Aprilia RS125 v KTM RC125

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Two-stroke versus four-stroke; nostalgia versus contemporary; a noisy, belligerent pain in the cock versus a leisurely lifestyle and a soundtrack that resembles a Flymo. Yes, we’re talking Aprilia’s RS125 versus KTM’s RC125. The RC125 is the pick of the four-stroke learner brigade. While the Japanese variants are smoother and more refined, the KTM is certainly the sportiest and brags genuine big-bike substance: partly because it was developed simultaneously with the bigger RC390. It’s also brimming with neat little trinkets such as the machined assortments and dummy race seat, that’s actually a rubberised pillion base.

Meanwhile, in the stinking two-stroke corner, Aprilia’s iconic RS125 is responsible for launching numerous road-racing careers and teenagers’ high street parades. Having been discontinued a few years ago in favour of the four-stroke RS4, a fairly mint RS can be prised from the used market for around £1,500 – a third of the KTM’s asking price. Is it worth the bargain?

On the day of 2015’s general election and clouded by a veritable feast of political bullshit, 44Teeth were armed with two of the funkiest offerings for restricted licence holders and doing it for the kidz. We trekked from Bristol down to Cheddar to sample these pocket rockets and enjoy Somerset’s finest stretches of Tarmac, plus the fabled Mendip TT course. To end things nicely, we ended at South West Karting’s indoor, erm, kart track for a session of fairing bashing to settle the score.


Despite the threats of austerity associated with its £4,499 price tag, Baron von Tory jumped straight for the KTM. I’m more of a liberal – you know, favours brown bread and partial to a finger in the botty, and was left with the keys to the Aprilia by proxy. I’m from an era when only two-strokes will do: the smell, the noise, the involvement. The simplistic engineering means they’re easier to work on/maintain/tune, and ultimately they’re faster. Much faster.

As we set off towards Cheddar and exited suburbia, it was immediately apparent Baron and the hairdryer KTM couldn’t match me and the rampant Aprilia, even with my tubby ass labouring power-to-weight ratios. He had me in first gear, leaving the lights at a standstill thanks to the RC’s four-stroke punch and (very) low-down grunt. Everything else was an embarrassment for the KTM, but let’s not mince our words here: this Aprilia is tuned to within a mosquito’s pube of its life.

By the time the RC has painstakingly reached its 70mph summit (75mph downhill with tailwind assistance), the RS is striding into top gear at 90mph with another few thousand revs to abuse. The gap in straight-line performance gap is seismic, as is the subsequent faffery that comes with handling such a beast.

A third of the price, the Aprilia also boasts three times the power…

Pulling away on the KTM couldn’t be any easier, regardless of its insanely short first gear. The controls are fluid and intuitive, light on your limbs and a doddle to use. It also fuels brilliantly, with a quirk-free, linear delivery. Then again, with 15bhp, it’s tricky not to be linear and sumptuously smooth, even for a single-cylinder.

It couldn’t be any different aboard the Aprilia. Only a fistful of revs and a patient clutch action will cure launches, although you can revel in the RS’s crisp (when it’s running right) powerband and narrow working parameter of useable revs. It’s the dirtiest, fluffiest, most irritating bike I’ve ever ridden below 5,000rpm, like it’s being run on camel spunk before becoming a smidgen more tolerable until the banzai go-zone erupts at 8,000rpm. Once there, it’s a joyous occasion and would give bigger capacity A2 bikes a damn good spanking.

Every excess millimetre of exposed limb punishes aerodynamics on this pairing, likewise unnecessarily easing off the throttle. As Baron touched on during his video rants, there’s a lot to be said for caning smaller capacity bikes: poncing around on bullish superbikes only masks riding deficiencies, and it takes a fair amount of extra forward planning for overtakes and judging corner speed.


The Aprilia’s engine may be highly strung but the chassis remains standard. Even in stock trim, the RS mimics a race bike for the road, nervously enthusiastic to fall on its side and you have to be balls-on-the-tank committed to every corner. At 126kg, the Aprilia is also nearly 10kg lighter than the KTM and that’s evident from the off. A culmination of the RS’s featherweight stance and complete lack of engine braking ensure a continuous passion for scarpering manically into bends, and the occasional panic braking moment. Given its state of tune, it’s no surprise that gear selection is vital aboard the Aprilia and we never quite found the perfect recipe of revs and gearing throughout the day, in any corner.

Entering the myriad of Cheddar Gorge’s twists and turns, it wasn’t long before I was holding up Baron and the KTM. The RC is simply easier to ride and fills you full of confidence from the start. It brags big-bike mannerisms, with perfectly neutral steering that’s just as perfectly controlled throughout its bank of lean, and while it may not be as devilishly sharp as the Aprilia, it’s also more precise, more fluid. The KTM is a step up in dynamics from the sparrow-limbed Honda CBR125 and, even with its budget OE rubber fitted, the RC can carry serious (and surprising) corner speed to accompany decent lean angles. Even the economical braking paraphernalia is ample for fast road sorties, as is the just-as-budget WP suspension.


At the end of a day riding the Aprilia, I developed a headache that rivalled a post-festival hangover. Accidently swallowing a litre of Spanish über fuel may have been a contributing factor, though the two-stoke clatter and idiosyncrasies no doubt also claim portion of the blame, and Baron is now permanently scarred after his brief encounter with the RS. But it was a fun-filled day on two very capable but hugely dissimilar learner steeds.

At that early stage in life, looking good and attracting gusset is as vital as anything else. Nowadays, in this modern society, I fear the Aprilia’s lack of contemporary etiquette may actually avert the female species. As much as I lust after a sorted RS125, KTM’s RC125 is the finished article and sits firmly on top of 44T’s learner recommendations. It may be horrendously slow but the RC is a proper little sportsbike. Want more technical bumph? Read it here









aprilia2Tuning an Aprilia RS125: At the age of 13, Will Holland was rebuilding my Triumph Daytona 675 British Supersport engines, so tuning a 125cc engine is a doddle. He owns this Aprilia.

The standard RS125 is a far less brutal affair, calmer to ride and a shit-load slower. A well-jetted derestricted version with an Arrow exhaust should punt out a genuine 23bhp. Aprilia claim the restricted, fully legal RS is limited to 15bhp. The derestriction comes via butchering the ECU and is well documented. Depending on the model, you’ll have to change the exhaust to ditch the catalytic converter. Unblocking the air intake tubes also aids horsey hunting. To see 31bhp on a very modest dyno, you’ll need a 34mm racing flatslide carburettor, which boosts power to around 26bhp.

Next up on Will’s list of tuning were some carbon reeds and a small airbox modification. This didn’t really give a horsepower hike but sounded nicer. Will then ‘tackled’ the engine – tackled, like a rugby player branding a Dremel, being the operative word – and started with skimming the cylinder head to bring the squish down a little, but didn’t really raise the compression too much. The head work alone allowed the one-dinger to reach 28bhp.

Next was a ‘road tune’ to the barrel: modified the inlet port, cleaned up the transfer port and exhaust port, basically got everything flowing better with no sharp edges. Following this was a reworked cylinder head and blanking off the powervalve, which gave a little over-rev. After a catastrophic engine failure, Will carried out a full engine rebuild and superfinished most of the internals, plus a roller bearing conversion to the big-end, a new con-rod, a Suzuki RM125 single-ring piston and a higher ‘race’ tune that got 30bhp. More head work and port reshaping got the magical 31bhp.

Before test riding a KTM RC125, Will was planning such delicacies as programmable ECUs and writing his own ignition curves, but even he fell for the KTM’s easy-going charm factor and is currently hunting down an RC for ownership. If you’re man enough, his Aprilia is now for sale…

Man love goes to: Will Holland for the Aprilia, South West Karting for hosting the race of 2015. Full vid coming soon.

This actually happened

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