Why Are Inner and Outer Bearings on Trailer Hubs Different Sizes

Question:

Why is wheel bearings diferent sizes? The inner are bigger than the outer. Why dont they make it the same size?

asked by: Koos

Expert Reply:

The Dexter Trailer Idler Hub Assembly # 8-258-5UC1 that you referenced actually uses the same # L44649 inner and outer bearing, which has a 1.063 inch inner diameter.

Many trailer hubs though do use different size inner and outer bearings and this simply has to do with the spindle they are designed to fit. Many spindles will have a tapered shape that requires a larger inner bearing and a smaller outer bearing. When purchasing replacement hubs it is important to verify the inner and outer bearings that your existing hub uses (along with matching the weight rating and bolt pattern).

The bearing numbers should be stamped right inside the bearings themselves but you can also measure your spindle at a few locations to determine the bearing sizes that are needed. I have attached an image showing the measurements you will need to take. I recommend using a digital caliper since the measurements need to be exact.

If you can tell me what bearing numbers your hub uses or the measurements you took on the spindle I will be happy to recommend the correct hub.

expert reply by: Chris R