Before measuring up your axle, it pays to dry fit all the components to the spindles. In a clean, dust free area, mount the bearings, hubs and any braking hardware you are using.
Place the assembled unit inside the tire and wheel you are using, and place a straight edge across the tire sidewall. Measure up from the sidewall edge to the highest part of the braking hardware and add at least 3/4" (minimum) to this.
Remove the hub unit and measure down from the sidewall edge of the straight edge to the hubface mounting surface of the rim.
Add the measurements together, multiply x2 for both sides of the trailer and add the overall chassis width. This is the hub face to hub face measurement for your axle.
If you are using dropper extensions, the room these take up over and above the braking components will need to taken into consideration.
Hydraulic disc brakes inherently take up more internal space between the wheel and the trailer chassis and in most cases when the brake pads wear down, the caliper unit will move closer to the chassis.
Hydraulic and electric drum brakes take up less valuable space, but consideration needs to be given for access to the manual adjuster, any bleed nipples, park brake levers and allowing space for the cables and hoses to move and flex.
For straight beam axles, the spring center measurement is also required before making your axle.
If you want to measure the axle directly off your chassis you need to clamp the guard approximately around the area where it is to go. If you are unable to clamp the guard or if the clamps will not hold, tack weld the guard in position.
Position your tire and rim inside the fender and line up the outside of the tire flush with the rim of the fender, both vertically and horizontally. If you are pushed for room within the fender, you can move the tire out so that the start edge of the tire tread is flush with the fender.
Position the wheel within the fender, until the tire is flush with the outside rim of the fender both horizontally and vertically.
Once the tire is in position, measure from the inside hub mounting surface of the rim, to the outside edge of the spring. If your springs are set up correctly this will be the same measurement as the outside edge of the chassis. We'll call this measurement "A".
Measure from the inside mounting face of the rim to the outside of the spring for measurement A.
Measure your chassis width across the central part of your chassis for measurement "B". The Hub to Hub face measurements will be measurement "A" x2 (doubled) added to measurement "B".
Measure spring bolt centers and the outside of the chassis for ensuring correct axle length
Measuring between the spring center bolt centers will give you the spring centers. Another way to get this is to measure your chassis width "B" and subtract the width of one spring.
These measurements should be all that is needed to get the axle manufacturer started. If you are going for a different style axle (ie, stepped or dropped axle) then further measurements will be required.
Axle showing hub to hub face measurments and spring centre measurements.
These measurements should be all that is needed to get the axle building started. If you are going for a different style axle (ie, stepped or dropped axle) then further measurements will be required.
Click here for information about building your own trailer axles.