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M-38/M-38A1 Rims and Back Spacing

• CATEGORIES: Features

Morgan stated in a comment that he was a little confused as to why some of the M-38/M-38A1 rims had back spacing changes. Can anyone help answer his questions?

Morgan wrote, “Trying to get a handle on M38/M38A1 military Jeep wheels is difficult at best (let alone all the other Jeep wheels!).

1. Do only military wheels (all 16″ ??) have weep holes? Correct me but I’ve noticed that maintaining a 12 o’clock alignment of the valve stem hole puts the weep hole of a 16″ x 4 1/2″ at 3 o’clock. And the weep hole of a 16″ x 5″ is at 9 o’clock. While the top lug hole on the 16 x 4 1/2″ lines up with 12 o’clock, it’s the bottom lug hole on the 16″ x 5″ that lines up with 12 o’clock.

In addition the backspace on the 16 x 4 1/2″ is about 3 1/4″ while the backspace on the 16 x 5″ is about 3 3/4″. Now admittedly, my research is limited and maybe I’ve only learned enough to be dangerous, but it’s the backspace that got me going.

2. I’m wondering if the shorter backspace on the 4 1/2″ (setting the tire farther from the frame and brake drum) would allow a tighter turn radius (without rubbing? or no issue?) than the deeper backspace on the 5″ (which would move the rim/tire closer to the frame?) ?? Why such a difference in backspace?

3. And of course if the mere presence of a weep hole would allow a quick accurate idea of a wheel’s exact measurements, that would be a plus. I think I’ve correctly learned that the accurate measurement of a wheel’s diameter and width is always inside the rim ?!?

4. I’ve also heard that the military wheels are a higher grade, and stronger ?!?


3 Comments on “M-38/M-38A1 Rims and Back Spacing

  1. Dave from Mn

    No idea for sure, but if they wanted to maintain overall width the same ,would explain putting extra rim width to the backspacing. Should be able to turn shorter with less backspacing if the stops are set to max turn without rubbing. I think that the later pickups got rims with weep hole also.

  2. Terry

    I read tears ago in a military vehicles magazine that the little hole in the jeep rim was not to weep water , but a manufactures tick- mark that was used on the assembly line to distinguish military spec. wheels for paint and assembly . Both military and civilian jeeps were built on the same line at the same time .

  3. Bob W

    The 4-1/2″ wide wheels have a safety bead and are M-38 wheels. The 5″ wheels do not have a safety bead and are truck wheels.

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