Front vs. rear wheel sizing

[C4 Pazzo]

Grady Clay made a recommendation in the ever-growing "Hester" thread to consider putting 6 x 15s in the front and 7 x 15s in the rear, with the same size tire, to slightly change the grip bias to the rear.

Originally Posted by Grady Clay

.....
The wider 7x15 wheel with the same size tire (185/70VR15) puts slightly more rubber on the ground. That changes the front-to-rear grip bias slightly toward the rear. Any move to the rear is advantageous.
I’ll repeat my recommendation:
7x15 in the rear, perhaps moved out as much as possible.
6x15 in the front, perhaps moved in as much as possible.
Both with current 185/70VR15 Michelins and ‘flat side’ LWB fenders. Grady

This got my attention because I have a set of 5.5 x 15s on my '70 911T targa and a set of 6 x 15s on my '69 912. I'm wondering if the same principles would apply for 5.5 x 15s and 6 x 15s, or if the 1/2 inch differential vs 1 inch differential would be insignificant. If not, I'd consider putting the 6s on the rear of each car and the 5.5s on the fronts of each. I'd need to mount the same tires on both sets, of course.
Thoughts?

[304065]

5.5's were originally designed for 185s and you could get 205s on the sixes. Everyone claims that 225s handle funny on sixes, I raced a few seasons and couldn't tell, but what do I know?

Anyway, handling balance is one thing, but remember that braking performance is a function of front tire traction mostly. I put the same question to my race mechanic, why not use 205 up front and 225 in the rear for better handling balance, but his answer was braking. Also rotating tires is easier when they are all the same size. For a street car I don't think it makes a huge difference.

[ZOA NOM]

An addition to Grady's assessment would be that not only does the wider wheel put more rubber on the ground, it tends to create a stiffer sidewall that is less flexible, which adds to the grip.

[Dantilla]

225s on a six?

I race my 944 on 7" wheels, and 225s are still pretty pinched. I'm not sure a 225 can perform properly on a six inch wheel.

I tried putting my 225 rain tires on an old 912E I used to own, but they would rub badly with any compression of the rear suspension.

Still, with 911s, adding tire to the rear to compensate for the rear-weight bias is a good thing.

[C4 Pazzo]

I hadn't thought about the ability to go to 205s on the 6s vs. 195s on the 5.5s. Makes this a more difficult decision. I'm guessing that i. there may be more effective ways to achieve the desired balance result (e.g., sway bars/sizing) and ii. For my street-driven cars the balance differences won't be that crucial.
I appreciate the input.