THE biggest changes to the high-performance Impreza WRX STi Type-UK which costs £25,995 on-the-road - £1,000 more than before. Extensive revisions for Subaru's iconic Impreza range deliver an even sportier drive while the interior has undergone a thorough upgrade for a plusher ambience.

Meanwhile the best-selling Impreza WRX gains inverted front and rear suspension struts - previously only used by the STi. This sharpens handling feel and enhances roadholding by reducing wheel movement during hard cornering or when covering bumpy surfaces. The 05 WRX - which starts from £19,995 on-the-road - can be spotted externally by its red painted brake callipers.

Hidden improvements include aluminium front suspension lateral links - which reduce unsprung weight - and more rigid suspension mountings for even more precise handling. Also aiding handling is a revised steering system with a cannon mount-type attachment for the steering gearbox and steering damper valve which reduces kick-back. Sure to appeal to enthusiasts, a driver's control differential (DCCD) becomes standard on the WRX STi.

The DCCD is operated via a switch mounted next to the handbrake and allows the driver to manually select the torque distribution front to rear, reverting to automatic mode every time the ignition is turned off. For example, he or she can choose between having a sharper cornering turn-in or more stable straight-line running. However, on the new 2005 Impreza WRX STi, the system is further upgraded by the fitment of a yaw-rate sensor and new front helical limited-slip differential.

The new front LSD is quicker-acting than the previous type and improves steering stability when cornering near the limit. It also improves the car's steering behaviour on slippery surfaces with less side-to-side tug. The 2005 Impreza WRX STi also has a completely revised suspension with new geometry including a caster angle raised by 1.5 degrees and a 15mm wider rear track and 10mm longer wheelbase.

Spring and damper rates have been retuned and the front and rear lateral links are now made from aluminium to reduce unsprung weight. Also changed are the anti-roll bars which are now bigger, further reducing body roll and increasing handling sensitivity. Even the front axle hub units and housings have been redesigned to improve the capacity of the wheel bearings, while the rear differential cushion rubber has been uprated to increase handling stability.

Other technical changes include the fitment of engine and floorpan underfloor covers to improve the aerodynamics. Like the rest of the 05 Impreza range, significant changes have been made to the interior to enhance the ambience while retaining the Impreza STi's sporty character. Specific new features for the STi include a new design of gear lever and three-spoke steering wheel.

Even the seat trim has come in for re-examination and, while the popular blue suede-effect centre section with red STi logos continues, the black cloth covering the side supports is now of a richer, more grippy material. The STi is designated and badged 'Type-UK' to distinguish it from unofficial imports which do not have the additional features standard on the British versions.

These include a Category One alarm/immobiliser, a special satellite tracking system, enhanced rust proofing to cope with the harsh UK weather, locking wheel nuts and window etching. Visual differences to the regular WRX include special gold-coloured spoked alloy wheels, colour-keyed sill spoilers and an interior featuring blue suede-effect seats with STi logos.

Also inside is a switch to spray the intercooler with water to retain power during high-temperature/altitude driving. Another device allows the driver to preset a warning buzzer and light to guard against over-revving the engine. The STi has a top speed of 151.5mph and 0-60 time of 5.2 seconds from an engine which has been specially developed to meet European Community Whole Vehicle Type Approval standards - unlike the Japanese home-market STi.

Tuned by Subaru Tecnica International Inc, up to 80% of the STi's all-alloy engine is new compared to the standard turbocharged 2.0-litre four-cam 'boxer' unit as fitted to the regular Impreza WRX.