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Triumph
Spitfire & GT6 Spring Rates and resultant Wheel Rates and Roll
Stiffnesses |
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from: |
Paul Geithner's Triumph Spitfire Technical Information |
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compiled by Paul
Geithner |
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| FRONT COIL
SPRINGS |
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| native
vehicle |
spring
part number
[b,c,d,e] |
identifying
marks [a,b,c,d] |
free length
(inches) [a,b,c,d] |
installed length
(inches) [a,b,c,d] |
spring rate
(lbf/in) [a,b,c,d] |
wheel rate factor
[2] |
wheel rate
(lbf/in) |
roll stiffness
(ft-lb/degree) [3] |
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| Spitfire
mk1, a.k.a. Spitfire 4 (except FC3214-FC39527) & mk2 |
209685 |
green |
12.6 |
7.8 |
150 |
0.56 |
84 |
147 |
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Spitfire
mk1, a.k.a. Spitfire 4
(FC3214-FC39527) |
210566 |
light blue |
12.2 |
7.4 |
150 |
0.56 |
84 |
147 |
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| Spitfire mk3
& mkIV |
214144 |
purple |
12.2 |
7.5 |
150 |
0.56 |
84 |
147 |
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| Spitfire 1500 [1] |
TKC1884 |
purple & white |
13.4 |
8.0 |
180 |
0.56 |
101 |
177 |
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| GT6 (all) |
212425 |
n/a |
12.5 |
8.1 |
200 |
0.56 |
113 |
197 |
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| aftermarket
Spitfire 1500 [x,1] |
TT4302 |
n/a |
9.2 |
6.9 |
330 |
0.56 |
186 |
324 |
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Sources:
a. direct measurement and inspection
b. "Triumph Herald 1200, Vitesse and Spitfire Workshop Manual", p/n
511243, by Standard-Triumph
c. "Triumph GT6 and Vitesse 2-litre Workshop Manual", p/n 512947, by
Standard-Triumph
d. "Triumph Spitfire and GT6 - A Guide to Originality" by John Thomason
e. Rimmer Bros. parts catalog
x. Moss Motors/TriumphTune catalog |
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| [1]: lengths and rates for Spitfire 1500 and
aftermarket springs are direct measurements |
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| [2]: wheel rate factor =
sin(theta)*(d2/(d1+d2))^2; see figure |
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| [3]: roll stiffness in ft-lb/degree = (wheel
rate*track^2)/1375 |
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| FRONT ANTI-ROLL
BARS |
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| native
vehicle |
spring
part number
[b,c,d,e] |
diameter
(inches) [a,d] |
spring rate
(one end, lbf/in) [4] |
wheel rate
factor [5] |
wheel rate
(lbf/in) [6] |
roll stiffness
(ft-lb/degree) [7] |
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| fixed
spring Spitfires and GT6s |
207093 |
0.6875 |
61 |
0.35 |
21 |
39 |
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| swing spring
Spitfires and GT6s |
217033 |
0.875 |
160 |
0.35 |
56 |
102 |
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| aftermarket 1"
Addco [y] |
707 |
1 |
273 |
0.35 |
96 |
175 |
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Sources:
a. direct measurement and inspection
b. "Triumph Herald 1200, Vitesse and Spitfire Workshop Manual", p/n
511243, by Standard-Triumph
c. "Triumph GT6 and Vitesse 2-litre Workshop Manual", p/n 512947, by
Standard-Triumph
d. "Triumph Spitfire and GT6 - A Guide to Originality" by John Thomason
e. Rimmer Bros. parts catalogs
y. Addco parts catalog |
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| [4]: ARB rate in lbf/in =
500000*D^4/(a*0.4244*b^2 + 0.2264*c^2); see figure |
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| [5]: wheel rate factor = (d3/(d1+d2))^2; see
figure |
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| [6]: NOTE: ARBs contribute only to roll
stiffness, nothing to droop and bump stiffness |
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| [7]: roll stiffness in ft-lb/degree = (wheel
rate*track^2)/1375 |
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| REAR TRANSVERSE
LEAF SPRINGS |
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| native
vehicle |
spring
part number
[b,c,d,e] |
spring type
[a,b,c,d,e] |
composition
[a,b,c,d,e,f] |
fitted spring
width (eye-to-eye) (in)
[a,f] |
track width (in)
[d] |
wheel rate factor
[8] |
total
semi-elliptical rate (2x each side's spring rate) (lbf/in) [9] |
spring rate each
side (lbf/in) |
wheel rate
(lbf/in) |
roll stiffness
(ft-lb/degree) [10,11] |
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| Spitfire 4, mk1,
2, 3 |
305894 |
fixed |
7 leaves:
0.2188" thick
1.75" wide
various lengths |
41.25 |
48 |
0.74 |
166
[a,b,d,f,z] |
83 |
61 |
103 |
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Spitfire
mkIV, early
(up thru FH50000) |
159640 |
swing |
5
leaves:
0.25" thick (bottom two)
0.375" thick (top three)
1.75" wide
various lengths |
41.25 |
48 |
0.74 |
323
[a,z] |
162 |
119 |
41 |
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Spitfire
mkIV, late (FH50001
and beyond) and all 1500 |
50 |
0.68 |
110
[d,z] |
41 |
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| GT6 mkI |
307324 |
fixed |
8 leaves:
0.25" thick
1.75" wide
various lengths |
41.25 |
48 |
0.74 |
305
[f,z] |
153 |
113 |
189 |
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GT6
mkII (a.k.a. GT6+)
early GT6 mkIII
(through KF20000) |
308499 |
fixed |
6 leaves:
0.234" thick
1.75" wide
various lengths |
41.25 |
49 |
0.71 |
185
[a,f,z] |
93 |
66 |
114 |
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late
GT6 mkIII
(KF20001 and beyond) |
159654 |
swing |
5 leaves:
0.3125" thick (bottom two)
0.375" thick (top three)
1.75" wide
various lengths |
41.25 |
50 |
0.68 |
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[z] |
192 |
130 |
87 |
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| aftermarket
Camber Compensator (Joe Curry model)
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n/a |
pure swing |
1 leaf:
0.25" thick
2" wide |
37 |
48 |
0.59 |
115
[a] |
58 |
34 |
0 |
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Sources:
a. direct measurement and inspection
b. "Triumph Herald 1200, Vitesse and Spitfire Workshop Manual", p/n
511243, by Standard-Triumph
c. "Triumph GT6 and Vitesse 2-litre Workshop Manual", p/n 512947, by
Standard-Triumph
d. "Triumph Spitfire and GT6 - A Guide to Originality" by John Thomason
e. Rimmer Bros. parts catalogs
f. TSSC "The Courier" issue #158, article "Suspensions Sussed" by John
Thomason, August 1993
z. calculated |
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| [8]: wheel rate factor = (fitted spring
width/track width)^2 |
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| [9]: published fixed spring rates compare
closely with calculated rates where k = G*N*W*T^3/3(L/2)^3, see figure;
semi-elliptical swing spring rate of 323lbf/in for later Spitfire is
actual measurement, which when converted to wheel rate correlates
precisely with published 110 lbf/in wheel rate by Thomason in "Triumph
Spitfire and GT6 - A Guide to Originality" [source d]; semi-elliptical
swing spring rate for late GT6 is interpolated from Spitfire swing
spring data. |
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| [10]: fixed spring roll stiffness in
ft-lb/degree = (wheel rate*track^2)/1375; swing spring roll stiffnesses
calculated by participation of fixed leaf only; calculation compares
with claim by Thomason on p. 77 of "Triumph Spitfire and GT6 - A Guide
to Originality" [source d] that the roll stiffness of the Spitfire
swing spring is 25% of that of the Spitfire mk3 fixed spring, and also
compares well with the hypothesis that net loss of roll stiffness with
the swing spring is offset with net gain in roll stiffness with a stiffer ARB
and that total vehicle roll stiffness is comparable between
predecessor fixed spring and successor swing spring swing axle vehicles
(e.g., Spitfire mk3 vs. mkIV and GT6 mk1 vs. late mk3). |
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| [11]: NOTE: camber compensator contributes only
to droop and bump stiffness, nothing to roll stiffness; data is for camber compensator model sold by Joe Curry. |
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| FACTORY
VEHICLE VERTICAL (BUMP/DROOP) STIFFNESS |
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| native vehicle |
total
front wheel rate
(lbf/in) |
total
rear
wheel rate
(lbf/in) |
total
vehicle
vertical stiffness (lbf/in) |
%
front
vertical
stiffness |
%
rear
vertical stiffness |
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| Spitfire 4, mk1,
2, 3 |
169 |
123 |
291 |
58% |
42% |
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Spitfire
mkIV, early
(up thru FH50000) |
169 |
239 |
408 |
41% |
59% |
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Spitfire
mkIV, late (FH50001
and beyond) |
169 |
220 |
389 |
43% |
57% |
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| Spitfire
1500 |
203 |
220 |
423 |
48% |
52% |
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| GT6 mkI |
225 |
225 |
450 |
50% |
50% |
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GT6
mkII (a.k.a. GT6+)
through early GT6 mkIII
(through KF20000) |
225 |
131 |
356 |
63% |
37% |
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late
GT6 mkIII
(KF20001 and beyond) |
225 |
261 |
486 |
46% |
54% |
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| FACTORY VEHICLE
ROLL STIFFNESS |
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| native vehicle |
front
(ft-lb/degree) |
rear
(ft-lb/degree) |
total
vehicle
(ft-lb/degree) |
%
front
roll stiffness |
%
rear
roll stiffness |
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| coil |
ARB |
total front |
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| Spitfire 4, mk1,
2, 3 |
147 |
39 |
186 |
103 |
289 |
64% |
36% |
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| Spitfire
mkIV |
147 |
102 |
250 |
41 |
291 |
86% |
14% |
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| Spitfire
1500 |
177 |
102 |
279 |
41 |
320 |
87% |
13% |
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| GT6 mkI |
197 |
39 |
236 |
189 |
424 |
56% |
44% |
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GT6
mkII (a.k.a. GT6+)
through early GT6 mkIII
(through KF20000) |
197 |
39 |
236 |
114 |
350 |
67% |
33% |
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late
GT6 mkIII
(KF20001 and beyond) |
197 |
102 |
299 |
87 |
386 |
78% |
22% |
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