MINI WRC
It’s the small things…
With more than 100 changes, the new 01B Mini WRC is an exercise in detail development
BY MARTIN SHARP
marque. It is not a complete new homologation, but it is an extensively updated one. 50 per cent of the updates are aimed at ensuring reliability and correcting mistakes, the rest at providing performance boosts. A four-day, pre-approval
T
gravel test in Spain drew positive comments about engine output improvements and rough stage dynamics from drivers, Kris Meeke and Dani Sordo, while post-test analysis and crack checking of all components with the correct sign-off mileage completed saw Prodrive release them for use.
WHEEL TRAVEL On gravel stages, the Mini WRC appears to some to have less wheel travel than its WRC rivals, but this is a reflection of Prodrive’s calculations, and design philosophy, which differs slightly to that of rival teams. Both Dave Wilcock and David Lapworth stress here the importance of useable wheel travel. A suspension travel increase can mean more unsprung mass, reduced levels of body control and, if the increased travel is to be used fully, softer suspension settings, which mean running the car higher, thereby raising the c of g. Rough gravel road tests
indicated to Prodrive that the full suspension travel lengths
he Mini WRC 01B is the latest version of the four-wheel drive competition car from the BMW-owned
used by rival cars are not needed. While Prodrive could, with a re-design, engineer more travel into the Mini WRC’s suspension, the Mini’s maximum stroke has been decided through design criteria based on Prodrive’s simulation models, statistical analysis and historical data from the company’s days of developing Subaru rally cars.
SEQUENCE OF EVENTS Part of this process involved breaking down stages into a sequence of events, from braking to launch to corner entry to mid-corner to exit, and weighting priorities to find the key events. By far the prime movers in reducing stage times were found
But the way we choose to run it, the heave is controlled separate to rebound.’ Prodrive also reasons that
extended damper strokes require lengthy bump stops for end- of-travel protection, which also means lengthy compressed bump rubber heights. Wilcock: ‘If you consider a full bump event with their [rival cars’] compressed bump rubber length and then what the stroke is to full rebound, it’s not too dissimilar to what we’ve got. [But] we’re able to use all of ours, right down to almost zero millimetres. Full stroke is full stroke.’ However, 2011 event
experience highlighted areas for improvement on rough gravel
“Everything upstream of the air restrictor throat is new”
to be mid-corner grip and corner exit, so these areas became the main focus. Wilcock points out that it is all about maximising the grip available, which is why recent cars have appeared with softer and softer suspension settings to target maximum grip, although ride height issues limit how soft one can go. While admitting the Minis run harder settings in bump than rivals, the Prodrive engineer points out that this is not the case with the rebound settings: ‘When you’ve got use of a helper spring, you can have a variable spring rate, like anybody can. They all do.
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www.racecar-engineering.com • May 2012
rallies. The team tended to run the cars above design ride height to cope with large rocks. This trades bump travel at the sacrifice of rebound travel, so an 01B rough rally suspension package re-positions the nominal ride height through strut top mount specifications.
Shock absorber manufacturer,
Öhlins’, engineers were at the 01B’s Spanish tests to help with the development process, and the team had a selection of dampers, all built up with different valving. The 01B damper settings are revised for both customer cars
(RRC, S2000) and World Rally Cars, and the Öhlins dampers remain compatible for front or rear applications, with different valve settings.
IMPROVED AIRFLOW A number of 01B engine performance improvements aim for a four to five bhp increase through improved airflow, packaging, coolant flow and management. Everything upstream of the air restrictor throat is new.
The Mini’s BMW WTCC-derived
engines were originally built at BMW Motorsport, yet Prodrive has been doing new engine builds and rebuilds since September 2011. There are no upgraded 01B engine internals, although BMW Motorsport’s experience of piston ring marks, indicating premature wear at high rpm, in World Touring Car Championship cars demanded a new ring pack, which is included in the papers submitted for Mini 01B, so all new rally car engine rebuilds will now adopt it. Other unexpected issues
that needed addressing included the car’s propensity to throw alternator belts. The cause was found to be heavy frontal impacts, which caused a collision between a corner of the bumper and the alternator belt. Indeed, the 01A front bumper’s vulnerability to cracking and breaking often resulted in it losing the lower portion through scraping on the ground, reducing overall downforce. This was temporarily solved by raising the
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