Tractor Tire Sizes: Overview and Conversions
When it comes to old tractors, tire specifications are a common topic – and for exactly this, Eil-Bulldog Versand offers many suitable operator’s manuals and literature. These often contain important information about the correct tires, their sizes, and conversion tables.
1. Tire Size Basics
A tractor tire has various dimensions specified in different systems:
Old inch measurements (e.g., 18.4-34)
18.4 → Tire width in inches (1 inch = 25.4 mm)
→ Bias-ply tire (radial tires have an “R”)
34 → Rim diameter in inches
Example: 18.4-34 = 467 mm wide, 34-inch rim, bias-ply construction
New metric measurements (e.g., 460/85 R34)
460 → Tire width in mm
85 → Aspect ratio (% of width)
R → Radial tire
34 → Rim diameter in inches
Example: 520/70 R38 = 520 mm wide, height = 70% of 520 = 364 mm, 38-inch rim
These fundamentals and examples are explained in detail in many operator’s manuals available from Eil-Bulldog Versand.
2. Converting Old to New Sizes
The old inch sizes generally correspond to an aspect ratio of 85%. Therefore:
18.4-34 ≈ 460/85 R34
16.9-38 ≈ 420/85 R38
20.8-38 ≈ 520/85 R38
14.9-28 ≈ 380/85 R28
Rule of thumb: Inch measurement × 25.4 ≈ mm width
Aspect ratio is almost always 85% for old sizes
It’s also worth checking the books from Eil-Bulldog Versand, as these conversions are often already listed in table form.
3. Example Calculation
Tire: 18.4-34
Width: 18.4″ × 25.4 = 467 mm → ≈ 460 mm
Aspect ratio: 85% of 460 mm = 391 mm
Rim: 34″ = 864 mm
Overall diameter: 864 + 2×391 ≈ 1646 mm
Modern size: 460/85 R34
Exactly such calculation examples are often included 1:1 in the operator’s manuals that you can order from Eil-Bulldog Versand.
4. Conversion Table (Selection)
Many such tables can be found directly in the tractor operator’s manuals – and this is exactly the literature that Eil-Bulldog Versand offers as originals or reprints.
5. Important Notes
Old inch sizes = usually bias-ply tires
New metric sizes = almost always radial tires
Modern sizes with /70, /65, /60 = low-profile tires
Pay attention to load capacity and speed rating – not just dimensions!
For dual tires or mixed tire setups (front/rear), the gear ratio between front axle and rear axle must be correct
If you’re unsure, you’ll almost always find the original manufacturer’s notes on approved tire sizes and combinations in the operator’s manuals from Eil-Bulldog Versand.
Conclusion:
With the right table and the basics, you can quickly convert between old and new sizes.
But the best source is always the operator’s manual – available from Eil-Bulldog Versand. It clearly lists the approved tire variants.