18.4-38 Tractor Tires

Buying 18.4-38 tractor tires

18.4-38 is one of the most common rear sizes on mid-size and large row-crop tractors, on two-wheel-drive and front-wheel-assist machines alike. It is 18.4 inches (about 467 mm) wide and fits a 38-inch wheel, and it is often run as a dual set for extra flotation and pulling power.

The dash means bias-ply. If you want to move to radial, the matching sizes are 18.4R38, also sold as 460/85R38 or 480/80R38. A radial puts a longer footprint on the ground and usually wears longer, but it costs more; our radial vs bias guide explains when that pays off. On a front-wheel-assist tractor, check the front-to-rear ratio before changing construction or brand.

What to check

• Tread: R-1 is the standard farm lug; R-1W has deeper lugs for wet ground and longer life.
• Ply rating or load index: match or exceed the tires you have, especially for duals or heavy drawbar work.
• Used tires: ask for the remaining tread in percent, photos of both sidewalls and the DOT date code.
• Pairs: replace both sides of the axle together so the tractor pulls straight.

Send us the quantity, new or used, and where the tires are going, and we reply with the options we can supply and the shipping.

What else is 18.4-38 called?

You will see the same tire written 18.4-38, 18.4×38, 18.4/38 or 18.4 38. They all mean a bias-ply tire 18.4 in (467 mm) wide for a 38 in (965 mm) rim. The radial version is written 18.4R38, and the metric radial equivalents are 460/85R38 and 480/80R38.

How does 18.4-38 compare with 16.9-38 and 20.8-38?

Owners on tractor forums ask this all the time, and the answer is that the wider tire is also taller. These nominal figures use the standard size formula (old inch sizes assume an 85% aspect ratio), so real tires vary by make.

So an 18.4-38 stands roughly 2.6 in (66 mm) taller than a 16.9-38 on paper. One forum member measured about 69 in for a 480/80R38 against about 67 in for a 16.9, which fits the table. Brands differ: others report some 16.9s as tall as some 18.4s. That is why you should match the make and size on both sides, and check the new height against your fender clearance and, on a front-wheel-assist tractor, with the lead-lag calculator.

What does a real 18.4-38 tire weigh and carry?

Figures differ by make, ply and tread. As one example, Carlstar publishes its 10-ply Farm Spec R-1 in 18.4-38 at 68.9 in (1,750 mm) overall diameter, 7,150 lb (3,243 kg) load capacity, 251 lb (114 kg) weight, 45/32 in tread depth and 26 psi maximum, for a 16 in wide rim. Treat that as one tire, not the size. Our price table above shows the load and ply for each model we list, and your quote confirms the exact tire.

Can 18.4-38 tires be run as duals?

Yes. Duals commonly use 18.4s, often with 16.9s on single-tire tractors of the same model. Duals add traction and flotation, but both tires on a side must be the same make and size, and the tractor needs the right axle, hubs and spacers. Check the tractor maker’s approval for duals before you buy a second pair.

When should you pick the radial instead?

If the tractor works long field days, a radial 460/85R38 or 480/80R38 costs more up front but gives a longer footprint and better fuel use. If it works light hours, a bias 18.4-38 is the cheaper, tougher choice. The cost guide shows the price gap.

What do 18.4-38 tires cost on our site?

We list 12 models in 18.4-38. 11 have a listed price, from $738 (Petlas TA60) to $1,454 (Titan Hi-Traction Lug) per tire, with a median of $1,013. Prices are per tire in US dollars and change with stock and season.

How tall is the 18.4-38 tire?

The nominal overall diameter is about 69.3 in (1,760 mm), which gives a rolling circumference near 218 in (5,528 mm). That figure is an estimate that assumes an 85% aspect ratio, the usual rule for old inch sizes. Real tires vary by make and load, so treat it as a guide and use the tire diameter calculator or the lead-lag calculator before you change size on a front-wheel-assist tractor.

Is 18.4-38 a radial or a bias tire?

It is a bias-ply size. The dash in the size marks bias construction, which costs less and has stiffer sidewalls. See the radial vs bias guide.