roger_scotty
Gold Member
The subject of wheels comes up commonly, so I'll put down what I know and hope others will add to it.
It helps to think of wheels not as one assembly, but as being built up out of two pieces with very different jobs.
The first part is the wheel rim. Rims are built to fit to tires, and nobody cares what brand of machine a rim goes on. The rim's job is to support a tire. Rims are identified by a series of numbers that are often stamped into the rim and identify the drop of the bead, the width of the rim where the tire fits, the inside diameter of that rim, and sometimes the year it the rim was made. These numbers are very standard, commonly in inches, and are universally recognized. This is all done so that tire manufacturers can specify what rims should be used with a certain tire size.
The other part of a wheel is the center web. The center web is the part that adapts a rim/tire combination to a specific tractor. The center is designed by the tractor manufacturer, and is the only part that makes the rim/tire assembly specific to a Ford, Chevy, JD, Yanmar. or anything else. As far as I know, the center doesn't have a universal marking system like the rim does. But there are some common terms are used to describe the part. These terms are the center knockout (hole) diameter, the characteristics of the bolt circle, and the center "offset".
THe center hole diameter and the bolt circle are both fairly standard. Most of the tractor (and car) industries use the same center holes and a limited selection of bolt circles. The difference in wheels comes from the offset measurement. Offset does vary from tractor to tractor - often varying within one manufacturer's different models.
Offset would be easy if the center were just welded into the center of the rim, but few wheels are that way. Offset is usually specified in terms of how many inches the center web is displaced from the center of the wheel. We all know that tractors need the option of allowing
the wheel to be mounted from either side so that the tractors tread width is adjustable. For that reason, most Ag wheel centers have a bolt circle made with a flat surface designed to be used with flat faced lug nuts or bolts. Making it that way allows the mounting lugs to pinch the wheel center from either side. If you think about it, having a flat center also allows the offset to bbe specified as a single number. The offset number is just the distance (usually in inches again) that the center web is moved away from center of the wheel rim before it is welded
The exception to that offset rule is where the bolt circle calls for a tapered seat type of lug bolt or nut. Tapered seats can only be used with the wheel mounted in one way, and are used when the designer has some reason to require that the wheel be mounted in only one way. One place you will see this used in tractors is where the offset is very large - like in super fat turf tires.
What this all means is that there is a simple alternative to ordering Yanmar wheels to fit Yanmar tractors. And it isn't scrounging through the junk yards for wheels to fit your tractor...fun though that is. All of those wheel parts are available from automotive and tractor wholesalers. A guy can order rims and center webs and weld them up himself. At worst he might have to drill a new pattern of lug bolt holes. There are also custom wheel shops that are well aware of how universal that the wheel parts are. If you provide them with the measurements above then they can make you up a set of wheels to fit anything.......good luck! roger_scotty
It helps to think of wheels not as one assembly, but as being built up out of two pieces with very different jobs.
The first part is the wheel rim. Rims are built to fit to tires, and nobody cares what brand of machine a rim goes on. The rim's job is to support a tire. Rims are identified by a series of numbers that are often stamped into the rim and identify the drop of the bead, the width of the rim where the tire fits, the inside diameter of that rim, and sometimes the year it the rim was made. These numbers are very standard, commonly in inches, and are universally recognized. This is all done so that tire manufacturers can specify what rims should be used with a certain tire size.
The other part of a wheel is the center web. The center web is the part that adapts a rim/tire combination to a specific tractor. The center is designed by the tractor manufacturer, and is the only part that makes the rim/tire assembly specific to a Ford, Chevy, JD, Yanmar. or anything else. As far as I know, the center doesn't have a universal marking system like the rim does. But there are some common terms are used to describe the part. These terms are the center knockout (hole) diameter, the characteristics of the bolt circle, and the center "offset".
THe center hole diameter and the bolt circle are both fairly standard. Most of the tractor (and car) industries use the same center holes and a limited selection of bolt circles. The difference in wheels comes from the offset measurement. Offset does vary from tractor to tractor - often varying within one manufacturer's different models.
Offset would be easy if the center were just welded into the center of the rim, but few wheels are that way. Offset is usually specified in terms of how many inches the center web is displaced from the center of the wheel. We all know that tractors need the option of allowing
the wheel to be mounted from either side so that the tractors tread width is adjustable. For that reason, most Ag wheel centers have a bolt circle made with a flat surface designed to be used with flat faced lug nuts or bolts. Making it that way allows the mounting lugs to pinch the wheel center from either side. If you think about it, having a flat center also allows the offset to bbe specified as a single number. The offset number is just the distance (usually in inches again) that the center web is moved away from center of the wheel rim before it is welded
The exception to that offset rule is where the bolt circle calls for a tapered seat type of lug bolt or nut. Tapered seats can only be used with the wheel mounted in one way, and are used when the designer has some reason to require that the wheel be mounted in only one way. One place you will see this used in tractors is where the offset is very large - like in super fat turf tires.
What this all means is that there is a simple alternative to ordering Yanmar wheels to fit Yanmar tractors. And it isn't scrounging through the junk yards for wheels to fit your tractor...fun though that is. All of those wheel parts are available from automotive and tractor wholesalers. A guy can order rims and center webs and weld them up himself. At worst he might have to drill a new pattern of lug bolt holes. There are also custom wheel shops that are well aware of how universal that the wheel parts are. If you provide them with the measurements above then they can make you up a set of wheels to fit anything.......good luck! roger_scotty
