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Change the Tire Size, Mess the Gas Mileage

By Junior Damato, August 25th, 2012

strong>Dear Doctor: I have a 2010 Honda Accord that has 215/65/16 stock tires on steel rims. I bought a set of Honda Civic alloy rims with 205/55/16 tires on them. Both rims are 16 x 6.5 inches and the offsets are 55 vs. 45, so that is not an issue as they do fit. Will using the smaller diameter tires affect gas mileage also? Is there anything else I should be concerned about if I switch to the smaller tires? What is your opinion on using these smaller tires on my Accord? Andy

Manufacturer photo: 2010 Honda Accord
Manufacturer photo: 2010 Honda Accord

strong>Dear Andy: We change tire sizes often, usually staying with the same outside diameter or going larger, not smaller. The change you are making is minor. There will be a slight loss in gas mileage and the ride will also be a bit stiffer. The odometer will rack up mileage a bit sooner, too. If you like the look and ride, then use them, but you must use on all four tires. Another choice would be to use the alloy rims on the stock tires and sell the Civic tires. The load-carrying weight is affected by the smaller tires. The computer and ABS will not be affected with the tire change.

strong>Dear Doctor: I have a 2005 Mercury Grand Marquis with the climate control ventilation system. Recently, when using the air conditioning on maximum and wanting to warm the passenger compartment temperature, I was unable to do so as the air blowing out of the dashboard ducts remained cold. To check if the heating system was operating properly, I selected "floor" and 90 degrees on the temperature control, but only cold air would blow out. I experienced this problem about two years ago and had the blend door motor replaced at a cost of almost $1,000. Is it possible the blend door motor could have gone bad less than two years after being replaced? Chuck

strong>Dear Chuck: Sorry to say it could very well be a faulty blend door again, or a binding blend door. I've also seen a lot of in-car temperature sensors cause this problem. Before condemning the motor, however, have the system scanned to see if there are any fault codes in the system.

strong>Dear Doctor: I have a 2008 Cadillac CTS with a wandering passenger sideview mirror. I have the curb assist turned off and I have set the memory seat positions/mirror for drivers 1 and 2. In spite of this, once I use a fob to unlock the doors, the passenger side mirror wanders around and usually ends up pointing at the ground. I disconnected the battery for a few minutes to try to reset the system to no avail. Any ideas on how to keep the mirror "at home"? Mike

strong>Dear Mike: The sideview mirror system, like the seats and radio, has memory settings. Since your mirror is not setting as it should I would recheck the mirror settings. I would also slide the electric adjustment button position over to the driver's side before shutting the key off. See if that makes any difference. The next step would be a trip to a shop that has a Tech 2 scan tool to go into the Body Control Module and watch the system. There are no bulletins listed currently on this fault.

strong>Dear Doctor: The brakes on my 1999 Chevy Suburban K2500 don't function correctly. When I apply the brake pedal going over a pot hole or bump the ABS brakes stop working. If I release and re-apply the pedal they will return to slow down mode. No vibration or chatter, hint of any computer error, no dashboard light. It feels like I'm driving a Model A mechanical brake vehicle. The shop replaced the rear drums shoes, all adjustment mechanical parts, and said front brakes have plus 40 percent life remaining. They charged me $1,200 and the SUV is exactly the same as before shop rework. Surely a safety issue. Gary

strong>Dear Gary: It's no secret that the brakes on these SUVs are small, and in my opinion, poor. Even the brake booster is small. From your letter it seems the ABS system is activating without reason. A common fault is rust buildup in the front ABS sensors that sit in the knuckle. We can sometimes remove the plastic sensors and clean out the rust. In some cases the sensors will break and need replacement. Test the system before spending any money. Simply unplug the ABS unit for testing purposes. By unplugging the ABS unit the brake system will act like a system without the ABS feature. Also make sure the rear brakes are properly adjusted and the system has been bled.

strong>Dear Doctor: I want to add a roof rack to my 2005 Toyota Camry. How do I choose a model that easy to install and will it fit well on the car? George

strong>Dear George: There are only a couple of companies that offer roof racks. I have installed a lot of the Thule brand on many vehicles. Thule is a good quality rack.

Big Drop in Fuel Mileage: Get Engine Test

10/19

Big Drop in Fuel Mileage: Get Engine Test

strong>Dear Doctor: I have a 2014 Ford F-150 with the EcoBoost engine. The dealership cannot tell me why my gas mileage is at 9 mpg. It was 24 mpg when I purchased it. Can you help me out? Gerald

Gas Mileage Misread: Fuel System Needs Attention

10/12

Gas Mileage Misread: Fuel System Needs Attention

strong>Dear Doctor: I own a 2006 Ram 2500. The mileage calculator says I'm getting 30 miles per gallon in fuel economy, but I'm actually getting about 20 mpg. What should I do? Mark

Car Shakes at Idle: Check for Multiple Fault Codes

10/05

Car Shakes at Idle: Check for Multiple Fault Codes

strong>Dear Doctor: My 2009 Toyota Camry with 199,600 miles has a check engine light showing the codes P0101 and P0170. I have already replaced the MAF sensor, PCV valve, throttle body, the car's computer, O2 sensors, cam sensor, crank sensor, fuel pump, injectors, and fuel pressure regulator. I also checked for multiple vacuum or air leaks, and the cabin air filter, spark plugs, alternator, and battery have all been checked over the course of a year. Now the car has both codes showing consistently and it shakes at idle. What should we do? Cheyenne

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