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Here's a graph of some primary springs, adjusted for the distances they are measured. Linear line .. not exact, but close enough for my simplistic brain. SLP & Speedwerx are measured at a different distance than AC OEM springs. Cutler's I believe are measured the same is OEM.
The solid vertical black arrows are where AC measures (full shift out on the right).
This graph helps illustrate something that people often forget. Final spring force is at full shift out. When you're in a climb, your at ~45 mph, far from full shift out at ~90 mph. Just because two springs have the same final rate of ~275 lbs, they don't necessarily have the same rate at mid shift. Assuming the rates are linear (which they aren't really), mid shift on a 75/275 spring is 175 lbs. Mid shift on a 125/275 is 200 lbs.
Something I picked up from Dynamo Joe.
