Hey guys,
Just want to point out few things based on my findings and forum experience.
How to calculate the mileage for our crds: we all know the factory odometer is not very accurate. The odometer for a standard older car used a cable with some gears from the transmission to spin other gears that moved odometer digits. You change the tires (bigger or smaller than factory wheel), you mess up the reading since the wheel spins more or less than it was designed to. Our crds use an electronic signal that does that rather than cable with gears. To make a long story short, the factory wheels are designed to be the most accurate for the odometer. Also, the odometer has a +/- 5% error with factory wheels. Nothing new so far.
What I would like to highlight is this. One crd can have +1% error, another crd - 5% error, with the same wheels. It is very important to make sure you test how accurate is the odometer, to know exactly how big the error for your crd's odometer is. Many folks said that, I'm not laying out anything new, but this is how the "calibration" should be made:
Wait till you have a few hundred miles trip. Get a Gps and punch in the destination on a specific route. Note what is the total distance the Gps says (let's say it's 362 miles) Following that route, zero out your odometer before you start driving. Drive as many hundred miles on the odometer as possible (let's say it's 300 miles - a round number makes the math easier). When the odometer reads a round number (300 miles) , look on the Gps to see how many miles you actually drove. Let's say you realize it was 330 miles (based on gps). In this case, 30 miles difference would mean the odometer reads - 10% compared to reality (this happens when you go with bigger wheels). This means the mileage based on odometer is pretty much showing less miles/gallon than in reality.
In my case, the odo shows about 7% less than Gps, using stock rims with bf Goodrich 245x70x16.
Those wheels are a little taller than the stock ones. I never understood (or believe) how people can get 30mpg with crds... Now I do. I knew the odometer and speedometer are not as accurate as they were with stock tires, but, except speedometer that's easy to check vs Gps, never knew how much were off. What threw me off even more is that I thought that speedometer and odometer are directly dependent of each other. They aren't. My speedometer now shows about 0.5 miles less at 70 MpH than the Gps. The odometer is -7% off... I never got better than 25mpg (this with new rockers and lifters and gde eco). After getting the electric fan I got additional 2 mpg on Highway (27 mpg). After calculating the odo error, I got 30 mpg. All this with driving at an average of 73 MpH going from new York City to Cleveland on a relatively straight road, I80.
I am still so surprised of the difference and was thinking to pass this along, to further highlight the importance of knowing the real odometer error in order to get the proper mileage.