Figuring out the correct rim size for your tire can be a bit tricky – in fact, it’s one of our top tech support questions here at Steiner Tractor Parts.
Many people assume that the tire size and the rim size are the same thing, but that’s untrue. Here’s a quick guide to the reasons why and how to measure your tires and rim to be sure you are getting the right replacement parts.
Many farm tractor tires are sized with two sets of numbers ( more modern ones use three numbers, like the tires on your car). The first number is the width of the tire, the second number is the diameter of the rim.
The tire width, however, isn’t going to be the same as the rim width. This is because your tire needs to fit inside the rim – so your rim width measurement is a little smaller than the tire width measurement. This pulls in the side walls of your tire to fit inside the rim.
The easiest way to be sure you get the correct size rims is to measure the ones you are replacing. Measure from the inside (bead to bead) to get the correct width. The number you come up with should be about one inch smaller than the outside measurement of your rim.
https://www.steinertractor.com/pdfs/measure_rim_instructions.pdf
There are three special cases that can make this process a bit complicated:
- Tractor pulling. If you are tractor pulling, you’ll probably want to adjust your rim size to be a little wider than normal. You can give yourself a little better traction by upsizing your rims to be the same size as your tractor tire. This will keep the tire’s side walls straight instead of pulling them in. It is very difficult to get the tire on the rim this way, but it can be a worthwhile tractor pulling strategy.
- Old Rims. In the early days (pre-1940), tractor rims were significantly narrower than those sold today. The same size tires were often used, but they were pulled in towards the rims more – resulting in a more ballooned-out look. If you are using an older tractor for farming or tractor pulling, I recommend replacing both the rims and the tires to more modern sizing. If, on the other hand, you are doing a pristine restoration of an older tractor, then you’ll want to track down the more narrow rims and old-style tires with the correct bead height to match the flanges.
- Old literature. In the mid-1950s, tire manufactures revamped the numbering system. Much confusion has been caused by people using original shop manuals and spec sheets to replace the tires and rims on their tractors. Older methods differentiated between “conventional” tire sizes and “wide base” sizes. If you don’t pay attention to converting the old sizes to modern ones, you can end up with the wrong tires for your tractor. Talk to your tire salesman if you are unsure how to order the appropriate size.
Once you have your rims, it’s time to get your hands dirty and put the new ones on. Here’s a tutorial I did this past May on how to replace your rims using ordinary shop tools. I hope it helps!
Glenn says
You made a diagram to show measuring the width of a rim, So what about making a diagram to show measuring the diameter, you only show the width, so how do you measure the diameter for a ford 8n tractor, front rim. Using a example for a tire size of 6.5 x 16.
Suzette Thomas says
Glenn I am going to have one of our techs help me out. I will make a quick video and post it as soon as possible.