· Conversions
kg = pounds / 2.204
km/h = mph / 1.609
kW = bhp * 0.746 (or PS * 0.736)
litre = imp. gall * 4.546 (or US gall * 3.637)
· The following relationship exists between EC and DIN HP ratings:
1 HP (EC 95/1) » 1.015 HP (DIN)
A suitable conversion for SAE HP is not known, though the following relationship is believed to exist:
1 HP (EC) > 1 HP (DIN) > 1 HP (SAE)
i.e. SAE power and torque numbers are larger than DIN, which are larger than EC.
The characteristics of the DIN and EC standards are:
· DIN 70020 (TBC) = 1013 hPa pressure and 20°C temperature.
· EC 95/1 = 990 hPa dry pressure and 25°C temperature.
(dry pressure is calculated as normal pressure less humidity)
· Values for the drag coefficient (cd) and the cross-sectional area (a) determine the aerodynamic resistance to motion (Ra), according to the formula:
Ra = k * cd * a * v2
where k is function of air density. Empirical values for cd range from 0.24 race/prone to 0.39 road/upright, and a from 0.4 race/prone to 0.9 road/upright. In all cases, I've omitted k,
set a=1, and varied cd to make the resistance curve (Rtotal) cross the net tractive effort curve at the measured to speed.
For these spreadsheets, the values of the individual parameters to Ra are unimportant, as long as they result in values for Rtotal that meet the cadence tractive effort at the
measured top speed.
Rtotal > TE – implies overdrive
Rtotal < TE – implies under-gearing
The net Tractive Effort (TE) accounts for all of the rotating transmission losses, therefore Rtotal is the sum of the retarding forces, i.e. air resistance (Ra) and gradient resistance
(Rg).
· It is known that the rolling resistance due to the tyres is an exponential function of speed. However, tyres are designed so that this resistance doesn't start to ramp up within the
designated speed rating of the tyre. Under this constraint, it approximates to a (small) constant, and is not incorporated into the calculations.
· Mass of fuel is 0.7 kg/lit
· Mass of oils (fork and engine oil) is 0.9 kg/lit (guessed – heavier than fuel, but lighter than water)
· Gear-change time is guessed. Having sampled both the Sprint ST and the 996, the 996 is definitely slicker.
· Mass of accessories is guessed.