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11 February 2001 |
(See end of article for useful/relevant part numbers).
Having studied the 'Suspension - Terminology'
article you should now have a ‘job description’ understanding of previously possibly
un-comprehended words associated with suspension control. Now - what to do with
it? The first thing we need to establish is an order of priority before
distributing hard-earned 'beer vouchers' in all directions. Fortunately, this
is a good deal less complicated than is generally believed.
Despite the five main factors that control the front
suspension geometry – kingpin inclination, caster angle, camber angle, track,
and bump-steer – we are only really able to alter three of those easily.
King-pin inclination is non-adjustable, as it’s a feature of where the
swivel-pins are mounted on the hub at the factory. It will alter as other
adjustments are made, but we can do nothing easily about correcting/optimising
it independently, as these are fixed in position on the swivel hub. Trying to
keep it within sensible bounds will rely on careful wheel rim choice and ride
height settings. Bump-steer can be changed/optimised, but is pretty difficult
to deal with. Measuring/sorting it out is straightforward enough, it’s applying
the result to the components. This will be left for an independent article on
its own. That leaves us with caster, camber, and track – and that’s the order
of priority at the front. Out of those three, only two need full replacement
components.
Tie-rods - caster adjustment
Out of the easily
adjustable options left, caster is the most important to get right and equal –
so the first ‘essential’ item to buy. Odd caster angles will make the car weave
when going at it in a straight line and behave inconsistently when
cornering/exiting the corner. Caster is controlled by the tie-rod length, so
having adjustable ones is a must. Not withstanding the fact that the standard
ones are made from licorice, bending at the slightest hint of aggravation. Currently,
there are two style options – adjustable but retaining the standard bush
mounting same as the standard ones, or those using spherical-bearing rod-ends
(‘Rose’ joints).
The bush-mounted
types are numerous and various in their designs – some good, some bad, some
completely over the top. What you’re looking for is something that is
stronger/stiffer to cope with bending loads exerted by the use of
angle-limiting bushes without being complete over-kill (extra weight increases
un-sprung weight, that’s not good), but has simple and easy adjustment.
Something employing left/right handed threads and multi-pieces simply inflates
the cost. And avoid anything with the adjustment/locking in the middle of the
rod – these are un-safe. This pares suitability down to an adjustment at one
end – all that’s needed. And strangely enough, Mini Spares/Mini Mania can
supply just such an item at reasonable cost!
Bush-wise there’s
been an epidemic of options produced in all manner of ‘superior’ materials,
most of which work satisfactorily. Harder varieties need regular inspection and
replacement as they tend to ovalise/split after relatively low mileage on daily
drivers. I advise running a hard bush on the front/outer side of the tie-rod
mounting bracket, a standard/more compliant one on the rear/inside. The harder
bush gives greater stability under braking, the softer one a longer ‘life’
through compliancy. An interesting consideration is that the very hard bushes
resist body-roll, thus acting as an in-built anti-roll bar and therefore assist
in cornering. This has merit, though I’ve never tried to quantify it. Mounting
bracket support straps should be used when very hard bushes are fitted. I’ve
seen these brackets bend when the car’s used in anger!
The rod-end style
uses a pretty-much universal design. The main difference being whether the
rod-end is screwed on to the tie-rod or mounted in the subframe bracket. The
former being the most common, and certainly serves the purpose more than
satisfactorily. There’s no need for heavy-duty rods to be used; rod-end
movement eradicates the bending stresses. Higher-grade material is preferred.
An important point to remember when fitting these tie-rods though is to make
sure the bracket straddling the rod-end is positioned with its sides vertical.
Having them horizontal could limit the rod-end travel causing the bracket to
buckle/break. Definitely not good.
Bottom arms -
camber adjustment
Camber is our next consideration,
controlled by the bottom arms. Again there are currently two general style
options, but adjust-ability limited to only one. ‘Fixed’ negative camber arms
are available in three designs – one piece forged with corrected swivel-pin
hole location, ‘cut-and-shut’ welded, or stretched. In reverse order, stretched
arms can be OK – but is reliant upon the job being done properly. The arms
should be heated to the relevant temperature, eased (stretched) to desired
length slowly and consistently with heat still being applied to maintain
temperature, then buried in dry sand to cool slowly and naturally to maintain
material integrity. Cut-and-shut arms should be welded and a fillet added
across the join both sides, the welding quality needing to be of the highest
standards to avoid fracture. One-piece forged with re-sited swivel-pin location
is obviously by far and away the best bet, and is readily available in several
offsets from Mini Spares/Mania.
An important
consideration - both stretched/cut-and-shut methods have the unfortunate side
effect of changing the caster angle at the same time, the tie-rod mounting hole
moving out the same amount as the swivel-pin one. Not so much a problem when
adjustable tie-rods are used, but it has a greater adverse affect on adjustment
values than the forged one-piece style. Loss of caster angle is much reduced
using the one-piece option. Not so much of a problem where adjustable tie-rods
are used, but even so the Mini Spares/Mania ones are by far the best option
when trying to maximize geometry set-up.
Bush availability is
pretty much the same story as the tie-rods, as is regular
inspection/replacement. Something to remember here – do not do the bottom arm
pin-retaining nut up tight until the car is placed down on the ground. If
tightened when the cars up in the air, the bush can be twisted out of shape
once on it’s wheels causing premature deterioration and possibly ‘squeaking’.
Adjustable bottom
arms.
As we’re looking at
doing this suspension-prep on a sensible budget, I’m keeping the choice down to
the widely used, off-the-shelf types. There are a number of excellent
alternatives, but are considerably more expensive. The choice is of two, and
there’s not much between them. Originally, and for the longest time, rod-end facility
was applied by cutting the inner bush-mounting bore off then welding on a
threaded tube at a certain angle into which the rod-end screwed. No problem
providing the welding was of a high standard. However, Mini Spares' continual
search for the best products at the price saw them re-designing the adjustable
bottom arm by making them one-piece forged. Although the welded-on variety was
reasonably trouble-free, with few reported failures, the one-piece forged items
were seen as a way of eliminating the possibility of failure and consequently
limiting ‘public liability’ insurance claims! For ultimate strength and weight
reduction in a generally over-engineered component, these have to be the way to
go. The only real problem with either of these styles is the inner locating pin
has to be removed to facilitate adjustment, which means jacking the car up each
time. Time consuming and unsettles the car suspension each time, making set-up
a lengthy process. A number of the previously hinted at alternatives allow
adjustment without doing this - but at severe cost.
Much discourse over
the suitability of rod-ends on road/high-mileage cars has been ‘enjoyed’; the
main issues are longevity and noise transmission. So for the record – the
myriad of rod-ends available allows a suitable one to be chosen for its given
environment. Those supplied as standard fitment to Mini Spares/Mania
‘off-the-shelf’ suspension components tend to be a budget grade, suitable for a
year’s tarmac racing - around 500 competitive miles. Fitment of extreme quality
rod-ends would make them un-competitive in the market place. Using higher-grade
items will give you decent life - so Mini Spares/Mania now offer the forged
one-piece arms without joints for those that wish to source their own. Extra transmitted
noise? You won’t notice it, and is imperative for maximizing handling – and
that’s what we want.
Tracking
Track is altered by the rod-ends screwed on to the steering
rack track rods, the standard ones being generally well up to the task. The
only consideration would be on severely lowered cars or on cars having extreme
negative camber where the rod-ends are only held on to the track rods by a few
threads. These will need either replacing with ‘longer’ ones, or a suitable
full nut welding on to the standard ones – both to increase thread engagement.
Triumph Spitfire items are usually used for the former, available from Mini
Spares/Mania. I favour the latter as the replacement rod ends are only a few
threads longer than the Mini ones. Welding a nut on doubles this extra
engagement. If the latter route is used, make sure the nut and rod-end are
screwed on to a track rod, but not pinched up together. The threads need to be
‘in line’ and spaced to allow the unit to be screwed on and off of the track
rod easily without damaging the threads. You obviously need to retain the lock
nut. A good tip here is to bore a 3/4" nut out using a 1/2" drill
bit, sliding it on to the track rod so it's about half way along it, then
welding it to the track rod. Gives you a good area to use for adjusting track
instead of wrestling about using either Vise-grips or an adjustable pump
wrench!
Here we’re only concerned with camber and track, both
of which are generally/more easily adjusted using the same component – the
outer radius arm bracket. In contrast to the front, track is the most important
factor of the two; acutely altering how the car handles and its over-all
stability so should attract the largest input of time and money. Whilst too
much (or more than recommended) toe-in will have no real side effects other
than increased/unnecessary drag and tyre wear on the outer edges, toe-out makes
for attention-grabbing performance. A little toe-out makes the car skittish
with a sharp turn-in/over-steer (back end trying to over-take the front), a lot
makes it completely un-ruley in any other mode than flat-out, with severe
over-steer at the slightest hint of steering input. And you just don't ant to
get involved with what happens when lifting off mid-corner! Definitely not for
the in-experienced, faint hearted or those of a nervous disposition.
Rear camber
Camber on the rear is used to fine-tune handling.
Negative camber is used to increase rear-end grip when cornering, this can
increase under-steer if the front end isn't adjusted to counter this. Positive
camber the direct opposite. Neither have the severity of track variation
though. There is a train of thought - indeed some positive proof in theory -
that adding negative camber will increase roll stiffness. By only a very small
amount - but there nonetheless.
Track adjustment is a 50/50 deal – toe-in is easy to
correct, toe out very difficult unless brackets with track adjustment facility
are used. More on these later – we’ll consider the fixed-track types
encompassing the standard item, fixed negative camber type and adjustable
camber type. All these can be easily adjusted to remove toe-in or add toe-out.
Reducing toe-in is by the simple expedience of fitting shims between bracket
and subframe, elongating the bracket to subframe mounting holes situated on the
underside of the bracket. Ridding the car of toe-out entails elongating the
inner radius arm pivot shaft hole towards the rear of the car. A right pain as
this alters ride height (raising it) at the same time and is an arduous job.
Once the correct track has been reached by doing this - it is really necessary
to make a 'key' that fills in the hole left by the pin movement to stop it
returning there at an unexpected moment.
It is for the above mentioned reasons that the Mini
Spares/Mania rear brackets are manufactured to ensure, as often as possible,
that they give a toe-in setting on a vast majority of subframes. Far easier to
sort that a chunk of toe-out!
Camber adjustment is made by moving the radius arm
pivot shaft outer end up or down. Unlike the front, this adjustment is unlikely
to alter the track. The standard bracket can be filed up or down to suit, and
then a key fitted to maintain position once the right setting has been reached.
Fiddly and very time consuming/frustrating. The fixed negative camber brackets
available are supposed to alter camber settings by 1.5degrees negative. I’m
afraid I can’t see the point in using these as they will only add this amount
to whatever your standard existing settings are – these likely to be neither
desirable nor even from side to side to start with. But then for those who do
not have access to geometry re-alignment equipment, it may be the only option.
This leaves the adjustable camber brackets – and is what is most recommended in
this trio as you attain desirable settings that are exact each side.
Nirvana has to be track and camber adjustable
brackets. There are a few styles on the market; all deal with adjustment to the
pivot shaft outer end only. To decide which you prefer you need to consider
functionality. THE most important point is the settings you use should not
alter unless you want to alter them. This implies decent/fixed mechanical
location then acuteness of adjustment, the finer increments available the more
accurate the settings achievable. Once again, the Mini Spares/Mania offerings
are manufactured with these criteria in mind. The others available simply don't
meet the criteria.
For road-used racers - heavy-duty adjustable bush-type
tie-rods, fixed negative camber bottom arms, and adjustable rear camber
brackets are the best compromise/deal. For a little further investment, the
adjustable rear camber/track brackets give a nice edge. Budget allowing – you
can’t beat fully adjustable suspension with rod-ends on the front – road or
race. Definitely worth the investment – and will get you more performance on
the road than an equal amount spent on the engine. Maximum adjustability and
location make rod-ended components a must on race cars.
Useful part numbers:
|
21A1091 |
Heavy-duty
adjustable tie-rods (pair) |
|
31G1155 |
Tie rod rubber bush |
|
C-STR628 |
High-grade
reinforced rubber bush to replace 31G1155, car set (78-80SH) |
|
C-STR629 |
Nitrile rubber
bush to replace 31G1155, car set (90SH) race use only |
|
C-AJJ3364 |
Negative camber
bottom arms, 1.5 degrees over standard (pair) |
|
C-AJJ3364A |
Negative camber bottom
arms, 2.00 degrees over standard (pair) |
|
C-AJJ3364B |
Negative camber
bottom arms, 2.50 degrees over standard (pair) |
|
21A1882 |
Standard post '66
bottom arm rubber bush |
|
21A1882MS |
Nitrile rubber replacement
for standard bush, more resilient (70SH) |
|
C-STR632 |
Poly-nylon bottom
arm bush (75SH), performance street |
|
C-STR631 |
Poly-nylon bottom
arm bush (90SH), race use only |
|
C-AJJ3363 |
Rod-end adjustable,
one-piece forged bottom arms (pair) with rod-ends |
|
C-AJJ |
Rod-end adjustable,
one-piece forged bottom arms (pair) without rod-ends |
|
GSJ612 |
Genuine Rover track
rod end |
|
GSJ734MS |
Non-genuine track
rod end |
|
C-AJJ1572 |
Longer track rod end.
Gives more thread engagement where cars are severely lowered,
or have serious negative camber |
|
MS69 |
Fixed negative
camber rear radius arm brackets (pair) |
|
MS70 |
Adjustable camber
rear radius arm brackets (pair) |
|
MS73 |
Camber and track
adjustable rear radius arm brackets (pair) |
|
TOOL10 |
Caster/camber gauge |
|
TOOL11 |
Tracking gauge |
Notes:
'SH' refers to 'Shore Hardness' - a scale of
determining material hardness.