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« on: August 30, 2022, 20:00:36 »
Michael and Jonas,
My apologies for a long pause in contributing to this essential topic. My poor defence being the hours I am wasting on setting up a new lap top, demonstrating my ignorance of all things digital.
To begin with, when reading Michael Trotter's posts, I realise what a chasm exists between a proper engineer, like Michael and an amateur fitter, like me. Thus I have no doubt that my opinion on the clearance of cam to peg is quite wrong and the cam is machined with more clearance on lock as compared to straight ahead. Which being the case I am now puzzled by the too often observed, incorrectly adjusted Bishop Cam steering box, binding as lock is applied. In my experience there is a tendency, during adjustment, to reduce straight ahead free play too much and this seems always to result in the peg binding in the cam as the rocker arm travels from the straight ahead position. This prevents the self centering action of the caster angle operating and makes your Ace or Aceca an absolute pig to drive....
To address the specific problem described by Jonas, one of the symptoms of excessive toe in is poor straight line stability. If, as Michael suggests, this is the situation with AEX 31 then it will be interesting to hear the results of a revision to the toe in adjustment.
Turning to the general question of toe in I used a tracking pad for many years, such as Michael describes, but eventually concluded that the drag due to tyre rolling resistance probably varied as the square of speed and any slip angle detected at walking pace might be misleading at sixty or seventy miles an hour. The other doubt in my mind was repeatability, or rather the lack of it: Slip angles measured on each run seemed to have quite a large scatter. I now use the 'Trackace' system mentioned by Jonas. The other thing about the effects of drag on front wheel alignment concerns the early versus the later Ace chassis: The early cars, including '31, have hard mounts for the inner wishbone whilst the later car uses rubber bushes which one might suppose give greater compliance. As far as I am aware the toe in setting remained the same for both when you might expect the early 'solid' wishbone to require less toe in angle ?
Jonas mentions choice of steering box oil and I don't believe that this will have any effect on straight line stability. In the interests of longevity I use a synthetic gear oil - Mobil SHC 75W - 90, but I'm sure his Penrite is satisfactory.
Steering box brace: It was not me that was involved in a batch, but I have made a couple for myself. I remember David Sanderson telling me that the LHD Ace steering box mount is far less rigid than the RHD mount and I think the steering brace requirement could have come from SCCA racing. Whatever the instigation you can't have too much of a good thing so braces all round - RHD and LHD. However I doubt that the brace would affect straight line stability as any flexing would be more likely during brisk cornering.
Finally (sigh of relief) I am wondering about some of the calculations shewn in this thread. Mixing fractions of a degree with decimal points is not a good idea. It does seem to be the modern way, but 2.5° is not 2° 50' it is 2° 30' . On this basis '31 with 40' of toe in (0.66°) then it is over 3/16 of an inch
Barrie
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