Getting a shock from your car? Your tires might be to blame.

Dear Car Talk

Dear Car Talk | May 01, 1997

Dear Tom and Ray:

I've heard that you both graduated from MIT in Mechanical Engineering. If
this is true, then we have that in common. But I hope we don't have my car
problem in common. My car builds up a static charge. And as soon as I get
out of the car and touch the frame, I get zapped. It's quite painful. I've
tried wearing shoes with different soles, kicking the door shut, and now I
just close the door by pushing on the window. However, the static charge
remains in me, and the next thing I touch which is grounded zaps me.

Some of my friends have suggested that my hair is too long, or that I have
some sort of extra-chargeable seats. The most common comment I get is that
I have an "electrifying personality." Short of shaving my head, what
suggestions would you have to keep me from building up such a large static
charge? -- Christine

TOM: We happened to solve a similar mystery about static electricity on our
radio show a few years ago, Christine. A toll-taker called us, and told us
that whenever a then-brand-new Honda Accord came by and the driver handed
him a quarter, he'd get zapped! POW! So much so that he began ducking down
in his booth whenever he saw a new Accord coming along.

RAY: It turned out that the new Accords were using a relatively new, "low
rolling resistance" tire, which reduced rolling friction to improve gas
mileage. And, you guessed it; static electricity leaves a car primarily
through the tires. In changing the rubber compound to increase mileage, the
tire maker had made the tire a poorer "grounder." So those new Accords were
not dissipating static electricity as well as most of the other cars on the

TOM: And while the tire maker claims to have improved the grounding ability
of that particular tire, the truth is that many tires are now "low rolling
resistance" tires and probably don't dissipate static electricity as well
as tires of old. It's one of the prices we're paying for better fuel
economy. And my guess is that your tires are the crucial element in this
equation, Christine.

RAY: Assuming that you're otherwise perfectly happy with your tires and
your mileage, there are a couple of other things we can suggest. The
simplest is to "discharge" yourself through something else. If you hold
your metal car key, for instance, and touch IT against the grounded car,
the charge will jump from the end of the key to the car, leaving your
finger "unzapped."

TOM: But if you don't want to bother with it at all, most auto parts stores
now sell "grounding strips" that hang from the frame of the car and touch
along the ground. I've tried those and they work pretty well -- although
since they scrape along the ground, they do wear out after several months
and need to be replaced.

RAY: Of course, it's possible that the friction of the grounding strips
will reduce your mileage by as much as the "low rolling resistance" tires
increase it. But you'll have to figure that out, Christine. After all,
you're the mechanical engineer. My brother graduated from MIT in Chemical

TOM: And my brother graduated with a degree in Animal Husbandry, and even
practiced for a few years ... until they caught him at it!

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