Is it worse for car tires to have too much air, or not enough?

Both are about as bad.

Too much air and the bow causing increased ware down the center.

Too little and they wear too much on the rims of the tire.

Both cause too much wear. Also, too much at high speeds can explode due to heat. But too little can come off as well.

In short, keep them at the right pressure.

Too Much Air In Tires

It is most decidedly worse to have too little air in your tires than too much air, although the tires should be inflated to the MFG recommended pressure.

Too little air causes the tire to be overloaded, since the air pressure carries the weight of the vehicle, and it's occupants. A tire that is underinflated, hence overloaded, has a great deal of rolling resistance(friction) relative to the road. Friction equals heat,and heat can cause the tire to disintegrate, thus causing a rapid decompression(a.k.a. KABAMMO!). Remember: the air pressure inside your tire wants to equalize with the outside air pressure.

While I do not recommend overinflation, I do recommend inflation pressure be checked while the tires are cold(i.e. driven less than 1 mile), and adjusted to the vehicle manufacturers specs, not what is stamped on the tire, which is the maximum, not the recommended, inflation pressure.

Older tires (4 years or older from date of manufacture) should be replaced , as the rubber compound can become brittle due to exposure to the elements. This opinion, however, has been recently called in to question by the RMA (Rubber Manufacturer's Association) as being unduly alarmist.

Make up your own mind about the age. The inflation pressure question has been proven.

Not enough will cause uneven wear on your tire and seriously decrease your gas mileage.

Too much air will cause slightly more wear in the middle which really isn't that significant and on a hot day there is an outside chance that the tire could explode.

Also, just driving down the highway will cause your tire to heat up considerably.

I would say not enough is more of a problem, because I don't think the danger of the tire exploding is that great, unless you have them aired up ten or twenty psi over the recommendation.

too little is worse but if it's hot too much is also bad. Just get a tire guage and check all tires. Get them pretty close to whatthe manufactures suggest in the handbook. You'll get better gas milage that way.

It is MUCH worse for tires to have too much air or not enough. The ideal air pressure is what is correct.

too much air=bumpy ride, tend to explode especially on long, hot rides but fuel efficient

not enough=not bumpy, tend to drag the car, not fuel efficient

i say it's worse for car tires to have too much air.

too much air causes the tyre to bulge in the centre thread, causing it to wear in that area. underinflation causes it to wear on the outer threads, caused when turning.

In both instances grip is drastically reduced & weakens your suspension.

Not enough

not enough ...... the tires will blow out much easier .