All About Steering on FWD Cars

On steering, suspension and things, Based on an article that first appeared in our magazine, and is now updated with information that has come to light since
Dear old Fred Hulse, sitting at his drawing board all those years ago, probably agonised more over how to attach the front suspension to the chassis of the latest project he had been given than any other part of the vehicle.
With the exception of the gearbox and differential (which were themselves quite ground-breaking) the rest of the design was fairly standard type stuff for that period.
Recent evidence dwelt on within this magazine suggests that the engine was adapted from V-twins left over from an earlier period, so there was no necessity to design a motor from the ground up.
It has been put forward that Fred was part of the team that developed the Alvis FWD suspension layout, I remain unconvinced until more information becomes available, Really, if you think about it the choice of layout was extremely limited in those far-off days, cart springs meant beam axles. Macpherson struts were a kind of highland dance, and unequal-wishbones were something left over from the Christmas dinner.
There could have been another reason for Fred’s deliberations —- the company accountant. You can almost hear his words “Fred, this is a low-cost runabout, a motor-cycle combination replacement; it won’t ever be driven to it’s limit, if drivers want speed they’ll get a Morgan, so keep it simple—and cheap!”
So Fred went ahead and gave us eight springs, and it all worked very well indeed, especially a little later when friction dampers were added, That is until, in the mid thirties onward, a few sporting drivers started devising ‘specials’ using BSA FWD components but with much more powerful engines. With little real knowledge we can only surmise that these cars gave excellent straight line performance, but like the Alvis were probably a bit of a handful on very hard corners, but the real reason for the bad steering reputation that Alvis acquired was that a design fault allowed a drag link to get under a bottom spring on hard cornering and stayed there!, obviously with the inevitable consequence.
When I was a service engineer during the sixties I worked a lot in central London,and often at a loss as to what to do in my lunch break I got into the habit of making for the reading room of whatever library was local. I must have looked through every book about motoring that ever was, and one of the books I found included a detailed account of the exploits of the Alvis FWD car, which was made and raced during the latter end of the twenties. Two things I recall however are that the front suspension layout was identical to the BSA, and secondly that the car had acquired a reputation for questionable steering at high speed.Another book that I found was ‘Specials’ by John Bolster, and amongst the cars mentioned was ‘Dorcas’. This racing car had BSA suspension and drive and a pretty beefy engine; there was a ‘photo of this machine airborne at the top of the test hill at Brooklands, and apparently it set up a class record time that was never beaten!! As I remember it the ‘photo was too indistinct to make out whether or not any changes had been made to the suspension layout, if this machine was used for circuit racing it is highly likely it was modified.(A picture of this machine appears in “Features”) You may ask, “Why are we going away from the supposed theme of this article to talk about these forgotten vehicles?” Well, the reason is that it all has a bearing on what I am going to elaborate on, and that is that under certain extreme circumstances the BSA steering can exhibit rather strange phenomena.
First let us look at the layout of the front suspension on all BSA FWD cars (with the exception of the Series Seven Scout, which never went into production).
Each front wheel carrier is mounted on four leaf springs; these are rigidly fixed to the chassis in such a way that fore-and-aft movement is impossible, This is achieved by the use of a chassis bridge piece into which the top springs fit perfectly. The inner ends of the top springs are positively located and secured by a bolt passing down through this bridge; the bridge itself is secured to the chassis by eight bolts which also enclose the springs and are screwed into threaded blocks located below the lip of the upper part of the chassis. The lower springs are located and fixed with distance pieces into the well of the chassis, further security being provided by similar threaded blocks located under lips of small ‘windows’ through which the springs pass.
The wheel carriers (or swivel units as most owners refer to them) are fixed to the springs with quite large bolts top and bottom. Steel sleeves are located in the bushings of the “stirrup” assemblies top and bottom, they are a few .001″ longer than the bushing, with thrust washers each end, so that when the bolts are tightened each sleeve is locked to its bolt, but free to move within the bushing. Washers under the bolt head and the nut ensure that the spring eyes are also locked tight, obviating any unwelcome play in the swivel unit mounting.The steering mechanism is quite straightforward and normal for the period. The primary track-rod is connected to the outer end of the n/s drop-arm, which is itself connected to the o/s drop-arm by the main track rod. These drop-arms are fitted by means of taper-and-key to the lower king-pin stubs, and are angled towards each other to provide the requirements of Ackerman steering geometry.Just a brief note on Ackerman. It is a concept developed in the 1800s, and the theory is that all four wheels should roll around a common point in a turn. You can see this effect if you put your BSA on full lock; it will be seen that the wheel on the inside of the bend has turned further than the outer one. In oval track racing it was normal to tune this angle to give optimum steering performance according to the radius of the curve in the track, but in road cars such as the BSA it is a fraction of a degree, effectively causing the toe-in to progressively change to toe-out on full lock.
Some of the early models appeared without friction dampers, but by 1931 all models had them as standard. Later Scouts had Luvax shock absorbers, and the drawings of the Series Seven showed much more powerful looking devices, type unknown to the author. With full working weight on the front wheels there should be (to borrow an aeronautical term) anhedral outwards from the chassis.

A few notes on BSA steering adjustments and settings

 

 

 


Castor angle, to the uninitiated, is provided primarily to give good self-centring action on the steering. The best example I can think of is those little wheels (castors!) on you’re sofa, except that on cars the pivot point is only very slightly inclined. The degree of inclination is called castor-angle, and I have never been able to find any on a BSA. However, if you study a drawing of the side view of a three-wheeler it does appear that the chassis is designed to slope downwards from the front, this will give the effect of an angle. I read somewhere that FWD vehicles need to have neutral or negative castor so I’m unable to speak with any authority on this subject.
Camber angle is easier to see, and is the degree of ‘lean’ on the front wheels, positive when the wheels lean outwards. The design of the front suspension layout creates a positive camber angle of 2.5º to 3.0º, but in practice it is directly proportional to the amount of ‘sag’ on the front springs. see article on camber angleKing-pin inclination means that an imaginary line through the steering pivot centre strikes the road at slightly inboard of the centre of the tyre ‘footprint’. Obviously variations in the camber angle will not change that relationship, but if there is excessive camber present then the footprint itself might be outside the centre point, (i.e. the tyre is not contacting the road squarely) possibly resulting in a reduction in steering accuracy. When rebuilding the front-end I found it a good plan to match in length a set of four springs for each side, (don’t laugh!, they can vary), if you cannot get the camber right then elongate the lower main spring attachment holes in the chassis. With the ‘fat’ tyres that I fitted to JP I found it all worked better with no angle at all. I always thought that camber was built in to give a car a more rakish look, but I daresay someone will come up with a perfectly good reason for it!
In all the literature I’ve read about BSAs I have never come across any mention of wheel alignment. Should there be ½”, ?”, ¼” toe-in? I have no idea. Even if you know what it should be that’s only half the battle. Most BSAs use spoked wheels, which often run a bit out of true, so before setting up the tracking it’s a good idea to find a mean point on each wheel, mark it, and set up the tracking with both marks at the 3 o’clock position, (or 9 o’clock if you are looking at the n/s wheel!). I expect there are all sorts of sophisticated devices available today, but I made a contraption of dexion and set the wheels to ¼” (and lived to tell the tale!), and I know that Ray Waters used a device made up out of track rods, (string and a bent nail anybody?). One of the most important parts of setting the track is to make sure the steering is at the ‘dead-ahead’ position. (remember Ackerman steering affects toe-in).
Going back briefly to castor angle, if the rear spring is sagging, or if an extra heavy load is being carried (or both), this can tend to exaggerate any castor angle that exists, which, in my experience can degrade steering performance. Remember, if you can get the rear spring into the ‘drainpipe’ easily, it needs resetting! (Sid Rayfield always swore by a 4:00 X 19, pumped up to 40 psi, i.e. the largest wheel available and minimum tyre ‘squash’). Unfortunately there was the downside of the back end ‘hopping’ on every bump, which just goes to show that some things you cannot win.
One final note, it is not unknown for drop-arms to move on their tapers, causing any manner of problems, usually the steering goes ‘stiff”. Grinding them in sometimes works, but if the key is wobbly in its slot it might mean having the slots machined to a bigger size. I think I fitted pieces of shim, but this is not very satisfactory in the long term.
SPEED! How much we take it for granted these days, modern cars go fast, they steer well, and usually display none of the ‘funny ways’ that one gets used to when driving pre-war vehicles, especially three-wheeled ones. Few people try and drive fast in examples of our chosen marque, (by fast I mean over sixty, everything’s relative). Up to this speed, in a straight line it all works more or less as it should, it’s only when attempting a hard bend that things can get a bit out of hand (again this is mostly applicable to trikes). Think again; if you regard those front springs as simple wishbones, wishbones need to be rigid and are designed to have fixed pivot points. Springs can curve over 60% of their length, and that is where the design lets down the speed merchants. On a hard right-hander the nearside bottom springs arch upwards in the centre, the wheel tucks under, and the main track rod (which is rigid) forces the off-side wheel into excessive toe-in, making it necessary for the driver to correct (not if the wheel is airborne!). I recall that at the end of a half hour ‘belt’ round Silverstone the passenger of a Morgan that we had been having a good old dice with informed me that he saw daylight between our o/s tyre and the tarmac, and that the wheel was not only going backwards, but it was toeing in at quite a lot more than the designer intended. Looking closely at a ‘photo taken at that event it is just possible to verify this effect.
By the end of the thirties car designers were starting to realise the limitations of suspension systems that had changed little since WW1, and BSA designers were no exception. The light and agile V-twin three-wheeler of 1928 had gradually evolved into a sports tourer nearly twice as heavy and with a much more powerful engine to pull it all along, but with no meaningful changes to the front end. It is very sad that, when at last a suspension system was designed that brought the car right up to date WW2 happened, and all car production was virtually stopped. To add insult to injury, Hitler’s bombers then proceeded to destroy the BSA factory and the entire car tooling with it.The Series Seven Scout had many new features, but the one we are interested in is of course the suspension system, which is illustrated here. H It is quite obvious that BSA had become aware of the shortcomings of the eight spring layout and had settled on one massive spring across the full width of the car. This had six leaves, and at the top a wishbone lever, pivoting on special brackets that probably supported the wings, and what looks like a much simplified bridge piece, with a lever type shock absorber operated by a link from the spring attachment point.
A special point of interest is the steering pivot placed in a central position,this feature meant that the tendency for the old style main track-rod to whip was eliminated, it being replaced with two short track-rods of equal length, this layout was also safer in that in the event of a track-rod failure one-wheel steering would still be possible.
Bearing in mind my earlier comments about bottom springs I would have preferred a top spring, but this would have presented problems with the ‘hump’ on top of the differential drive casing. The spring was dead straight, and therefore less liable to arching under cornering stress than the old ‘sloping down’ design, which was slightly curved, and therefore vulnerable to that effect. Anyway, it’s all very academic now.
As mentioned, the BSA FWD design has, over the years attracted many enthusiasts as a basis for ‘Specials’, mostly used for such sporting events as hill climbs and even outright racing. The first such vehicle that springs to mind is of course ‘Alt’cock’. This machine has featured many times in our magazine, and as far as this article is concerned is of great interest from the point of view of changes to the front suspension. As the name suggests, Alt’cock was made out of bits from many different makes and types of vehicles, and has been raced and hill-climbed for a great many years by the late Frank Bruce-White, who, in the early months of 1970 wrote a very detailed account of the history and technical specification of this vehicle. Details explained in that article certainly answered a lot of questions I would have liked to ask about the front suspension. Up to that time several ‘photos had appeared in the magazine over the years, but the quality of the print made it impossible to say for certain how it was all put together. Back in the halcyon days of the old ‘Eagle’ meetings we were treated to a talk by F. Bruce-White about this vehicle around about the same time. Briefly the front-end is configured thus:- The power unit is a Douglas dirt-track air-cooled flat twin (capacity has varied from an initial 494c.c. through 746 to 820c.c., (however this info is dated March 1970, so it has probably changed since then). This engine is right at the front, and drive is transferred to an Austin 7 differential by way of a lay shaft over this diff to an Albion motor-cycle gearbox, then via a clutch and another chain back to the diff. This system of chains provides the correct direction of rotation. Dual inboard brake drums are grafted to the A7 output shafts, and the whole thing is then married up to BSA FWD wheel carriers, phew!!The Series Seven idea of the one large spring wheel-to-wheel was employed, but in the right place on top (presumably located below the lay-shaft taking drive to the rear of the differential), however the bottom springs were retained, albeit with a reduced number of leaves, and YES you have guessed right, this layout caused the steering to behave in exactly the same way as I have described earlier.
According to the driver of this machine (and I quote) “On cornering, the outside wheel depresses quite a lot which causes the transverse spring to flatten and push out, whilst the bottom two leaf springs tend to bend in. This caused the outside wheel to tuck up under the chassis and run on the side of the tyre.” He went on to describe how these contortions of the front wheels caused some considerable amusement to onlookers. The fix for this problem was to lengthen the bottom springs to the point of negative camber;(the picture here clearly shows this) the resultant improvement was, apparently, dramatic! Which I suppose begs the question, “Is your camber really necessary?” It could also be said it was making two wrongs into a right I suppose.
Frank Bruce-White was severely restricted in what he could do to Alt’cock by the constraints of the VSCC, who, naturally, insisted on all parts having been available pre-1930, but no such limitations apply to the Emeryson 500 cc racers of 1949 onward. These vehicles were out and out racing cars, and strictly speaking do not qualify for inclusion in an article on BSA steering, as the only thing BSA on these Formula 3 cars was the wheel carriers, half-shafts and wheel hubs; but I think it’s worth mentioning them. Paul Emery built his first one in 1949, and the Norton and JAP 500cc engines used were capable of around 50bhp, enough to propel these little cars weighing in at 600 pounds at quite alarming speeds. Paul decided that he didn’t want a differential, which must have made the steering interesting, and the front brake was an inboard 8″ with Bendix hydraulics, whilst the suspension used unequal wishbones of 8 and 10 inches. (More info on www.500race.org/Marques/Emeryson.htm)The only other example of suspension adaptation that I know about was mentioned fairly recently by New Zealander Ralph Watson, (January 1997 magazine). This was a racing machine built by the Stanton Brothers in the fifties using BSA components. According to Ralph this car had a single transverse spring front and rear (it was a four-wheel conversion) with front wishbones; I wonder how that one performed. As for the suspension on the Watson machine, it looks standard apart from front shocks. We gather from the article that Ralph wrote for this magazine that it went very quickly indeed, but have no information on how the steering behaved on the track I’m afraid.The days are probably long past when fools like me try and make BSA trikes go fast round the likes of Silverstone, and even if they did it would not be worth while making major changes just for a couple of events a year; but I think it’s worth mentioning how I planned to overcome the problem of wayward steering. I say planned because that’s as far as it got, I lacked the engineering skills and the equipment (and as this was in the early seventies—the enthusiasm) to carry out a lot of the changes I dreamed up, and this was one of them. The answer, quite simple in concept, is to provide a stiff bar rather like a track-rod or anti-roll bar to connect the two swivel units together. This would have to be ball-jointed at either end so as to allow the suspension to do its job, and it would have to clear the underside of the chassis by about 3 to 4 inches.I think the biggest problem was how to fix it each end. I thought about having an extra piece welded onto the bottom half of the ‘stirrups’ on the swivels. Another idea was to make a clamp to fit on to the outer end of the bottom springs, this latter method would be easier, but not so elegant; anyway it didn’t happen, and the world was deprived of another useless idea!! I do hope that someone, somewhere, will benefit from what is contained in this little article, if you can learn from someone else’s experience it can save a lot of stress, and it’s cheaper!!

Peter Bowler

 

 

 

Photos

 

 

 


1. Close up of Alvis 1.5litre sports FWD gear. Taken by psb at Penshurst place Kent in the sixties.
2. Ackerman gleaned from the web
3. “A good set of springs” Martin Mackenzie Ford engined trike, prepared for racing at Santa Pod sprint meeting sometime in the early seventies ‘photo psb.
4. If studied closely the picture of our Silverstone outing does show some irregularities in the front wheel alignment, however the o/s wheel was back on the tarmac when this picture was taken
5. Series seven reproduced from an original factory drawing
6. Alt’t’cock (picture anon), note the negative camber.


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