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DEVELOPMENT BACKGROUND

In 1995, sports car enthusiasts around the world were delighted by the launch of the MGF. This marked the return of the MG marque to volume-produced open sports cars for the first time since 1980. It soon firmly established itself as the top selling sports car in the UK, and began to sell strongly in export markets including Europe, Japan and Australia.

Little production car development was sanctioned in the BMW-era, apart from the introduction of the Stepspeed (CVT / six-speed) derivative in 1999, as part of the 2000MY update. However, when MG Rover Group gained its independence in 2000, the pent-up enthusiasm of MG engineers could at last be directed into a high-intensity programme for a new-generation MGF.

The first inkling of the new direction came with the exclusive MGF Trophy 160 SE model, announced in January 2001. This drew from racetrack experience (MGF Trophy and MGF Cup championships) and represented the ultimate high performance evolution of the existing chassis and body. However the designers and engineers were now thinking well beyond this, with ideas for significant advances in chassis, body structure, aerodynamics, powertrain and style.

The launch of the MG TF, nearly six months earlier than anticipated, once again demonstrates MG Rover Group’s ability to deliver outstanding products within industry-leading time scales and with an ethos to be ‘lean, mean and efficient’ with a ‘will to do’ central to everyone’s thinking.

The TF retains the ‘real world’ affordability and practicality that set the MGF apart from rival cars, but is even more faithful to the MG brand ethos of ‘Outrageous Fun For All’.

CHASSIS: ENTIRELY NEW SUSPENSION

The simple substitution of high-rate, compact coil springs for the Hydragas units, with unchanged suspension linkages, had been evaluated experimentally some time ago, but this would not have delivered the class-leading standards of handling and driver involvement central to the latest generation of MGs. The challenge of incorporating the latest technology in suspension geometry, coil springs and gas-filled dampers within the MGF architecture was taken up.

Advanced computer design studies were carried out to optimise the suspension geometry and elasto-kinematic characteristics. Simulator vehicles confirmed the potential of the new system. One thorough Main Board test-driving session with a simulator was all it needed for motorsport enthusiast and MG Rover’s Product Development Director, Rob Oldaker, to receive the green light for the new suspension concept to be fully engineered to production status.

The rear suspension trailing arm pivots from a forward extension of the subframe, forking at the rear to attach, via firm bushes, above and below the hub carrier. This provides longitudinal wheel location and reacts torque purely in the vertical plane. A maximum-length link runs from the rear base of the hub carrier to a pivot on the centre rear of the subframe, thus completing what is effectively a very wide-based lower wishbone with a large swing radius.

The other links comprise the upper suspension arm and a lower steer-control link mounted forward of the hub carrier. A new rear anti roll bar, with modifications to suit the new configuration, is operated by a short swinging link connected to the hub end of each trailing arm. This new suspension combines optimum camber control with much greater resistance to unwanted steer effects. It is the key to the MG TF’s more responsive and throttle-adjustable handling, plus its improved steering ‘centre-feel’. Customers wanting an even more sporting edge to their TF 120, TF 135 or TF 160 can specify the Sports Pack 1, which has suspension lowered by a further 10mm (i.e. 20mm lower than MGF).

Both front and rear subframes were modified, with raised and angled turrets for the top mountings of the coil over damper units. By moving the lower operating pivots for the spring units further outboard on the upper suspension arms, more conventional leverage ratios and spring rates could be employed compared with the previous system. The change also meant that the damper forces were contained within the stiff subframes instead of being fed into the bodyshell.

The subframes themselves are now solidly-mounted to the bodyshell, as on the performance Trophy model, contributing to enhanced structural

stiffness and precision of control. Another advantage of the new suspension is that it allows a 10mm lower ride height to operate, to the benefit of appearance, stability and handling. A lower centre of gravity also reduces pitch under acceleration and braking.

At the front, the wishbone suspension configuration otherwise remains similar to MGF, but with reduced camber and parallel tracking in place of toe-out, plus revised pivot bushes and a stiffer anti-roll bar, up from 19mm to 20mm diameter, to complement the improved steering system. Tyre life is improved with this revised geometry.

It is in the rear suspension (especially important on a mid-engined car), that the most fundamental changes have been made. A completely new multi-link axle has been engineered to provide precise control of rear wheel geometry in all conditions to offer exceptionally involving and responsive control.

SHARPER STEERING

The MGF was one of the first cars to exploit the packaging and energy-efficiency benefits of Electric Power-Assisted Steering (EPAS). In the major chassis upgrade for the TF, the steering has been given 10% ‘faster’ gearing; (the rack ratio goes from 19.0:1 to 17.5:1 with 2.8 turns lock to lock, from 3.1) for greater and sharper steering response. In addition, the EPAS control software has been further developed.

The speed-proportional system now offers more weight at low speeds and a more progressive weight as speed increases. To further enhance steering response, the lateral stiffness of the rear pivot bush on each front lower wishbone has been increased. These changes combine with the new suspension and increased body stiffness to give the new TF even more enjoyable and confidence-inspiring steering qualities under all conditions.

BEEFIER BRAKING

For the new TF 160 model, MG/AP Racing front brakes similar to those introduced for the MGF Trophy 160SE model are specified. The front ventilated discs are 304 mm in diameter (up from 240 mm) and the special stiffened alloy four-piston callipers are red-finished to show behind the alloy wheel spokes. The TF 160 combines this competition standard brake with ABS control. This TF 160 braking specification is also available on TF 120 and 135 models as part of the optional Sports Packs 2 or 3.

On ABS-equipped models (standard on TF 120 and 160, optional on TF 115 and TF 135) the new multi-link rear suspension layout has facilitated a revised brake effort balance, allowing the rear brakes to work harder and reducing stopping distances.

WHEELS AND TYRES

To fully realise the potential of the new chassis, an extensive tyre development programme confirmed the benefits of the 16" Goodyear F1 tyre and led to the specification of the new Continental Premium Contact on 15" wheels. All TF models have alloy wheels as standard, and all have wider tyres at the back than at the front to reflect the mid-engine mass distribution.

Standard equipment on the TF 115, TF 120 and TF 135 are 15" x 6J wheels (eight-spoke on TF 115, square-spoke on the TF 120 and TF 135) with 185/55 R15 tyres at the front and 205/50 R15 at the rear; the TF 160 has a new 11-spoke design, 16" x 7J wheel with 195/45 R16 front and 215/40 R16 rear tyres.

A comprehensive range of 16" wheel options is offered, either individually or as part of the Sports Option Packs, including a ‘gunmetal’-finish ultra-lightweight 11-spoke design. A steel spacesaver temporary spare wheel is standard on the TF 115, TF 120 and TF 135 models, with the option of the Instant Mobility System (IMS) that comes as standard on the TF 160. IMS comprises a sealant gel and an electric pump. The alternative option for TF 160 buyers is a spare 16"x7J, 11-spoke alloy wheel with 195/45 R16 tyre for temporary use.

AERODYNAMIC BALANCE

The striking new style of the TF was carefully honed in the wind tunnel as well as in the studio to ensure it delivered excellent lift balance – so important to a car’s dynamic behaviour. The new front bumper incorporates a carefully-evolved spoiler profile, which crucially reduces front-end lift. To balance this, the rear deck has been re-shaped to incorporate an effective boot lid spoiler. The drag co-efficient, 0.36 in standard form, reduces to 0.35 with the optional lowered suspension Sport Pack, a reduction of 5%, while lift is reduced by 28%. Lift balance (front-to-rear difference) has been reduced by 55%.

STIFFER STRUCTURE

Intensive analysis of the MGF body structure identified key improvements to body stiffness to seek ways of adding to the improved chassis precision and ‘feel’ of the new TF. On-road testing with accelerometer measurement was related to laboratory rig testing and extensive computer modelling.

The resulting package of improvements offers significant benefits in both measured and perceived robustness. In addition to the solid mounting of both front and rear subframes, the front subframe has a diagonal cruciform tubular brace on the underside, linking its four-corners to the floor pressing of the underbonnet area.

The bracing behind the centre fascia console from the floor tunnel to the substantial cross tube that carries the steering column has been considerably strengthened. There are two bolt-on tubular braces arranged in triangular form across the top of the engine bay. Combined with the new, re-shaped and one-piece outer sill and rear wing pressing, these items improve the torsional stiffness of the shell by 20%, and reduce scuttle shake.

PEPPED-UP POWERTRAIN

The MG TF has a range of four powertrain choices with even higher all-round standards of performance and throttle response. At the top of the range, the TF 160 has a regular production version of the Trophy’s high-output 1.8 VVC engine, developing the same peak power of 160Ps (158bhp, 118kW) at an eager 6900rpm. This replaces the former 145Ps (143bhp, 107kW) 1.8 VVC engine, and gains its extra power from enhanced breathing.

There is a new low-loss intake system with a larger throttle body, improved porting profiles and a low back-pressure, dual mode exhaust system. The freer-flowing exhaust features thin-wall catalyst technology and an electronically-controlled pneumatic valve that optimises exhaust flow according to operating conditions. This retains low-speed refinement while enhancing performance and characteristic sports car sounds at higher speeds.

The efficiency of the new TF 160 unit is demonstrated by the way it combines increased performance (top speed up from 130mph/209km/h to 137mph/220km/h) with reduced CO2 rating (down from 189 to 179g/km).

For the new core model in the range, the TF 135, (replacing the 1.8i), a more powerful version of the normal 1.8 litre engine has been developed. This uses TF 160-style induction and exhaust systems plus high lift cams, bringing a power increase from 120Ps (118bhp, 88kW) to 136Ps (134bhp, 100 kW). In addition, the engine ECU has been re-mapped to optimise throttle response, and the VVC / TF 160 gear ratios have been adopted for improved in-gear performance. Against the clock, the TF 135 is now creditably close to the former VVC model, with a top speed of 127mph/205km/h.

In the new TF range, the unique-in-class choice of a EmCVT sports auto cum six-speed ‘manual’ transmission, with steering-wheel shift controls, continues in the form of the TF 120 Stepspeed. This retains the 120Ps (118bhp, 88kW) engine, and the flexibility of either ‘normal’ or ‘sport’ fully automatic drive, plus a sequential-change six-speed mode, controlled either by twin up/down toggles on the steering wheel or via the centre floor lever.

The entry-level 1.6-litre version of the MGF has proved popular since its launch in early 2001, making up around one in eight of all MGFs sold, and this now has its equivalent in the new TF 115 model. The sweet, short stroke 1.6-litre unit produces a power output of 116Ps (114 bhp, 85kW), with a top speed up from 116mph/187km/h to 118mph/190km/h, while also having a class-leading low CO2 rating at 169gm/km.

All the manual transmission models benefit from an improved gearshift linkage, with a short-throw lever and revised gear linkage geometry to reduce friction in the shift system for enhanced gear selection.

SHARPER STYLE

MG Rover Group’s Product Design Director, Peter Stevens, is deeply experienced in sports car design, having worked on every type from Lotus Elan to McLaren F1. While retaining the essential ‘modern classic’ character of the MGF, he and the design team have given the MG TF a harder, more aggressive look, honed in the wind tunnel for high-speed stability. The new front bumper/spoiler moulding has a sharper, more emphatic treatment, with a full-width character line and a black graphic framing the lower air intake, with its provision for ‘Fogstar’ fog lamps.

Entirely new headlamp units, with sleek silicon-protected polycarbonate covers, each house twin high-efficiency 70mm projector lamps, a sidelamp and a front direction indicator. A new upper air intake design features a horizontal body-colour crossbar, while larger MG badges are used front and rear.

In side profile, the MG TF is lower and sleeker. A new sill and rear quarter design, now formed in a single pressing, has a dart-like sill feature and more crisply shaped side air intake. This new ‘monoside’ pressing does away with a panel seam under the door and has a cleaner lower sill flange, as well as contributing 20% extra body stiffness.

Cooling air intake protection at front and sides is a black hexagonal mesh, with a bright-finish option.

The new bootlid has a ‘cleaner’ top surface and an integral raised rear lip spoiler, stretching the visual length of the car. Built into the spoiler lip is a new high-level brake lamp, with fast-acting LED illumination. The tonneau panel finishers on each side have been changed to an alloy finish, matching the admired fuel filler cap. In harmony with the new front bumper, the new rear bumper has a distinctive feature line and a black graphic surrounding the aperture for the new larger twin round exhaust tailpipes. As on the MG saloons, the new MG TF rear lamp units have clear lenses for the direction indicator and reverse light sections.

 


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