COIL SPRING RATE CONVERSION - A. Hyde 5/2000

Background Math: relating to force

1 lb = 0.454 kg (1 Newton N =1 kg = 2.2 lb) 1 lbf = pounds-force (not pounds foot lb/ft)

Now 1 lbf = 0.454 x 9.81 (accel due to gravity) -> lbf = 4.45 N (Newtons)

lbf/inch = 4.45 / 25.4 gives N/mm = 0.175 (unitless conversion factor)

Easy conversion between Pounds-force per inch AND Newtons per millimetre

To Convert lbf/in to N/mm (Pounds-force per inch to Newtons per millimetre)

lbf/in x 0.175 = N/mm, Example: 100 lbf/in x 0.175 = 17.5 N/mm

To Convert N/mm to lbf/in ( 1 / 0.175 = 5.714 )

N/mm x 5.714 = lbf/in, Example:100 N/mm spring x 5.714 = 514 lbf/in
OR
N/cm x 0.5714 = lbf/in

lbf/in to N/mm Chart

100 = 17.5

220 = 38.5

450 = 78.75

120 = 21

240 = 42

500 = 87.5

130 = 22.75

260 = 45.5

550 = 96.25

140 = 24.5

280 = 49

600 lbf/in =105 N/mm

150 = 26.25

300 = 52.5

650 = 113.75

160 = 28

320 = 56

700 = 122.5

170 = 29.75

340 = 59.5

800 = 140

180 = 31.5

360 = 63

900 = 157.5

190 = 33.25

380 = 66.5

1000 = 175

200 lbf/in = 35 N/mm

400 lbf/in = 70 N/mm

1200 = 210

EIBACH ERS SPRING DATA
# 200   60    60 (typical part number for Eibach ERS springs

Length mm ID mm           Rate N/mm

200-60-60 Rate 60 N/mm ~ 342 lbf/in, block 85 mm

200-60-70 Rate 70 N/ ~ 400 lb, block 89 mm

200-60-80 Rate 80 N/ ~ 457 lb, block 94 mm

200-60-90 Rate 90 N/ ~ 514 lb, block 92 mm

180-60-70 Rate 70 N/ ~ 400 lb, block 75 mm

180-60-80 Rate 80 N,/ ~ 457 lbblock 80 mm (15% stiffer than 70 N)

180-60-90 Rate 90 N/ ~ 514 lb, block 80 mm (30% stiffer than 70 N)

170-60-80 Rate 80 N/ ~ 457 lb, block 64 mm (170-64=104 travel) (15% stiffer than 70 N) New product length

160-60-70 Rate 70 N/ ~ 400 lb, block 65 mm

160-60-80 Rate 80 N/ ~ 457 lb, block ...

160-60-100 Rate (100 N / ~571 lb, block ...

TENDER SPRINGS

60-60-60 Free length 95 mm, Solid height 37 mm, flat spacing 27 mm c/c

4 active coils, 7.2 to 7.4 flat wire, OD=, ID=60

40-60-30 free length 64, static to block 25.5

HELPER SPRINGS (only one spec available, then catalog to TENDER springs)

60-60-2

60 length, 60 ID 2 N rate / ~ 11 lb block 13 mm

Further reading:
Link to Stock Car Products - Spring Technical Information - excellent webpage
Example : If a spring's rate is linear (most racing springs have linear rates) its rate is not affected by the load put onto the spring. For example, a linear rate spring rated at 500 lb. per inch will compress 1" when a 500 lb. weight is placed onto the spring. If another 500 lb. weight is put onto the spring the spring will compress another inch. At this point the load on the spring has increased to 1000 pounds. The rate of the spring, however, remains constant at 500 lb. per inch.

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