Why is wheelbase important

Wheelbase is a factor of: seating position, fuel tank, engine and gearbox length

A huge amount of fan attention has been focussed on wheelbase this year.  Even in recent years some teams’ preference for longer wheelbases has driven a lot of assumptions.  A typical F1 car is over three metres long; this length is largely dictated by the need to package the driver, fuel tank, engine and gearbox along the centreline of the car.  With engines being fairly fixed in length, fuel tanks needing to be sight centrally for weight distribution reasons, it settles down to fuel tank length, gearbox length and how far back from the front axle line the driver sits to determine the wheelbase.

Wheelbase length is often seen primarily as a factor in how the car suits fast or slow turns.  The common assumption that shorter cars go better around slow tight bends and longer cars go best in longer fast turns.  This proves to be largely false, the difference in the longest to shortest cars is only a few percent, certainly not enough to substantially change the cars ability to corner around the hairpin at Monaco.  Indeed Monaco proves to be no litmus test for wheelbases as longer cars have frequently won there.  I am told that wheelbase changes by a few percent, affect lap times in just thousandths of a second.

If wheelbase is not a factor in agility, then why is it so important and closely guarded? There’s two main reasons: weight distribution and aerodynamics.  As the components that decide the wheelbase are also the major masses in the car (driver ~65kg, engine 100Kg, gearbox ~40kg) by placing these strategically along the wheelbase a more forward or rearward weight bias can be achieved.  This is critical as it decides how well the tyres are worked.  Tyre are the biggest area for potential lap time improvement, even more so than aero, however far harder to achieve.  Teams have run up to 49% weight over the front axle in 2009, the cars layout will have a major impact on how much weight gets placed in the right place, without too much ballast being needed to meet the desired distribution.  For a more forwards weight bias you want the major masses moved forward, thus the drivers feet closer (but not allowed in front of) the front axle, longer gearboxes to space the heavy engine and gearbox from the rear axle.  In moving these masses sometimes wheelbases have to be altered to get the components in the right place.

Then there’s aerodynamics, probably more important than layout as tenths gained from aero are easier to reap than with tyre usage. Teams will want to create space for the airflow to twist and turn in order to get the downforce figures the designers are chasing. Often this has lead to long wheelbases as the designers want space between the front wheels and sidepods for bigger bargeboards, or space between the engine and rear wheels for a slimmer coke bottle shape. Ferrari has probably been the team happiest to stretch wheelbase for aerodynamic benefit. This year BMW Saubers Willi Rampf told me the cars wheelbase was purely a function of the cars aerodynamics.

But, if long wheelbase is an aero benefit and has no loss in agility, then why doesn’t everyone go for longer wheelbases. Well, the offset of along car is weight. By definition a longer car has more structure and hence will be heavier to achieve the same stiffness as a shorter car. Teams with restricted resources may not be able to afford the resources to design ever lighter structures from more expensive materials, this perhaps backs up the reason Ferrari go for longer wheelbases, they can afford the expensive carbon gearboxes and months of detail design work to make a longer car as light and stiff as a shorter one.

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