[scissorhands]

I have 2 Citroen Ax10RE's one with 145/65/13's the other with 135/80/13's. The manual recommends 135/70/13's. The Ax with the 145's is much better to drive powerwise, remembering this is a gutless 45bhp vehicle that cant stand load, ie passengers or hills. The AX with the 135's feels too tall geared. The diameter is greater by 35mm and the circumference is 6% longer, so its like I'm always driving up a slight rise... The 135 AX is higher of the ground too by 17.5mm. I havnt done any mpg around this as I'm a newby without instruments and havnt driven them enough. My reckoning is that the viability of tyre diameter modifications would be model dependant. The main consideration being loading ability of the vehicle in question. If its a powerful donkey with lots of power that climbs hills without any loss of speed at constant throttle I'd say yes.