1970s Radial tire adjustment

[34837]

My 73 Deville came to me with radials, first available as an option that year. The spare is also apparently original. So- from what I've read tweaks to the front suspension were necessary for radials, can I assume that this would have been done in the factory? The car was bought of off a dealership that had ordered most available options, don't have a build sheet but original bill of sale denotes a CB radio as only add on. Thanks!

[Big Fins]

How are the tires wearing? Nice and even? Any lateral feathering of the tread? This issue would mostly indicate a toe issue. Toe-in should always be 1/16" in. When radials replaced bias ply tires, we were always to increase the right side caster by a half a degree positive. Camber was generally set at 1/2 positive. The camber setting also depends on the size of the persons riding in the vehicle.

The originals were labeled as LR78-15. Any modern replacement should be 235/75R-15.

If you're getting good wear patterns, you may not need to make any adjustments.

[klinebau]

Typically, a radial tire will want more caster than a bias ply.  The caster specs for bias ply are usually negative and a radial tire will want positive caster.  The suspension will probably not allow much more caster than zero, but the most positive caster you can get evenly on both sides will be best.

[James Landi]

What does your owner's manual and door tag say is the recommended tire inflation?  Makes a world of difference if your tires are over inflated.

[35-709]

Radial tires need 7 to 10 psi (32 to 35 psi) more pressure than the old bias-plys.  Yes, the ride may be a little  stiffer, but that is the trade-off for better handling and increased tire mileage.  Use any pressure you want, but the fact remains radials need more pressure to perform as they were intended.
And yes, I wholeheartedly agree with "klinebau"  that cars with radials need positive caster.