High speeds and bad tires can contribute to hydroplaning

Dear Tom and Ray: I have a history of hydroplaning. I slid and rolled over in a GMC Jimmy while making a sharp right turn during a rainstorm. I also have hydroplaned in a Jeep Cherokee while driving in a light drizzle and going in a perfectly straight line. I now own a Honda Civic. As I will obviously be driving in the rain once more, what is the best strategy for not letting it slide around? I had thought that not turning too fast would be a grand solution, until the Jeep incident. Any thoughts on the matter? Thanks!

Adam

Ray: Yeah. Slow down.

Tom: It's hard to know what happened in each situation, Adam. But there are several factors that often lead to hydroplaning.

Ray: The first one is speed. If you're going too fast and you hit standing water, the vehicle is going to hydroplane (that is, the tires will not be able to channel enough water out through their grooves, and the tires will ride up on top of the water, losing their contact with the road).

Tom: So if you drive like a knucklehead in the rain, whether you're going straight ahead or not, you're a candidate for hydroplaning.

Ray: Tires also can be an issue. Knobby, aggressive SUV tires are notoriously bad on wet pavement. It has to do with both the nature of the rubber compound used and the fact that they have deep grooves and, therefore, a smaller rubber patch on the road to begin with. So they tend to slide fairly easily. And while the deep grooves can help evacuate water, if you're going too fast, that's not enough.

Tom: Another factor is the size of the puddle you hit. If you live where there's flash flooding and standing water builds up on the roads, you have to be extra careful. If you drive into 2 or 3 inches of water, even at what normally is a reasonable speed, you easily can hydroplane.

Ray: And finally, your four-wheel-drive system could have been a factor. The GMC Jimmy and the Jeep Cherokee both have old-style "on-demand" four-wheel-drive systems (as opposed to modern, full-time all-wheel-drive systems). Those old-style systems are never supposed to be used when driving on normal roads -- dry or wet -- because they force the two front wheels to turn at the same combined speed as the pair of rear wheels.

Tom: If you try to steer a vehicle without letting each of its wheels turn at different speeds, you easily can lose control and flip it over. Or you could make it hard to regain control once you start to hydroplane.

Ray: Those old-style four-wheel-drive systems are supposed to be engaged only when you're stuck, or when you're actually driving on mud, sand or snow.

Tom: So make sure you have good tires on your Civic, watch out for large puddles and slow down, Adam. That should keep you on terra firma. Did we mention that you should slow down?

Dear Tom and Ray: How do I know when I should change my spark plugs? I mean, will my car do anything different? I was getting my oil changed, and the guy said I should change my spark plugs. How would he even know? Thanks.

Maureen

Ray: Well, generally speaking, there are four reasons to change your spark plugs, Maureen. One is, simply, time. A lot of cars now use platinum plugs that are supposed to last 100,000 miles, so you shouldn't need to change them often. But if your car has 110,000 miles on it and you know for a fact that you've never had your plugs changed, your mechanic would be correct in recommending a new set.

Tom: The second reason we suggest new plugs is if we've examined them and found that the electrodes are worn out. When the electrodes wear out, the spark-plug gap (the space that the spark jumps between) grows. That leads to reduced mileage and can lead to a misfire, which is when a cylinder fails to fire.

Ray: We might also notice that the ceramic insulation around the center electrode is cracking. That can cause a plug to fail, too. If we notice either of these signs of impending spark-plug geezerdom (ISPG), we'd probably recommend that you replace all of the plugs.

Tom: The third reason we might change your plugs is if you already have a misfire that we suspect is caused by a bad spark plug.

Ray: And the fourth reason we tell our customers they need new plugs is if we got a special "case price" on them from our supplier, and we need more room in our parts department.

Listen to "Car Talk" at 9 a.m. Saturdays and 5 p.m. Sundays on KRCU 90.9 FM -- Southeast Public Radio. Write to Tom and Ray at Car Talk Plaza, Box 3500 Harvard Square, Cambridge, Mass., 02238. Or e-mail them at the Car Talk section of cars.com.