Will going from 195 to 185 result in better fuel economy?

This chart shows the differences between the stock 195 and oversized 205s :
DimensionTire A: 195/65 R 15
(25 x 7.68 x 15)Tire B: 205/65 R 15
(25 x 8.07 x 15)Difference
Width
Sidewall height
Overall height
Circumference
7.68" (195.00mm)
4.99" (126.75mm)
24.98" (634.50mm)
78.48" (1993.34mm)
8.07" (205.00mm)
5.25" (133.25mm)
25.49" (647.50mm)
80.09" (2034.18mm)
+0.39" (+10.00mm)
+0.26" (+6.50mm)
+0.51" (+13.00mm)
+1.61" (+40.84mm)
RPMs will drop by 35. Speedo will read low by 2.01%. My thought is the reduction in RPM should off set the addition of a slightly wider foot print. Ideally, I would like to go taller to a 205/70/15 but this might be too drastic:
DimensionTire A: 195/65 R 15
(25 x 7.68 x 15)Tire B: 205/70 R 15
(26 x 8.07 x 15)Difference
Width
Sidewall height
Overall height
Circumference
7.68" (195.00mm)
4.99" (126.75mm)
24.98" (634.50mm)
78.48" (1993.34mm)
8.07" (205.00mm)
5.65" (143.50mm)
26.30" (668.00mm)
82.62" (2098.58mm)
+0.39" (+10.00mm)
+0.66" (+16.75mm)
+1.32" (+33.50mm)
+4.14" (+105.24mm)
RPMs will drop by 86 and speedo will read low by 5.01 %.

 

Sorry this didn't print the way it was intended.

 

No problem on the formatting just they look like numbers are derived from the aspect ratio. I've found aspect ratio to be unreliable. For example, using the specifications from TireRack.com which list the measured 'rev/mile' shows it is not a function of aspect ratio:

	Column 1
0	[th]ratio[th]rev/mi[th]vendor
1	[tr][td2]195/65R15[td2]831[td]Continental
2	[tr][td2]195/65R15[td2]836[td]Dunlap
3	[tr][td2]195/65R15[td2]829[td]General

Source: TireRack.com

The critical dimensions are:

• rim width - to fit on the original wheels
• tread width - to fit inside the top of the rear wheel well and not impact the top edge on a bump
• overall diameter - to fit inside the front and rear limits of the wheel well

Bob Wilson