Features - Technical
MAY 3, 1998
Formula 1 Update
BY PETER WRIGHT
This year the designers and engineers have had to cope with new limitations on brake equipment - calipers that must be made from a material that has a Young's Modulus no greater than 80Gpa; single calipers with a maximum of six pistons and two pads; and a maximum disc thickness of 28 millimetres. The circumferential grooves in the tyres have not brought down longitudinal grip to the point where tyre adhesion is the limiting factor during braking from high speeds, and so the brake wear is still high, giving the thinner discs a life problem.
Metal matrix aluminium and beryllium-alloy calipers are out and have been replaced with the lightest alloy that meets the 80 Gpa regulation. A small percentage of Lithium added to aluminium achieves this specification. Carbon Industries are developing new carbon-carbon materials for discs and pads, trading a lower disc wear rate for higher wear in the pads, the thickness of which is not limited.
The flurry of variable brake-balance control systems and "fiddle-brakes" that appeared last year have now been trimmed back by the FIA. Only front-to-rear balance variation, as a function of brake effort is allowed, and no possible steer effect from lateral variation is permitted.
Grooved tyres, and the late introduction of Goodyear's wide front tyres to match Bridgestone's, has caused many of their teams (Ferrari is the exception) to re-think weight distribution and wheelbase parameters. It is also apparent from the amount of suspension geometry testing, that the characteristics of the new tyres and what they require in terms of kinematic control, is not yet fully understood.
I rashly predicted last August, in an article on tyres, that "With a width limit, that only affects the rear tyre at present, there will be a trend towards moving weight forward and widening the front tyre to compensate. It is the only way to get more tyre width, and hence more rubber onto the road." For once a prediction has come true and McLaren, with their light Mercedes engine and 25 or so kilograms of ballast to play with, has managed to arrive at just the right forward weight distribution to suit the wide front tyres. Others are hurriedly packing ballast around the pedals and wondering where they can reduce weight at the rear of their cars.
Weight distribution and wheelbase can only be varied significantly, at this late stage, by moving ballast or by moving the front and rear wheels longitudinally. Moving the rear wheels backwards is limited by half-shaft angularity, and moving the wheels either end means new bodywork and wing configurations - a lot of work.
Suspension arrangements are finely tuned to use the very high push-rod loads to relieve the loads in the bottom wishbones under cornering and braking. This is why the pull-rod arrangement was abandoned, as it added to bottom wishbones loads. Under braking, the rear leg of the front bottom wishbone is very highly loaded and the sweep forward or rearward of the push-rod, in plan view, affects this load. Moving the wheel longitudinally disturbs this fine balance of loads, and with CFRP wishbones they must be re-optimised.
It is interesting, but probably not very significant, that the two leading teams - McLaren and Ferrari - have come up with radically amended torsion-bar and damper arrangements at the front. The differences between the old, vertical torsion-bar/horizontal damper and the new horizontal torsion-bar/vertical damper arrangements will be in packaging (space and weight), rising-rate characteristics, and structural stiffness. Maybe the changes make a differenceÉ.
New gearboxes mean sleepless nights; radically new gearboxes mean nightmares. Arrows, Stewart and Prost's engineers and mechanics must be very short of sleep this year. Their team principals must be having nightmares. All three teams now seem to be getting on top of their gearbox problems but they have had a compounding effect: gearbox faults are not usually quick to fix, and it is impossible to run the car until they are. New parts, particularly castings, CFRP cases, and shafts and gears, take time to manufacture and so the test programme cannot continue while the gearbox is not functioning. As an inevitable consequence, the development of the rest of the car and the opportunity for the race engineers and drivers to learn how to set them up is severely compromised, with ensuing poor race results.
Just what problems these teams have been having is not public knowledge, but it is clear that Prost's problems are structural, connected with the rear-mounted clutch arrangement. Taking the input shaft to the back of the gearbox and then forward again into the gear-cluster, changes everything. Bearing sizes, rotating inertias and shaft bending loads are all different and designers at Prost have been through the painful process of compiling a new database for their gearbox design.
Likewise, Arrows and Stewart have had to learn from first principles about the use of CFRP in the hot, highly loaded gearbox environment. Differential expansion rates between CFRP, steel and aluminium, high temperature properties of the new materials, the effects of hot oil and vibration on them, are all new and there are no short cuts to learning about them.
The raison d'tre of CFRP gearboxes can only really be weight. In a situation where taking a kilogram off the engine-gearbox assembly means a kilogram can be used as ballast at the front of the car, those who finally have reliable CFRP gearboxes could perhaps, have an advantage.
Most teams now have computer-controlled differentials, using electro-hydraulics to alter the pressure on the friction discs of a Salisbury-type differential. What manner of mechanical differentials are being emulated inside them is not stated publicly, but you can bet that some fairly esoteric concepts are or will be presented to the FIA, hopefully for approval. The rules on how the characteristics are altered have been tightened up this year, and swapping between types of differential can only be performed in the Pits.