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Old 05-26-2013, 12:53 PM   #365
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"I don't know why people say changing the tire size should make a difference since the computer uses the same numbers for mileage and the odometer (unless they are using a GPS for miles with their calculations)."

Because it duz.....think about it.

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Old 05-26-2013, 01:31 PM   #366
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Different tire size means different tire circumference, which would mean different distance traveled per revolution of the tire.
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Old 05-26-2013, 01:35 PM   #367
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Originally Posted by Wazbro View Post
I don't know why people say changing the tire size should make a difference since the computer uses the same numbers for mileage and the odometer (unless they are using a GPS for miles with their calculations).
For the sake of this argument assume that the amount of fuel the TV consumes is strictly a function of the actual distance traveled (not what the odometer / computer says - but actual distance). Say 1 gallon of fuel to travel from Town A to Town B. Say Town A and Town B are 1 mile apart.

The TV calculates distance by the number of rotations of the tires. If everything is calibrated correctly then the odometer will measure the correct distance from Town A to Town B and the mileage will be correct. (1 mpg)

If however the owner decides to put on tires that have twice the circumference - then the TV will think the distance from Town A to Town B is now half of what is really is - the number of tire rotations is half that of the smaller tires. (0.5 miles)

Given in this example that the TV uses the same amount of fuel regardless of the tires - the computer will think that the mileage with the larger tires is half that with the smaller tires. Same amount of fuel used...but only half the distance measured. (0.5 mpg)

Hope this helps...
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Old 05-26-2013, 01:42 PM   #368
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Originally Posted by MaxTow View Post
If however the owner decides to put on tires that have twice the circumference - then the TV will think the distance from Town A to Town B is now half of what is really is - the number of tire rotations is half that of the smaller tires. (0.5 miles)

Given in this example that the TV uses the same amount of fuel regardless of the tires - the computer will think that the mileage with the larger tires is half that with the smaller tires. Same amount of fuel used...but only half the distance measured. (0.5 mpg)

Hope this helps...

Ah, but it doesn't do that....the odometer knows that x amount of drive shaft rotations means a certain amount of distance is traveled. If you change the tire size, you change that amount of distance, so the odometer becomes in error, and then so is the mileage, but you really don't know that for sure because all calculations are done against the odometer reading, which is now wrong.
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Old 05-26-2013, 02:31 PM   #369
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I have a SuperChips FlashPaq tuner that I use to tune the TV for heavy towing and back to 87 octane gas when not towing. It has a setting for tire circumference to correct the speedometer if you change from OEM tires. No mental gymnastics required.
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Old 05-26-2013, 03:41 PM   #370
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EcoBoost issue

Agency’s Inquiry Covers 400,000 Ford Pickups
By CHRISTOPHER JENSEN
Published: May 26, 2013
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The National Highway Traffic Safety Administration said Sunday that it was investigating consumer complaints about “sharp reductions” in acceleration on 2011 to 2013 Ford F-150 pickups that are equipped with the 3.5-liter EcoBoost V-6 engine.

The action — called a preliminary evaluation — covers about 400,000 of the F-150 pickups, the safety agency said. A Ford spokesman Michael Levine wrote in an e-mail, however, that number was too high and should be “over 325,000.”

The F-150 is one of the automakers most popular, lucrative and thus important vehicles. And the twin-turbocharged EcoBoost V-6 is one of Ford’s main engines, used to power not just the F-150 but sport utility vehicles like the Explorer, crossovers like the Flex and cars including the Taurus.

Ford is aware of the investigation and will cooperate with the safety agency, a spokeswoman Kelli Felker wrote in an e-mail.

The safety agency decided to investigate after receiving 95 complaints from F-150 owners saying they experienced unexpectedly power loss during hard accelerations. About a third of those complaints said the problem occurred in damp or rainy conditions. There were no reports of accidents.

“Attempting to pass a vehicle accelerating from 55 miles per hour and truck either stutters or stalls,” one owner wrote the agency in February 2012. “This almost caused a head-on collision. I am scared to pull out in traffic or pass anyone.”

The safety agency said Ford had sent three technical service bulletins to dealers telling them how to cope with “intermittent/stumble misfire on acceleration” in humid or damp conditions.

The EcoBoost is a family of engines in different sizes. Ford has widely touted the EcoBoost’s turbocharging and direct-injection technology as providing excellent power as well as fuel economy.

The investigation covers only the 3.5 liter V-6, which made its debut in the F-150 for the 2011 model year. In 2012, about 43 percent of the F-150s were equipped with the optional 3.5 liter EcoBoost, Mr. Levine, the Ford spokesman, wrote in an e-mail.

In the safety agency’s preliminary evaluation, if investigators find additional reason for concern, the inquiry would be upgraded to an engineering analysis.

A preliminary evaluation does not typically result in a recall. That’s more likely — but not certain — with an engineering analysis.

Recalls happen most quickly when automakers are convinced there is a safety problem. It has sometimes taken the agency a year to complete a preliminary evaluation and another year for an engineering analysis.

Last July Ford recalled about 11,500 of its 2013 Escape crossovers because of a fire hazard with its 1.6 liter EcoBoost four-cylinder engine.
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Old 05-26-2013, 04:02 PM   #371
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Originally Posted by MaxTow View Post
For the sake of this argument assume that the amount of fuel the TV consumes is strictly a function of the actual distance traveled (not what the odometer / computer says - but actual distance). Say 1 gallon of fuel to travel from Town A to Town B. Say Town A and Town B are 1 mile apart.

The TV calculates distance by the number of rotations of the tires. If everything is calibrated correctly then the odometer will measure the correct distance from Town A to Town B and the mileage will be correct. (1 mpg)

If however the owner decides to put on tires that have twice the circumference - then the TV will think the distance from Town A to Town B is now half of what is really is - the number of tire rotations is half that of the smaller tires. (0.5 miles)

Given in this example that the TV uses the same amount of fuel regardless of the tires - the computer will think that the mileage with the larger tires is half that with the smaller tires. Same amount of fuel used...but only half the distance measured. (0.5 mpg)

Hope this helps...
But given that example when you use the odometer to calculate the fuel used compared to the pump you will be using the same mileage number,

I know the mileage will be off, what I said was the mileage should be off the same amount for the computer MPG calculation and the gas pump calculation since you are using the same source for mileage driven.
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Old 05-26-2013, 04:05 PM   #372
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"I don't know why people say changing the tire size should make a difference since the computer uses the same numbers for mileage and the odometer (unless they are using a GPS for miles with their calculations)."

Because it duz.....think about it.

Bob
Quote:
Originally Posted by SteveH View Post
Different tire size means different tire circumference, which would mean different distance traveled per revolution of the tire.
I'm talking the difference between computer and calculated not actual mileage.....think about it.
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Old 05-26-2013, 05:02 PM   #373
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Originally Posted by Wazbro View Post
But given that example when you use the odometer to calculate the fuel used compared to the pump you will be using the same mileage number,

I know the mileage will be off, what I said was the mileage should be off the same amount for the computer MPG calculation and the gas pump calculation since you are using the same source for mileage driven.
Looks like I misinterpreted your original statement.

Yes, you are correct. Assuming the TV calculated fuel consumption is identical to a pump reading - and you use the same odometer reading for both calculations, then the results will be the same. That is, either in error if the tires are mismatched to the odometer, or correct if the tire size is matched.

Garbage in - garbage out.

A change in tire size will have no impact on the vehicles calculation of fuel consumption.
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Old 05-27-2013, 10:07 PM   #374
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"A change in tire size will have no impact on the vehicles calculation of fuel consumption."

But it will and does have an effect on the DIC calculation, that is precisely why the tire height is programmable on GM vehicles.

You won't get an accurate readout, mpg, speedo or odo, if the PCM is set for 29" tires and your running 31". Been there done it.


Bob
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Old 05-28-2013, 12:57 AM   #375
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Hi, changing tire sizes, brands, and tread patterns can cause your actual fuel mileage to increase or decrease; Usually the latter.
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Old 05-28-2013, 07:17 AM   #376
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Quote:
Originally Posted by ROBERT CROSS View Post
"A change in tire size will have no impact on the vehicles calculation of fuel consumption."

But it will and does have an effect on the DIC calculation, that is precisely why the tire height is programmable on GM vehicles.

You won't get an accurate readout, mpg, speedo or odo, if the PCM is set for 29" tires and your running 31". Been there done it.


Bob
Yes, But you are assuming the driver is using the odo for the calculation and not their GPS or something else. I get customers telling me everyting (odo, mileage, etc.) is a lie because their GPS says so.

Also, the only certified accurate speedo (and thus, odo ) are law enforcement vehicles. All the rest are + or - 5% or so.
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Old 05-28-2013, 07:21 AM   #377
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Also, the only certified accurate speedo (and thus, odo ) are law enforcement vehicles. All the rest are + or - 5% or so.
I know that's right, but I'm not too sure about the law enforcement speedo, or even their speedometers.
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Old 05-28-2013, 07:24 AM   #378
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True that! In reality they read 20mph slow. Otherwise they wouldn't blow by me on the interstate, with no particular place to get to, while talking on their cell!
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