I had a lot of trouble finding good performance tires for the 14" rims. During my search it became apparent that 15" also is becoming rare amongst performance tires.
It seems that the tire manufacturers are targeting the 16" to 18" market and some even up to 20".
I therefore think we should be careful not to place ourselves in the situation of having trouble finding tires again in a few years.
The problem is if you take that view the manufacturers will keep increasing the diameters, and we will never have a stable availability.
That is why my first thoughts have been 16" all the way around, but 17" on the rear could be ok too.
Well I'm sorry but I think 16" are too big for the front. In fact I agree with Anders and would sooner keep my 14" at the front, rather than fit 16". I also don't want to go above 16" at the rear. So my cheap option would be to keep the original 14" front and have some 16" for the rears.
As far as the width go, I think 6.5" is the minimum for the front, but I would like to go 7.5 on the rear wheels. The 195/60R14 were always borderline too big for the original 6" wide rims.
The reason I don't want to go beyond 6.5" wide at the rear is that you don't have the room on the inside to the suspension. To have 7.5" widths you would have to change the offset, and that can lead to bearing problems. Changing bearings is something you don't want to have to do too often!
So if some of you wish to have 16" x 6.5" wide with the correct 29 mm offset for the front, I'll have two but for the rear and keep my 14" fronts! (actually I'll have three as I would like a spare in case of damage)
As for tyre availability, sizes that are no longer easily available become available through vintage tyre supplies after a while, just like you can get correct Bagheera rear tyres (185HR x 13 XVS) now.
Regarding tyres, if 225 is too wide I'll fit 215, but I have seen 225 on a 6.5 rim and it was O.K. It may not be the optimum, but there is a tolerance. If you fit wheels and tyres too much bigger it won't look right IMO as this car was not designed for the new huge wheels with ultra-low profiles. Others may disagree. I'd sooner it looked right.
Roy