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Your thoughts on roll oversteer please
#11
Roll oversteer is primarily related to a geometric steer effect of the suspension. Almost all systems (except the trailing parallel links of a Mini) steer one way or the other to some extent so to remedy by altering spring geometry is entirely normal.

Oversteer is otherwise related more to the tyre performance, in turn related to the weight loading and any camber change. The relative stiffness of front and rear springs in roll, chassis rigidity, roll centre height, major influences on the weight on tyre.

All oversteer, and roll oversteer particularly, is like walking a tightrope, an inherently unstable condition where every wobble grows. The Seven has both strong roll and weight related oversteer. Hence the characteristic lively handling of full height cars,
unnerving to those only accustommed inherently stable moderns.

If for some curious reason (hot rod maybe) someone wanted to cure the roll oversteer of the saloons any axle  locating framework would hopelessly conflict with the conventional shackles. 
(Decades ago I started to make a spring mounting below the chassis of my RP but fortunately never completed. Sadly another RP chassis was sacrificed in the process)

Stiff springs and shock absorbers, by reducing all movement, reduce the effect of geometric influences and errors.
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#12
Ian, it is kind of you to imply that I might have something sensible to say about the handling of the Williams cars. Well, you've driven them, what did you think? I suppose that's a bit unfair, perhaps you didn't feel at liberty to explore the ragged edge!

They are very conventional cars in layout. Flat springs, conventional rear dampers adjusted tightly, separate front dampers on the car with the wider front track and an extra static disc in the other car. They really don't roll much. they aren't super light like Simplicity but the c of g is comfortingly low. One sits a little further back than in an Ulster. It maybe they gain a little stiffness from the deeper crankcases. The engines are bolted down at all corners. There is no chassis boxing. I have heard it claimed that the rather tubular body construction with undertray lends stiffness which, I take leave to suggest, is insignificant if true.
Both cars are on 15" cross plies. The ex Ironside car came with 16" rears and was much better (less twitchy) on 15s, quite possibly roll centre related but it is certainly my experience that tyre type and pressure makes a lot of difference. I would advocate going to some trouble to stop the rear spring leaves moving sideways (extra clips or binding or both). I do not doubt that Lotus could literally run rings round them but in my experience on the whole they go where you look.
I find them safe and predictable. I do not think I have ever been aware of roll oversteer with these cars whereas, with my '33 Tourer with "semi flat" rear springs, I have to set it up before the corner if I wish to avoid an unpleasant surprise. Mind you, I am hardly comparing like with like in most respects.
I think the "design trick" is to avoid circumstances the original design dislikes. Well balanced wheels are a really good idea! I don't think I have added a lot to the debate - sorry! John Miles' article is a lot more use here than I am.

Regards,
Stuart
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#13
Yes Stuart as John wishes to build a car based on yours I though there would be no one better placed to provide sensible feed back on how they handle. As you point out you very kindly let me drive both, which something I am forever grateful for, as I recall they were both extremely pleasant cars to drive, even if a little cramped for someone long legged like myself. You obviously have driven then a lot over the years and probably much closer to the limit than I would have felt a liberty to do, can I ask how do you find the wide track when compared to lets say an Ulster or speedy? do you feel the reduction in roll is due to the extra width? Have you noticed if there is any difference in turn in/understeer over a conventional sports front axle
I would agree with your comments about extra clips on the rear springs, that made a worthwhile improvement to my car.

PS, can anyone post copies of the John Miles articles here, I believe they would make worthwhile reading for many.
Black Art Enthusiast
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#14
Wide front axle.
Well, you would think the car with the wider axle would be less inclined to fall over but I suspect the relative lack of roll is more related to a low c of g.
In my ignorance I might expect turn in to be sharper with the narrower front track but it's not a thing that's really impressed itself on me. What is apparent with the wider axle is the effect of inadequate damping. Is "patter" the correct expression? It seems such an inadequate term for that moment where the axle swings like a pendulum. The wider track axle is more sensitive to inadequacies of balance or damping, as seems reasonable to me intuitively.

Minor considerations: the good news is that if the front goes through a gap, the back definitely will. The bad news is you have more chances to hit a pothole.
Of the two cars, I do prefer driving the car with the wide axle on twisty roads which says something about its handling at fairly sensible speeds. Incidentally, the LMW has wider front than rear track.

Regards,
Stuart
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#15
With car suspension there are so many variables that it’s difficult sometimes to say exactly what will happen. But, generally, widening an axle will reduce weight transfer and produce more grip at that end in the steady state, because the load is shared more equally between the tyres. On turn in, the roll action will tend to load up the outside tyre on the wider axle. ( load transfers diagonally across the car), so you might expect sharper turn in with a wide front axle, turning into progressive oversteer in steady state. Not a bad thing to have.
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#16
Interesting reading this, makes me think I have a problem with my Arrow (speedy chassis) as the front spring is quite soft. Buts that's a future problem - need to get it on the road first.
Just curious and a bit off topic, but thinking about the suspension on single seaters, with the diff significantly offset, I do wonder if this induces marked torque steer?
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#17
(13-02-2018, 07:57 PM)Ian Williams Wrote: ....I am very much in agreement with Steve regarding tight dampers, stiff front end and tyre pressures.

That's good to hear Ian. I'm no chassis engineering guru. I leave that to such as Alan who has it as his profession and is, therefore, someone to listen to as he knows what he's talking about as opposed to some who just think they do. However, I do watch how cars behave and I do think about how my car behaves and my experience is that the above (together with some tight binding of the springs) is the way to go before even thinking about going 'exotic'.  The car goes where it's pointed and such as the exit from Ettores on the Prescott Long Course with the car simply drifting on power to the next, left hand, apex with no steering input is an absolute delight - when you get it right!! 

As to my good friend Stuart, here he is practising what he preaches

   

Steve
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#18
A soft front spring means less grip at that end - understeer. Not a bad thing, but if it’s too soft you might find the turn in, especially on tight bends, isn’t very sharp.
Re offset axles, I can see how this might induce torque steer, but I wonder if on an austin7 there’s enough torque to worry about. Anyone got one?
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#19
This is turning into a very interesting and informative discussion. My thanks to everyone who is contributing to my learning experience and hopefully preventing me from making fundamental errors in my build.

I'm sorry about this next question which illustrates my lack of knowledge. From Stuart's experience and Alan's input it would seem that a wide track front axle is desirable. So my question is, how is the wider track achieved? 

John
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#20
Perhaps Alan will explain his statement which is contrary to conventional theory and practice. 

Cars are fitted with front anti roll bars to increase effective stiffness and induce understeer. On dirt track cars when the track is wet, the suspension torsion bars are swapped for soft rated ones to improve grip.

My RP Seven with original rear shock absorbers could be cornered sprirtedly in the wet on smooth tyres but with stiff hydraulic shock absorbers slid easily (albeit controllably).

Perhaps on a very light car there is a very low tyre loading below which adhesion reduces. Or with soft springs do the istrong friction sas become so dominant they reduce adhesion?
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