MOTORSPORT: IRS slows V8 Supercar testing

The new independent rear suspension system designed to give V8 Supercars a more modern image this year is turning out to be a practical step backwards.

According to Nissan Motorsport, the problem is adjusting the roll centre of a V8 Supercar - which took just a few seconds with the old ‘Project Blueprint’ cars and their live rear axles located by an adjustable Watts link – has blown out to more than 30 minutes.

That means teams cannot complete as extensive a program at a test day as they could previously.

It also means no adjustment of the roll centre during races, a process previously easily carried out within a scheduled pit stop.

Raising or lowering the roll centre is performed to adjust the handling balance of the car as its tyres wear. Usually, the roll centre will be higher when tyres are fresh.

The move from live axle to IRS was part of an extensive upgrading of V8 Supercars technology via the Car of the Future regulations, which come into force this year.

Also part of the deal are a control floorpan and rollcage, a new-generation MoTec M190 engine control unit that allows a drive-by-wire throttle, an Albins sequential-shift six-speed transaxle that replaces the Holinger gearbox, 18-inch Dunlop tyres (replacing 17s), a control wheel package and AP brakes.

The engine in CotF is mounted lower and further back, the driver is more centrally located and the fuel tank is shifted in front of rear axle. The aim is cut at least 100kg from the kerb weight of the car.

The move to CotF also opened up the category to other makes besides Holden and Ford, and Nissan was the first manufacturer to commit, linking with Kelly Racing to form Nissan Motorsport and mount a four-car attack based on the Altima mid-size sedan that launches in Australia later this year.

Team co-owner, driver and technical director Todd Kelly revealed the roll centre issue to motoring.com.au during an exclusive interview.

“With the rear-end a roll centre change which would previously take three or four seconds and you can do in a pit stop now takes 35 minutes because you have to move the rear arms,” he explained. “So the amount you can get done to get your head around tuning the car is probably a quarter of what we could do at a test day with the old car.

“So the simulation software and what the guys do back at the shop at their desks has now become a lot more important than what it used to be.”

Mr Kelly said there would no doubt be some methods devised to speed the process of adjusting rear suspension roll centre, but he doubted the issue would be fully overcome.

“When you adjust it a reasonable amount you have to do adjustments on the upright, toe and bump steer and camber and bits and pieces like that. So when you have worked out what changes you want on the roll centre you will have all your shims worked out to drop straight in, but it is still quite time consuming because you need to undo the bolts on all the arms just to do a simple roll centre change.”

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