Width
The nominal width of a tyre, in fact, is its width with a normally inflated wheel. Approximately this parameter is expressed in inches, more precisely - in millimeters. The latter option is used in bicycle tyres marked according to the “French size” (see the corresponding paragraph).
As well as the fit size (see "ETRTO Standard"), this indicator determines the compatibility of a tyre with a particular rim. However, if the size must exactly match the size of the rim, then in the case of the width, the selection rules are somewhat different. It doesn't have to exactly match the inside width of the rim - a tyre that is 1.5 to 2 times as wide is considered the best option. Up to 2.5 times is allowed, but care must be taken here: a tyre that is too wide on a narrow rim will behave worse in corners and may break off the rim. Also, excessive width impairs handling at low speed and with a pressure drop (even a small one), accelerates sidewall wear. In turn, a tyre that is too narrow is more likely to puncture and damage the rim due to abnormal loads on it.
Recall that if the marking of the tyre matches the marking of the standard tyres of the bicycle, it is guaranteed to fit it. This is true for width as well. At the same time, there are tables that allow you to determine what "non-native" tyre width is suitable for a particular rim.
ETRTO
The main dimensions of the tyre are in accordance with the ETRTO standard (the name "ISO standard" is also found). Indicated in millimetres, while the first digit corresponds to the width of the tyre, the second to the inner diameter.
The variety of markings used for bicycle tyres (including french size
650x23C,
650x25C,
650x28C,
650x35C,
650x43C,
650x48C,
650x54C,
700x20C,
700x22C,
700x23C,
700x25C,
700x26C,
700x28C,
700x30C,
700x31C,
700x32C,
700x33C,
700x34C,
700x35C,
700x38C,
700x40C,
700x42C,
700x43C,
700x45C,
700x47C,
700x50C) at one time created many problems for both users and specialists.
...Moreover, in most cases, inches were used for marking, and this is a less accurate unit of measurement than millimetres. Moreover, formally identical sizes with different designation formats often differed in fact — for example, 1.75 "and 1 3/4" inches could correspond to different actual sizes in millimetres. Also, manufacturers most often indicated in the characteristics the outer diameter of the tyre, and not the inner one, and without actual fitting it was far from always possible to choose a product to fit the rim size.
To remedy the situation, the ETRTO (ISO) standard was developed. Dimensions according to this standard are perhaps the most important parameter for selecting a bicycle tyre. First, ETRTO covers the two main characteristics that determine rim compatibility — bore diameter and width. See above for the meaning of width; and the tyre and rim must match in terms of the rim diameter — otherwise the installation will be simply impossible, no matter how perfect the other characteristics of the “rubber” may be. Secondly, ETRTO uses a designation in millimetres, which allows you to choose the tyre size with maximum accuracy.
There are tables that allow you to translate some branded "inch" markings into ETRTO values; such tables can be found in special sources. However, the need for such data rarely arises: most modern manufacturers, along with branding, also use the ETRTO standard.Load
The maximum load that the tyre can carry in normal operating condition (installed and inflated to operating pressure). Usually, this parameter is given with some margin — adjusted for the fact that during the ride there may be short-term high loads that exceed the weight on the wheel during uniform movement. So if the load on the tyre is close to the maximum indicator, but does not exceed it, you don’t have to worry about the integrity of the tyres (of course, when using them as part of the assignment). Moreover, even with a significant excess of the permissible load (by 20 – 30 kg), the product most likely will not burst immediately. However, exceeding the load definitely cannot be allowed: with an increased load, the likelihood of a tyre “explosion” increases dramatically, and it is highest at high speed, on bumps and in sharp turns — that is, in the most traumatic situations.
When determining the load on each wheel, you need to determine the total mass of the bike and the rider, and also take into account that the rear wheel accounts for about 65% of the weight, the front wheel for about 35%. To simplify the calculations, if special accuracy is not required, you can take 2/3 of the weight for the rear wheel, and 1/3 for the front wheel. For example, if a person weighs 80 kg and a bicycle weighs 10 kg, then the total weight will be 90 kg, and the front wheel will have a load of approximately 30 kg, and the rear wheel will have a load of 60 kg. However, modern “a...dult” bicycle tyres for the most part have rather high maximum load rates — often 120 kg or more. So it makes sense to look closely at this indicator mainly in specific situations: if a bike is needed for a very large and massive person, if we are talking about a children's bike (“children's” tyres can have very limited load limits), or if you plan to carry heavy cargo. If we talk about cargo, then its weight is distributed over the wheels, depending on where the luggage is located. When placed on the rear (boot or “bicycle pants”) or front wheel (city bike basket), the weight is added to the load on the corresponding wheel, and if the cyclist carries a backpack, then the weight of the combined weight of the backpack and the person is distributed according to the proportion described above.
Puncture protection
The presence of additional
protection against punctures in the design of the tyre.
Such protection is a layer of special material (dense rubber, Kevlar, etc.) placed between the cord and the tread, thereby increasing the total thickness of the tyre from the outer part of the tread to the chamber. As a result, many small sharp objects (like a carnation or glass shard) that could pierce a normal tyre do not pose a danger to a protected model. Of course, this design does not give an absolute guarantee against punctures, moreover, the additional layer usually does not apply to the sidewalls; however, other things being equal, “protected” tyres are definitely more reliable than unprotected ones. Their unequivocal disadvantages include a higher cost, as well as a slightly greater weight.
Weight
The total weight of the tyre.
This indicator affects the overall weight of the bike, but this influence is so insignificant that in most cases it can be neglected — especially since the difference between tyres similar in size and use can be some tens of grams, or even grams. In fact, paying attention to weight makes sense mainly when used in professional racing, where the struggle sometimes goes for tenths of a second — and, accordingly, every extra gram can be decisive. If tyres are bought for simpler use — for example, amateur "rides" on roads or even cross-country — this parameter can not be given much attention.
