Tire Size Mystery

[posplayr]

I dont think I have ever seen this before. It is a definition of the old style tire designations we have in the GS Manuals.

Standard Inch
Example: 3.25H-19
The Standard Inch systems are found on older motorcycles. Tires with these Inch markings do not include an aspect ratio designation, which is 100%. It means the cross-section tire height is 100% of the width. Inch size tires are all bias-ply construction and not belted. They are no longer being fitted on new motorcycles and are gradually being phased out of use.

In the above size, 3.25 is the width, H is the speed rating, and 19 is the rim diameter in inches. The aspect ratio is not listed, but is 100% of the tire width.

https://www.denniskirk.com/help_center/tire-sizes.jsp#standard


The GS1100E used a very common set of tires which were

F 3.5V19 4PR (Radius = 13"; width=3.5")
R 4.5V17 4PR (Radius = 13"; width=4.5")

Today these are generally converted to:

F 100/90-19 (radius = 13.04"; width=3.94") (most popular/best fit)

R 120/90/17 (radius = 12.75";width=4.72")
R 130/90/17 (radius = 13.11"; width 5.12") (most popular best fit)
R 130/80/17 (radius = 12.59"; width=5.12")

You can see the 120/90/17 is a little short dropping the rear, while the F 100/90/19 is a near perfect match in height.

 

[Grimly]

It's perfectly true and only in the 50s and 60s did 100% ratio tyres start to disappear, the common 'full-size' tyre becoming the 90% ratio. This carried on, unstated, until 70% aspect ratio tyres became popular in the car world, but bike tyres carried on with th old, arcane system, for a long while.

 

[Guest]

And to think I had a 510/V/18 on my 750 at one time. Talk about how it screwed up the handling....