Determining Truck Speeds using Rimpull and Retarder Curves

Question How fast can a Vovlo A40D go up a 12.5% grade with a 2.5% rolling resistance And a full 40.7 ton load (total vehicle weight 150,200 lbs)? We use the Rimpull curve To determine this

Start by Finding Your Vehicle Weight Most rimpull charts show the Weight of an empty truck And a truck loaded to full Weight Capacity. Otherwise start with the Weight down here.

Determine the Total Resistance 12.5% positive grade resistance working against the truck + 2.5% positive rolling Resistance working against the truck = 15% total resistance. On the grade scale find the total resistance (15% in this case)

Read Up from the Weight Line to the Grade Line

From This Point Read Over to the Rimpull Curve This blue line is The rimpull curve

Now Read Down the Maximum Speed the Machine Power Can Sustain We can go 5mph with a full load Up a 15% effective grade.

Rimpull Curves Only Work for Effective Grades Against a Vehicle Retarder Curves are Used for Favorable Grades

Braking a Large Truck For large haul trucks drum or disk brakes would heat up quickly To control speed on downgrades large trucks use hydraulic resistance applied to the drive train For very short distances one can go faster and hold the truck back, but over longer hauls the hydraulic resistance system would overheat too.

How Fast can a Fully Loaded Volvo A40D go down a 12 How Fast can a Fully Loaded Volvo A40D go down a 12.5% favorable grade against a 2.5% rolling resistance?

Figure the Resistance 12.5% negative or favorable grade trying to make the truck roll away + 2.5% rolling Resistance opposing the truck movement (rolling resistance is always against you) Give a total effective grade of -10% - minus means a favorable grade and the need To use a retarder chart.

Take the Weight and Read Up to the Favorable Grade Line

Now Read Over to the Retarder Line Yipes – Which Line?

That Depends on Your Gear and Road If you are only going down a short downgrade then you could be geared to high or low range – read to either high or low range. If it is a more sustained down grade or you are regularly going downhill then don’t overheat the retarder – use the continuous curve.

Suppose it is a lot of downhill You can go 18 mph.

Notes on Vehicle Travel Times The rimpull and retarder curves represent maximum speed the vehicle can mechanically achieve. You may have congested areas or sharp turns where travel speed must be lower We normally brake haul roads into segments when grades or conditions change Each segment is assigned a speed based on vehicle capability or another speed constraint

We Determine Vehicle Travel Time for Each Road Segment Equation for Travel Time One can then add up the time for all the haulage segment to get the travel time Another note – drivers seldom achieve maximum allowed speed. One can divide by a driver efficiency to get actual time About a mile or more drive one will probably get about 90 to 95% Divide your time by (.9 or .95) Your travel time will rise to account for less than 100% perfect drivers.