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On Wheels for Cycle Tourists

After the ubiquitous puncture, the wheels are the parts of a bicycle that cause the most problems. Cycle tourists, especially those on long expeditions or travelling to remote regions, have slightly different requirements with respect to wheels. Unlike, for example, road racers who enjoy the benefit of a mechanic in the team car who will change a broken wheel in less than a minute, tourists need to be completely self-sufficient. Many regions lack cycle shops and quality components are completely unavailable in some countries, so repair on the road, apart from being time-consuming, is often not possible. The main criterion is therefore durability: wheels must not fail in normal use. Apart from crashes, the only acceptable failure mode for a bicycle wheel is brake wear rendering the sidewalls too thin. This can be anticipated and dealt with in advance. Fortunately, the necessary degree of reliability is possible because the traditional tensioned-spoke bicycle wheel has the highest strength:weight ratio of any manmade structure. Given that most tourists carry (often too much) luggage, considerations like weight are minor, and some others, for example aerodynamics, are non-issues.

This article does not place much emphasis on recommending individual brands of wheel or component because availability varies, and manufacturers change specifications so quickly that the information would soon be out of date. Instead, here we will consider what factors are important to wheel durability. This information will help the reader select appropriate components from those available when building their own wheels, having wheels built for touring or repairing them.

Wheel Size

There is a large variety of wheel size standards available today, but for our purposes only two sizes really matter: the American "mountain bike standard" called 26", and the European "road bike standard" called 700C. A 700C wheel is a little larger than a 26" one: The nominal bead diameter (the wire in the tyre which holds it on the rim) is 622 mm for 700C, and 559 mm for 26". Both have advantages and disadvantages, but I believe that nowadays wheel size is not a major consideration: pick the bike you like and whatever wheel size the frame takes will be fine. A smaller wheel built with the same components and number of spokes is theoretically stronger, but in practice these sizes are similar enough and the selection of components available is wide enough that it is possible to build adequately strong wheels of a reasonable weight in both sizes. A larger wheel rolls over obstacles more easily (for example, compare riding over a pothole on a bike, or on a pair of rollerblades), but again, both wheels are of a sufficient size for it not to be a problem.

Tyre availability used to be a consideration, but is much less so today. A few years ago when 26"-wheeled mountain bikes first became available, most 700C tyres were skinny high-pressure ones suitable for road racing rather than touring with luggage, and most 26" MTB tyres were 2.5" wide knobblies only suitable for soft dirt tracks. Nowadays the picture is very different. Thanks in part to the invention of the "hybrid" and the revival of touring, 700C tyres 45 mm wide, or high pressure 26" slicks as narrow as an inch are both available. For the international traveller, there can be problems with availability in some countries, and the 26" size probably still has the edge here. However, in the developing world tyres of both sizes are often unavailable or of extremely poor quality and the prudent traveller will carry a spare or be prepared to improvise. This also applies to those who ride a bike equipped with wheels of a different size from the two options considered here. This includes most folding bikes such as Moultons, Bike Fridays or Airnimals, and many types of recumbent.

Hubs

Hubs tend not to give too many problems-maintain the bearings once a year and all will probably be well. I would suggest, however, using a hub which takes normal cup and cone bearings, rather than cartridge bearings. Cup and cone bearings can usually be serviced by replacing the ball bearings and greasing them. The bearings tend to be a standard size (e.g. ¼" for rear hub bearings, 3/16" for the front) and so are available everywhere. In contrast, cartridge bearings tend to be manufacturer-specific and thus all but impossible to obtain quickly, and are much more expensive. They do not last as long, needing replacement as often as every 3000 miles. I had this experience with a Suzue tandem hub being used on a solo bike, where one might have expected the bearings to have lasted longer than usual since they were being loaded with less than half the design weight. Their greater shielding from the elements is outweighed by the smaller size of bearing race, and they literally fall to bits. Fortunately, standard major brand hubs, e.g. Shimano Deore, take cup and cone bearings and cartridge bearings tend to be more a feature of "boutique" hubs from small, high-priced manufacturers.

A major advantage of the more modern freehub system over the older freewheel is bearing location. Shimano freehubs have each bearing beside the rear dropout of the frame. A freewheel hub has the right hand bearing substantially inboard of the dropout. When the bearings loosen this can lead to flexing of the axle, causing it to break. This can manifest itself as an inability to keep the rear wheel straight in the frame. Fewer bikes have freewheels nowadays, but if yours does and you tour off the beaten track, it is probably sensible to carry a spare axle and to keep an eye on the adjustment of the rear hub bearings.

The other main consideration with the rear hub is the rear dropout width, and the effect of the number of cassette sprockets on the wheel. Modern hubs tend to specify an Over-Lock Nut (OLN) distance (figure 1) of either 130 mm ("road" standard) or 135 mm ("mountain" standard). On older frames and hubs you may also see 120 mm (5 speed/6 speed) and 126 mm (6 speed/7 speed). Modern sprockets are placed slightly closer together, and hence the difference in the number of speeds listed for the various OLN standards.

How to measure the over locknut distance of a hub

Figure 1: How to measure the over-locknut distance of a hub

On a derailleur-geared bike the spokes on the right hand side form a shallower angle between the rim and the hub, because they are tighter than those on the left side of the wheel. This is called dish, and the asymmetry provides space for the gear cassette. It also weakens the wheel, because the looser spokes on the left hand side of the wheel do not provide as much support to the rim as the tighter ones on the right. Increasing the difference between the tensions of the left and right side of the wheel increases the dish, and decreases the strength of the wheel. This is a liability as the rear wheel already has a harder job-it transmits drive torque as well as supporting more weight of the rider and carries most of the luggage. Tourists (and for that matter, racers, at least with respect to their day-to-day training kit), should seriously consider making an effort to reduce rear wheel dish to improve wheel reliability. This can be achieved in several different ways:

•  Use a wider rear dropout spacing, e.g. 135 mm v. 130 mm. Does not make a lot of difference, since half of the increase is "wasted" on the left hand side, so this only knocks 2.5 mm from the dish-worth having, but not wonderful.

•  Use an assymetrically-drilled rim. The spoke holes are drilled offset to make those spokes on the left hand side shallower, and those on the right, steeper (i.e. equalise spoke tensions somewhat). Assymetrically-drilled rims suitable for touring may become more available in the future.

•  Move the hub closer to the centreline of the bike. This can be done by using a narrower freehub and putting extra spacers on the left side of the hub. The downside of this is that fewer gears fit on a narrower freehub, so the gear range of the bike is reduced. However, clever selection of gears can ameliorate this problem. Shimano cassettes are easy to take apart, and one can build up custom cassettes which still have a practical gear range and acceptably-sized steps between gears while using fewer sprockets.

•  Use a hub-geared bike rather than a derailleur. There are now hubs available with gear numbers and ranges that compare favourably with triple chainring derailleur setups (e.g. Rohloff), allowing an equivalent gear selection and completely dishless wheels-the rear wheel is as strong as the front. However I have never tried this hub myself, because of its tremendous expense. The other disadvantage is that a hub gear is theoretically less efficient than a derailleur setup, but this may be less of a problem with modern internally-geared hubs and derailleurs that work in the "real world"of grit and rain rather than the lab.

Incidentally, dish is also a disadvantage of disc brakes: the front wheel is also dished to provide space for the disc. Not enough to weaken a wheel as badly as at the back but a shame nevertheless.

Rims

Profile : Quality rims have a double-walled structure, allowing the rim to behave like a girder. Many manufacturers offer variations on the basic box section, and rim profile does not seem to be a problem at present-there are many good choices. Unfortunately the same cannot be said for other aspects of rim design; see below.

Material : Quality rims suitable for touring are made from aluminium alloy. Steel rims are much heavier, have poorer braking which becomes no braking when wet, and are not available in double-walled cross-sections which significantly strengthens the wheel. Exotic materials such as carbon fibre are for racing. However, aluminium rims vary widely, and some are much more appropriate for touring than others. A major problem is that most currently-available "quality" rims are hard anodised. This is bad because while it costs more, it makes a less durable wheel: the anodising forms a hard, brittle layer on top of the aluminium. When the rim is drilled for the spoke holes, the anodised layer cracks, and these cracks migrate into the metal, where they extend under pressure from the spokes. The end result is a wheel which must be binned before its time as the rim has cracked at the spoke holes and the spokes are pulling out, even though the sidewalls may have plenty of life left in them (figure 2). In my experience, this is less of a problem with dishless wheels (e.g. front wheels and "single speeds"), but for 36 or fewer-spoked rear wheels on derailleur-geared bikes it is the standard failure mode. Therefore look for non-anodised, sometimes called "silver" rims. There are few available though-at the time of writing, Mavic appears to offer no such rim and their MA3, which replaced the (cheaper) MA2, cannot be recommended. For general purpose 700C wheels, the ST17 "Elegant" or ST19 from DRC, or the Ambrosio Evolution (silver) and Nexus seem to be reasonable choices at the moment.

Anodised rim cracking at the spoke holes
A "silver" rim does not crack, and wears out at the sidewalls from braking after 20,000 miles
(a) Cracking around the spoke holes of a hard anodised rim (b) A non-anodised rim with thousands of miles shows no such cracking.

Figure 2: Avoid anodised rims if possible

Anodising also impairs braking for a while, until the anodised layer has worn off. This problem has been solved not by stopping anodising rims, but by machining down the sidewalls at the end of manufacture. The sidewall is therefore thinner and the rim will not last as long. This "feature" also comes at an increased price, but again, is becoming harder and harder to avoid.

Number of Holes : Obviously this parameter is selected together with the hub. Rims are commonly available drilled with 28, 32 and 36 holes today. For tandem use, a much smaller selection of 40 and 48 hole rims and hubs is also available. For touring, 36 is really the minimum that should be considered. With fewer spokes, nothing is gained in terms of saved weight, but the wheel is significantly weaker-especially the rear, which as mentioned above has a more stressful life and yet is inherently flawed. For serious expedition use, 40 or 48 spoke wheels based on tandem hubs are practical and well worth considering. One can shorten the axle with a hacksaw and respace the hub to fit a single frame with 130 or 135 mm rear spacing. In addition to the benefit of increased spoke count, tandem rims are usually wider and stronger than rims designed for single bikes, even mountain bike rims. But this is overkill for most people: I have built a pair of such wheels but only use them when on extended tours in isolated regions, riding on unmade roads with full camping kit. They are unnecessarily heavy and slow for most purposes. Most of the time, 36-spoke wheels (7-speed and 130 mm rear spacing) with 28 mm tyres are about perfect. They are light enough with low rolling resistance so that they are fast and efficient on the road, yet are durable enough to handle even rough tracks laden with a moderate touring load (figure 3).

With properly-built wheels it is not necessary to ride a tank for the bike to be reliable

Figure 3: Touring with light wheels is possible on even very rough surfaces if the wheels are built properly: Damian Connaughton descends a road of loose sharp stones in the Himalayas carrying full camping kit, riding standard 36 spoke 700C touring wheels with 28 mm tyres

Sockets : Are made from stainless steel and support the spoke nipple in the rim. Some rims, especially lightweight ones and deep-section aerodynamic rims, lack sockets completely. Some rims are equipped with "single eyelets", and some with "double eyelets". Double eyelets transfer spoke force to both walls of the rim, and single eyelets only to one. Single-eyelet rims (e.g. the Mavic MA3) are thus more at risk of spokes pulling through since all the force is transferred onto one wall of the rim, rather than spread over both (the old Mavic MA2 had double eyelets, which is another reason why it was superior to its replacement). Very thick and heavy rims seem to be able to get away without eyelets simply because there is so much metal supporting the spoke. An example is the Sun Rhyno, but this rim is unusually, one might suggest excessively, heavy.

Spokes

Spokes are made in several different types of steel, but good stainless steel ones are recommended, because they are less likely to rust and become impossible to adjust than cheaper, non-stainless, ones. DT, ACI and Sapim enjoy good reputations. Spokes are available in straight gauge and in swaged versions (also called "double butted"). Swaged spokes are narrower in the middle (for example, 2 mm or 14 gauge at the ends, and 1.8 mm or 16 gauge in the central portion), making them slightly lighter. More importantly though, the narrower middle section of the spoke stretches more when the spoke is loaded, and thus removes stress from the ends of the spokes. Because spokes fail by breaking at the ends due to fatigue, the lighter swaged spoke paradoxically makes for a more durable wheel. "Triple butted" spokes are also available, which are 13 gauge at the hub end. Spoke fatigue is also minimised by having the hub flange support the spoke at its head, so push the spoke up to the hub flange when building wheels. With respect to lacing patterns, standard cross-three (that is, any spoke crosses three others on its way from the hub to the rim) for 36 and 40 spoke wheels and cross-four for 48 spoke wheels are recommended. Radial wheels look cool, but the spokes can damage the hub as they are pulling at the weakest part of the flange. Rear wheel spokes must be tangential (i.e. crossed rather than radial) anyway, as a radial spoke is unable to transmit torque.

Some people complain of frequent spoke breakages, whereas others do not. If a wheel frequently breaks spokes, this is unlikely to be caused by carrying too much luggage, riding "hard", or rough roads, but is instead almost certainly because the spokes were not "stress relieved" when the wheel was built. During wheel building the spokes are bent where the spoke goes into the nipple at the rim end, and at its head end to allow the hub flange to support the spoke. The tension of the spoke keeps the steel highly-stressed at the bends. Metal at or near its yield stress fatigues quickly, and this becomes manifest as spokes breaking frequently. For the spokes to be reliable, relieve these stresses by going round the wheel and grabbing pairs of nearly-parallel spokes and pulling them together as hard as you can, then finish up with any necessary fine-truing. This is also worth doing on new wheels that came with a mass-produced bike, because the wheels are likely to have been machine-built.

Spokes can be reused, but must occupy the same position in the wheel (right or left side, "trailing" or "leading"), because if they are moved the spoke is stressed in a different direction and will fail, rather like a paper clip which may be bent the same way many times without damage, but when bent in the opposite direction breaks when bent only three or four times. The only time I have ever broken a spoke on a wheel I built myself was when using spokes from a wheel that I delaced and used in a new one. About ¾ of the spokes would have been in the wrong place in the new wheel. It stayed perfectly true for about 500 miles, then broke a spoke. I realised what had happened, re-built the wheel with new spokes and it has been perfect ever since (some years, and several thousand miles). Therefore if you are replacing a rim that has worn out but you want to use the same spokes, tape the new rim alongside the old one, loosen all of the spokes and then move them across to the new rim one at a time so that the new wheel is laced the same way with all spokes in the same positions.

To calculate the correct length of the spokes for a new wheel involves some trigonometry. If you have access to a computer with a spreadsheet program, you will find a Microsoft Excel spreadsheet here, which will calculate the correct spoke length for you, given the measurements of your hub and rim.

Spoke nipples are available in nickel-plated brass, or aluminium. Brass ones are more durable and recommended for touring.

Tyres

Tyre width is a very personal thing. Wider tyres give a comfier ride and provide more cushioning for the rims when bumping over bad roads, especially important when carrying luggage which cannot unweight itself from the bike momentarily when the rider goes over a pothole. Narrower tyres are lighter and (in practice) have lower rolling resistance, making them faster. Fashion amongst tourists at the moment seems to lean to wider, which is reasonable because they carry luggage. The problem is that fashion always goes to extremes, and many cycle tourists today are providing themselves with unnecessarily hard work by riding excessively heavy, wide and slow tyres. This is exacerbated because most wide tyres run at lower pressures, which also increases rolling resistance. The table below suggests tyre widths for different applications. If you are unusually light or heavy, you might move up or down a size accordingly-

True Tyre Width*
Luggage
Suggested Purpose
19-23 mm None, maybe a spare tube Racing
25 mm < 5 kg. Spare tube, sandwiches Training, Audax, or one day road rides
28 mm < 9 kg. Touring kit in saddlebag or small rear panniers only General riding, e.g. commuting; lightweight touring on roads and dirt tracks, not camping
32 mm < 14 kg Cycle camping on roads and the odd track
35-42 mm 12-20+ kg Touring with full expedition kit in four panniers Extended tours in remote regions; poor roads. Camping, carrying multiple days' food & water
45 mm + None Off-road racing

*True tyre width is the real width of the tyre at its widest point. Honest advertising leglislation does not appear to apply to tyres, and manufacturers' ratings are often wildly out.

"Real" punctures, caused by thorns, metal or glass penetrating the tread are mercifully rare. "Snakebite" punctures, caused by the tyre bottoming out and the tube being caught between rim and tyre can be a problem if the tyre is too narrow, because narrow tyres are also shorter radially and provide less distance in which to absorb shock before the tube gets pinched and punctures. Such punctures are easily identified because they are found on the rim (valve) side of the inner tube rather than the road side, and are usually a pair of nicks in the tyre. (Hence the term snakebite-they look as if they were inflicted by the fangs of a snake biting the tube). Running tyres at high pressure is important to avoiding snakebite punctures and also protects the rim from damage. I typically run tyres at about 100 lbs/sq in, pretty much ignoring the manufacturer's recommendation. This higher pressure provides the twin benefits of lower rolling resistance (and so increased efficiency and speed), and prevents the tyre bottoming out when one rides over a pothole, rock or other obstacle. This is quite safe because tyres blow off the rim at about twice their rated pressure, not just a few pounds more.

Bicycle tyres run at several times atmospheric pressure (e.g. 85-100 lbs/sq in for a typical road tyre, compared with 15 lbs/sq in atmospheric pressure). It is unnecessary to deflate tyres for air travel or when at high altitude because the pressure inside the tyre will not change enough to have any effect. However, under-inflated tyres risk damaged rims.

Tread is not worth worrying about. Nearly all tourists spend most of their time on roads, even if they are unsurfaced. Therefore knobblies, as used for mountain bike racing, are not appropriate, because they are designed to provide cornering traction off road. To achieve this, the material of the knobbles must be harder than the surface the rider is on, because otherwise the knobbles cannot bite in. On a road, knobblies are a liability-you can feel the tyre squirming around as you corner. Most road tyres, even very narrow ones, come with some kind of recessed tread to make them look like a miniature car tyre. This is superfluous, and probably stems from people being used to looking at car tyres and expecting to see tread. Bicycles are different though: the entire tyre is narrower than the gaps between the tread of a car, and often the grooves of the tread are so thin that water would not run into them anyway. Yet even with completely slick tyres cyclists do not crash in the wet because it is the contact patch that is important, not the tread or lack of it. Since their tyres are narrower, have a rounded rather than square cross-section, and run at much higher pressures, bicycles are not at risk of aquaplaning and so do not need tread other than for marketing reasons.

Tyres have carbon added to them to improve the grip over raw rubber. This is why good tyres for any vehicle are black. Avoid fancy coloured tyres, which have powdered silica added to allow the tyre to be dyed-it is not as efficient as carbon and these tyres grip the road more poorly in the wet. However, any rubber tyre grips wet metal poorly and so do not try to corner banked hard over on iron manhole covers and the like!

A tyre should last several thousand miles, only needing to be thrown away when the tread is completely worn through. Many tyres fail unacceptably quickly for other reasons. For example, Continental Top Tourings have a loyal following, probably because they are quite puncture resistant, but cannot be recommended because they always fail at the sidewall long before the tread is worn out. Only experience, coupled with good record keeping, really tells one which tyres are worth buying and which are not.

Conclusions

Most tourists should use wheels with 36 spokes, but perhaps 40 or 48 spokes are appropriate if they tour with an unusually heavy load, in very remote areas or on particularly bad roads. Rims should be double-walled aluminium alloy, non-anodised with double stainless-steel eyelets. Lace the wheel using a crossed pattern with stainless steel swaged ("double butted") spokes, and stress-relieve the spokes at the end of wheel building. Treadless black tyres between 25 mm and 40 mm, depending on load and terrain, are usually recommended.

For further reading on cycle wheels and how to build them, see The Bicycle Wheel by Jobst Brandt (ISBN 0-9607236-6-8). A good internet resource is the website maintained by Sheldon Brown, at http://www.sheldonbrown.com/wheelbuild.html.