|   Dragging on the tire contact patch discussion (quite boring) | Cloxxki
Sep 29, 2002 12:35 PM | | I'm sure others have come up with this before, I may have heard this from someone before I re-invented the theory.
It's about the influence of axle height on rolling resistance, especially on loose soil.
It has been pointed out that large-diameter rims help bringer the rolling resistance down, because the tire requires less deformation to come to that consistent contact patch. This story IMO goes the most for hard surfaces.
Now something else.
To make it all simpler, imagine a slick tire, no tread at all, apart from a single suction pad (that the right word?) that created a vacume as it hits the glass surface the wheels happen to rolls over.
Pressing down the suction pad hardly requires force, getting it loose rather more so. This is the same effect as a knobby tire on i.e. muddy surfaces.
Suggesting the equal contact patch between 26" and 29", and the same weight, knobs of otherwise identical tires will go just as deep. One might conclude rolling resistanc eis equal, but then the axle-height factor is forgotten.
The 29" hub is place some 11% higher than the 26" one, being pushed forward by the same weight/force. The higher placed hub, my guess, has more leverage to get the single suction pad / those knobbies in the mud loose and continue the wheel's rotation.
Reports are, 29" is especially fast over loose soil, could this maybe be the main reason?
Some minor side-effects should be noted:
- 29" wheels has 11% more space to pile up mud
- ...but it takes 11% more mileage to get that to happen
- not sure about tire-deformation's effect on clogging tires.
Am I making any sence with the leverage thing, is the difference really that 11-odd%, or am I forgetting something here?
Sorry if I bored you!
BTW, I just came back from a 30-mile sub-max race simulation. Was supposed to get up at 5 to be able to race at 9, but woke up 8-ish. Had something to straighten for today, and now I feel I'm entitled to making no sence at all. I wish I stocked beer, could use one right now... |
| |
