WHEEL. 



rubbing agakift the fides of the rule made by them. But 

 both thefe inconveniences are avoided by broad wheels ; 

 which, inilead of cutting and ploughing up the roads, roll 

 them fmooth, and harden them : though, after all, it mull 

 be confefled, that they will not do in ftiff, clayey crofs roads ; 

 becaufe they would foon gather up as much clay as would 

 be almoft equal to the weight of an ordinary load ; and alfo 

 in pafilng along roads abounding with loofe Hones and other 

 obitacles, which a narrow wheel may avoid pafling over, 

 and a broad one muft furmount, the broad-wheel carriage 

 will certainly be drawn lefs eafily and lefs fptedily than a 

 narrow-wheeled one, though not on account of any addi- 

 tional fritlion arifing from the preflure of the weight on a 

 greater quantity of furface. Broad wheels are hkewife 

 more liable to an inequahty of prefTure between the axle and 

 box than narrow ones, and confequently to a greater wear 

 and tear. 



Jacob's Obf. on the Structure and Draught of Wheel- 

 Carriages, 1773, P- 8i> &<^- S^^ °" ^h*^ fubjctt of the 

 preceding article, Defag. Ex. Phil. vol. i. p. 20I, &c. 

 Fcrgufon's Left. p. ^6, Sec. 4to., and Appendix by Brew- 

 iler. Martin's Phil. Brit. vol. i. p. 229, &c. 



We fliall here fubjoin fome additional remarks on wheels 

 and axles for carriages. The eflential qualities of wheels 

 are ftrength and durability, and it is defirable that they 

 fliould be as light as is confident with ftrengtli : for quick 

 travelling carriages lightnefs is very neceflary. 



Wheels to four-wheel carriages fhould be made as near of 

 a height as the conftruftion and appearance will admit ; and 

 if not required for heavy work, the lighter they are made the 

 better. The fixtures from whence the draught is taken 

 fliould be placed rather above the centre of the largeft wheel, 

 for advantage of draught. 



The members of a wheel are of three defcriptions ; viz. the 

 nave, or ftock, which is the central piece ; the fpokes, or radii ; 

 and the feUies, or circumference. The nave or ftock is made 

 of elm, in which all the fpokes are fixed, and in which the 

 axletree-box, or wheel-box, is confined, to receive the axle- 

 arms on which the wheel revolves. The fpokes are ftraight 

 timbers made of oak, firmly tennoned in the nave, in the 

 direftion of radials, to fupport the felhes, or wheel-rim» The 

 fellies are made of a(h, or beech, and form the rim of the 

 wheel ; the whole circumference is ufually divided into 

 (hort lengths, in the proportion of one length to every two 

 fpokes. When the fellies are fixed on the fpokes, the iron 

 band, or tire, which maintains the wear, is nailed on in lengths, 

 and keeps the fellies together. The diameters of wheels 

 regulate the number of fpokes and fellies they are to con- 

 tain : for the larger the circumference of the wheel is, the 

 greater is the number of fpokes required in proportion ; for 

 they ftiould not in any wheel be more than fifteen inches 

 diftant on the fellies, or circumference. 

 ' The ufual height or diameter of wheels for coaches and 

 I travelling carriages extends to five feet eight inches, and 

 I are divided into four proportions. Thofe which contain 

 ! from eight to fourteen fpokes, and only half that number 

 < of fellies, are called eights, tens, twelves, or fourteeiis, which 

 I are the number of fpokes in fuch wheels, or of fellies in a 

 ■ pair of wheels. The height which regulates the number is, 

 I for an eight-fpoke wheel, not to exceed three feet two inches ; 

 I for a ten, four feet fix inches ; for a twelve, five feet four 



inches ; for a fourteen, five feet eight inches. 

 ! Thefe are the extreme heights for the different numbers 

 I of fpokes to each wheel, which fliould be rather more than 

 I lefs, in particular for the fore-wheel of a four-wheel carriage, 

 which receives more ftrefs than the hind one ; andthecoach- 

 I maker's rule is, when the hind-wheels are of that height to 



require fourteen fpoket, the fore one, if under the neceflary 

 height before ftated, ihould have twelve; never allowing 

 the fore-wheels to have but two fpokes lefs than what is 

 needful for the hind ones. 



There are three defcriptions of wheels ; viz. the ftraked, 

 the hooped, and the patent rim : the differences of thefe 

 are only in the rims. 



The ftraked wheel is made with the fellies in feparate 

 lengths or pieces, which are joined together at the ends by 

 dowels ; that is, a round pin which enters part into one piece 

 and part into the other, being clofely fitted into holes made 

 in each. The iron with which it is plated is called the 

 ftrake, and is put on in pieces of the fame length as the 

 pieces of the feUies, and faftened by nails ; the joints of the 

 iron are made to fall over the middle of the pieces of wood fo 

 as to unite them firmly together. The hooped wheel is fur- 

 rounded by a hoop of iron in one entire piece. The patent 

 wheel is made with a hoop of wood in one entire piece, by 

 boiling or foftening the wood until it can be bent into a 

 circle ; this is furrounded by a hoop of iron in an entire 

 piece, and faftened by nuts and rivets. 



According to the ufual method of conftrufting ftraked 

 wheels, their peripheries are compofed of a number of pieces or 

 fellies joined together ; but thefe are weak, and fubjeft to fe- 

 veral inconveniences. As the joints are the weakeft parts of 

 the wheel, they are moft liable to yield inward ; for which rea- 

 fon the wheelwrights leave them higher than the other parts 

 of the rim, in confequence of which the wheel is not 

 exaftly round withinfide the circle of the rim. Befides, 

 the fellies being fegments of a circle, fawed or hewn out of 

 ftraight wood, they are on this account rendered fo brittle, 

 from the crofs direftion of the grain near the joints, that 

 they are with difiiculty kept together, even though almoft 

 twice the quantity of timber be employed that would other- 

 wife be neceliary. The ftrength of fuch a wheel depends 

 on the thicknefs of the iron tire or rim that furrounds it, 

 and hence the carriage is loaded with an ufelefs weight, both 

 of wood and iron. To obviate thefe inconveniences, Mr. 

 Viny invented the procefs for bending timber into a circular 

 form, pratlifed for fome time by Meffrs. Jacob and Viny, 

 and is now continued by others. In wheels made of tim- 

 ber thus bent, the rim confiils either of a fingle piece of 

 wood, or two fellies only, and is cafed with a fingle hoop 

 of iron. By this mode of conftruftion, the grain of the 

 wood is kept parallel throughout, fo that the periphery of 

 the wheel is every where equally Itrong ; its thicknefs is 

 confiderably leflened, infomuch that though little more than 

 half the ufual quantity of timber is employed, the wheel is 

 of itfelf ftrong enough to fuftain the common burthen laid 

 on fucli wheels, without the aififtance of iron tires, which 

 are only applied to them as a fafe-guard, to preferve the 

 wood from the injuries to which it would otherwife be necef- 

 farily expofed from the roads ; and hence a lefs quantity of 

 iron is fufhcient, and even that will be fairly worn out be- 

 fore it becomes ufelefs. Befides, the wheel is rendered much 

 lighter, and at the fame time much ftronger and more 

 durable, than wheels conftrufted of detached pieces of 

 wood and iron, in the ufual manner. Thefe patent wheels 

 are very fuperior to the common fort, in their neat light 

 appearance, and in the length of time they wear, as two fets 

 of the former will v/ear as long as three of the latter : their 

 prefervation depends very much on the hoops that the wheels 

 are rimmed with. Some perfons ftill prefer the common 

 fort of wheels, on account of their being more eafily repaired 

 than the hoop-wheel ; but though the repairing of the latter 

 is more difficult, they are much lefs fubjeft to need it. 

 As the rims of wheels wear fooneft at their edges, they 



ftiould 



