All Things Car

Plain talk help about buying or owning a vehicle, from shopping tips to ownership information and more

Archive for the month “October, 2011”

What’s with that weird light on my dash that looks like a butt? A brief discussion of the Tire Pressure Monitor System (TPMS)

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     If your vehicle is a 2007 or newer (and a few older models as well), there is a good chance you have seen this symbol at some point during your ownership.  I have had many customers call, trying to describe it to me, and to ask what the heck it is, and what it is trying to tell them.  In all reality, what it is saying is “Check your tires!”  Since a certain SUV had issues with tires a number of years ago, the US Government issued a mandate that any vehicle built from 2007 forward would have an acceptable Tire Pressure Monitoring System.  They can be a nuisance, but they are there for the protection of the consumer.

     Living in Minnesota, with the changes in climate that we experience, this symbol has a tendency to show itself frequently during the Spring and the Fall seasons, when temperatures vary greatly from day to day.  When it gets colder, the air pressure in our tires will drop.  When it gets warmer, it increases.  This will often trigger the light you see above.  Other factors can cause a tire to become improperly inflated, including punctures from nails, screws and other debris.  It is worth while to have the tire checked out if you see this light.  Many of these can be repaired, saving you the cost of a tire replacement.

     Additionally, if you have recently purchased tires (especially if you did not get them from the dealership), it is possible that one of the sensors was broken during the tire mounting process.  Each tire has a pressure sensor in the valve stem that sends a signal to the “brain” of the system.  If a sensor is broken, it will read the pressure as “zero” and trigger the warning light.

     Since you won’t know the cause when you see the indicator, the first thing you should do is take a few seconds, walk around your vehicle, and make sure you aren’t driving on a flat.  With most of us having roadside assistance either through our manufacturer’s warranty or through our auto insurance, if you see a flat, call for help and get it fixed before you move your vehicle.  You don’t want to drive on a flat tire to the service station, ruining an expensive tire in the process.

     If all of the tires appear to be reasonably inflated (many of today’s vehicles actually have a display in the trip computer that will tell you the pressure in each individual tire – check your owner’s manual or call your salesman), then drive to a service station as soon as you can, and figure out which tire(s) is under/over inflated.  If this light is on, it is a situation that should be remedied as soon as possible, for the following reasons.

  1. If you actually do get a flat tire, and have been ignoring this indicator light for a period of time, the system will be unable to alert you further that you have a severe problem, and this could end up costing you money.
  2. An over or under inflated tire will have an effect on fuel economy, potentially costing you money
  3. A tire that is not at the proper inflation pressure will not wear evenly, and will shorten the life of the tire, costing you money.
  4. An over or under inflated tire will have an effect on ride and handling of your vehicle, effecting comfort and safety.
  5. An improperly inflated tire can pose a safety hazard, since the potential for tire failure is increased, endangering you and other drivers around you.

In short, while we know the Tire Pressure Monitor System warning light will never appear at a time that will be convenient, it’s worth taking a few seconds to check it out.  It could save you money, and could even save a life.

Mike Bidwell
Mankato Motor Co.


What is the difference between horsepower and torque, and what’s with all this RPM talk anyway?

     When you read anything about car shopping, everybody wants to talk about the power of an engine. But it gets very confusing making the comparisons. One car emphasizes how many horsepower the engine produces. Another talks about low-end torque. Some cars look like they should have the same power, but feel very different when I drive them. And then there is the @4000 RPM tag after the number. What does that mean?
Putting it simply, torque is the power an engine produces to get a vehicle moving, while horsepower is the ability to keep it moving. From there, it all depends what is important to you. If you like the “seat of your pants” thrust at the stop lights, or if you are purchasing a vehicle to pull a trailer or haul a heavy load, torque is your answer. If you are looking for more of a touring car, and passing power is more up your alley, then a high-horsepower sports car (2 or 4 doors – they make both these days) will be more appealing.
There are a number of other factors that can complicate matters, and that’s a topic for a different discussion, but the type of transmission, the gearing in the differential/transaxle is a factor (often discussed in pickups and large SUVs), and of course, that RPM term we see next to the horsepower and torque ratings.
RPM (Revolutions Per Minute) refers to how fast the engine is revving when it hits that peak horsepower or torque number. Low-end torque means that you don’t have to wind the motor up very far at all to get to the peak torque, and get the load moving. Many diesel trucks emphasize that you will be producing a lot of torque right at the engine speed the engine idles at. That means that when you first put it in gear, you have essentially all the “get it going” power you need to start towing or hauling. You don’t have to “step on it” to get into the power to get moving.
Horsepower, you will typically see with a relatively high RPM number. Some are “high-revving” motors, which mean that as you wind up for aggressive driving, the horsepower is there to finish the drag race. A daily commuter car will be just fine having the peak horsepower at a more moderate RPM, and may even provide a fuel efficiency advantage as a result of this design.
Which is more important to you will depend on what you need the car to do. I hope this brief explanation of the two is helpful as you research your purchase. Above all, however, remember that research is important, but nothing will tell you as much as a 10-15 minute test drive. Make sure the salesperson takes you on a route that will allow you to experience the elements of the car that best fit what you are going to need it for. If you need torque for carrying a load or pulling a trailer, make sure you are able to climb a hill on your drive. If you are more of a spirited driver, make sure you get the chance to accelerate up to highway speeds. If you are looking for a travel vehicle, make sure you get to drive on a variety of road surfaces, and at both city and highway speeds. Then combine your reading with your driving, and see if you are in the right car. From there, your decision will be easier. Happy shopping!

Mike Bidwell
Mankato Motor Co.

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