1982 308 / Original Metric vs. 14" Wheels/Tires

235-60-14" would be a ~5 mm taller and 15 mm wider; whereas, 225-60-14" would be ~6mm lower and 5 mm wider. (You aren't going to have a lot of width/aspect ratio combination options available in 14" -- but TireRack has a nice Shop by Size panel to show what might be available.)

To calculate a tire's diameter:

Tire Diameter = [(Tire Width) x (Aspect Ratio/100) x 2] + Wheel Diameter

So your stock 220-55-390 are:

Stock diameter = (220 x 55/100 x 2) + 390 = 632 mm

 

Hi
I went down this same road 10 years ago. I bought my 1982 308 in 2007 and I still have it. love the car.
Like you I was going through the tire dilemma, I wanted to keep the original tires and rims (which I still have).

I talked to Michelin who sent me to Coker because they bought the molds for the tires.

Talking with my mechanic about my options, I ended up going with the 16 inch rims and tires. Here is why.
If I went with Coker I would be spending about $400 per tire every couple of years and going through the hassle
of ordering for them and waiting for them to come in.
As you can tell I drive my car, its not a hanger queen.

16 inch tire option is that they are still easy to get and come in different performance ranges (hard or soft compound). The 14 inch rim option does give you more side wall but the question is for how long will they be available and only in limited performance range.

I hope this helps, good luck
Cheers
Mark

 

The correct tire for the 14 in is 205/70x14 which fills the arch slightly better than 16 in option (IMHO) but is a less good tire both more expensive and less choice as well as older technology - go look at the many 14 vs 16 in threads in this section

 

Pretty sure they will as the 108947 center cap seems to be used on all 308 factory wheels (and a bunch of others):

https://www.ferrariparts.co.uk/part/ferrari/108947