Tire circumference

[Frank in WV]

I was trying to find the data on different heghts and circumferences on tires to no avail. A 13.6x38 would yield what height and circumference? In comparison a 12.4x38 would yield what difference? Thinking of dropping from 13.6 to 12.4 to pick up a little more power and hopefully not loose to much tire footprint.

 

[Mike N Mo]

According to the Firestone charts, their Traction Field and road 13.6X38 is 61.5" tall with a rolling circum. of 180", and flat plate of 168 sq in. The Field and Road 12.4X38 lists 59"tall, rolling circum 178", and flat plate of 140 sq in. I realize that the circumference doesn"t calculate correctly with the stated diameter, but that"s what their chart lists.
In my experience different manufactures" will have slightly different dimensions for tire diameters, so your mileage may vary. At least on the surface, it doesn"t look like your ground speed would change much by going to the 12.4 tires

 

[Ole Sow 53]

Try this address:http://www.natpa.com/div1rules.htm
This is NATPA web site.

NATPA.COM RULES DIVISION I.

11.2 x 38 - 120 sq. in. 12.4 x 38 - 140 sq. in. 13.6 x 38 - 168 sq. in