Launch: 2015 Yamaha YZ250F and YZ450F

Twenty-fifteen motocross bikes are on the move and if you've been out of the scene for a while you may be wondering which way to get back into it – 250F or 450F? Thanks to Yamaha Motor Australia and the launch of the 2015 YZ-Fs I had the chance to not only see how far things have progressed in a few years but to work out which Yamaha is best suited to a 40-plus weekend wannabe who's keen to be back in the dirt.

Rocking up to Queensland Moto Park for the launch I was met by Yamaha Australia's Scott Bishop who was keen to get me straight onto the 450, for entertainment value, no doubt, while Serco Yamaha's Michael Marty was far more compassionate and insisted I wait for the 250F before stepping up to the big league. Did I have something to worry about when it came to the 450? Before I'd have the chance to find out at least three other riders warned me about the power of the YZ450F.

I saddled up on the 250F first and wow, how things have changed! If you replace bikes every season and you're looking to update your 2014 YZ250F to the 2015, the changes won't blow your mind, but if it's been a while between new bikes the 2015-model will deliver a whole new experience.

It was a good thing race team mechanics were on hand to fill up, because I wouldn't have even known how to fill the fuel tank. The fuel filler is now hidden beneath the front section of the seat. Just yank out the front 100mm of seat foam and fill her up! Unlike the 2013 YZ250F and every model before it, there's no carburettor and the exhaust exits the rear of the cylinder, not the front. Oh, and the air filter is tucked under a plastic shroud between the front of the seat and the handlebars. Incidentally, this plastic shroud is held in place with three quick-release fasteners for 2015. Last year it was bolted on. Sure it's handy not needing tools to get to the air filter, but the race teams will likely go back to bolts for maximum security. I had some serious catching up to do!

Yamaha's 2014 model YZ250F was where the big changes were made and where it was transformed to be in line with the 450F that was completely revamped back in 2010. The '14 250F was a completely new package, featuring the reverse-cylinder engine design, its first taste of fuel injection, new frame and new suspension components to suit.

For 2015, the changes are less dramatic. Fuel injection and ignition settings have been tweaked to pump up mid-range power, the design of the piston has been modified, the bike's been made easier to start through changes to the exhaust camshaft and throttle action has been lightened. The standard blue version of the 250 and 450F score factory-looking black rims and, of course, new graphics adorn both bikes.

The beefed-up mid-range is the most notable upgrade for the '15 250F and it's definitely a tweak that's felt on the track. Earlier model Yamahas and most other 250Fs had to be kept in the engine's sweet spot to pull hard out of turns. With surprising mid-range power from the new YZ250F, I could get away with mediocre corner speed and still have the bike pull strong out of turns in third gear. I was so amazed at the engine's ability to do this I pulled off the track a couple of times to confirm I was still in third gear.

The 250F doesn't just impress with its chunky middle, it's also sharp and responsive off the bottom and keeps making power high in the revs when you feel you should be grabbing the next gear. In a race situation, this bike will impress with its over-rev capabilities that will enable riders to hold a gear rather than having to upshift.

The new YZ-F produces impressive power for a 250 four-stroke, but sadly I don't think it has the sound to match. Perhaps it's one of those changes I'm yet to get used to, but instead of hearing a healthy exhaust note, what I noticed more was the sucking sound coming from the airbox that's now in front of the rider, rather than buried within the subframe like it was in the good ol' days. The race-prepped championship-winning YZ250F of the Serco Yamaha team was also being ridden at the launch and with a Yoshimura exhaust system it sounded a whole lot tougher than the stockers.

In a class where power is everything, the new YZ-F is right on track and will provide a competitive platform to go racing. But the good news doesn't end there. The new blue bike is also a top handler. Weighing in at 60kg, I'll always go straight for the fork and shock clickers to soften the ride, but the race team mechanics at the launch encouraged me to have a ride before making any adjustments. The only thing I had adjusted all day was the height of the clutch lever! Serious racers are likely to fine-tune the suspension to suit themselves and the tracks they're racing on, but the rest of us would find it hard to fault the way the stock Yamaha handles.

The 2015 YZ250F truly feels like a bike you could race straight from the showroom floor. Just grab an aftermarket pipe for a cooler exhaust note on your way out the door.

Like the 250F, the 2015 YZ450F hasn't been radically updated. It's also had tweaks to the fuel injection and ignition settings, but with a different goal. Yamaha has focussed on smoothing out the power of the 450F. It seems the main criticism of the YZ450F since its re-invention in 2010 has been its rideability and Yamaha is obviously focussed on making the powerful beast easier to ride.

When I first jumped on the 450F, it was just to get action photos in the can. My intention was to hand it straight back to the journo I'd “borrowed” it from, but up until my forearms packed up for the day, I couldn't get off it. There's no way I can ride this or any other 450 MX bike to its full potential, but the power of the YZ450F is so immense you just can't help but be impressed. It's got grunt right from the get-go and feels like it has a rev ceiling you'll never reach. It's incredible!

A good portion of my time on big blue was at low or no throttle. That might sound like I didn't give it a thorough test, but not even pro riders Josh Coppins and Jacob Wright were wringing its neck. The YZ450F has so much power it makes pace without the need for mega revs.

Almost as impressive as the power is the way the 450 handles. The YZ450F would barely know I was on its back. I wouldn't have been surprised if it threw me off at the first square-edged bump , but the ride was amazingly smooth. Like the 250F, the standard suspension settings were unchanged. So much of my time on previous 450 four-strokes has been spent trying to find a suspension setup to suit my size, or lack of it. To jump on a stock 450 and feel comfortable with its handling characteristics was a revelation. If the 2015 YZ450F feels this good out of the box imagine how awesome it could be when dialled in to suit the rider.

After a day on the latest YZ-Fs, the choice between 250 and 450 was simple. The YZ450F is so impressive I'd love to own one, but without dedicating serious ride and physical training time I wouldn't get close to riding the YZ450F to its potential or for any decent length of time. However, I could see myself and plenty of other riders throwing a leg over the YZ250F whenever the opportunity arises without the need to train like a madman just to enjoy the ride. I'll take a new YZ250F, the special edition red and white model, please.

TRANSMISSION
Type: Five-speed
Final drive: Chain

DIMENSIONS AND CAPACITIES
Claimed wet weight: 105kg (including oil and fuel)
Seat height: 965mm
Wheelbase: 1475mm
Overall length: 2170mm
Minimum ground clearance: 330mm
Fuel capacity: 7.5 litres
Oil tank capacity: 0.9 litres

TRANSMISSION
Type: Five-speed
Final drive: Chain

DIMENSIONS AND CAPACITIES
Claimed wet weight: 111kg (including oil and fuel)
Seat height: 965mm
Wheelbase: 1480mm
Overall length: 2180mm
Minimum ground clearance: 335mm
Fuel capacity: 7.5 litres
Oil tank capacity: 0.9 litres