Moriwaki MD250H vs Aprilia RS125 Shootout

Two-stroke against four-stroke track bikes


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Modern sportbikes are wonders of technology, packed with aircraft-grade aluminum, magnesium and titanium. And yet, most street-going sportbikes scale in at ready-to-ride weights of more than 400 pounds.

So, how about if you could have a sportbike that weighs fully half of what a Yamaha R6 does?

Well, the Moriwaki MD250H fits the bill, with a sub-200-lb claimed tally of pounds.

So we loaded up the race-only Moriwaki alongside a revvy Aprilia RS125 two-stroker and headed off to the Streets of Willow racetrack to gauge the performance of these GP-bred tiddlers.  Despite ultra-modest power output, the ring-dinger and the thumper were able to dance around much more powerful literbikes thanks to their incredible agility. Our day at a Fastrack Riders event was more thrilling than it would’ve been with larger and more powerful bikes, and it proved to be one of our most memorable days at the track.

On the left is the Moriwaki MD250H powered by a four-stroke Honda motor. On the right is the Aprilia RS125, one of the last sport motorcycles available with a two-stroke engine.

Changing of the Guard?

When the opportunity to test these bikes together opened up, we envisioned the shootout as a two-stroke-versus-four-stroke comparo, delving into the positive attributes of each. However, it soon became apparent the Moriwaki is a pure-bred racebike while the Aprilia is a hot-rodded streetbike. As such, the differences were too huge for a true shootout, but our findings were nevertheless interesting.

Aprilia RS125 – Almost Streetable

The RS125 is a mixture of disparate qualities. On one hand(lebar), it’s a tiddler GP bike in the traditional sense, characterized by its two-stroke 125cc engine. The RS125 comes by its Grand Prix persona authentically, as Aprilia has had much success in the 125cc and 250cc GP categories. The RS comes equipped with the racing livery of Jorge Lorenzo’s 2007 world championship-winning 250cc GP bike, a Fortuna cigarettes sponsor that displayed “Spain’s No.1” in countries where tobacco sponsorship is outlawed.

Aprilia leans on its multitude of roadracing world championships to deliver its two-strokin’ RS125. Although street-legal in Europe, American imports are limited only to racetrack use. Italian exotica doesn’t come any cheaper than its $5,499 MSRP.

On the other handlebar, the RS125 has few parts in common with Aprilia’s actual 125cc GP bike. This RS is instead built for an entry-level sportbike rider in Europe, so it is a larger, heavier and less powerful machine than its GP brethren. It’s also cleaner, incorporating a catalytic converter in European versions to meet emissions regulations.

Unfortunately for North Americans, the RS125’s tuning can’t meet our EPA regs, so the little Aprilia is imported only for racetrack use. U.S.-spec RS125s are shipped with a power-up kit that includes a freer-flowing exhaust system, a new ECU with special tuning for the race-type exhaust valve, and tweaked jetting for its 28mm carburetor.

Moriwaki MD250H – Breeding improving the race

Japan’s Moriwaki Engineering plucked four-stroke Honda CRF250X dirtbike engines and installed them in a bespoke aluminum beam grand-prix-style frame as an evolution from the 125cc two-stroke GP engines. It is perhaps the narrowest four-stroke motorcycle you can buy.

Japan’s Moriwaki Engineering has long history of building racebikes, and the MD250H is what it sees as the evolution of the 125cc two-stroke GP racing platform, recognizing the gradual extinction of two-stroke motorcycle engines.

As in motocross, the theory is that a 250cc four-stroke powerplant is roughly the equivalent of a 125cc two-cycle engine, so Moriwaki hatched a deal with Honda to supply the liquid-cooled 250cc single-cylinder powerplant from the CRF250X off-road dirtbike.

"...the Moriwaki is built from the ground up as a pure racing machine..."

The MD250H borrows heavily from the Honda RS125 racebike platform, using its fork, wheels, brakes and radiator attached to a bespoke Moriwaki-designed aluminum twin-spar frame designed to hold the Honda dirtbike engine. Moriwaki also builds its own swingarms and exhaust systems.

Unlike the Aprilia, the Moriwaki is built from the ground up as a pure racing machine, and it’s so tiny that the RS125 looks like a liter-sized sportbike in comparison. Its wheelbase of 48.4 inches is nearly 10 inches shorter than a Ducati Streetfighter, and its claimed tank-empty weight of just 194 pounds is about 200 pounds less than a GSX-R600!

Corner Speed Connection

With only around 30 mild but enthusiastic horses at the rear wheel, these lightweights rely on corner speed to yield quick lap times. And what fun it was riding around the outside of literbikes ridden by moderately talented trackday pilots! It was oddly and deeply satisfying to keep the throttle pinned through the track’s Turn 1 kink on both bikes.

Tearing around on these tiddlers at Streets of Willow was hugely entertaining.

We need to give a shout-out to the friendly crew at Fastrack Riders who let us barge in to their event. For more about the trackday provider, check out this article we wrote.

I couldn’t wait to sample the racy Moriwaki, so I quickly called dibs before Pete did. Swinging a leg over its short 29.0-inch seat is ridiculously easy, but finding the ultra-rear-set footpegs is a challenge. Tight ergos require much folding of limbs – this wouldn’t be a good choice for those who shop at the Big & Tall store. Unlike most GP bikes, this one fires up with electric assist.

With just 15 degrees of steering sweep to each side, the MD’s turning radius is approximately the same as a Kenworth’s. It is so limited that no less than two (!) journos from another magazine tipped it over while turning around in the pits at a previous test!

The MD250H is an amazingly potent track tool.

It's a well-worn cliché to say, “You only have to think about a turn and you're leaning into it,” but it's truly not hyperbole with this bike! It’s so responsive that it requires several laps before your gray matter can tune in to its incredible agility. A 24.5-degree rake and 122mm of trail don’t sound very aggressive, but the bike is so light and the wheelbase so short that it can be bent onto its side in less time than you can say MotoGP.

“Truly telepathic steering response!” raved Senior Editor Pete Brissette. “I’ve never ridden a bike that’s so sensitive to the slightest change in body position or minor steering inputs. It’s almost unnatural. My first session or two on the MD was spent learning to not over steer or apex multiple times in some of the larger turns.”

Feedback at both ends is very direct, especially through the spindly-looking but effective 35mm fork and its low-mount clip-ons. The MD is very low and mass-centralized, and its little 1.8-gallon fuel tank is filled with a high-tech foam insert that eliminates fuel sloshing that can subtly alter weight distribution when accelerating and braking.

The Aprilia RS125 is considerably larger and heavier than the Moriwaki, but it still comports itself well on a racetrack.

Super-narrow (95/70-17, 115/70-17) slick-type Dunlop KR racing tires contribute to the Moriwaki’s nimbleness, and we were impressed with their grip, never really finding their limits. “Never any question of loss of side grip,” Pete notes, “and they translated plenty of feel.”

In comparison to the diminutive MD250, Aprilia’s RS125 seems like a 600cc sportbike, with much roomier and humane ergonomics that can accommodate full-size adults. Aside from its engine displacement, everything is bigger with the Aprilia – including its weight, about 100 lbs heftier than the Moriwaki.

The RS125 actually steers with 600-killing dexterity, but it requires much greater effort to turn quickly than the incredible Moriwaki. A lazy 25.5-degree rake and wider tires (110/70-17, 150/60-17) contribute to its blunter handling.

“The Aprilia has a stable and responsive chassis, but still not as lightning-quick steering as the Honda,” says Pete.

Similarly, the RS125’s suspension isn’t in the same league as the MD250, with softish, street-biased springs and shock preload the only adjustment. Conversely, the higher-end Showa suspension on the Moriwaki is race ready with full adjustability. The racetrack also revealed the Aprilia’s relative lack of ground clearance, as there was more than enough grip from the Dunlop GPR-A tires to scrape its footpegs

The RS125 is equipped with Aprilia’s typically excellent detailing, but the Moriwaki exemplifies a higher level of componentry and refinement.

The RS125’s braking performance is quite good, as it uses a large 320mm single-disc brake and a radially mounted 4-piston differential-bore caliper. However, it can’t top the exemplary feel and performance of the Moriwaki’s Nissin 4-piston caliper biting on a 296mm floating rotor. Having to slow 100 fewer pounds contributes greatly to its ability to get it quickly slowed.

Engine-eering

Both bikes are powered by a liquid-cooled single-cylinder engine fed by a carburetor, and that’s where any similarities end. The Aprilia is handicapped in this comparison because of its street-legal roots. A full-race 125cc two-stroke GP motor will annihilate the Moriwaki’s CRF250X mill in terms of peak power.

Despite the Aprilia’s power-up kit, its 125cc two-stroke motor struggled to keep pace with the four-strokin’ Moriwaki.

The two-stroke Aprilia RS125 engine was co-developed by Rotax, and it incorporates an anti-vibration balance shaft, crankcase reed-valve intake and an oil-injection system to automatically mix oil with fuel. Some Aprilia scooters use “Pure Jet” technology to clean two-stroke exhaust emissions, but the company’s Rick Panettieri says its addition to the RS125 would bump up the MSRP by about $1,500, giving it an unappealing $7,000 price tag for such a lightweight street machine.

As expected from a small two-cycle engine, torque isn’t a strong suit. It needs to be turning at least 7500 rpm before any meaningful power is delivered, and peak torque (if you can call it that) of 17.6 ft-lbs arrives way up at 10,000 rpm. Max horsepower of 27.0 hits just 250 rpm later, and power falls of precipitously almost immediately after. Despite the racier pipe and ECU tuning, the motor feels corked up. Much of every lap was spent with the throttle at its stop.

This narrow range of power forces a rider to be precise during every gear shift, as there’s not much pull on tap even when in its optimum rev range.

“The 2000-rpm powerband range is too small,” Pete laments. “It demands the bike be on the pipe almost all the time. If I weren’t well into the powerband, or even a bit beyond, into over-rev, shifting would drop me out of the powerband.”

Rev for rev, the Moriwaki’s 250cc four-stroke motor out-muscles the limper Aprilia two-stroke mill.

Thwarting perfect shifts is a gearbox not as slick as we would like. The two-cycle motor supplies almost non-existent engine braking, making the first few corner entries more adrenaline-inducing than expected.

The Honda-sourced four-stroke mill in the Moriwaki feels muscle-bound in comparison. Aside from being reluctant to pull full throttle cleanly until 6000 rpm, it proved to be incredibly cooperative with its broad spread of power. Thanks to Gene Thomason Racing in Torrance, California (310/618-1908) which strapped these bikes to the dyno for accurate rear-wheel power figures.

The MD’s motor tugs surprisingly strong from 8000 to 12,000 rpm, aided by the bike’s scarcity of mass. Peak torque of 17.6 ft-lbs hits at 7500 rpm, so there’s enough grunt to allow a short-shift and still maintain a quick pace, even able to run a gear high without losing much time. A maximum of 32.6 hp is reached at 11,000 rpm, and there’s a generous 2000-rpm over-rev zone in which power gently tapers off.

This torque dyno chart dramatically demonstrates the Aprilia’s grunt disadvantage.

“Using this tiny 250cc Single to chase down 1000cc superbikes was nothing short of invigorating fun!” Pete exclaims. “Once again I realized that it’s much more entertaining to go fast on slow bikes than to go slow on fast bikes.”

Current 125 GP racer Daytona Anderson tearing it up on the four-stroke Moriwaki. This 12-year-old rips!

The burly sound the thumper emits belies its small displacement. The 250X powertrain has some wide gear spacings in its 5-speed tranny, so it's sometimes preferable to rev it out to the 13K rev limit so engine speeds don't drop too low during upshifts. The gearbox is smooth and slick, and there’s barely any engine braking so there's no real need for a slipper clutch.

If there’s a negative about the Honda CRF250X motor, it’s that it’s not the more powerful CRF250R motocross bike engine that can better compete with race-spec 125cc two-stroke powerplants. Competitive power is said to be available by bolting in the 250R’s lumpier camshafts.

As it is, the 250X motor doesn’t have the top-end pull of a 125cc two-stroke such as a Honda RS125 like we got to sample for a few laps. Raced by 12-year-old Daytona Anderson, the Honda GP bike accelerated much more vigorously at full revs, a result of more power and slightly less weight. It would be quicker than a stock MD250H in the hands of an expert, but it was so incredibly peaky that it was very difficult to manage. I surely turned  better lap times on the easier-to-ride Moriwaki.

After winning the SCMiniGP overall title in 2009, Anderson is devoting the 2010 race season to riding his 125 in WERA and USGPRU competition (which both have classes and generous contingency programs for the MD250H). The kid shows amazing speed for being so young and only recently beginning racing on pavement. Keep an eye on him at DaytonaAnderson.com.

The ultra-peaky powerband of Anderson’s Honda RS125 racebike proved tricky to master.

The Verdict

This bike pairing was brought together by their small displacements and track-only intentions, but yet they exist on different planes altogether. The MD250H is a pure racing machine, stripped down to the bare minimum to achieve the ultimate goal of quick lap times. Its Honda engine is superior to the Aprilia’s lump in every performance measure, and its one-third less weight is a huge advantage when cutting fast laps.

The MD250H is a stunningly intoxicating motorcycle. Pricey, though.

Our seat-of-the-pants impressions were corroborated by Fastrack’s lap timers. Pete went 3.1 seconds faster on the Moriwaki, and I clocked a time 6.3 seconds quicker on it. Let there be no doubt the MD250H gets around a racetrack more rapidly than the RS125. There were several track sessions in which not a single rider overtook the scything Moriwaki.

"Let there be no doubt the MD250H gets around a racetrack more rapidly than the RS125."

However, GP levels of performance don’t come cheap. The Moriwaki has a retail price of a haughty $12,699, more than twice the RS125’s MSRP of $5,499. Also factor in a larger chunk of change when it comes time to rebuild the more complicated four-stroke powerplant. Considering the Aprilia’s rational ergonomic package and its exotic nature despite a reasonable price, a convincing case can be made for the highly amusing Italian bike. 

The Aprilia RS125 is a more accessible bike in terms of both ergonomics and price.

“Despite the Aprilia’s lily-livered power,” says Pete, “I think I’d still prefer it to the MD for the simple fact that its ergos are more sensible for adults, even shorter folks. And considering the MSRP is around half that of the MD, I could spend, I dunno, another $3Gs to tune the engine and upgrade the suspension, and still have money left over to spend on finding someone willing to legalize (wink) the Aprilia for the street.”

But if you’re looking for a small-bore track bike, the Moriwaki/Honda machine has much higher capabilities that proved to be endlessly entertaining. It must have been demoralizing for the ZX-10R and CBR1000RR riders at Willow who were regularly ridden around the outside of turns by the toy-sized Moriwaki. But those frowns were totally upside down inside the helmets of the MD250 rider screaming around the track with improbable speed. It makes a rider feel like an underdog even though he or she might have the best bike on the track.

The MD250H’s combination of track focus, composure, extremely light weight, incredible agility and shockingly flexible engine gives it a personality and effectiveness that can’t be matched by any other production machine. The price is lofty, but the rewards are extraordinary.

Chasing each other around the racetrack has rarely been this much fun.

Tale of the Tape – Specs at a glance
  Aprilia RS125 Moriwaki MD250H
Engine 124.8cc 2-stroke 249.4cc 4-stroke
Bore/Stroke 54.0 x 54.5mm 78.0 x 52.2mm
Rev Limit 10,750 rpm 13,000 rpm
Peak HP 27.0 hp at 10,250 rpm 32.6 hp at 11,000 rpm
Peak Torque 13.9 ft-lbs at 10,000 rpm 17.6 ft-lbs at 7500 rpm
Transmission 6-speed 5-speed
Chassis Twin-spar aluminum Twin-spar aluminum
Rake 25.5 degrees 24.5 degrees
Trail 102mm 122mm
Wheelbase 52.9 inches 48.4 inches
Seat Height 31.7 inches 29.0 inches
Fork Diameter 40mm 35mm
Front Brake 320mm, 4-piston caliper 296mm, 4-piston caliper
Fuel Capacity 14 liters (3.7 gals) 7 liters (1.8 gals)
Claimed Weight 302 lbs (street-equipped) 194 lbs
MSRP $5,499 $12,699

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