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Re: Re:
On soft going, the rules are indeed different.
When a tyre sinks into soft ground the contact patch lengthens to include more of the circumference and so the weight is distributed over a larger area. In this circumstance the larger the wheel diameter the less it will dig in and theoretically the lower the rolling resistance. However, if the ground is very soft with a firm layer below, like with soft snow or sloppy mud, then a narrow tyre that will cut through to the grip below may be more efficient as all that a wider tyre will do is cut a wider trench across the landscape.
Using very low air pressures and large diameter fat tyres on semi soft surfaces, like moist soil, can prevent the tyres from digging in. And in such situations the wider, softer and larger diameter the tyre, the softer the ground that can be efficiently ridden.
However the danger of 'snakebite' punctures on tree roots etc, increases the lower the pressure used. One solution is to use high volume tyres like the Fatbikes. Another is to have suspension to soften any impact, or to use heavy duty tyres and tubes, where the total thickness of the compacted rubber between rim and pinch point harmlessly absorbs the shock.
My previous comments and calculations relate to shock absorption on rough but relatively solid terrain.JamesM":3ukf7xyh said:
On soft going, the rules are indeed different.
When a tyre sinks into soft ground the contact patch lengthens to include more of the circumference and so the weight is distributed over a larger area. In this circumstance the larger the wheel diameter the less it will dig in and theoretically the lower the rolling resistance. However, if the ground is very soft with a firm layer below, like with soft snow or sloppy mud, then a narrow tyre that will cut through to the grip below may be more efficient as all that a wider tyre will do is cut a wider trench across the landscape.
Using very low air pressures and large diameter fat tyres on semi soft surfaces, like moist soil, can prevent the tyres from digging in. And in such situations the wider, softer and larger diameter the tyre, the softer the ground that can be efficiently ridden.
However the danger of 'snakebite' punctures on tree roots etc, increases the lower the pressure used. One solution is to use high volume tyres like the Fatbikes. Another is to have suspension to soften any impact, or to use heavy duty tyres and tubes, where the total thickness of the compacted rubber between rim and pinch point harmlessly absorbs the shock.
