Rolling Resistance
There are a number of sources of information about
appropriate values of Coefficient of Rolling Resistance Cr,
not all are online so I've summarised some below.
J. Carvill in "The Mechanical Engineers Data Handbook
"
suggests the following for pneumatic tyres.
|
Drive Surface |
Cr |
|
New Asphalt/Concrete |
0.01 |
| Worn
Asphalt/Concrete |
0.02 |
| New Small Cobbles |
0.01 |
| Worn Large Cobbles |
0.03 |
| Rolled New Gravel |
0.02 |
| Loose Worn Gravel |
0.04 |
| Medium Hard Soil |
0.08 |
| Sand |
0.1 - 0.2 |
Wikipedia has an online
article with more data - some of which is:
|
Type & Drive Surface |
Cr |
|
Very Low Resistance Radial Tyre |
0.0025 |
| Standard Dirty
Tram Rails |
0.005 |
| Car Tyres on
Concrete |
0.01- 0.015 |
| Car on Stone
Plates |
0.02 |
| Car/Bus on Asphalt |
0.03 |
Obtaining data for rolling resistance on grass is a bit
more difficult. There are some references.
BICICLETTA has
published data for mountain bike tyres
here. They summarise
that rolling resistances on grass are about 6 (six) times
those on good road conditions, this may suggest Cr values of
around 0.06 - 0.08. Resistance on gravel is about twice that
on the road. Wider tyres and lower inflation pressures
are reported to reduce rolling resistance on off-road
conditions.
Sauer-Sundstrand
the hydrostatic drives manufacturer provides some
interesting data for commercial vehicles in their
Applications Manual:
|
Drive Surface |
Cr |
|
Sand |
0.25 |
| Wet Soil, Mud |
0.20 |
| Fresh Deep Snow |
0.16 |
| Loose Soil, Gravel |
0.12 |
| Grassy Field, Dry
Croplamd |
0.08 |
| Packed Soil, Dirt
Roadway |
0.02 |
| Pavement |
0.08 |
| Steel on Steel
Rails |
0.004 |
Clearly the various off-road conditions can give rise to
much larger rolling resistances than hard, smooth road
driving. This will be reflected in vehicle power
consumption.
Aerodynamic Drag
J. Carvill in "The Mechanical Engineers Data Handbook"
suggests the following for Drag Coefficient Cd for different
vehicle shapes:
|
Vehicle |
Cd |
|
Sports Car with Sloping Rear |
0.2 - 0.3 |
| Saloon with
Stepped Rear |
0.4 - 0.5 |
| Open Top
Convertible |
0.6 - 0.7 |
| Bus |
0.6 - 0.8 |
| Truck |
0.8 - 1.0 |
| Motorbike & Rider |
1.8 |
| Flat Plate (face
on to flow) |
1.2 |
| Long Streamlined
Body |
0.1 |
| Sphere |
0.47 |
NB, Cd and Cr are not the same thing - don't confuse them.
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