Tire Size and Crawl Ratio Comparator
Compare crawl ratio for off-road use. Use the calculator below. Results update as you type.
How the Tire Size and Crawl Ratio Comparator Works
This comparator works by multiplying first gear, transfer case low range and axle ratio, then scaling the result for tire size. It shows how bigger tires reduce effective crawl ratio.
- Enter the 1st gear ratio, for example 4.17.
- Enter the low range ratio, for example 2.72.
- Enter the differential ratio, for example 3.73.
- Enter the old and new tire diameters, for example 31 in and 35 in, and read the crawl ratio: 42.3 on 31 in and 37.5 effective on 35 in.
The Formula
The formula is Crawl Ratio = 1st Gear × Low Range × Axle Ratio, and Effective Crawl = Crawl Ratio × (Old Diameter ÷ New Diameter).
Crawl Ratio = G1 × Low Range × Axle Effective Crawl = Crawl Ratio × (D_old ÷ D_new)Worked example: 4.71 × 4.00 × 4.10 = 77.2 on 31 in tires. On 37 in tires the effective value is 77.2 × 31 ÷ 37 = 64.7.
Conversion Table
The conversion table shows crawl ratio on 31 in tires and the effective value on 35 in and 37 in tires for 6 drivetrains. Crawl ratios run from 42.3 to 81.4.
A 4.00 low range nearly doubles crawl ratio over a 2.72 low range. Trail builders often target 60:1 to 80:1 effective crawl on large tires.
| 1st Gear | Low Range | Axle | Crawl Ratio (31 in) | Effective on 35 in | Effective on 37 in |
|---|---|---|---|---|---|
| 4.17 | 2.72 | 3.73 | 42.3 | 37.5 | 35.4 |
| 4.17 | 2.72 | 4.10 | 46.5 | 41.2 | 39.0 |
| 4.71 | 2.72 | 3.73 | 47.8 | 42.3 | 40.0 |
| 4.71 | 4.00 | 4.10 | 77.2 | 68.4 | 64.7 |
| 4.17 | 4.00 | 4.88 | 81.4 | 72.1 | 68.2 |
| 6.29 | 2.64 | 3.73 | 61.9 | 54.9 | 51.9 |
What Is the Tire Size and Crawl Ratio Comparator?
The Tire Size and Crawl Ratio Comparator is a tool that compares low-speed off-road gearing across tire sizes. Crawl ratio is the total gear reduction from engine to wheel in the lowest gear.
A higher crawl ratio gives slower, more controlled movement over rocks and steep grades. Larger tires reduce the effective crawl ratio, which the comparator measures.
Common Uses
This comparator has 4 uses: rock-crawler builds, transfer case choices, axle choices and trail planning.
- Build rock crawlers: Hit a target effective crawl ratio.
- Choose transfer cases: Compare 2.72 and 4.00 low ranges.
- Choose axle ratios: Balance crawl with highway RPM.
- Plan trails: Know control limits on steep terrain.