Suzuki GSX-R600 (2004-2005) - Review & Buying Guide

Suzuki’s GSX-R600 was the firm’s supersport contender for 30 years. First introduced in 1996 and part of the range until 2016, the GSX-R was one of the most focussed 600s money could buy. The model really got into its stride in 2004, with the launch of the K4. Previous models – the early SRADs and K1-K3 iterations – borrowed heavily from Suzuki’s GSX-R750s of the time, featuring the same frame and styling, but both the SRAD and early Ks were pegged back by the need to a) restrain costs, and b) make the 750 an aspirational model for 600 owners wanting to trade up to a more powerful engine as well as superior suspension and brakes.

By 2004 750s were no loner the feeder class for superbike racing. Litre bikes had taken over, so the GSX-R750’s place in Suzuki’s range was no longer crucial as it once was. The competition in 600cc supersport racing was also white hot, so the need for more powerful brakes and higher quality suspension was greater than ever.

The K4 was the beneficiary of this perfect storm, gaining fully adjustable usd forks for the first time, as well as a heavily braced swingarm (previous denied to the 600) and radially mounted front brakes, as well as a compact, more powerful engine and even racier overall dimensions. Underwhelming braking was an issue with early GSX-R600s; not so the K4/K5. New four-pot Tokico calipers and 300mm discs gave the 2004 bike stopping power equivalent to its 750 stablemate, while its claimed 124bhp engine gave the Suzuki the most impressive numbers in class.

This era of GSX-R600 still has fans today. And it’s little wonder. Excellent reliability, strong performance, nimble handling, and sharp looks make the K4/K5 models a strong contender for best early 2000s middleweight on the used market.

Pros & Cons

2004 Suzuki GSX-R600 - Prices

GSX-R600 K4
Rough £1800-£2200; Tidy £2600-£3000; Mint £3400-£3600

An all-new model. Heavily revised engine from K3; new chassis, sharper styling, 43mm Showa upside-down forks, radially-mounted 4-pot front calipers, claimed 124bhp, 161kg. Colours: blue/white, yellow/black, black/red

GSX-R600 K5
Rough £1900-£2400; Tidy £2850-£3200; Mint £3500-£3800

Colour/graphics updates only, although anniversary issue model comes with GSX-R750F inspired colours, blue seat and Yoshimura end can. Colours: blue/white, 20th anniversary blue/white, black/silver, red/black

2004 Suzuki GSX-R600 - Engine & Performance

The Supersport category was a fierce arena in the early noughties, with manufacturers updating models at least every two years to stay competitive on the track and in the showroom. For 2004 Suzuki’s aim – as always – was to make the GSX-R600 lighter, more powerful, and even more compact than before.

While the K4 retained the same oversquare 67 x 42.5mm bore and stroke of the K3, giving a capacity of 599.4cc, its engine gained new, more compact crankcases and was shrunk to reduce overall length. Internal components were lightened where possible – the valves, for example, were changed to titanium – and 10 grammes was shaved off each con rod. Lighter, more compact crank journals (30mm in place of the old bike’s 32mm parts) removed unwanted mass off the crank, aiding performance and the engine’s ability to rev.

Despite the move to lighter, racier componentry the K4/K5 motor is an impressively robust unit with very few reliability issues. Peak power (a claimed 124bhp chimes in at 13,000rpm) but the motor will keep spinning beyond that already heady rpm, making it a match for late 1990s 750s like Suzuki’s own GSX-R750WT – a remarkable feat for a middleweight.

As you’d expect of any engine making its numbers so high up in its rev range, the GSX-R600 K4/K5 offers an intense riding experience that requires nothing less than 100 per cent commitment. This isn’t a machine to bimble down to the shops on or labour through short-shifts on a work commute. No, this is a sportsbike that wants to give its all on every ride and explore the five-figure territory of its tacho as often as possible.

Ride a K4/K5 as intended and it’ll reward with an intensity of performance that’ll keep you coming back for more. The light, slick gearbox is a joy to snick through clutchless changes – it doesn’t even need a quickshifter, it’s that good, and the motor’s high rpm surge is among the strongest of all 600s of this era.

2004 Suzuki GSX-R600 - Handling & Suspension (inc. Weight)

Like its engine, the K4/K5 GSX-R600 chassis was also heavily reworked from the previous model. The frame is 15mm narrower at its widest point compared to the K3; a move made possible by the engine’s modest dimensions. Frame construction was also altered with the chassis’ main sections made from aluminium extrusions rather than separate parts welded together.

Dimensions were shrunk in every direction, with 10mm shaved off the wheelbase to improve turn-in and handling. Stability was maintained through a longer, braced swingarm – made possible by the engine’s reduced length. Race-style usd forks were fitted for the first time – fully adjustable 43mm Showa items with radial mounts for the new four-pot Tokico brake calipers. Overall dry weight is two kilos lighter than the K3 at 161kg.

The GSX-R600 always enjoyed sharp handling by virtue of a chassis passed down from the 750 SRAD and 750Y models, but the introduction of higher quality suspension on the K4 lifted the middleweight GSX-R out of its previously ‘budget’ role. The K4/K5 models are every inch the mini superbikes Suzuki intended them to be.

Owners rave about the K4’s rapier steering and sheer agility, as did many testers who labelled the GSX-R the sharpest 600 of its time. Only a tendency to warp the front discs – more of an issue on bikes used on track than road – provides cause for concern. Both front and rear suspension will by now be in need of a refresh (this model GSX-R is 20 years old at least), so look for a bike that’s already had this done or factor in the cost - £700-upwards – into any negotiation.

2004 Suzuki GSX-R600 - What to look for

Warped brake discs
A common issue, especially on bikes that have been ridden hard or used on track. Get a test ride and check for judder. Budget £150-plus for replacements, depending on brand. 

Overall finish
The K4-K5 GSX-R engine is strong, so, provided previous owners have regularly refreshed the oil, mechanical issues shouldn’t rear their head. Paint finish isn’t a GSX-R strong suit, however. Bodywork paint chips easily, as does the black finish on the frame and chassis components, so give any prospective purchase a thorough examination. 

Ex-race/track bikes
This era of Suzuki 600 proved effective as Supersport racers, so a fair number of K4/K5s made their way onto the track as either race bikes or trackday tools. An ex-race bike can be a good thing if you its history and want to benefit from performance upgrades, but very few will have stayed sunny side up so check for crash damage, missing components and general wear and tear that comes with hard use. 

Aftermarket add-ons
These can be a mixed bag. Quality exhaust systems – Akrapovic, Arrow, Yoshimura etc – are worth having. Generic bolt-on end cans are not, so get the stock system thrown in with a sale. Reflashed ECUs can boost performance, provided the work’s been done by an experienced mechanic. Uprated fork internals and quality aftermarket shocks are also welcome additions, particularly given this era of GSX-Rs age – stock suspension is likely to be past its best by now. The key to any aftermarket extras is to ask the seller to throw in the original parts too; they’ll be expensive to replace if not. 

Low screen
The K4/K5 is a pukka sportsbike with a riding position made for hard riding and track use, so comfort isn’t really a GSX-R strong USP. Many owners fit a double-bubble screen to improve distance comfort. 

Throttle Position Sensor
Can fail and will throw up a warning light on the dash and a C28 fault code through the ECU. A cheap and easy fix, however – replacement parts can be had for less than £20. 

Injection system
The stepper motor that operates the Secondary Throttle Valve Actuator (STVA) can fail. A tell-tale that there’s a problem is the motor’s inability to rev beyond 6000rpm. Like a TPS fault, this throws a C28 fault up through the dash. Budget around £120 for a genuine used replacement.

2004 Suzuki GSX-R600 - Rivals

2004 Honda CBR600RR - Honda’s RR model CBR600 first appeared in 2003, boasting MotoGP looks and superbike-spec technology. Rapid, agile and oh-so easy to extract the best out of, it proved to be a race winner and a favourite with road riders. Not quite as sharp as the K4-K5 GSX-R, however, but a great all-round package nonetheless.

2004 Kawasaki ZX-6R - Critics can argue that Kawasaki cheated with its early noughties ZX-6R, boasting the capacity of its road-intended model by 37cc to 636 to increase low and midrange torque (a 599cc variant was available for racing). But it was a smart move, giving the ZX an edge on the road the screaming GSX-R, CBR and R6 can’t match. If only the riding position wasn’t so extreme…

2004 Yamaha YZF-R6 - Rapid Supersport contender, updated for 2005 with usd forks, radially mounted front calipers, and a claimed 123bhp power output. Arguably the GSX-R’s strongest rival on both track and road. Sweet handling matches the strength of the motor in terms of performance. Like the K4-K5, be mindful of ex-race bikes and track tools – the tell tail signs of wear and tear will be there.

Honda CBR600RR, 2004 | Approx Price: £2500-£3900

Read more

Power/Torque

117bhp / 47.2lb-ft

Weight

169kg

Kawasaki ZX-6R 636, 2004 | Approx Price: £2500-£3900

Read more

Power/Torque

118bhp / 50.7lb-ft

Weight

174kg

Yamaha YZF-R6, 2004 | Approx Price: £2500-£3900

Read more

Power/Torque

123bhp / 50.5lb-ft

Weight

162kg

2004 Suzuki GSX-R600 - Verdict

The K4/K5 models mark a strong period in the GSX-R600’s evolution. They also represent the time when this Suzuki 600 evolved from dumbed-down sportsbike (in the sense that previous models didn’t benefit from top-notch suspension) to pukka mini superbike status. There are many reasons to consider a K4/K5 now – cost, strength of design, ace handling, fun to ride being just a few – over other 600s. Go for standard spec and the best condition you can find and you’ll have a ball.

If you’d like to chat about this article or anything else biking related, join us and thousands of other riders at the Bennetts BikeSocial Facebook page.

2004 Suzuki GSX-R600 - Technical Specification