Any - DIY Skidpan Testing

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Fri 16 Dec 2016 10:19
Any - DIY Skidpan Testing - edlithgow

If you wanted to do this, 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.

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Fri 16 Dec 2016 10:32
Any - DIY Skidpan Testing - RT

Depends what's meant to be achieved. The larger the better, I'd suggest, as a smaller circle means slower speeds which are more difficult to adjust especially as soon a slip occurs.

The drive train will affect things - FWD cars tend to power understeer, while RWD cars tend to power oversteer - 4WD can be either depending on how the drive is transmitted.

Those 4WD cars which are essentially a FWD car with additional drive to the rear tend to handle like a FWD car (except Subaru's which are cleverer).

Personally I like non-FWD based 4WD cars which tend to give slight lift-off understeer and slight power oversteer - plus the Subarus which do the same - I'm aware that the fancy electronics of modern cars can hide the inherent character.

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Fri 16 Dec 2016 11:02
Any - DIY Skidpan Testing - Railroad.

You will have difficulty doing this on any standard production car manufactured from 2012 onwards (as well as many before that), as all are fitted with Electronic Stability Program ESP. It's exactly what the system is intended to prevent.

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Fri 16 Dec 2016 11:19
Any - DIY Skidpan Testing - gordonbennet

The electronics can still be switched off on most, but on some they default back on above a certain speed, so for slow skidding practice you should be able to keep the interference at bay.

I haven't practised sliding for many years, and finding somewhere in Britain where you wouldn't end up in trouble doing so is increasingly difficult, i learned quite a lot chucking cars about on the banger track in my teens, also i dislike the natural understeer and other disadvantages of FWD cars and have avoided owning them as much as possible.

Fresh snow is the obvious time for us in Britain (no help to the OP) but unless you know the ground pre snow is fraught with the danger of seriously expensive damage if you find a kerb boulder tree stump etc on a full sideways drift.

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Sat 17 Dec 2016 02:04
Any - DIY Skidpan Testing - edlithgow

Main objective is to test (and maybe "tune") my tyres. Skid control practice could be a secondary (though perhaps more useful) objective.

I tried that in an large empty icy car park in Aviemore (ski resort in Scotland, so when there isn't snow it has a massive excess car-park capacity) many years ago but it wasn't very long before the cops turned up and told me to stop it.

Car is 1986, so stability control systems aren't an issue, though it is unfortunately FWD, which is rather hard to avoid these days.

I thought the slower the better within reason, since it allows a smaller circle which will be easier to find space for.

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

THINK that's right but havn't seen any worked examples to check it against.

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, apart from maybe aerodynamic downforce which I doubt my car has very much of.

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Sat 17 Dec 2016 04:30
Any - DIY Skidpan Testing - RT

Most mid-80s FWD cars will be poor in those conditions anyway with poor suspension geometry, both front and rear, and large amounts of torque-steer to confuse things. The original Saab 900 is one of the few exceptions.

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