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Hello!

We just received our Cactus with BlueHDI 100 engine, and before this new engine was released, I remember the brochure saying that the 16-inch wheels had better fuel economy than the 17-inch wheels. However, the updated brochure featuring this engine, the fuel economy is the same. Does anyone know whether these numbers can be trusted?

Looking at the 16-inch wheel, the design is very, very open, with only four thin square outlines and then you can see the brakes and everything quite exposed. Could this potentially become a worry some years down the road with the parts being exposed like that? The 17-inch wheels seem to have more "stuff" in the way, perhaps offering a bit more protection?

Also, what are the "ultra low rolling resistance" wheels? You can't seem to purchase these, or are they named different? The latest Cactus Airflow concept even has "ultra ultra low rolling resistance" on it (which, quite opposite to the fully open 16-inch wheel design, is fully closed).
 

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I believe that there are 5 factors affecting fuel consumption regarding wheels, which are:

1. DESIGN

The aerodynamic aspects of the wheel design are really quite insignificant except at high speeds.

2. DIAMETER

Within the confines of car wheel diameters (say, 10" to 22") this too is not significant.

3. WEiGHT

Larger wheels tend to weigh more, and so do the tyres on them. This is important for fuel economy.

4. WIDTH

Wider tyres give a larger footprint on the road which increases rolling resistance and hence reduces economy.

5. COMPOUND

Rubber compound can affect rolling resistance - see above.

4 & 5 are really the "grip" side of the equation, and this is generally where the trade off comes - grip for acceralation, cornering and braking or better fuel consumption.
 
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