Originally Posted by
John E
If your 42T ring looks almost as small as your bolt circle would accommodate, you have a 144mm BCD. Otherwise, it is likely to be a 130, which will accommodate a 38T inner ring, for a noticeable 10 percent reduction in pedal effort.
Sakae Ringyo made a huge variety of cranks, including 144mm, 130mm, 110mm and 86mm BCDs, so it's hard to say what the OP might have. To make matters worse, SR would use the same model designation for multiple BCDs, and different model designations for the same BCD. A picture of the OP's actual crank would be helpful.