AS 125 R

Presented in Gardone Riviera in May 1985 and marketed soon after, the AS125 R, where R indicates the presence of the new Austrian Rotax engine in place of the previous Hiro, is the last update of the ST/STX series before the advent of the revolutionary AF1.

The AS-R in fact evolves little from the STX in terms of aesthetics and chassis, although the new Rotax engine is totally new. Characterized by the presence of the RAVE (Regulation Aprilia Valve Exhaust) exhaust valve, the modern Rotax 127 engine provides much better performance than the old Hiro.

The AS-R is therefore a more powerful and more enjoyable bike to ride than the STX, although not as refined as its most fearsome competitor, the new Honda NS-F also introduced in 1985.

The price in 1985 was Lire 3,430,000 turnkey and the available colours were red/metallized grey with a red saddle and pearl white with a grey saddle. A strange case for an Aprilia, the AS-R proved to be long-lived enough to remain in production throughout 1986 without undergoing any particular changes or variations in colouring.

The model number of the As 125 R remains AS 125 R and the DGM is 51771.


The bike in brief
The AS-R is the third evolution of its predecessor, the ST. The fairing, tank, side panels and tail remain unchanged from the STX, but the radiator has a new fairing and the front end has a different shape.

The arrangement of the battery, oil tank mixer and air filter remains unchanged.

The instrumentation remains unchanged, but the electric blocks gain a red ground switch on the right-hand control to switch off the engine.

The AS-R also differs from its predecessors, the ST/STX, in that the drive chain is located on the right and the exhaust system on the left. A feature imposed by the adoption of the new Rotax engine, famous for this diversity.

The AS-R's chassis is based on that of the ST/STX, although some functional improvements have been introduced:

  • Slight reduction in wheelbase from 1370 mm to 1365 mm.
  • New Marzocchi front fork built to Aprilia specifications with centre pivot and again with 32 mm stanchions.
  • New swingarm, again combined with the familiar APS suspension, which is updated in its linkages and combined with a new single shock absorber.
  • The braking system features another 240 mm disc at the front, now served by a new twin-piston caliper. A new master cylinder with a larger diameter and rectangular instead of circular reservoir is also used. At the rear, a new 230 mm brake disc replaces the previous drum.

The size of the wheels remains unchanged.

The measured dry weight is increased from 113 kg to 117 kg.

The new Rotax 127 engine is the first Rotax engine fitted to an Aprilia road bike. It has forced circulation cooling, reed valve intake and automatic mixer. The balancing shaft counter and electric starter are still absent.

The real novelty, however, is the presence of the RAVE exhaust valve, or Regulation Aprilia Valve Exhaust, an ingenious and quite simple system that uses the exhaust gases to pneumatically open and close a valve that varies the exhaust timing.

When the valve is closed, the cylinder is optimised for low and mid-range power, while when the valve is open, the exhaust diagram is more suited to the search for maximum power. The RAVE therefore allows the use of a cylinder with a more powerful diagram, while maintaining optimum power delivery at all rpm.

The fuel supply is entrusted to a Dell'Orto PHBH 26 BS carburettor and not PHBH 28 as also erroneously indicated in the official Aprilia brochures.

The exhaust system, on the other hand, is fitted with a different expansion with a separate tailpipe, which is located on the left side of the bike. This is an unusual position, but typical of Rotax engines that, in contrast to almost all other manufacturers, have the transmission chain on the right and the exhaust on the left.

The measured power of 20.71 hp at 9500 rpm (18.48 hp at 8500 rpm on the STX) is well below the 26 hp declared by Aprilia, but it is still enough to make the AS-R the most powerful and fastest 125 with over 140 km/h recorded against the 129 km/h obtained by the STX.

In the 400-metre revival tests from 50km/h, the AS-R's engine proved to be elastic, recording a time of 19.157 sec and an exit speed of 104.046 km/h (22.598 sec and 86.124 km/h for the STX). The engine weight is 21 kg.