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PERSONAL TRANSPORT: GROUND, WATER, AIR
Correction of the bicycle eight. Personal transport
Directory / Personal transport: land, water, air Modern bicycle models are full of new materials and technologies. But in most cases it concerns the frame, steering wheel, transmission. Only the spoked wheel remains practically unchanged in design: a central steel bushing on the axle, steel spokes, a metal rim and a rubber tire on it. Of course, the inventors do not stand aside here either, offering, for example, various bushing options, oval and even variable-section spokes, different profiles and materials (steel, duralumin, carbon fiber) of rims, etc., but this does not change things: spoke the wheel is still the lightest, and therefore indispensable. The spokes connect the hub and rim together, holding it and at the same time evenly distributing the load on the latter and transferring shock loads back from the road through the hub with the axle to the frame. For connection, there is a hook with a head on one end of the knitting needle, and a knurled thread on the other (cut threads would have weakened the knitting needle). In addition, the spokes in the wheel are located not along the radii, but along the tangents to the bushings, so that they mainly work in tension. It is not at all a fact that even with new wheels all the spokes will be tensioned as expected, especially for relatively cheap models. But even if everything is fine in this regard, then after running in, you will probably have to tighten the spokes. And if adjusting the tension of the spokes is a relatively simple job, then more serious troubles often occur, and when they are eliminated, it is impossible to do without pulling the spokes. The most common damage to the wheels, after punctures, is the "eight" - the end bending of the rim (local deviation from the plane of rotation) during a sharp collision with an obstacle or due to the weakening of the spokes during prolonged use without tightening them. Visually, this is detected by the "wobble" of the wheel during rotation (the cycloid curve of the extreme bending point, when viewed from above, writes out a narrow "eight"). Often part of the rim deviates (bends) so much that it begins to touch the brake pads (or in the absence of a brake, the tire on the fork feather) and prevent the wheel from rotating.
There are several easy ways to save the wheel. The simplest is to straighten the resulting figure eight, which is called "over the knee". Many times I used this folk technology.
Turning the bike over and placing it on the ground, leaning on the handlebars and seat, I slowly scroll the wheel and find the most convex (deflected) place. It is even better to search for this place with a piece of chalk: only now the wheel must be spun quickly, and the chalk should be slowly brought from the side of the fork pen (side) to the rim to the "teal" - the place of their contact. I put my knee here, and with my hands I grab the tire with the rim on the left and right and straighten it with effort. I scroll again and if I find another bulge, then I straighten it again. Usually, several such manipulations are enough to reduce the curvature of the rim, and the wheel already entered the fork with side clearances, without touching the feathers during rotation. After such a repair, it is already possible to ride a bicycle, but it is not very pleasant: it seems that the wheel seems to be hanging on the axle, and at high speed the steering wheel even begins to shake. To straighten the "eight" completely ("into a circle"), you will have to use another method - tightening the spokes, taking into account the curvature of the rim that has appeared. You should scroll the wheel and outline the most convex points of the rim. Then loosen the outer row here at the nearest two to four knitting needles, and pull the nipple one turn on the inner row. By gradually loosening-twisting the corresponding spokes, it is possible to achieve sufficient evenness (flatness) of the rim without disassembling the wheel. After several such repairs or an unsuccessful "landing", a radial displacement of the rim and the appearance of an ovality ("egg") are possible.
To identify ovality, the bicycle is also turned over and with a piece of chalk, bringing it closer from the crown of the front fork while slowly scrolling the wheel, the ovality is determined. To eliminate it, loosen in the hollow and pull all the knitting needles in the convex place. Then tighten everything evenly to the norm. You also need to strongly compress in pairs all the knitting needles in the left and right rows and again stretch the weakened ones. The result is an almost round wheel. Before the next spring-summer season, it is necessary to “align” the wheels with a “bare” rim, and, if necessary, more thorough straightening. The most difficult wheel repair is its complete disassembly and subsequent assembly. On the knee, such a repair cannot be done. For accuracy, an assembly fixture is required. The simplest conductor is made on a suitable sheet of plywood or chipboard. A hole is drilled in the center along the diameter of the wheel axle. After complete disassembly of the wheel (removal of all spokes), the rim is straightened "for roundness" by fitting the rim line with an even drawn circle on the surface of the sheet. A well aligned rim should be perfectly round and flat. If the needles are faulty, you should pay attention to the condition of the thread, the anti-corrosion coating and the wear of the neck of the hook. To facilitate work, the threads of the spokes and parts of the rim at the points of contact with the washers of the nipples (around the holes) are lubricated with grease or machine oil. The assembly begins with the spokes filling the hub body in the "rhythm" head on the left (outside) - head on the right (inside). Here you need to pay attention to the following: if the holes in the flanges of the sleeve have a countersink on one side, then the spoke head must be on the opposite side - the countersink is designed to bend the spoke. In addition, upon closer examination of the bushing, it is impossible not to notice that the holes on the bushing flanges for the spokes are shifted relative to each other by half a step. Then the sleeve with the axle is screwed into the center of the fixture, the spokes are distributed over four future rows, and a bare rim is placed. When tying on the first nine spokes, you must insert them into the corresponding holes in the rim (in those that are offset to the flange where the spoke is inserted). The spoke should be screwed to the nipple adjacent to the valve (or, in its absence, to the hole for it). Looking ahead, I note that the finishing knitting needle of the last row should be located on the other side of the valve and not intersect with the leading knitting needle. Otherwise, it will be difficult to connect the pump hose to the valve.
When baiting the threaded nipples for the first time, the direction and "rhythm" of the spokes of the wheel should be clearly defined. For example, the rear wheel of an ordinary adult bicycle has 36 spokes. We divide into four rows - it turns out nine knitting needles in a row. The first lower one is baited through three holes on the fourth one. The second row - in the opposite direction, starting with the middle empty hole and then to all the middle ones. The third row - in the same direction as the second row into a free hole along the way and beyond. The fourth, last top row has the same direction as the bottom first. It "spokes" into the remaining holes of the rim. The traditional set is called semi-tangential when the direction of the spokes approaches the tangent to the hub flange. Their position makes the wheel more rigid in relation to the moment of rotation (and braking). Most of the wheels are assembled in three "crosses" (but there can be two, four, and even five). This means that each spoke intersects with three others coming from the same hub flange. It remains only to evenly tighten all the knitting needles. This should be done at random, and not in a hurry. If the ends of the spokes protrude from the nipples into the rim, then they must be filed. The prepared wheel is removed from the fixture and placed in the bicycle fork. Now, if the rim is broken (and this, unfortunately, also happens) or the bushing is worn out, feel free to buy new ones, disassemble the wheel and replace it. It is possible to replace the regular bushing or rim in the wheel with "non-native" ones. Then it is possible that the number of holes for the spokes at the rim and the bushing does not match. Not scary. There will simply be fewer knitting needles and the “rhythm” of the “spoke stitching” will be a little off. The margin of safety is usually enough. It is not uncommon to design vehicles with bicycle wheels where reinforcement of the hub or rim (or both) is required. Then a new expanded sleeve is machined. The flanges for fastening the spokes also increase in diameter - you can estimate it by trying on a standard spoke to a regular rim or by drawing a simple drawing. Bogie wheels with a widened bushing and on conventional ball bearings (rather than standard ones, without cages) will be more reliable and last longer. Such wheels are also used in the manufacture of such exotic eco-transport as velomobiles and cycle rickshaws. In the case of large hubs in combination with small diameter rims, fewer "crosses" (no more than two) are used to avoid bending the spokes at the nipple. Motorcycle and moped wheels are arranged in a similar way, since both are "derived" from bicycles, only with an engine. And therefore their repair is identical. Also, using the simplest conductor and welding machine, you can make a particularly strong wheel by welding strip metal or thicker steel wire (rod) instead of standard spokes. In the latter case, a radial set of spokes is used (along the shortest distance from the flange to the rim, without crosses). In this case, the spokes do not intersect with each other. Author: A.Frenev
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