1. Determining Truck Speeds using Rimpull and Retarder Curves

2. 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

3. 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.

4. 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)

5. Read Up from the Weight Line to the Grade Line

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

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

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

9. 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.

10. 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?

11. 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.

12. Take the Weight and Read Up to the Favorable Grade Line

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

14. 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.

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

16. 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

17. 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.