Post by riffraff on Oct 16, 2006 17:19:02 GMT -5
If you have installed a straight axle kit in your bus and you are running spacers to keep the tires from rubbing on the springplates, you should have the lug holes drilled and tapped to accept a 14mm lugbolt.
If you look at your Type 3(wide5) or Type 1 drums, you will notice that it takes a smaller diameter lug bolt (12mm)than the drums on the front of your bus. The front drums on your bus take a larger diameter lug bolt - 14mm.
Take your 12mm hole drums to a machine shop and take one of the lug bolts from the front drums on the bus, and get the machine shop to drill and tap the rear drums to accept the larger diameter lug bolt. That way the lug bolts front and rear are the same diameter.
The physics of the relationship between lug bolt diameter and strength are relatively straightforward.
The larger lug bolt will increase the surface area of the threads by about 14%. So you have 14% more "gripping" area for the lugs. Also, although the diameter of the bolt is only 14.3% larger (12mm/14 mm= 0.857 ), the cross sectional surface area is 26.5% greater ((Pi(6^2)/Pi(7^2))= 0.7347, so there is ~26% more metal to resist being sheared by the stress.
The relationship between cross sectional surface area and resistance to shear is linear, so the 14 mm lug bolt resists the shearing forces 26% better than the 12 mm lug.
Also, the stresses being put on the lug bolts because of the spacer are considered “double shear”, so the effective strength of the bolt is half what it would be in single shear. At least with the 14 mm lug, you make up for half of the additional stresses introduced by the double shear, meaning that the ability of the rear lug to resist shear will be 50% of what the front lug is, but if you kept the 12 mm lugs on the rear, the ability to resist shear would only be about 39% of the front lugs.
That is also why it is very important to check the lug bolts for proper torque. The frictional bond between the spacer and drum and spacer and wheel will resist the torsional and shear stresses of weight, acceleration and braking in direct proportion to the torque of the bolts. So proper torque on the lug bolts diminishes the shear forces on the lug itself.
If you look at your Type 3(wide5) or Type 1 drums, you will notice that it takes a smaller diameter lug bolt (12mm)than the drums on the front of your bus. The front drums on your bus take a larger diameter lug bolt - 14mm.
Take your 12mm hole drums to a machine shop and take one of the lug bolts from the front drums on the bus, and get the machine shop to drill and tap the rear drums to accept the larger diameter lug bolt. That way the lug bolts front and rear are the same diameter.
The physics of the relationship between lug bolt diameter and strength are relatively straightforward.
The larger lug bolt will increase the surface area of the threads by about 14%. So you have 14% more "gripping" area for the lugs. Also, although the diameter of the bolt is only 14.3% larger (12mm/14 mm= 0.857 ), the cross sectional surface area is 26.5% greater ((Pi(6^2)/Pi(7^2))= 0.7347, so there is ~26% more metal to resist being sheared by the stress.
The relationship between cross sectional surface area and resistance to shear is linear, so the 14 mm lug bolt resists the shearing forces 26% better than the 12 mm lug.
Also, the stresses being put on the lug bolts because of the spacer are considered “double shear”, so the effective strength of the bolt is half what it would be in single shear. At least with the 14 mm lug, you make up for half of the additional stresses introduced by the double shear, meaning that the ability of the rear lug to resist shear will be 50% of what the front lug is, but if you kept the 12 mm lugs on the rear, the ability to resist shear would only be about 39% of the front lugs.
That is also why it is very important to check the lug bolts for proper torque. The frictional bond between the spacer and drum and spacer and wheel will resist the torsional and shear stresses of weight, acceleration and braking in direct proportion to the torque of the bolts. So proper torque on the lug bolts diminishes the shear forces on the lug itself.