HSV GTSR W1 v BMW M6 2017 Comparison

Some say Australia’s most premier Supercars are unsophisticated. Just glorified taxis.

Although their layout is antiquated with a heavy 490kW V8 up-front driving through narrow rear tyres, thanks to Australia’s best racing engineers working day and night, they are now extremely capable (and FAST!) race cars.

In a nutshell, the quintessential Aussie racing category stands apart from others as our cars are simply over powered, under tyred and run spool differentials. Having both rear wheels turning at the same speed is a recipe for understeer and engineers combat this with extreme front-end suspension geometry and castor levels up at 19 degrees -- more than double a typical road car.

As a result, Supercars move around a lot and are sensitive to throttle input, so international racers arriving for co-driver stints invariably need extended ‘seat time’ to get fully acclimatised

So which road cars could possibly come close to the feeling of driving a V8 Supercar on the track?

Well, the new HSV GTSR W1 and BMW M6 seemed likely to make the grade, so we took these two 450kW-plus street missiles to Melbourne’s iconic Sandown Raceway.

In the pits
Good straight-line handling is crucial for Sandown as the circuit is basically two long straights book-ended by slow to medium-speed 90-degree corners. But the extremely low-grip track surface circuit also places a premium on efficient chassis balance and good power down ability.

The HSV GTSR W1 – the last HSV to use the Holden-developed Zeta chassis – wins the output race with 474kW/815Nm from its 6.2-litre supercharged V8. The BMW M6’s 4.4-litre twin turbocharged V8 is rated at 441kW/700Nm.

Supercar teams are naturally cagey on their own power figures, but it's fair to say most are approaching 650hp (490kW) and 475 ft-lbs (650Nm), so our two road warriors are impressively close in that department.

Question is: can the road tyres of the W1 and M6 transmit so much V8 grunt to the slippery Sandown pavement when, as I know first-hand, Supercars struggle.

Mass is the biggest handicap for our road registered rockets. Race cars are stripped of all but the bare essentials and light-weight materials are used where practical and/or permitted.

A race-ready Supercar tips the scales around 1400kg and we’re looking at 1895kg for the W1 and 1865kg for the M6. I suspect blame for most of the lap time discrepancy we’re about to discover can be attributed to the 500kg advantage enjoyed by the racer.

Remember, we have to accelerate the extra mass, stop it, turn it, and then accelerate it again and less weight means faster response. When Supercars undertake their sponsor/media/VIP ride days at Sandown, a passenger (average weight say 80-100kgs) slows times by around 1.5sec per lap so our road cars are conceding 4-5sec even before we exit pitlane.

Tyres are the only part of a car which touch the ground, so I’m pleased to see both the HSV W1 and BMW M6 are equipped with boots which are 265mm wide at the front and 295mm wide at the rear.

A Supercar runs 300mm wide tyres all round (obviously a bespoke racing slick) so we can concede another handful of seconds per lap to the race car right there.

Hats-off, however, to HSV for tyre choice. With its R-spec Pirelli Trofeo tyres, the W1 immediately looks to have an advantage over the more street oriented Michelin Super Sport rubber preferred by BMW for the M6. I would expect HSV’s tyre selection will give its Aussie-made sedan a 1sec per lap advantage.

Road car suspension is always a compromise between outright performance and comfort, even in ultimate high-performance cars like these. Sandown never relents and its mix of a bumpy surface and high kerbs will push both suspensions to their limits.

Not even the Aussie-developed SupaShock suspension under the W1 should be expected to match the ability of a Supercar to smash over the harshest kerbs for lap after lap. And Sandown is a circuit where race cars can minimise their steering angle and actually shorten the track distance by jumping over the kerbs. This is clearly another time deficit the road cars cannot possibly counteract.

Brakes on a Supercar are a particular area of focus and the road cars won't stand a chance, especially in repeatability.

The huge brake rotors in all three cars virtually fill the entire inner wheels and it's all about leverage, surface area and cooling for optimum retardation and repeatability, but pad material is a concern.

Road cars must employ a soft pad material in order to heat up quickly and work immediately. On a race circuit, the downside is they heat too much and fade when pushed hard. That aside, the tussle between the two road titans over who has the best stoppers will be interesting.

On the track
Starting the lap, accelerating in second gear I used every centimetre of the flat concrete kerb on the outside of the final turn.

The Supercar is extremely grip limited in the rear over bumps and necessitates a frustratingly slow throttle ramp. Naturally, acceleration is rapid but you don’t get full throttle until past the pit entry line.

HSV’s locally-developed W1 behaved surprisingly well and was the opposite to the wheel spinning, tyre frying monster I expected. Power down and delivery was remarkable, throttle ramp was very fast and wheelspin negligible -- even over the bumps.

On the other hand, the BMW M6 wasn't quite as poised, but on cold tyres it had just enough grip for a reasonably straight exit with not too much wheelspin. Throttle progression was fast, but the more road-oriented tyres overheated after one lap and the rears became prone to snap oversteer.

Both road cars were seriously fast approaching Turn One. We’re talking in excess of 245km/h in fifth gear, with the M6 not feeling quite so rushed (although the speed was identical).

This is an amazing speed for road cars and only just shy of a Supercar's 260km/h. All three cars accelerate equally hard through the cogs, but the shorter gearing in the Supercar ensures the engine operates in its working window a little better and you can usually pluck sixth gear by the end of the straight.

When changing gears in a Supercar you don’t release the throttle as the shift-cut breaks the torque and a positive pull of the sequential gearbox’s lever (combined with perfect timing by the driver) delivers optimised engine speed and avoidance of the rev limiter.

The M6 had the only automatic transmission and the three-stage shift speed worked well in ensuring speedy engagement. The W1 has too much torque for HSV/GM’s ‘native’ automatic transmission and its conventional H-pattern lever meant upshifts were the slowest of the three cars.

Vital mid-corner speed in Turn One (a third gear corner) actually comes from effective braking and while Supercar drivers jump on the middle pedal at the 150m sign, I added 20m in the road cars.

Braking feel and confidence was excellent in the W1 and I felt like I could push hard for many laps.

On the other hand, the BMW was a little inconsistent in feel, I noticed fade after just one stop and, with my confidence diminishing, I reckon I never quite optimised its barking performance. Once I even tricked the antilock braking system into locking a front tyre for 20m.

Turn-in for both road cars was great -- perhaps a little too good in the M6 with rear grip the limiting factor. It's marginal, but the auto transmission’s conservative downshift timing sees the desired gear selected just a bit too late. With lateral load already onboard, the late shift and lack of appropriate throttle blip causes rear brake lock and sends the rear tyres over the edge into oversteer.

The HSV W1 was confidence-inspiring with a slight understeer to neutral characteristic when lent on hard and no sign of nervousness. The manual transmission required a big heel and toe throttle blip on the downchange and it was nice to have that control. This was a big advantage for the W1 in corner entry.

Sandown’s Turn Two, Three and Four complex is an area with aggressive kerbs and a location where the Supercar can really short cut and gain some time. A more subtle approach is needed for the W1 and M6 – we’re mindful they need to get back to the manufacturers in top condition… I drove around the kerbs.

Both cars required a hint of opposite lock through the usual oversteer inducing Turn Three exit but the balance was generally good.

Up the back straight, top speed numbers pretty much matched the start/finish straight. With the engines working hard and both sounding amazing.

The fast left hander under the bridge saw more of a braking disparity between our two contenders and the racecar. The Supercar can attack it in fifth gear with 300kgs of aerodynamic downforce at that speed assisting a minimum corner speed of 190km/h.

In the absence of any significant aerofoils or venturi tunnels, our road cars were a gear shorter and produced lift for a wilder ride over the top.

Pushing in under brakes as deep as I dared, the HSV won the battle for balance. I felt this was a corner where the M6 moved around on the tyre tread blocks and its generally oversteering balance had me focussed.

A couple of times I needed to remind myself that although these cars produce straight line speeds to virtually match the Supercar, they are still road cars and needed to be driven accordingly.

Up and over the Turn Nine exit kerb, but power down didn't suffer in any car. Second gear in both road cars was a little tall and this softened the initial shock to the rear tyres and allowed for a surprisingly quick throttle ramp. Speed was up and the cars were straight before maximum torque hit.

Ending the lap, I left a bit of time on the table in both road cars. Braking into Turn 11 in the Supercar is just on the 50m mark at the top of fourth gear. I got a bit closer to this mark in the road cars but couldn't quite release the brake as early and carry speed. I tried in the W1 but understeer was the result and I missed apex through the last turn.

The M6's conservative downshift again locked the rear wheels and the resultant oversteer also compromised my run through the final corners.

At the chequered flag
Crossing the line, the Supercar produces a very fast 1:09.30 lap time. Best for the HSV GTSR W1 was an unbelievable 1:19.30 with the BMW M6 slower although with a still staggering 1:20.80

So the Supercar is roughly 10sec up the road in a race against these two fabulous street fighters.

Fit slick tyres, dial-up some negative camber at all four corners and that deficit will be virtually halved. Toss-out some of the heavy luxury items and we’d almost be on Supercar pace. Incredible.

The debrief
HSV’s W1 has the edge over the BMW M6 in the race circuit comparison, but without doubt tyres play a significant role.

What was really surprising was that I expected the W1 to be a bit of a monster, difficult to drive and perhaps a car only a pro could get the best out of. In fact, it was quite the opposite - very easy to drive, confidence inspiring, extremely well balanced and not at all nervous.

Another impressive aspect of the W1 was the lack of intrusion from the stability control. My fast laps were with the ESP turned off, but even with it on, the W1, like a Porsche 911, was only 0.1sec slower per lap. This confirmed how good the base chassis set-up was.

We’re really giving the BMW M6 an uppercut as this comparo is entirely race focussed. Sandown wasn’t on the minds of BMW’s engineers when they developed the M6 so not surprisingly, in that environment, the stability control was way too conservative.

The battle will continue when we take these two beasts out on the road... that's coming soon... along with the final verdict.