Everybody knows that 2-stroke engines can produce more power than a comparably sized 4-stroke. The RS125 can be tuned to around 33 horsepower, whilst the RS4 125 can only get to about 25 horsepower with a 180cc kit. The RS4 125 canít replace the RS125 performance-wise, but it does benefit from a reliable torquey 125cc four-stroke engine that doesnít need a rebuild every 10,000 miles. The RS4 125 is also more environmentally friendly using less fuel and oil compared to the 2-strokes.
I tested the RS4 125 in a learner-legal version that generates 15 horsepower at 10,500 rpm. Peak torque of 8.1 ft-lb occurs at 8500 rpm. Its 75-mph top speed enables safe riding on motorways, and the engine isnít going to blow up after long runs on the highway. The four-stroke torque curve enables cruising from 8,500 rpm and a very decent fuel range.
I, however, tested on a race track, so I spent pretty much all the time testing in the range between 10,000 and 11,000 rpm where the engine pulls much better than anywhere else in the power range. Itís a narrow range for riding fast, and I quickly found out that losing revs must be avoided at all cost. Compared to a 2-stroke, though, thereís plenty of midrange. I had lots of fun slipstreaming the other journalists on the circuit just like they do in the 125 GP championship, but it got slightly boring as soon as I found myself without anybody to chase down.
The brakes on the RS4 125 are very sharp, consisting of a 300mm disc and a 4-pot radial calliper. I hardly used the 200mm rear brake at all as, letís face it, the speed needed to be brushed off was never great.
The RSVís dry weight is a claimed 295 pounds, which is a lightweight for a 4-stroke but about 30 pounds heavier than an RS125.
Iím quite large for the RS4 125, but in the pictures you could briefly think that Iím on the RSV4 rather than the RS4. The suspension is not adjustable, and to my surprise Aprilia has found a good standard set-up as I had nothing to complain about chassis-wise. I presume the small motorcycle handles even better with a lighter rider, which I again presume most 16-year-olds are. The tires are of sizes 100/80-17 front and a 130/70-17 rear.
I was impressed with the amount of ground clearance when leaned over, and I noticed a considerable loss of revs as soon as I went from full lean to upright position due to the taller effective gearing of the larger part of the tire. I was not aware of this initially, as I sometimes shifted up at full lean, which is natural on a large-capacity bike. But on the 125, itís best to just use the motorís over-rev zone to better transition as the bike is lifted upright on corner exits. Thereís still not enough power to upset the rear tire, and nothing to gain until max power has been reached whilst having the bike stood up.
Aprilia offers a quick-shifter as an accessory, and thereís no doubt this is of great benefit to the small 125, as acceleration suffers on the version without quick-shifter. The RS4 125 is pretty much a premium 125 in the first place, but with the quick-shifter itís like a superbike for the youngsters.
The pricing in the UK is not that stiff compared to the competition which mainly are the Honda CBR 125R (£3,270 OTR) and Yamaha YZF R125 (£4,249 +reg+tax). The Aprilia RS4 125 RRP is £3,999 OTR + £99 for the quick shifter. The cool little tiddler will hit American dealers early in 2012 at a price yet to be determined.
I only tested the RS4 125 on the circuit, but itís evident that the small 125 will work as a very good road bike as well. No expensive 2-stroke oil, just fuel and very little of it. The fairing is nearly identical to the big RSV4 superbike, and two large headlights make sure this 125 looks like any other motorcycle in a cars rear view mirror. The stylish exhaust is hidden low by the fairing, and it sounds a bit more grown up than a 2-stroke.
The seat is sporty, and comfort levels are the same as on any sportbike, and this goes for the ergonomics in general. The rear seat cowling can be replaced by a pillion seat, and underneath thereís room for a few bits and bobs. The mirrors are wide and give good view of traffic coming from behind.
All in all the Aprilia RS4 125 is a proper dreambike for youngsters, but itís also got some benefits for those a bit older who are yet without a full motorcycle license. It looks like a fully grown sportbike and has enough top speed to follow motorway traffic even in restricted form.
Scooters are a good means of transport, but the RS4 125 is for those that really want to ride in the same way as you do on a full-size sportbike. With the added benefit of the quick shifter all you do is push the starter button, engage first gear and then keep the throttle twisted whilst shifting up. Remember to use the clutch when downshifting thoughÖ