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Dampers - Fitment data |
29/08/2001 |
Following
the various articles I've done on suspension modifications and vehicle
lowering, the most often asked question is 'do I need shortened dampers?'. This
is impossible to answer confidently for all cars since lowering a car by a
certain measurement is a relatively inaccurate description. It all depends on
what the car ride height was before lowering took place. Simply stating it was
'standard' is just as inaccurate - there are few Minis on the road today with
the standard factory documented ride height. Largely brought about by the
suspension settling/wearing in use and the rubber springs deteriorating over
time. The official factory manual states a specific measurement from the center
of the wheel hub to the top of the arch line. All well and good, but most folk
effect their measurements from the sill line to the floor! Particularly where
bodywork has been renovated and/or modified to take larger wheels and tyres.
Typically a 12" wheeled Mini is 9.75"/248mm from sill to floor and
rear is 11.00"/279mm - measured at the sill ends immediately before the
arch line/edge curves up. 10" wheeled Minis tend to be around
0.50"/13mm less at each end except for real early ones which are another
0.50"/13mm lower at the rear.
Whatever
has or has not been done to your Mini by way on body repairs or modifications,
the critical measurements as far as damper fitment goes is the distance between
the mounting points. These are easily measured with whatever dampers are on the
car removed, car sat on a level-ish surface, and the rubber springs in place
(the dampers do not influence the cars ride height). Simply measure the
distance between the top and bottom from mounting pin centers and the rear
lower mounting pin centre and underside of the arch where the top rear mounting
pin locates.
To
assess which dampers you will need length-wise, select suitable dampers that
will fit these dimensions and be in the middle of their stroke length. In fact,
because a Mini has more droop than bump, the fitted length should be biased
towards allowing more travel as the wheel droops than it does when compressing
(over bumps). The more operational stroke length the damper has, the more
universal its fitment. The less operational stroke it has - the more limited the
wheel travel will be before trouble occurs. The other key factor is knowing how
much bump and droop travel occurs to avoid bottoming the dampers out. Allowing
this to happen will irrevocably damage the fragile internal valving essential
to the dampers performance. The Mini has surprisingly little over-all travel,
barely 3"/76mm in total on the front of a road car and as much as
1.50"/38mm less on a racer with around 1"/25mm more at the rear. Most
of that is in droop, probably 60%.
So
by way of a theoretical example to illustrate - typically 'as standard' the
front damper mounting pins are around 10.25"/260mm center to center.
Selecting a damper to have this distance in the middle of its travel will
require a damper with an open length of no less than 11.75"/298mm and
closed length of no more than 8.75"/222mm. Adding into this equation the
allowance for the 60% in droop, this shuffles the figures to around
1.80"/46mm to the open and 1.20"/30mm to the closed lengths. So the
new figures would be a damper with 13.55"/344mm open length and
9.70"/246mm closed length.
From
the table shown below - you can see that many of the performance dampers listed
are very close to these limits with no margin for safety. In fact the only one
that really covers all the bases is the Kayaba Gas-A-Just in the performance
damper arena. Dampers with very little operational stroke will restrict wheel
movement. Fine on a Formula 1 car, but has serious consequences on a Mini -
like causing wheel spin to occur far earlier than normal. This reduces grip,
drive and promotes under-steer. None of which improve cornering speeds at all!
From this it can be seen that when lowering a Mini it is very advisable to fit
the modified front damper brackets that MSC/MME do (part number C-AJJ3359) to
improve the damper's lot.
TABLE OF DAMPER LENGTH COMPARISONS
|
Damper type |
Fully open
length between fixing centers |
Fully closed
length between fixing centers |
Operating
stroke length |
|
|
|
|
|
|
Short length:
|
Inches
mm |
Inches
mm |
Inches mm |
|
Spax front
M11 |
12.25
311 |
8.75
222 |
3.50
89 |
|
rear M12 |
15.00
381 |
10.25
260 |
4.75
121 |
|
Koni front |
11.75
298 |
8.75
222 |
3.00
76 |
|
rear |
12.375
314 |
9.25
235 |
3.125
79 |
|
Gaz front |
12.00
305 |
9.25
235 |
2.75
70 |
|
rear |
14.125
359 |
10.75
273 |
3.375
86 |
|
AVO front |
12.125
308 |
8.75
222 |
3.375
86 |
|
rear |
14.00
356 |
9.50
241 |
4.50
114 |
|
|
|
|
|
|
|
|
|
|
|
'Standard'
type: |
|
|
|
|
Unipart front |
13.00
330 |
8.50
216 |
4.50
114 |
|
rear |
15.75
400 |
9.75
248 |
6.00
152 |
|
Kayaba front |
12.875
327 |
8.25
210 |
4.63
117 |
|
rear |
15.00
381 |
9.50
241 |
5.50
140 |
|
Kayaba Gas-A-Just
front |
13.00
330 |
8.00
203 |
5.00
127 |
|
rear |
15.313
389 |
10.25
260 |
5.06
129 |
|
Spax front M1 |
13.00
330 |
9.25
235 |
3.75
95 |
|
rear M2 |
15.50
394 |
10.625
270 |
4.88
124 |
|
Koni front |
13.00
330 |
9.50
241 |
3.50
89 |
|
Rear |
15.25
387 |
10.625
270 |
4.63
117 |
|
Gaz front |
13.125
333 |
9.375
238 |
3.75
95 |
|
Rear |
15.50
394 |
11.00
279 |
3.50
89 |
|
AVO front |
13.125
333 |
8.875
225 |
4.25
108 |
|
rear |
15.125
384 |
10.125
257 |
5.00
127 |
|
Bilstein
front |
12.75
324 |
9.25
235 |
3.50
89 |
|
rear |
16.00
406 |
9.50
241 |
6.50
165 |
|
Useful part
numbers: |
|
|
|
|
|
|
|
552018 |
Kayaba Gas-A-Just gas pressurised
mono-tube – front |
|
|
552019 |
Kayaba Gas-A-Just gas pressurised
mono-tube – rear |
|
|
342001 |
Kayaba Up-grade standard gas damper –
front |
|
|
342002 |
Kayaba Up-grade standard gas damper –
rear |
|
|
442001 |
Kayaba standard replacement damper –
front |
|
|
442002 |
Kayaba standard replacement damper –
rear |
|
|
C-STR1675 |
Koni standard ride height adjustable
damper – front |
|
|
C-STR1794 |
Koni standard ride height adjustable
damper – rear |
|
|
C-STR1717 |
Koni lowered ride height adjustable
damper – front |
|
|
C-STR1795 |
Koni lowered ride height adjustable
damper – rear |
|
|
NGM1 |
Spax standard ride height 'knurled
knob' adjustable damper – front |
|
|
NGM2 |
Spax standard ride height 'knurled
knob' adjustable damper – rear |
|
|
NGM11 |
Spax lowered ride height 'knurled knob'
adjustable damper – front |
|
|
NGM12 |
Spax lowered ride height 'knurled knob'
adjustable damper – rear |
|
|
NGM1A |
Spax special softer rate adjustable for
standard road use – front |
|
|
NGM2A |
Spax special softer rate adjustable for
standard road use – rear |
|
|
C-STR306 |
Spax original adjuster, standard ride
height – front |
|
|
C-STR307 |
Spax original adjuster, standard ride
height – rear |
|
|
C-STR308 |
Spax original adjuster, standard ride
height - rear for van/estate/woody |
|
|
C-STR304 |
Spax original adjuster, lowered ride
height – front |
|
|
C-STR305 |
Spax original adjuster, lowered ride
height – rear |
|
|
GSA971388 |
Unipart standard front |
|
|
GAS971389 |
Unipart standard rear |
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