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tire size

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69longhorn

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Hi there,
does anybody know the correct original tire size my 1978 GMC 1/2ton was built?
thanks from Germany
69 longhorn
 
Look at your RPO codes in your glovebox. You can also look on your dirver's door if you have a factory door.
 
I would guess two sizes:

215 75 15 or 235 75 15.

I know my 87 1/2 ton was only available with these two sizes.
 
Did you check the inner fender or maybe the air cleaner seen a few canadian 75 with on the air cleaners 77 had then on the driver side inner fender might have dirt on it un less yours is very clean.

1/2 Ton how meany leafs is it a 4x4 or 4x2 did it come with trail package.
 
I believe it's possible that a 78 could have had bias ply tires, L78-15 on 4x4 and 4x2 with optional tires or GVW. G or H78 for cheapos. Otherwise GR78 HR78 or LR78-15.
 
I forget now for sure but in canada the Metric tire sizing started 80 or 81 so you still could get both sizing for one two years after .
 
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