Tires: using radials on 30s cars, bias ply tires, war cars

Question
Mr. Smith,
I have been doing some research over the last few months about using the newer radials that can be used on pre-war cars and look period correct.  I have a 1937 Packard 120 sedan that currently has 700-16 tube type bias-plys that will need replaced.  I am interested in possibly using radials, but I have heard conflicting opinions on what is required to use them successfully.  I have heard you have to have the rims reinforced.  I have heard that tubeless radials won't hold air on pre-war rims that were designed for tubes.  I have heard that radials introduce greater stresses to the rim because of the more flexible and shorter sidewall design.  I have also read from a radial tire manufacturer for collector vehicles that radials introduce less stress on an older rim.  And, I have read that tubeless type tires were always able to work with older rims and hold air.  I am interested in your opinion on this!  Thank you.
Dennis

Answer
Dennis,

You said:  "I have heard you have to have the rims reinforced."

Radial tires concentrate the stresses applied to rims and rims designed for bias ply tires need to be reinforced if radial tires are used.  Personally I think you might be able to get away without reinforcing the rim if the vehicle isn't driven much - but I admit not having enough experience in this area to make a definitive statement.  

You said:  "I have heard that tubeless radials won't hold air on pre-war rims that were designed for tubes."

That is probably true.  The air tightness of the rim was never an issue when tubes held the air.

You said:  "I have heard that radials introduce greater stresses to the rim because of the more flexible and shorter sidewall design."

I don't think it's the shortness of the sidewall, it's the fact that stresses are concentrated in a small area due to the radial cords - as opposed to a bias ply tire where the cords involved in the footprint extend further around the circumference.

You said:  "I have also read from a radial tire manufacturer for collector vehicles that radials introduce less stress on an older rim."

I'm pretty sure he doesn't remember rims cracking when the radials were popularized in the 1970's.  But it's also possible that what he says is true when comparing older high pressure bias ply tires and new low pressure radials.

You said:  "And, I have read that tubeless type tires were always able to work with older rims and hold air."

There are some compatibility issues with the beads seating on the rim.  But I think the real problem is the rims themselves.  There are rims the were manufactured that are airtight, but then there are some that aren't.