In 1884, the question of the ridge in the middle of a smooth tire-track in dust (but not in mud) arose on one of RBT's ancestors.
The second explanation sounds more plausible.
Cheers,
Carl Fogel
AN UNSOLVED TRICYCLE PROBLEM. [1189]—Can any of your tricycling readers tell me why a rubber tyre leaves a double rut in dust, and a single one in mud? The fact is indisputable. The impression of the wheel has a small sharp ridge along its centre dividing it into two parallel ruts. I can hardly find any riders who have noticed it! Plenty have offered amusing suggestions, all hitherto inadequate. In extremely thin dust, the ridge is less perfect. In dust 2 in. deep, it is overwhelmed by the falling in of the sides. D. M.
A TRICYCLE PROBLEM. [1206]—"D. M." asks, in letter 1189, why a tricycle wheel leaves a double rut in dust. I have watched the production of the phenomenon referred to long before the invention of tricycles. This little ridge of dust in the middle of the wheel-track is piled by the air rushing from each side into the wake of the wheel. It is the upward motion of the hinder part of the tire which gives rise to the effect. M. H. C.
IMPRESSION OF TRICYCLE TYRES. [1207]—I have frequently observed the impressions left by the wheels of a tricycle, as referred to by "D. M." in last week's Knowledge. I think the peculiar form of the impression is simply due to the alternate expansion and contraction of the rubber tyres. When the tyre is revolving on a dusty road, that part in actual contact with the road (bearing the greatest weight) is flattened, and therefore leaves a depression rather wider than the tyre. The ridge in the centre is caused by the contraction of the tyre immediately after it has passed its point of contact with the road. This contraction of the rubber (from either side of the depression) draws the dust to the centre of the tyre, and thus forms a ridge in the centre of the depression, so that, as long as tho wheel revolved, there would be continual expansion and contraction, causing trough and ridge.
The absence of the ridge from a trough made by a tyre in mud might be due to one of two causes: either the mud sticks to the tyre and obliterates the evidence of contraction, or, the mud may be too tenacious to be drawn to the centre of the trough and "ridged" by the contracting power.
I have made no experiments to test the accuracy of my opinion, although I have held the same for some years.
On first noticing it I attributed it in some way or another to the air under the tyre, at the point of contact, being expelled, and rushing in again from behind to fill the vacuum, carrying a certain amount of dust with it, which, when deposited, would form a ridge.
Interesting experiments of this kind can be tried, and "dendritic" markings be artificially produced. If two pieces of smooth slate be wetted and rubbed together until they become sticky, and then suddenly drawn asunder, the mud produced by the attrition will assume the form of tree, fern, sea-weed, or something "dendritic." I have often observed the same effect produced by a "dry process " when walking along a dusty pavement on a still day, for when the sole of the boot is lifted from the pavement in walking, dendritic markings will be formed in the dust impressed by the foot. The finer the dust the more perfect are the markings. That ancient fossil, the Oldhamia radiata of the Cambrian rocks (supposed to represent a kind of sea-weed) is believed by some geologists to be nothing more than a "marking," caused, probably, by one of the processes above-named, and thought to be so because a weight suddenly lifted from a piece of tissue-paper will produce markings not unlike Oldhamia. C. CARUS-WILSON, F.G.S., F.R.G.S.
> In 1884, the question of the ridge in the middle of a smooth > tire-track in dust (but not in mud) arose on one of RBT's ancestors.
> The second explanation sounds more plausible.
> Cheers,
> Carl Fogel
> AN UNSOLVED TRICYCLE PROBLEM. > [1189]—Can any of your tricycling readers tell me why a rubber tyre > leaves a double rut in dust, and a single one in mud? The fact is > indisputable. The impression of the wheel has a small sharp ridge > along its centre dividing it into two parallel ruts. I can hardly find > any riders who have noticed it! Plenty have offered amusing > suggestions, all hitherto inadequate. In extremely thin dust, the > ridge is less perfect. In dust 2 in. deep, it is overwhelmed by the > falling in of the sides. D. M.
> A TRICYCLE PROBLEM. > [1206]—"D. M." asks, in letter 1189, why a tricycle wheel leaves a > double rut in dust. I have watched the production of the phenomenon > referred to long before the invention of tricycles. This little ridge > of dust in the middle of the wheel-track is piled by the air rushing > from each side into the wake of the wheel. It is the upward motion of > the hinder part of the tire which gives rise to the effect. M. H. C.
> IMPRESSION OF TRICYCLE TYRES. > [1207]—I have frequently observed the impressions left by the wheels > of a tricycle, as referred to by "D. M." in last week's Knowledge. I > think the peculiar form of the impression is simply due to the > alternate expansion and contraction of the rubber tyres. When the tyre > is revolving on a dusty road, that part in actual contact with the > road (bearing the greatest weight) is flattened, and therefore leaves > a depression rather wider than the tyre. The ridge in the centre is > caused by the contraction of the tyre immediately after it has passed > its point of contact with the road. This contraction of the rubber > (from either side of the depression) draws the dust to the centre of > the tyre, and thus forms a ridge in the centre of the depression, so > that, as long as tho wheel revolved, there would be continual > expansion and contraction, causing trough and ridge.
> The absence of the ridge from a trough made by a tyre in mud might be > due to one of two causes: either the mud sticks to the tyre and > obliterates the evidence of contraction, or, the mud may be too > tenacious to be drawn to the centre of the trough and "ridged" by the > contracting power.
> I have made no experiments to test the accuracy of my opinion, > although I have held the same for some years.
> On first noticing it I attributed it in some way or another to the air > under the tyre, at the point of contact, being expelled, and rushing > in again from behind to fill the vacuum, carrying a certain amount of > dust with it, which, when deposited, would form a ridge.
> Interesting experiments of this kind can be tried, and "dendritic" > markings be artificially produced. If two pieces of smooth slate be > wetted and rubbed together until they become sticky, and then suddenly > drawn asunder, the mud produced by the attrition will assume the form > of tree, fern, sea-weed, or something "dendritic." I have often > observed the same effect produced by a "dry process " when walking > along a dusty pavement on a still day, for when the sole of the boot > is lifted from the pavement in walking, dendritic markings will be > formed in the dust impressed by the foot. The finer the dust the more > perfect are the markings. That ancient fossil, the Oldhamia radiata of > the Cambrian rocks (supposed to represent a kind of sea-weed) is > believed by some geologists to be nothing more than a "marking," > caused, probably, by one of the processes above-named, and thought to > be so because a weight suddenly lifted from a piece of tissue-paper > will produce markings not unlike Oldhamia. C. CARUS-WILSON, F.G.S., > F.R.G.S.
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