the loss actually comes from things like the parasitic drag of bearings and seals, the quality of the gearbox oil you use (there is resistance met when the gears splash through the oil), the heat loss and noise created by the tyre's, you'll need 50psi or around 3 bar to reduce noise and heat loss to it's minimum without blowing the tyre, you'll need to heat the gearbox oil up to it's co-efficient temperature (a 20 or so minute drive before going straight onto the dyno will be perfect), a wheel alignment on the day to eradicate any loss due to unwanted misalignment drags, with the tyres make sure the sidewall height is optimum for transference of power, make sure the gearbox oil is brand new...things like degraded gearbox oil can make it's temperature drop by 10degrees which can show as much as a 20% gain in the HP between the fly and the wheels if corrected with the new box' oil. an oil change too will give an instant few horses, reduce as much unsprung mass as you can to save more weight (which is a drain on the engine and final drive) and sprung mass. remove your abs, remove your air con, get a racing cat installed to minimise back pressure whilst maintaining emissions standards barely. you'll get less drag strain and friction, your engines power will go up, and the gap between flywheel horses and wheel horses will be reduced. hope this helped, good old fashioned running over mapping, every time!