Well, this is a more complicated topic than I expected. As I thought, there are hundreds of people on the internet with different explanations and cures. Some are much more scientific than others. Here in Straight Dope is the best summary I have found!
Certainly there are at least two different phenomena – one where the whole car and its occupants are electrostatically charged, and another which seems more recent, where the occupants get a charge within the vehicle. More recently still, apparently some modern low rolling resistance tyres no longer conduct enough electricity, and the original whole vehicle charge problem has returned.
I’ve previously had static shocks from two Toyota Corollas, several years apart. The zaps stopped completely in each case when I fitted a proprietary, slightly conductive trailing rubber anti-static strap under them. Many people have had the same results. But I just fitted one to our Honda Fit and got a painful shock for my troubles. Perhaps there was something else that happened to the Toyotas – maybe by coincidence we bought seat covers for them at around the same time as the straps were fitted? And we have another Corolla which has never shocked me…
Last night the air temperature was cold for Auckland (maybe 10° C, 50° F, so not cold by continental standards!), and the wind had been blowing down from the high country over several hundred km of wet ground, so its relative humidity wasn’t low. But even had it been saturated, at that temperature its absolute humidity would have been lower than usual.
I checked the new strap on the Honda this morning, and it measures something less than 300 k Ohms. So I’m reasonably confident that the car was close enough to ground potential when that nasty little blue spark took me completely by surprise.
Which implies that it was me, not the car, which was highly charged. And that it was the insulating qualities of my polyurethane soles which preserved that charge. I’m now working on the hypothesis that friction between my Merino wool jacket and the synthetic seat is responsible. (Everything else I was wearing was cotton.)
I’ve also checked the interior of the car with the meter. It’s certainly quite different from older cars. Although there is a lot of shiny “brushed stainless” it’s almost all totally non-conductive. There is only one possible object you can touch inside it which has any electrical connection to the car body, and that is the button on the hand brake. Every other control is plastic. The steering wheel and its various buttons, and all of the gearshift, all plastic. All steel parts of the body and door are covered by plastic trim. Seat controls, seat belt anchors, the whole radio, all plastic covered. Even the “cigarette lighter” power outlet is covered by a plastic door when not in use.
The ignition key fits into the lock between two plastic projections (which are what you use to turn it when you are using it in “keyless” mode using the credit-card-sized electronic “key”). Even the screw holding the internal door handle is insulated – it must go into a plastic insert. It is simply impossible to ground yourself to the car except by that little handbrake button!
Holding the key and using it to create a discharge isn’t a good option. The keys are expensive, with their sensitive little package of security electronics inside the thick plastic “handle” end. Anyway, I seem to get worse shocks when I’m not the driver. So I’ll try touching the handbrake before, and as I get out. Wish me luck!
