TechMod :  Tires
Eugène van der Meer, Bemmel (translated by Michelle Walton)

Diagonal vs. Radial
Next the classification of the different tyre types (sport, touring, custom, all/off road) is the most important distinction between diagonal and radial tyres. As long as there have been motorcycles diagonal tyres have existed, in point of fact, it is known as the mother of all tyres. The origin of the name comes from the pattern of the support construction - called the skeleton. The skeleton is constructed from multiple layers (mostly artificial) of material that is woven in a special manner. With the diagonal tyre the layers cross in a diagonal direction with each other. Such a layer of material is called a corded-layer and gives the tyre itís bearing capacity. Therefore the more layers, the more the tyre can bear. The conís of the diagonal tyre are that if the tyre is pushed in, the corded-layers move over each other with the expected results (unwanted) of rubbing and the tread has relatively little stability.

The radial tyre, which has become common since the end of the 1940ís, made itís debut in the motorcycle world only 20 years ago. The name is thanks to the squared directional position of the threads in the skeleton where they no longer cross over each other. From this you get less development of heat as the layers do not rub over each other. To give this construction more stability a zone/band of one or more layers is placed around the skeleton of the tread. The rubbing of the layers stays to a minimum for the tread. You can also see zones/bands in a diagonal tyre, the so called belted tyre, but then you get the rubbing of the layers. The con of this construction in the radial tyre is the side of the tyre, called the wall, the walls become weaker if they become the same height as that of the diagonal tyre. This has been resolved when a broader en lower tyre was designed. The biggest pro of the radial tyre is the lessened deformation, the so called growth of the tyre, the appearance of which gives more stability.

Since the introduction of the radial tyre there has been much experimentation which has given us many diverse variations of the radial tyre. One of the most well known is the nul grade tyre where the zone/band is laid in the same direction as that of the tyre. This resists the centrifugal forces (the forces directed from the centre to the perimeter of the wheel) this means less growth and deformation to the tread. A pro from this is the good forward stability at higher speeds and the lessened wear of the tread.

Description of the Tyre
About the walls of the tyre there is a sea of information available that explains how and why about the rubber that sits on the rims. Lets look at the important bits.

Generally the measurement and speed description of the tyre is given in metric:

180/55 ZR17 (73W)
 180  Width of the tyre in mm
  55  Height of the tyre in percentage of the width
  Z  Speed Code
 J :  tot 100 km/u
 N :  tot 140 km/u
 P :  tot 150 km/u
 S :  tot 180 km/u
 H :  tot 210 km/u
 V :  tot 240 km/u
 W :  tot 270 km/u
 Z :  boven 240 km/u
  R  Tyre type
 B :  Zone/band Tyre
 R :  Radial Tyre
 - :  Diagonal Tyre
  17  Diameter of the rim in inches (1 inch = 2,54 cm)
 73W  Load/Speed index

This last number/letter combination (73W) requires further explanation. The Load Index indicates the maximum weight the tyre can bear. The speed Index indicates the maximum speed can be ridden during a short period. If the Speed Index is in brackets then the description of the Speed Code is valid.

 
 LOAD INDEX                                             SPEED INDEX
 LI    kg   lbs   LI    kg   lbs   LI    kg   lbs       code   km/u    mph
 36   125   276   54   212   467   72   355   783          B     50     31
 37   128   282   55   218   481   73   365   805          C     60     37
 38   132   291   56   224   494   74   375   827          D     65     40
 39   136   300   57   230   507   75   387   853          E     70     43
 40   140   309   58   236   520   76   400   882          F     80     50
 41   145   320   59   243   536   77   412   908          G     90     56
 42   150   331   60   250   551   78   425   937          J    100     62
 43   155   342   61   257   567   79   437   963          K    110     68
 44   160   353   62   265   584   80   450   992          L    120     74
 45   165   364   63   272   600   81   462  1019          M    130     81
 46   170   375   64   280   617   82   475  1047          N    140     87
 47   175   386   65   290   639   83   487  1074          P    150     93
 48   180   397   66   300   661   84   500  1102          Q    160     99
 49   185   408   67   307   677   85   515  1135          R    170    105
 50   190   419   68   315   694   86   530  1168          S    180    112
 51   195   430   69   325   716   87   545  1202          T    190    118
 52   200   441   70   335   739   88   560  1235          U    200    125
 53   206   454   71   345   761   89   580  1279          H    210    130
 V/VB    240    150
 (V)/(VB)  >240   >150
 W    270    167
 (W)  >270   >167
 ZR   >240   >150
 

Dot Description
The dot Description indicates that the tyre passes the requirements of the American Department of Transport and may therefore street worthy. After the Dot Description is a number that indicates when the tyre was produced. A .209 reveals the tyre was produced in week 20 in the year 1999. 1989 is in this case unlikely as that would mean the tyre is 12 years old and not suitable for use, but to exclude confusion you will find a symbol embossed on the tyre, the 1980ís indicated by a square, the 1990ís are indicated by a triangle, For the first decennium of 2000 I have yet to find a symbol.

Tyre Combinations
The combination of different brands/models is not a problem as long as the correct size and speed category are selected. On the other side of the story is about the difference between two tyres of different brands/models. Combinations that are not permitted or are not recommended are:

  • A Radial tyre on the front with a Diagonal or Belt tyre on the rear
  • A Belt tyre on the front with a diagonal tyre on the rear
The other way around is permitted, thus a radial on the rear and a belt tyre on the front or a diagonal tyre on the rear and a belt tyre on the front is therefore no problem. The rule of thumb is the an Ďolder fashionedí type may be placed on the front than on the rear wheel.

General tips
Some general tips (more information welcomed):

  • Keep an eye on the tyre pressure. Not only the handling and the grip but also wear and tear.
  • During the winter often extra air is not necessary as the service temperature of the tyres, during riding, does not change significantly from summer In the winter the pressure is measured while the tyres are cold and can differ significantly if the air pressure is colder than 10°C.
  • If the tyre does not suit you, then try a completely different brand. Which is of course easier said than done, you do not buy tyres like a pound of sugar. If you are not satisfied or are due for new tyres ask for the experiences of other riders. The difference in the types of tyres (radial or diagonal) can also vary widely. There are many Diversion 900 riders that have changed from the standard Exedra G601/G602 (diagonal) to the Battlax BT-020 (radial) and have an opinion to share.
  • It is not recommended to change from the standard size, not counting the width of the tyre is decided by the width of the rim. Choose for a wider tyre then the heel (the innermost edge of the tyre) sits closer together with the result that the tyre will bulge. You shall miss part of the quality of the tyre design. You could also have a problem with legal responsibility if something goes wrong, so, be warned.
This is what I have found about tyres so far that would be of interest to Diversion Riders. The information was found in Moto73 and on various pages on the internet. May you ride many good and safe kilometres and keep the black rubber underneath.

Eugène van der Meer, Bemmel
 


Links Michelle Walton has used to understand and translate this article from Dutch to English:
 
- Michelin, what is a tyre?
- Longstone Tyres, what is a radial tyre?

Last update 24-Feb-2006