Page:Report from the Select Committee on Steam Carriages.pdf/142



Mr. Richard Trevithick. 17 August, 1831. It is my opinion, that all wheels now in use on common roads are much too narrow; but this ought to be accommodated to the materials that the road is formed with: for instance, narrow wheels on an iron road do not yield to the pressure of the weight, but keep themselves perfectly horizontal, and do not pulverize; but every Macadamized road, more or less, is subject to this inconvenience, and the narrower the wheels, the greater mischief is done to the road, and more resistance is given to the horses. The usual notion, that wheels grind the road, is wrong; if any difference, it is the roads grind the wheels, the road-material being generally the harder of the two; but the roads are injured by the wheels crushing the stone, by a narrow surface bearing on small points, or on single stones, the tenacity of which will not support the weight under narrow wheels; under wide ones, they would sustain no injury, because the wide wheel reduces its weight on each inch of surface in contact with the road, as the number of surface inches is increased by its additional width, and settles down the road firmly, and gives each stone a side support also, therefore by double the bearing on the road, half the weight is taken off from every bearing surface inch, and that in addition to the side support, by being bedded firmly, a wide wheel will. I have no doubt, save four out of five, if not nine out of ten stones that are crushed at present, and reduce the road expences in the same proportion; but while the fancy of having carriage-wheels out of upright with crooked axles is continued, wide wheels would be a serious objection; the inside and outside of the wheel being of different diameters, and going different speeds, must cause an increase of load to the horses, because their rubbing on the road and tendency to twist move the stones out of their bed in the road, and, instead of bedding them firmly, has the contrary effect; another great evil arises from the use of narrow wheels, they sink lower into the road, and the road being in part elastic, whatever that may be, is a resistance added to the horses according to its perpendicular rise and fall; the passing over sand or snow gives a proof of this on a larger