth gear is the long start at Glen Helen.

With some math, we figured out that if we geared the FX up by going from the stock 13/51 gear ratio to a taller 13/50 combo, we could get the exact second- and third-gear ratios of a YZ250F. This gearing was great out of turns and down short straights, but it made the jump from third to fourth even more iffy. Since the MXA test riders wanted to grab fourth without having to say a few Hail Marys in hopes that the FX wouldn’t bog, we went to 13/52 gearing. By lowering the overall gearing, we made second gear even shorter, moved third into the sweet spot, and made it easier to grab fourth on fast straights.

In the end, we carried 50-tooth, 51-tooth and 52-tooth sprockets wherever we went. If we felt that the track design favored good drive in second and third gears, with less emphasis on fourth, we went with the 13/52 gearing. On tracks that were faster, had longer straights and allowed the test riders to carry more speed through the turns, we ran the broader and mellower 13/51 stock gearing. It was, as with the KTM 300XC, always a compromise.

Q: WHAT ABOUT THE MUFFLER?

A: The muffler that comes on the 2015 YZ250FX is the OEM muffler that comes on European YZ250Fs. The American muffler is a straight-through muffler without any obstructions in the perf core. The Euro muffler has a wing-like deflector in the core. In truth, we didn’t think that the Euro-spec muffler was a big issue, but we took the muffler from our YZ250F and put it on the YZ250FX and were amazed by the performance gain. Obviously, the consumer would be able to do just as well or better by buying an aftermarket slip-on muffler.

Q: WHAT ABOUT THE ECU MAPPING?

A: Unlike on the WR250F, the FX’s black box is programmable with the $291.95 GYTR Power Tuner. Anyone can reprogram his YZ250F, YZ450F or YZ250FX black box in a few minutes with the Playstation-style Power Tuner. All you do is punch numbers into the nine fuel boxes (3-percent change per number) and nine ignition boxes (1 degree per number) to get the setting you want. We richened the fuel 6 percent in the midrange and top end, and advanced the ignition 2 to 3 degrees in every box (see the included map diagram). The new map gave the YZ250FX more mid-to-top power. Throttle response was crisper, and the bike was faster; however, it traded some of the torquey feel of the stock map, and we might be tempted to run the stock map in the woods and the hopped-up map in motocross.

Q: WHAT ABOUT THE KICKSTAND?

A: As hardcore motocrossers, you’d think we would eschew the use of a kickstand, but that thing was sweet. We could come in from a ride, flip the stand down and walk away. Of course, all motocross racing organizations ban kickstands. Thus, we removed the kickstand…grudgingly.

Q: WHAT DID WE DO WITH THE SUSPENSION?

A: Very little. We added 10cc of oil to each fork leg to help hold them up longer in the middle of the stroke. Apart from clicker settings, that’s all we did. As for the shock, we had some issues—not with the shock exactly, but with the rear of the FX chassis. The first test rider who threw a leg over the YZ250FX had his boot bounce off of the rear fender. He regrouped and swung his leg up and over the rear of the FX only to discover that he couldn’t touch the ground with his boots. That was strange, because we had set the sag identically to the YZ250F that we were using for comparison. For some reason the YZ250FX was 15mm taller in the rear. At first we blamed it on the shock, which we discovered was 4mm longer. When we told Yamaha we wanted to install the shorter YZ250F shock, they said that we couldn’t do that because, although the FX shock was 4mm longer, it had 6mm less stroke. Putting the shorter but longer (yes, that’s true) YZ250F shock on could lead to the rear tire hitting the rear fender. When looking at the YZ250FX and YZ250F side by side, it was obvious that the FX swingarm was angled downward more than the YZ250F swingarm, and the seat height was higher as a result. We were about to consult Sherlock Holmes to solve the puzzle when Yamaha told us that because of the FX’s battery box, the rear fender had to be moved up for tire clearance. See, short test riders do come in handy.

As far as the shock went, it worked as well as on a YZ250F, which is very good.

Q: WHAT DO WE HATE?

A: The hate list:

(1) Weight. Remember back in the fourth paragraph where we said the YZ250FX is 9 pounds lighter than the WR250F? That was misleading, because it is 18 pounds heavier than the YZ250F. You can feel that much weight.

(2) Front brake. What front brake? The FX weighs more than a YZ450F. Better brakes would be a nice touch.

(3) Exhaust pipe. Harry Houdini couldn’t get out of Yamaha’s wraparound exhaust pipe if his life depended on it. Luckily, the head pipe and mid-pipe are very good and don’t need changing. The muffler was another matter.

(4) Vent hose. We don’t like the way Yamaha routes the gas vent hose. It’s an eyesore. We drill holes to route the vent hose underneath the airbox cover and out the front.

(5) Battery. The 4-1/2 pound, sealed, lead-acid, Yuasa YTZ7S battery was designed for all-around use, including cold weather. The battery in a KTM is 1 pound lighter. Any aftermarket iron-phosphate battery could save a couple of pounds.

(6) Tires. The stock Dunlop AT-81 tires are good offroad tires, but there are better motocross choices.

(7) Dzus fasteners. We love the idea of Dzus fasteners on the airbox cover but hate the execution. Remove the D-rings or cover the side-mounted ones with tape. Your pants will thank you for it.

(8) Seat height. Although the seat height is a bad deal for an offroad bike, it is what the jacked-up rear end does to the frame geometry that rung the most alarm bells. The tall rear end creates a stinkbug stance and steeper-than-optimum head angle.

Q: WHAT DO WE LIKE?

A: The like list:

(1) Engine. Mechanically, it is identical to the YZ250F engine but detuned for offroad riding.

(2) Suspension. Mechanically, the suspension components are the Kayaba SSS units from the YZ250F but softer.

(3) GYTR Power Tuner. If you want to get the most out of the YZ250FX engine, do yourself a favor and invest in a GYTR Power Tuner, or borrow one from a friend for five minutes.

(4) Clutch. The clutch pull is amazingly light, which Yamaha achieved by going from eight plates to nine, which allowed them to use softer clutch springs.

(5) Electric start. Watts up, baby.

(6) The bike itself. It’s been a long time since the Big Four made an offroad bike this good.

 Q: WHAT DO WE REALLY THINK?

A: There was simple logic in MXA’s approach to the 2015 Yamaha YZ250FX. We loved the offroad capabilities of the FX but wanted to skew it further in the direction of motocross. We didn’t, however, want to turn it into a full-blown motocross bike, because the YZ250F already exists (and is a better race bike by virtue of its lighter weight and more appropriate powerband). We also didn’t want to break the bank, throw the baby out with the bath water or ruin a good thing. So, we made minimal changes and loved the results. But, for most test riders, the jacked-up rear of the bike was a downer.

MXA YAMAHA YZ250FX SETUP SPECS

This is how we set up our 2015 Yamaha YZ250FX for track and trail. We offer these settings to help steer you in the right direction.

KAYABA SSS FORK SETTINGS
Most MXA test riders stayed close to the stock clicker settings (after we added 10cc of oil to each fork leg), with the faster riders going in four clicks. Our slower and Vet test riders loved the softer feel of the YZ250FX forks and thought that they would be good enough to race with in stock trim on everything but a jump track. There is a risk of bottoming when you drop three spring rates and lighten the low-speed compression damping. For hardcore racing, we recommend this fork setup for the 2015 Yamaha YZ250FX (stock specs are in parentheses):
Spring rate: 4.4 N/m
Oil quantity: 345cc (335cc)
Compression: 11 clicks out
Rebound: 11 clicks out
Fork leg height: 5mm up
Notes: Most of the fork’s internal components are exactly the same as the YZ250 forks; however, the fork-valve shim spec is stacked much differently and the springs are 27mm shorter and three rates less compared to the YZ250F’s (4.4Nm to 4.7Nm). There is less low-speed compression and rebound damping for a plusher feel, especially over small bumps. The high-speed compression has been increased for more bottoming control.

KAYABA SSS SHOCK SETTINGS
Our most noticeable shock change was the 108mm of race sag. We did this to lower the rear of the chassis to help balance out the handling issues caused by the Yamaha engineers raising the rear of the chassis to accommodate the battery. For hardcore racing, we recommend this shock setup for the 2015 Yamaha YZ250FX (stock specs are in parentheses):
Spring rate: 56 N/m
Race sag: 108mm (90mm to 100mm)
Hi-compression: 1-1/2 turns out
Lo-compression: 10 clicks out
Rebound: 11 clicks out
Notes: The shock body is the same as on the YZ250F, however, the eye-to-eye length is 4mm longer (462.5mm to 458.5mm) and the stroke is 6mm shorter (128mm to 132mm). Rear-wheel travel is 15mm less for more fender space to make room for the battery (and the seat is raised up 15mm). As for the damping, the shim stack is different than on the YZ250F, but the spring rate is the same. Compression damping is more progressive because of the shorter shock stroke, while the rebound damping has less low speed and more high speed.