2011 Aprilia RS4 125

Aprilia’s outgoing RS125 has been living on borrowed time. There was nothing wrong with its performance – with about 34bhp from 125cc, it was a fireball compared with most rivals – but its power advantage was a blast from the past. It was the last of the high-performance two-stroke motorcycles, which meant its power-to-weight ratio far exceeded any comparable four-stroke, as did its noxious emissions.

Aprilia shoehorned the RS125 through Euro 3 emissions regulations with a mix of strangulation and catalysts, but the more stringent Euro 4 standard spelt its downfall. Finally the unthinkable has happened: Europe’s most popular sports 125 (100,000 units manufactured) has been superseded by a four-stroke.
The new bike’s specification is impressive. The little single-cylinder engine has fuel injection, double overhead cams and four valves, but the output is governed by Europe-wide legal requirements for learners and peak power is just 15bhp – less than half its forebear’s.

The styling should cause more than a few stirrings among teenagers, however, with bodywork that’s so close to the look of the RSV4 superbike that at first glance you could easily mistake the 125 for a 1.0-litre machine – especially since one colour option is a replica of Max Biaggi’s Superbike World Championship winner.

Oddly, when you swing a leg over the 125, there’s more space than on the superbike, which is the tiniest and most cramped in its class – in contrast, the 125 is one of the largest of its type, on the perfectly reasonable assumption that youngsters old enough to ride it might be in their teens or early twenties, but they will be fully grown. The riding position is more upright than that of the RSV4 superbike and provides more legroom, so despite the sporting pretensions it’s a comfortable place to be.The RS4 isn’t quite the all-new bike Aprilia implies, however, because it’s closely based on sibling-brand Derbi’s GPR 125. The two share a frame and the engine is from the Derbi, too, with the injection replacing a carburettor and a new cylinder head and piston.

It goes well enough, propelling the sharp-steering chassis to an indicated 70mph or so, but you need to grab a handful of revs to stop it bogging down when you pull away. It also feels flat when you rev it past its 10,500rpm power peak, but it’s pretty strong in the mid range.

What you really need is Aprilia’s £700 race kit. It’s illegal for learners, but it’s worth considering once the test has been passed because it boosts power to a much-healthier 25bhp. It’s still not a patch on its two-stroke antecedent, but a lot livelier than the standard bike’s 15bhp.

I can’t comment on the precise package you’ll get from your Aprilia dealer because the test bikes on the track-only launch used costly, sticky Pirelli Supercorsa tyres in place of the usual Sava MC25 Bogart rubber from Slovenia, and the chassis was lightly tweaked to sharpen the steering.

I wish they wouldn’t do this, but I still think it’ll be one of the best-handling bikes in the sector.



Aprilia RS4 125
Price/on sale: From £3,999/now
Power/torque: 14.8bhp @ 10,500rpm/8.6lb ft @ 8,000rpm
Top speed: 70mph
Fuel tank/range: 3.2 gallons/270 miles
Verdict: Great for what it is but highlights the loss of the peppy two-stroke. The playing field is levelled by engine type and legislative power limits, so cheaper 125s will perform well, but the RS4’s handling and styling have an edge.