Old cars and higher speeds


#1

I have a 1999 Cavalier approaching 250,000 miles. Out of concern for my old car, and to save fuel, I limit my top speed below the maximum legal limits. On shorter trips, I don’t go over 60, since there isn’t much time to be saved with higher speeds. On longer trips, hundreds of miles, I’ll go 70.



Most of my longer trips are to west Texas, where maximum speed limits are 75 and 80. By not going that fast, I save fuel, but what about car wear?



I’m wondering how speed affects the longevity of a car’s parts. Each part will have a certain number of cycles per mile in a given gear, but does the speed of those cycles make a difference? Does the need for increased power to sustain higher speeds make a difference? Would I be better off going only 60 or 65 instead of 70? Or might 70 be easier on the car’s parts than 60?



I realize there’s no absolute answer, but I’d appreciate insight as to whether this really matters, and, if so, how it matters.


#2

Is it well-maintained? Are its tires less than 5 years old and with good tread? Brake maintenance up to date? If not, you shouldn’t drive it at any speed.

Otherwise you can go the speed limit.

The difference between 70 and 80mph as far as the drivetrain is concerned is going to be pretty minimal. The difference between 70 and 80 mph when being struck from behind by a guy going the speed limit will be much less minimal. Go the speed limit.


#3

I don’t think it makes a difference. The amount of times the piston goes up and down is based solely on the final drive ratio and the distance. Whenether you’r going 60 or 80, the piston goes up and down the exact same number of times for each mile, the same total for the trip.

The only difference is that at the higher speed you’re running with the throttle slightly more open and a bit more gas going in to overcome the added wind resistance and rolling resistance. This means that the combustion forces are slightly higher. There’s also a bit higher drag, so there’s a bit more wear on the drivetrain components.

Honestly, I seriously doubt if any of this affects longevity of the vehicle. 60 or 75, I doubt if the car feels the difference in any meaningful way.


#4

The car is well maintained. I do most of it myself, but I prefer to have professionals check the front end. It was aligned recently. They replaced a tie rod end and found the other related components to be in good condition.

I suspected that the difference caused by different speeds, within the limits specified, would be minimal, but I wanted to ask for opinions here. I started going slower when the car got to higher miles, due to uncertainty about the effect of speed.

Thanks for the insight.


#5

Higher speeds means more air resistance and therefore the car uses more force to push through the air. A 5 mph difference isn’t enough to produce additional wear and tear. Now if you were going 80 to 90 mph all the time it might show up in more tire wear, more transmission wear, etc.

On the whole, little to no difference. Proper maintenance is more a much more important factor in a cars longevity.


#6

A 1999 is not an old car. My 1998 BMW 328i will still cruise at 90+ mph and get 30+ MPG. Since you have 250k miles on your car, you probably maintained it well. It should not make a difference driving it like it was new.


#7

I call it old because of the mileage, not the actual age. The outer layer of paint is breaking off and parts of the interior are broken, which also make me think of it as old. I don’t care much what it looks like, but I try to keep the working parts in good shape.


#8

Keep up the good habits.For a variety of reasons, older cars are not as capable and driving them a little slower is a good idea, for safety and longevity. Not only is it harder to push air at highers speeds, but the forces are greater, lubrication is more difficult and parts are generally under greater stress. The slower the better (within reason), but IMO, 70 mph is not too much to ask. I wouldn’t pound it much above that though in a 99 Cavalier with that many miles. You are at a stage where something could break at any time.


#9

Agree that a well-maintained car can go just as fast. However, a Cavalier with that many miles on it will have a looser engine, and at those speeds, will consume oil in all likelihood. Just check the oil with every tankful of gas.


#10

I doubt if it will make a material difference. It will save a little fuel, but I doubt if that is your goal. I would and have not worried about it. You 1999 Cavaller likely will not notice any difference.


#11

Each part will have a certain number of cycles per mile in a given gear, but does the speed of those cycles make a difference?

Technically, yes. Realistically, from your perspective, no.
Let’s take a bearing for example. When it moves, it generates heat. The ability to dissipate heat is limited so the speed of rotation will determine operating temperature. The slower it turns, the lower the operating temperature. The faster it turns, the faster it generates heat and so the operating temperature goes up. In application, the bearing and supporting structure is designed to keep the bearing temperature within acceptable limits with a huge safety margin built in. Your operating the car at speeds well above the posted speed limits will never exceed the ability of the mechanicals to withstand the degrading effects.

Does the need for increased power to sustain higher speeds make a difference?

The engine is under more load and so it takes more fuel and generates more heat to move the same mass with increased resistance. Again, the vehicle is designed to compensate for this and it will not degrade the lifetime of the components in any measurable way.


#13

That’s a good post. The only thing I’m doubtful of, is that the safety margins of cars like Cavaliers is that great. After touring a parts supplier at a local plant and hearing the stories of how often the “over constructed” parts (specifically burnished cranks that would dissipate heat better) are rejected, even at the same price, has reinforced my idea that planned failure is built in. CR considered the Maverick one of the best engineered cars they have ever tested. So many of the parts began to fail at the same time it must have had a well planned life expectancy.

Wear-wise, the Cav. is about to “calve”. IMO, best done at something less than 80mph.


#14

A '99 Cavalier with 250,000 miles must be pretty scary at 70…It’s not the engine and transmission that’s the problem, they don’t care. It’s the steering and suspension and corrosion that slowly degrade the driving safety of automobiles…


#15

The simple answer is …your better off to stay on the lower end of the speed. Wear n tear. Safety and MPG. I wouldnt worry about getting rear ended by somebody going 10mph faster than you


#16

Thanks, everyone for the insight. I now understand the issue much better than before.