Tire size for 74 Valiant Brougham
I'm told that D78-14 or DR78-14 tires are original. When I shop, I see P185-75R14 or P-185-70R14s available as modern "closest" sizes.
If your car was equipped with 14"x4.5" rims (common on base models), then it looks like the OEM tire size was D78-14 or 6.95-14 (see
Plymouth Valiant, Plymouth Duster, and Dodge Demon specifications). The aspect ratio of the D78-14 is 78%, which is close to 75%, with an overall diameter of 25.50". According to
Barry's Tire Tech, the aspect ratio of the 6.95-14 is 82% with an overall diameter of 25.30". The P185/75R14 has an overall diameter of 24.93" while the P195/75R14 has an overall diameter of 25.52".
FJR... you said P195-75R14 were on your Dart. I would think this is a more common size than the 185s. Only difference is that the 195s are a little under 1/2 an inch wider right? You have no issues with the tires rubbing on the rim? They work good for you?
The P195/75R14 is easier to find than the P185/75R14 and is a closer match to the OEM tire diameter. The 10 mm difference is 0.39". Although the 4.5" rim width is less than the 5.0" minimum approved for my
Canadian Tire AW+ tires, The tires fit fine and I have not had any issues with them.
My Dart is a parts car now and I ran both the OEM steel and aluminum wheels (14x6 Keystone Classic?). I'm now running P195/75R14 tires on 14x4.5 steel rims on the front of my 65 Barracuda and P225/70R14 tires on 14"x7" Cragar SS rims on the back. Those Cragars are too wide & have too much offset for the front of the Barracuda.
If you stick with an OEM rim, you will likely not have any fitment issues - more likely if you start using aftermarket rims with weird offsets.
I see in all posts guys are using 75 aspect ratio. Anyone know what's the difference between the 70 and the 75s? Are the 75s preferred?
The aspect ratio (70% vs 75%) is the ratio of the tire's height to its width. A 75-aspect tire is 75% as tall as it is wide so the 70-aspect tire has a lower profile. Lower profiles handle better while higher profiles ride better.
If you're interested in having an accurate odometer/speedometer, pick the tire size (diameter, aspect ratio, & section width) that gives you the correct overall diameter. You can change the required tire diameter and keep the odometer accurate by matching the speedometer pinion to the new size.
If your car already has usable tires on it, I would wait until it arrives and then worry about upgrading. I may be mistaken but, if your car has front drum brakes, you may have a 4" bolt circle. Disc brakes have the LBP 4.5" BC, which gives you much bigger rim selection.
