APU, Reefer & Tire Reference - Trucking Calculator Help

APU Units — Diesel Fuel Burn

An APU (Auxiliary Power Unit) lets a driver run HVAC, electronics, and the sleeper without idling the main engine. Fuel burn varies by load (heating vs. cooling vs. idle standby). The ranges below represent real-world average consumption under typical operating conditions.

APU Model	Type	Fuel Burn (gal/hr)	Notes
Green APU	Diesel APU	0.10 – 0.20	Very fuel efficient. Popular for owner-operators. Runs full HVAC + 120V outlets.
Thermo King TriPac Evolution	Diesel APU	0.15 – 0.25	Industry standard. Good cold weather performance. Integrated with some Kenworth/Peterbilt factory options.
Carrier ComfortPro APU	Diesel APU	0.15 – 0.22	Quiet operation. Common on Freightliner Cascadia trucks. Diesel-powered HVAC + battery charging.
Rigmaster Power	Diesel APU	0.15 – 0.25	Runs full 120V/240V AC generator. Heavier fuel use due to generator load capability.
Webasto AirTop / BlueCool	Fuel-Fired Heater / A/C	0.08 – 0.15	Heater-only units burn less. A/C models draw more. No generator — HVAC only.
Espar Airtronic / Hydronic	Fuel-Fired Heater	0.08 – 0.14	Heating only. Very low fuel burn. Popular in extreme cold-weather regions.
IdleAire / Shore Power	External Electric	$0 fuel	Plug-in at truck stops. Usually $2–4/hr fee. Enter $0 APU fuel burn and use the Broker/Flat fee field instead.
Main Engine Idle	No APU	0.80 – 1.20	The expensive option. Idling a diesel semi burns roughly 1 gal/hr and adds engine wear. APU pays for itself fast.

Fuel burn rates are approximate averages. Cold weather heating loads and summer A/C loads will push rates toward the top of the range. Standby / minimal load rates will be at the bottom.

Reefer Units — Diesel Fuel Burn

Reefer fuel consumption depends heavily on ambient temperature, set point temperature, load density, and how often the unit cycles. These are real-world average ranges for actively running units (not standby).

Reefer Model	Fuel Burn (gal/hr)	Notes
Carrier X4 7300 / 7500	0.50 – 0.80	Current generation Carrier trailer reefer. More efficient than older models. Common on newer fleets.
Carrier Supra 750 / 850	0.55 – 0.90	Older Carrier units. Higher fuel burn than X4 series. Still widely used.
Thermo King SLXi 300 / 400	0.50 – 0.75	Modern Thermo King units. Good fuel efficiency. Smart cycle technology reduces run time.
Thermo King Precedent	0.55 – 0.85	Older generation TK unit. Higher fuel consumption. Very common in used trailer market.
Daikin Transport Reefer	0.45 – 0.75	Less common in North America but known for efficiency. Often on specialty cold-chain trailers.

How to estimate your reefer hours for a trip:

Reefer units typically run continuously while loaded, cycling on and off to hold temperature. A reasonable estimate is:

Trip Hours = Total Miles ÷ Average Speed (mph)

Example: 500 miles ÷ 55 mph = ~9 hours. Add loading/unloading wait time (1–4 hrs typical). Enter the total in the calculator's "Reefer Run Hours" field.

Tire Reference — Cost & Lifespan

Tire costs vary by brand, size, and supplier. The ranges below cover typical commercial truck tires in the US market. Lifespan depends heavily on routing (highway vs. local), load weight, inflation maintenance, and driving habits.

Position	Typical Count	Cost Per Tire	Expected Life	Approx CPM
Steer	2 (single axle)	$450 – $650	100K – 150K mi	~$0.007 – $0.013
Drive (Tandem)	8 (dual rear axles)	$350 – $550	80K – 120K mi	~$0.023 – $0.055
Trailer (Tandem)	8 (dual trailer axles)	$200 – $400	80K – 100K mi	~$0.016 – $0.040
Typical Total	18 tires	—	—	~$0.05 – $0.10/mi

What increases tire wear:

Driving heavily loaded (max GVW)
City/local routes with frequent braking
Under-inflated tires (biggest killer)
Misaligned axles
Hot climates and long summer runs

Ways to extend tire life:

Check inflation weekly (use TPMS if available)
Rotate and rebalance at each oil change
Align axles annually or after any hard impact
Retread drive and trailer tires when possible
Buy in bulk from tire wholesalers, not roadside

Brake Wear Reference

Brake lifespan is highly variable. Mountain routes, heavy loads, and frequent stops will destroy brakes far faster than flat highway runs. Use the ranges below as starting estimates and adjust based on your actual history.

Axle Position	Cost Per Axle Set	Typical Life	CPM
Steer Axle	$200 – $350	150K – 250K mi	~$0.001 – $0.002
Drive Axles (×2)	$300 – $500 each	100K – 200K mi	~$0.003 – $0.010
Trailer Axles (×2)	$250 – $450 each	100K – 175K mi	~$0.003 – $0.009
5-Axle Total	~$1,300 – $2,250	avg ~150K mi	~$0.009 – $0.015/mi

Calculator Tip: In the calculator, enter the total number of axle brake sets (5 for a standard tractor-trailer), your best estimate of cost per complete axle brake job, and your estimated life in miles. The calculator converts this to a CPM and charges it against every mile of your trip.