On-Board Air Sizing

Calculate the air volume and time needed to re-inflate tires after airing down, and find the right compressor for your rig.

Tire Size

OD (inches)

Width (inches)

Rim (inches)

Pressure Range

Aired-Down PSI

Target Highway PSI

Setup

Number of Tires

Compressor CFM

Vol / Tire

5.32 ft³

Total Air Needed

33.3 SCF

Fill Time (4 tires)

16.6 min

Airing from 12 → 35 PSI on 4 × 35" tires at 2 CFM

Compressor Reference

Click a row to use that CFM rating in the calculator above.

Model	CFM	Type
VIAIR 300C Popular budget choice	0.54	12V portable
VIAIR 400C Good mid-tier	0.68	12V portable
ARB Twin Motor CKMA12 Industry standard OBA	3.09	12V on-board
ARB Single CKSA12 Popular single motor	1.98	12V on-board
Smittybilt 5.65 CFM High output budget OBA	5.65	12V on-board
Warn 4.9 CFM Reliable mid-tier	4.9	12V on-board
Extreme Outback 6 CFM High output	6	12V on-board
CO₂ Tank 5 lb (burst) Fast, but limited capacity	15	CO₂
Engine-driven (PTO) Truck-mounted, high output	12	Engine-driven

Notes

• CFM ratings are at 0 PSI — effective output drops significantly at 30–40 PSI. Actual fill time will be longer.

• 12V portable units work best for occasional airing up; permanent on-board air is preferred for frequent off-roaders.

• Formula: Air needed (SCF) = Tire volume (ft³) × (PSI_high − PSI_low) ÷ 14.696