Tire Sizing Questions

[Kahn Man]

I've decided I've had enough with bias-ply tires on my '57, and want to get the whitewall radials that Coker sells. Couple questions:

(1) Do I need P205/75R14 or P205/70R14? I have stock rims and wheelcovers. (I can't seem to figure out Coker's X-reference chart)

(2) Does anyone have any experience with the Coker Classic Radials versus the BF Goodrich Silvertown Radials?

I've heard horror stories like the rest of us about spokes falling out and beads falling out, but I don't have wires and I understand if you mount the tires from the back of the rim, the beads seat properly.

[nomadbird]

I'll try to answer this even though I'm no expert on this subject. As I understand it, the 7.50x14 may be replaced with either the P205/75R14 or the P215/70R14. You will find both radial equivalents have a smaller rolling radius than the 7.50x14 bias ply. I have never seen this published in any of the tire vendors literature. They do publish the outside diameter of their various tire sizes, but that doesn't mean much when you load them on the ground.

What this means is your radial equipped car will have slightly less ground clearance than it had with bias plys. Not much, but measureable. Here is another change you can expect with radials. Your engine speed will be higher to maintain the same true road speed. An automatic trans car with bias ply tires will register 2500-3000 RPM when cruising in the 65-70 MPH range. The same car with radials will be in the 3000-3500 RPM range at the same speed.

I hope your dissatisfaction with the bias ply tires isn't really caused by a worn idler arm bushing, weak shocks, or some other suspension or steering component.

Tom

[Kahn Man]

Yeah, that was a typo on my part. I ordered the Coker Classic P205/75R14s. I have not gotten them mounted yet because one came damaged, but the reason I switched was because I had radials on a '67 GTO. That car drove great! Granted there are significant differences in a 67 Goat and a 57 Bird, but at least it will keep me out of the grooves in the road. I've talked to several people with the tires and they all seem happy.