»Our bicycle wheels hold us up and roll us over the surface. They take the initial impact from the road and are designed to absorb much of the shock. Special spokes, rims and tyres are made for loaded bikes wanting to travel basically anywhere and everywhere. The strength of the rims, spokes and tyres is especially important because damaging any of them would be an extreme inconvenience on a touring bike.
»‘Overbuilding’ wheels (making them massive and heavy) is not a solution as it removes the shock absorption qualities. Fortunately, 125 years of cycling history, modern manufacturing and a lot of road testing have resulted in us now having amazingly rugged wheels at acceptable weights.
»Weight is a greater issue than in other areas of the bike because the energy-demand of adding a gram to the wheel perimeter (tyre/tube/rim) is tripled due to the need to rotate this extra mass.
»The chance of getting a puncture should be eliminated if possible. But puncture proofness is just part of the tyre requirements. When you are cycling on the flat on a smooth road at 20kph, about 40% of your energy is going into rolling resistance of the tyres.
»Great wheels, a key part of meticulously designed bikes, allow us the freedom to travel far and wide. Surely no other product can offer as much. Let’s look at the components in more detail.
Tyres offer us more or less rolling resistance, shock absorption, puncture-proofness, long life, resistance to being cut, “grip” as in not slipping on corners, weight and the associated amount of work to overcome inertia.
The bikes we are talking about are designed for daily transport and for long distance travel, plus carrying loads. So a little extra tyre weight might be something to compromise on in favour of the other things.
Another issue is that of spare parts availability around the world. This sometimes gets alluded to as if it is acknowledged that bikes ought to be designed so they can have bits replaced anywhere on the planet. If you are riding the Eurovelo routes you are not far away from any spare part. But if you are in most of India, Africa, Sth America or central Asia there is a whole list of things you can not readily get. This means...
- have high quality components to start with
- take great care of your bike (don’t allow people to go for a ride on it for example),
- carry your own spares for a few things (eg brake pads), and
- have access to the internet to get information
Many long distance riders carry a tyre, mostly a fold-up one which is a type, such as the Schwalbe Mondial, that is lighter because it does not use wire for beading. But is it ok for bike designers to say “this is a well designed bike and, by the way, make sure you carry a spare tyre in case the ones we put on it fail?” Why not just start with a tyre that won’t fail? And is it ok for them to say “we have designed your bike with a wheel size (26”) not because 26” is the better size to ride on but because if your tyres fail you can get them, albeit in low quality, in India, Africa and South America”? If the tyres don’t fail and last 10,000km or more there is no need to be able to find them in all corners of the globe. Riding that 10,000km without the spare and on 700C would have been, in most places, possible and better.
There are further technical reasons that favour 700C over 26" for all but the smallest frame sizes. Rolling resistance reduces as diameter increases. The road bumps look smaller to bigger wheels. Road shocks are better absorbed as spoke lengths increase. Bigger diameter tyres, at a given pressure, deform less so are faster in both rolling and cornering.
Referring to Tyre Sizes
There are times when it is good to know about this. Rather than rely on nominal diameter figures like 700, 28”, 29’r, 26”, 650B etc, it is safer to use the BSD (bead seat diameter) number. This is the cross section as indicated in this diagram. It is also referred to as ISO or ETRTO. They are the same thing.
»700C has a BSD of 622mm. This is the same as on the Northern European designation of 28” and the modern MTB size called 29er.
»584 is the BSD for the 650B size seen mainly on some French and Japanese bikes. More recently adopted in the MTB world and renamed yet again – this time as 27-1/2”.
»559 is the BSD for most MTBs prior to the development of the 29er
Tyre Pressure and Tyre Width
The lower the tyre pressure the ‘softer’ the ride but there is a point where, especially with a load, there is a risk of ‘pinching’ the tube and damaging the rim. So a bigger ‘bag’ size becomes a way of still having a softer ride but also not risking rim damage. Offset against the attraction of the bigger bag is the added energy needed to drive it all. More inertia. More rolling resistance. Where does the trade off between comfort and efficiency end up when it comes to tyre width? There is a tendency for the discussion to go around and around so can history/test riding or science answer this?
In the 1890s in Australia, after the horse which was expensive and needed to be fed, and before the car which wasn’t invented and would need proper roads anyway, the bicycle was king. Cycling was amazingly popular and the whole country, including the outback where there were often not even tracks to follow, was being criss-crossed by bike. The most common tyre width was 1-1/2” (38mm). The most common diameter was 30” which by 1900 was giving way to 28”. Pneumatic tyres were introduced in that decade also. The producers were responsive to the huge market which immediately chose anything that addressed all the issues better. Even then, before roads were paved, 38mm (1-1/2”) tyres commanded the strongest following. The 32mm “roadster” tyre was the second most popular.
There is a good case, in the touring bike category, to use the longest-lasting and toughest versions of mid-sized (35-37mm) tyres. Front tyres can be slightly narrower than rear ones as they have only 35-40% of the load, although, if you use the same size front and back, you can rotate them. In the case of Schwalbe Marathons and Mondials the one set of tyres can be expected to last 10,000km and even more and be reliable enough to not require you to carry a spare, although a tyre boot (see below) is recommended.
Extensive studies have been done on tyre pressures and rolling resistance. See Off The Beaten Path also Bicycle Rolling Resistance. It is also interesting that rim makers routinely recommend tyre pressures that are lower than the pressures tyre makers say their tyres are made for. This is because very high pressures, quite possibly within the capacity of a particular tyre, might crack a rim. DT-545d rims on VWRs have stickers showing maximum different pressure levels for different tyre widths.
Fitting Fatter Tyres
Bike frames and forks can be designed to accommodate a wide range of widths. It is not a big job to fit different tyres prior to a trip. A 700C bike could be run with 28C Marathons on the best roads (imagine Hokkaido), in endurance events (such as Audax) and on light tours. On almost all tours, 35C Marathon or Mondials could be fitted. On any long off-road tracks such as the WA MuddaBiddi or the Tasmanian Trail, 1.75" tyres could be fitted.
The frame clearance would need to be designed to accommodate the range, as it is on VWRs. Riding through rough country is easier and faster on lower pressure. This can only be achieved with wider tyres. You don’t waste energy bouncing around. Your tyres conform to uneven ground. Knobs on the tyres stop you sliding out in corners allowing you to move faster. Taking the mudguards off is wise when there is a lot of loose gravel...
Tyre Boot As An Emergency Repair
Made from a bit of motorbike tube, this is a lightweight alternative to carrying a spare tyre. It should be a width that suits your tyre width so it will wrap around but not overlap. You just slide it in and then finish putting the tyre on. In the example below, the tyre, which was damaged coming down the Western Ghats on an old gravel track, was used for many thousands of km after the boot was installed.
Rims and Spokes
As with tyres, we are willing to accept weight as long as we get strength and durability. Not having rim brakes allows a slightly thinner wall. In the profiles below, the rims are both 580gms but the one on the right is only for disc brakes. Having a wider profile allows a wider range of tyre widths to fit. In the case of the one on the right (DT-545d) from 1” to 2.4” is accommodated. The wider profile also makes for a more three dimensional shape making it stronger.
Rims are commonly made in either 32 spoke and 36 spoke versions. In the old days there were 40 holes on the rear and 32 on the front. In more recent times, 32 was introduced to both wheels on competition bikes to save weight and to reduce costs. With the best quality spokes, 32 may be enough, but there is a broad consensus that the better availability of 36 and the miniscule (about 30 grams per wheel) weight saving of 4 spokes, we should settle on 36.
Spokes are made from metal which is drawn from rolls of wire. Much depends on the quality of the metal to begin with. In stainless steel spokes, the Swiss DT is alone in being able to say they have never suffered inconsistency in quality. It seems to be acknowledged that DT is the best. They are not cheap but you never regret having them.
In summary a long distance rider wants bullet proof wheels able to accommodate from 28 to 50mm wide tyres and frame design made with the necessary clearances for this range.