17" Wheels on a 69 Dart with Stock Suspension

burdar said
The overall tire diameter and weight isn't the issue. It's where that weight is in relationship to the center of the wheel. The wheel/tire combo can be the same diameter and the same weight, but if more of the weight is out at the edge(farther way from the wheel centerline) the more inertia it will have. Is it enough to worry about? Maybe not.

I seriously doubt it. The wheel weights for the 17/18" wheels are less than most 15" set ups, especially for like size combinations.

The 275/35/18's on 18x9's on the front of my car were several pounds lighter than the 15x7" cop car rims with 225/60/15's I had on it. The 295/35/18's I have on the back were pretty much exactly the same weight, slightly less. The moment of inertia change is unlikely to be significant enough to cause any problems at all. And if you run narrower tires than that they might even be an improvement in weight and moment of inertia. It's funny, people seem to bring up the wheel weight issue when 17/18 or larger rims are involved, but no one ever says a thing about it when people switch from 14" pizza-cutter narrow bias ply's to a giant set of BFG T/A 275/60/15's. Those probably weigh twice what the OE wheels and tires weigh, and are taller to boot.

The bigger issue for the 7 1/4 will probably be the improved traction the modern tire compounds will offer compared to the hockey pucks that originally came on the car.