Well I agree but good luck trying to find any housing anywhere that's thicker than .400 on the rear
3/16" = .1875
attached is a plot of axle housing stiffness normalized to the the extreme duty Spicer D60 (3.5” with 0.4” wall). Wall thickness shown in 1/32” increments. This assumes equal axle lengths and material (elastic modulus). Bending and torsional stiffness are identical when normalized. Not sure where the OEM m220 falls? Need wall thickness and diameter data. But can easily add this. If m220 is a 3” with 0.25” wall it is only about 40% as stiff as spicer D60.
4 link is great and the truss is good, but you still have a relatively weak m220 axle... there's hundreds of threads on this on Plenty of Jeep forms for the past 20 years and it all boils down to what tire you want to run everybody basically says 37/38 is the maximum for the d44m220... it might help to run a truss or a brace or Special cover but the bottom line is that axle is just undersized for 40-in or larger tires.
I would love to see true 33's, 34's, and 35's on this graph.Attached is an update plot of axle tube housing strength and stiffness normalized to OEM SAS m220. Numbers used for oem are 2.75” with 9/32” wall. Got them off internet from Jeep axle. If anyone has actual numbers please include? I can update to be more accurate.
Wheel/tire load factors were generated based on weights and normalized to OEM SAS (34.4” and 90 lbs). 37s assume 110 lbs, 38s are 120 lbs, and 40s at 130 lbs. wheel/tire weight drives ultimate load factors. Load factors included are linear acceleration (f=m a), torsional equivalent (T= I a), and moment arm (leverage) increase. Torsional inertia calculated as I= m r^2 (strongest contributor).
Assuming linear superposition with load factors normalized to OEM. This is extreme worst case but may serve as a reasonable design threshold. Final load factors were 37s at 1.8 times oem, 38s at 2.0, and 40s at 2.5. These wheel/tire thresholds were included on plot.
normalizing everything to OEM allows for scaled comparison and doesn’t require actual loading quantification. It however assumes OEM m220 was designed for 35s at limit state.
This only compares axle housing capabilities. Housing is the most straightforward and simplest to compare from an engineering design point of view. But if the rest of axle is designed around housing strength (flanges, pumpkin, bearings, axle shaft) then all is good. Hopefully aftermarket manufacturers will do this. But doubtful. There seems to a bunch of variations in just housing designs.
Just strengthening/stiffening oem m220 housing doesn’t address other components and seems to become a rather expensive band aid ultimately resulting in alternative weak spots. Poor design philosophy from a systems point of view. Always chasing the next failure point.
the spicer extreme D60 axle tube housing is a beast. Almost 3x stronger than oem. If the shafts, bearings, pumpkin, etc was designed to match then seems like a great bolt-on choice for 40s.
Yup. For my 69 I went straight to the Sterling 10.25" and got an OEM electric locker from a 10.5" for $300 to put in it. She's heavy (400 lbs) but for less than a grand I have a full-floating ELD bulletproof axle with 5.38 gears and disc brakes.
FWIW, this OEM 10.25" has 1/2" thick 3.5" OD tubes
I will add those. Glad to see someone else likes “charts and graphs”. Reminds me of the silly Dave Letterman skits.
and 8 lug hubs.Yup. For my 69 I went straight to the Sterling 10.25" and got an OEM electric locker from a 10.5" for $300 to put in it. She's heavy (400 lbs) but for less than a grand I have a full-floating ELD bulletproof axle with 5.38 gears and disc brakes.
FWIW, this OEM 10.25" has 1/2" thick 3.5" OD tubes
