ASK THE MXPERTS: WHAT ARE THOSE NUMBERS ON MY SHOCK SPRING?

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Dear MXA,
One day while adjusting the shock spring on my KTM I noticed a row of numbers. I had never seen them before. I asked my buddy what they were and he said a serial number, but another guy said they were the spring rate. He didn’t know why there were two numbers, but guessed that one number was kg/mm and the other inch-pounds. What are they really?

You were as close as you could get while still being totally wrong. See the 54-260 on the spring above? The first two-digit number is the spring rate. The spring rate is 54 Newton/meters. The second number is the free length of the spring—which in the photo would be 260mm long. KTM does not use kg/mm, but if they did this spring would be a 5.5 kg/mm spring. The idea that the second number represents inch pounds doesn’t work for two reasons: (1) No one in Austria has ever heard of an inch, let alone an inch-pound, but if they did a 54 N/m spring would be 477 inch-pounds.

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