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PostSubject: DIY Skidpan Testing.   Fri Dec 16, 2016 10:50 am

Thinking of trying this to get some idea how bad my tyres are.

If you wanted to do this, I'm wondering what might be the minimum practical radius for the "endless corner"?

Full lock obviously imposes an absolute lower limit, but then you've got no control (which does at least eliminate a variable) and I think using high power on full lock might be damaging.

I've seen a range quoted. 30 metre radius seems quite common. One study used 25 metres but I think that was for large trucks.

The smaller the radius, the lower the speed, and the easier it'd be to find space for it.

I'd expect the limiting g's to be way under 1 on this car/tyre combo, so one g could be the upper limit.

IF I've transposed the formula right (long time since I did this sort of thing) r = v squared/a

For one g, the resultant circle at different speeds becomes

Indicated Speed (km/hr) : radius (m) (=V squared/a)
10 0.79
20 3.15
25 4.92
30 7.08
35 9.64
40 12.58
50 19.66
60 28.32
70 38.54
80 50.34
90 63.71
100 78.65
110 95.17
120 113.26
130 132.93
140 154.16
150 176.97
160 201.36

That look right? Havn't seen any worked examples to check it against, but it seems to imply that low speed operation in the 5-10 m radius range should be practical.

Published radii are higher, but they are testing at higher speeds. I suppose there may be some differences at high speed which will make the limit g force results more relevant to real road conditions, though I can't offhand think what they are. Naybe aerodynamic down force, but there probably isn't much of that on my car.
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