1. By the VIP plate on the trailer
There is a VIP plate on each trailer. It shows the GVWR on the plate, which means the trailer weight when empty plus the maximum capacity weight of the trailer. If the trailer with only one axle, rating of the axle is at least same or a little bigger than GVWR.
2. Ask the trailer manufacturer
If your trailer with 2 or 3 axles you can not judge axle weight rating by trailer VIP plate.
The trailer GVWR is determined by the rated of 2 or axles ratings. But this doesn’t mean that the ratings are always same for the axles. For example, the trailer GVWR is 6000 lbs, axle's weight rating might be 2,550 lbs and 3500 lbs. This means that if you ever have any questions about your trailer axle weight capacity you can seek out information directly from the manufacturer. This is also the simplest and most accurate method.
3. Check the stickers on trailer Axle
Often an axle's weight rating will appear on a sticker or plate on the axle beam itself, or sometimes the trailer's main identification sticker will include axle ratings. This is helpful unless of course the axles have been replaced during the trailer's lifetime.
4. Check Trailer Axle Beam Diameter
Typically an axle with a 2-3/8 inch diameter has a 3500lbs weight rating. One that with 3 inches diameter is usually rated for 6000 lbs or 7000 lbs. The one with 3-1/2 diameter beam is 8000 lbs axle.
But if your trailer is equipped with
torsion axle, this method is not useful.
5. Check axle hub/drum bolt pattern
Wheel studs number on the hubs can also give some idea to judge axle weight capacity. The axle hub with 4 wheel studs usually rated 2000 lbs or below. The axle hub with 5 wheel studs usually rating is 2500 lbs - 3500 lbs. Hubs with 6-wheel studs could be rated for axles from 3500-lbs up to 6000-lbs. Hubs with 8-wheel studs is the axle rated 7000 lbs or more. If you disassemble one of the hubs and remove its bearings, those bearing part numbers can also help you determine capacity. For instance, hubs for a 3500-lb axle often use bearings L68149/L44649; hubs for a 5K or 6K axle often use bearings 25580/LM67048.