Conclusion

Fuel efficiency variables interact, making predictions impossible.
You must test to determine whether or not a fuel efficiency technique will work for you.

After nearly two decades of testing, Bridgestone engineers have concluded that there are so many factors affecting large truck fuel economy that it is almost impossible to accurately predict the effect of changing them without thorough testing.

And, as The Maintenance Council and others have pointed out, some fuel economy methods that have nothing to do with tires can accomplish much more than changing tires can.

We’ve summarized TMC’s results in the chart shown at right. You’ll notice that the improvement you can expect varies considerably, and you will no doubt find that some methods are easier for you to implement than others.

The chart below, also derived from TMC data, shows the top ten controllable fuel economy factors.
Top Ten Controllable Fuel Economy Factors
Line#   IF YOU USE OR HAVE INSTEAD OF MPG Improves By: Rank
58 Drivers Best Drivers Worst Drivers Up to 35% 1
  Speed If you go slower by     2
34 With Poor Aerodynamics 5 MPH No Change 10-15%  
  Cooling Fans       3
5 With On/Off Types Zero Fan on Time 100% 7-18%  
1 Engines Electronic Mechanical 7-15% 4
  Tires Steer/Drive/Trailer Steer/Drive/Trailer   5
39   Rib/Rib/Shallow Rib Rib/Deep Lug/Rib 6-14%  
  Idling       6
15 With A/C on @ 1000 RPM Zero Idle Time 50% 7-10%  
59 Trailers Single Van Double Van 6-10% 7
25 Aerodynamics Full Roof Fairing Nothing Up to 15% 8
26 Aerodynamics Full Roof Fairing Raised Roof Sleeper 4-10% 9
  Speed If You Go Slower By:     10
32 With Excellent Aerodynamics 5 MPH No Change 5-8%  
Of the fuel economy factors most under your control, driver training is one of the most important.

Factors Affecting Fuel Economy in the Real World
Line# IF YOU USE OR HAVE INSTEAD OF MPG Improves By:
1 Engines Electronic Mechanical 7-15%
2   Recommended RPM
at Cruise MPH		 100RPM Above Recommended at Cruise MPH Up to 3%
3   Cruise Control No Cruise Control Up to 6%
4 Cooling Fans On/Off Viscous 1.5-5.0%
5 With On/Off Types Zero Fan on Time 100% 7-18%
6   Zero Fan on Time 50% 4-9%
7   Zero Fan on Time 20% 0.5-2%
8 With 2 speed
v. 1-speed		 20% Time On/
2-speed

20% Time On/
1-speed

 Up to 1%
9   10% Time On/
2-speed		 10% Time On/
1-speed		 up to 0.5%
10 Radiator Shutters Summer/With Summer/Without 0.5-2.0%
11   Winter/With Winter/Without 1.0-3.0%
12 Intake/Exhaust Restrictions No Intake Restrictions 25" of Water Up to 1%
13   No Exhaust Restrictions 40" of Water 0.3-2.0%
14 Air Compressors 12-13 CFM 15-17 CFM Up to 0.5%
         
  Idling      
15 With A/C on @ 1000 RPM Zero Idle Time 50% 7-10%
16   Zero Idle Time 25% 3-6%
17   Zero Idle Time 10% 2-3%
18 With Engine Only @ 700RPM Zero Idle Time 50% 3-4%
19   Zero Idle Time 25% 1-2%
20   Zero Idle Time 10% 0.5-1%
  Aerodynamics      
21 Trailer Gaps 25 inches 35 inches 0.5-1
22   25 inches 45 inches 1-2
23   25 inches 65 inches 2-5
24 Cab Roof Devices Standard Deflector Nothing Up to 6%
25   Full Roof Fairing Nothing Up to 15%
26   Full Roof Fairing Raised Roof Sleeper 4-10%
27 Other Devices 15 inch Cab Extenders Nothing 1-2%
28   Air Dam Front Bumper Standard Up to 3%
29   Tractor Side Skirts Tanks or Nothing Up to 3%
30   Nothing Bug Deflector Up to 1.5%
  Speed If You Go Slower By:    
31 With Excellent Aerodynamics 1 MPH No Change 1-1.5%
32   5 MPH No Change 5-8%
33 With poor Aerodynamics 1 MPG No Change 2-3%
34   5 MPH No Change 10-15%
  Tires Steer/Drive/Trailer Steer/Drive/Trailer  
35   Rib/Rib/Rib Rib/Lug/Rib 2-4%
36   Rib/Lug/Rib Rib/Deep Lug/Rib 2-5%
37   Rib/Lug/Shallow Rib Rib/Lug/Standard Rib 2-5%
38   Rib/Rib/Shallow Lug Rib/Lug/Standard Rib 4-9%
39   Rib/Rib/Shallow Lug Rib/Deep Lug/Rib 6-14%
40   Rib/Original Tread/Original Tread Rib/Retead/Retread Up to 7%
41   Worn Tires New tires 5-10%
42 Wind No Headwind 5 MPH Headwind 5-10%
43   No Crosswind 5 MPH Crosswind Up to 10%
44 Transmission Direct Drive Overdrive Up to 2%
  Transmission/Axle Lube      
45 In Summer Synthetic Mineral Oil Up to 0.5%
46 In Winter Synthetic Mineral Oil Up to 2%
47 Drive Axle Single Drive with Tag Tandem Drive 2-3%
  Weather Conditions      
48   10° Warmer Air Temp (up to 77°) No Change 1-2%
49   Summer Winter 8-12%
50   Summer Fuel Winter Fuel Up to 3%
  Break-in Period      
51   Truck with 10,000 Miles (tires NOT included) Zero Mile Truck 2-5%
52 Routes Flat Interstate Highway Flat 2-Lane Highway 4-11%
53   Flat Interstate Highway Mountainous Interstate 4-18%
54   Flat Interstate Highway Urban Route 50% Stop & Go 25-35%
55   Flat Interstate Highway Suburban Route 100% Stop & Go 45-165%
  Weight If you decrease weight 10,000 lbs. (for GW between 60,000 -80,000 lbs.
56 Flat Route 10,000 lb. Lighter Load Heavier Load 6-10%
57 Mountainous Route 10,000 lb. Lighter Load Heavier Load 7-12%
58 Drivers Best Drivers Worst Drivers Up to 35%
59 Trailers Single Van Double Van

6-10%
60   Smooth Sides Exterior Posts 2-4%
61 With Good tractor Aerodynamics 12.5'x8' Van 13.5'x8.5' Van Up to 2%
62 No Tractor Aerodynamics Features 12.5'x8' Van 13.5'x8.5' Van Up to 8%

Try before you buy

Bridgestone recommends that before you make a major investment in fuel-saving technology, you conduct your own tests to determine whether or not your investment will bring you a satisfactory return.


 You can—and should—test fuel economy before making a major investment in fuel efficiency technology.
Both short-term and long-term fuel economy tests are recommended to verify manufacturers’ fuel economy claims.
Short-term fuel economy testing requires tight control of all operational variables.

Over the next few pages, you will find suggestions from Bridgestone engineers for conducting your own fuel economy tests.

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