Suspension - Basic priorities
(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 compliancey. 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 it’s 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 maximise 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 maximising handling – and that’s what we want.
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.
Camber on the rear is used to fine-tune handling. Negative camber increases rear-end tyre contact patch when the body rolls and therefore increases it’s grip when cornering However, what is not often appreciated/known is that increasing rear negative camber has a two-fold positive effect. First, it raises the rear roll centre from ground height – anything gained here helps to counter skewed rear roll as the front roll centre is much higher – and second it causes the outer wheel to go progressively toe-out when cornering, so counters the extra ‘grip’ gained by greater negative camber. This all helps cornering stability and capability with a greater degree of control than simply whacking on a load of static toe-out tracking. Positive camber has the direct opposite effect – causing way too much rear end stability/reluctance to turn. There is a train of thought - indeed some positive proof in theory - that adding negative camber will increase roll stiffness by marginally increasing the rear track width. By only a very small amount - but there nonetheless and every little helps.
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.
SO when setting the rear suspension geometry – set the camber first then the track since these alter the ride height, then set the ride height. Although altering the ride height will affect the tracking slightly – it is hoped you have the ride height something like right before you start!
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. Due to unstinting development work by MSC, there will soon be available adjustable-on-the-car front bottom arms that will take either rod-ends or a trunion for standard/up-rated type bushes, The absolute best of all worlds! 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)
C-AJJ3360 Adjustable on the car bottom arms with trunions for std/up-rated bushings
21A1882 Standard post '66 bottom arm rubber bush
21A1882MS Nitrile rubber replacement for standard bush, more resilient (70SH)
C-STR632 Latest ‘angled insert’ 80SH natural rubber ultimate bushing for road use
C-STR631 Latest ‘angled insert’ 90SH natural rubber ultimate bushing for race use
C-AJJ3363 Rod-end adjustable, one-piece forged bottom arms (pair) with rod-ends
C-AJJ33?? 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
'SH' refers to 'Shore Hardness' - a scale of determining material hardness