Tires: H 78 -15 LT, series tires, tire sizing

Question
I have a 55 1st series p/u truck. Currently it has H78-15 LT's, the rims are an 6 bolt config. Wanted to know if these are outdated specs for tires. I am wondering if Can you tell me what tires will fit for replacement? or if will ST225-75-R15    will work

Tires Size:                      ST225-75-R15                   

Tire Brand:                     Free Star 8-ply (Load Range D)

Max Tire Load:               2540 lbs.

Answer
Jonathan,

H78-15's are what is called AlphaNumeric series of tire sizing - and that has been super ceeded by the current system - P metric.

But AlphaNumeric series tires didn't start being used in the the 1960's.  Prior to that they used a series of tire sizing schemes.  Unfortunately, my books don't go earlier than about 1970.

But Let's assume that we start with the H78-15 and try to match that.  I wrote up an exchange:

http://www.barrystiretech.com/vintagetireexchange.html

According to what I wrote up, an H78-15, a P225/75R15 is a bit wider and has a bit smaller load carrying capacity - so i would go there with the idea that you aren't going to use this truck as a work truck.

Do NOT - I repeat - do NOT use an ST225/75R15.  Those are designed for trailer usage and are built to much lower quality standards and will not stand up to the usage a truck puts tires through.

See if you can find P225/75R15's - and Tire Rack lists 19 different tires, so this shouldn't be much trouble.