The 1970 Dodge Data book says 14" with the A66 package;
http://www.hamtramck-historical.com/ima ... er0024.jpg
It seems like I remember something about that being changed to 15" later on in the model year, I will look......
Do you have a broadcast sheet for it? If so, it will tell you for sure what your car came with.
Edit;
Checking the broadcast sheets I have, they came both ways.
I have 5 on file with U82 tires & the "59" tire label in the door jamb. These were E60X15 RWL tires.
I have four on file with T87 tires & the "62" tire label in the door jamb. These were F70X14RWL tires.
I have one on with with T86 tires & the"62" tire lable in the door jamb. These were F70X14 WSW tires.
Near the bottom of this page;
http://www.hamtramck-historical.com/ima ... er0006.jpg
It shows the T86 14" white side wall tires standard with the 340 & the U82 15" tires available at extra cost.
No mention of the T87 tires there for the 340, but the fleet books were printed early in the model year, so they must have been added later.
So, time to check your broacast sheet & / or the original tire sticker in your driver's side door jamb to know for sure what your car came with.....