2011 Aprilia RS4 125 Review

The all-new Aprilia RS4 is Aprilia’s first step away from the 2-strokes that made them famous. The RS125 2-stroke will still be sold (in Europe), but the emergence of this new 4-stroke 125 shows Aprilia’s direction for the future. 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 can’t replace the RS125 performance-wise, but it does benefit from a reliable torquey 125cc four-stroke engine that doesn’t 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 isn’t 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. It’s 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, there’s 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, let’s face it, the speed needed to be brushed off was never great.
The RSV’s dry weight is a claimed 295 pounds, which is a lightweight for a 4-stroke but about 30 pounds heavier than an RS125.
I’m quite large for the RS4 125, but in the pictures you could briefly think that I’m 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.