2011 Aprilia RS4 125 Review
 

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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.

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