spedo / gas mileage

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tahoan
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spedo / gas mileage

Post by tahoan »

I have a 2005 AWD with approx 2800 miles. My gas mileage on my last fill up was 29.8 mpg which were all freeway miles. I was driving past a sign posted by the CHP which indicated my speed was 70mph. My spedo indicated I was doing 77mph. Question 1 - do I trust my speedo or the chp's sign?Question 2 - if the speedo is off, does that mean my odometer is off and my warranty is dwindling away faster than it should?Question 3 - Can I just call up the dealer and schedule an appt based on the chp sign?Question 4 - does this gas mileage seem high for an AWD without being broken in?Thanks a ton.
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joatmon
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Re: spedo / gas mileage (tahoan)

Post by joatmon »

1. Hard to know. There is some minimal slip in an automatic transmission, but check it out and let us know what RPMS the tach says you are going when the speedometer says 70 mph, and then other AWD users can chime in to compare, and we can even try math.2. If the sign was accurate at 77 and the speedo was wrong at 70, then the odometer would be incrementing too slowly, say 10 %. That would mean that your 36,000 mile warranty would actually be good for almost 40,000 real miles. It would also mean that instead of 29.8 mpg, you got closer to 32.8.3. You can call the dealer and see what they have to say. I do not think that there are any dealer calibratable adjustments to the speedometer, and if it is possible, it would take a jig the dealer won't have. But a phone call is free.4. the 2005 AWD is rated at 26 city/31 hwy. Guess it depends on how and where you drive, but 30 would not be unrealistic.You may want to check the air pressure in your tires. Some people have gotten Vibes with overinflated tires, and that would make the tires bigger, which would mean fewer rotations per mile, which would make the speedometer read lower than actual. Not sure what pressure would be required to make a 10% difference though.Charlie's pic from http://forums.genvibe.com/zerothread?id=6367
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Digger
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Post by Digger »

I am averaging 26 mpg with 5k on mine. Just put a short ram and TB spacer on which droped my MPG a bit.
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ColonelPanic
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Re: spedo / gas mileage (tahoan)

Post by ColonelPanic »

Wow, and weird, 7 MPH is quite a margin of error... My Vibe's speedo reads fast somewhere in the neighborhood of 4 MPH. I've verified this by a number of those radar signs on side streets at 25 MPH limits all the way up to interstates at 65 MPH. Plus, when I had a GPS, it was giving me similar numbers as well. Slower speeds are right on, faster speeds are always incorrect. When you were clocked by the sign, was there anyone else anywhere near you? I've found those signs to be inaccurate if you have compnay to the side or behind you.
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binary
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Post by binary »

The signs use a lower accuracy radar, and aren't calibrated often. So I read those with a grain of salt. But maybe your town has a maintenance schedule to calibrate them more often.That being said, we've always wondered how much fun it would be to hit triple digits passing one of those darn thing.
tahoan
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Re: spedo / gas mileage (joatmon)

Post by tahoan »

If the CHP sign was right, then ifMy car reads 77mph, then at 77k miles on my odometer would mean that an actual 70 mph would be equivalent to 70k miles. That would mean the 36k warranty would be up at 32,725.That is what I think. Maybe I am doing "fuzzy math" If I am backwards, then I would love to keep the benefits of the odometer not reading as high as it actually was.Please confirm.
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joatmon
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Re: spedo / gas mileage (tahoan)

Post by joatmon »

no, I misread, and it was me that was backwards. sorry 'bout that
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zionzr2
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Post by zionzr2 »

your mileage for hwy seems to be ok maybe a tad low... but that could be due to other factors....now if you were getting less than 27 on the hwy then there might be something going on that needs to be checked out..
harryyiii
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Re: spedo / gas mileage (tahoan)

Post by harryyiii »

Speedometer calibration has nothing to do with odometer accuracy. The odometer counts actual revolutions of the wheel, so the only inaccuracy will be the difference in tire OD. The speedometer gets an analog output based on a current or voltage generated by the spinning cable. The speedometer can vary a great deal with the same speed cable, but the odometer will always read the same. With electronics, there may not be a cable anymore, but the principle is the same. If you want to test the speedometer, drive down the hyway at exactly 60, and time the amount of time it takes to run one or more miles. If it is exactly a mile a minute, the speedometer is accurate.
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joatmon
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Re: spedo / gas mileage (harryyiii)

Post by joatmon »

These cars are electronic. The speed signal to the instrument cluster is a pulse train. I suppose between the speedometer and the odometer once could be accurate and the other not, but there is no calibration adjustments on it, unless you have the tool to reprogram the cluster, which the dealers do not have.I would like to be able to reprogram the cluster, I thought it would be interesting to lose power and torque and perhaps gain some mpg by putting on noticeably larger tires, but I currently prefer the accurate speedometer.
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mikey00
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Post by mikey00 »

If your speedo is off, your odometer is most likely off also. Use highway mileage markers to verify. You didn't change your tire size, did you?
tahoan
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Re: (mikey00)

Post by tahoan »

No, I didn't change the tires or wheels, but it came with the pontiac rims that are an upgrade. The tire size is 205/55R16. I don't know if that would change the OD of the tire or not relative to the base wheels.
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ColonelPanic
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Re: (tahoan)

Post by ColonelPanic »

I'm pretty sure the steel wheels are the same exact size as the alloys, although I can be corrected if need be. I don't think that is the problem.
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kostby
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Re: Question 4

Post by kostby »

EDIT: Does 29 mpg seem high for AWD?? Not really. If you're usually driving 70-77 mph on the highway AND1) have tires at correct air pressure2) keep the car relatively clean (washed & waxed, not hauling lots of extra 'junk' around)3) keep your foot out of the throttle and off the brakes (using cruise control)AND4) You're a NASCAR fan and practice 'drafting' whenever possible... My fwd Vibe has gotten as high as 41.2 mpg 'all-highway' miles with 4 passengers and luggage, when following a higher-profile vehicle (church van, at a safe distance) at 70 mph for 309 miles last summer.
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jasonvibe
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Post by jasonvibe »

do not worry about the odo. Most speedo's read high. MOST Motorcycle speedo's read way high . Often 5 to 8 high above 70mph. But the odo's are within 1%. Cycles do use electronic and cable driven speedos. Error in indicated speed is not error in mileage. I have seen it myself. In regards to your Vibe...You are talking 10%. That would be easy to check between mileage markers on any highway. Also there is a calibration for 'cycles(and probably cars) with electronic speedos. It's simply a variable resistor. This varies the amount the needle is deflected for a given signal. DON'T confuse a pointing needle error for mileage error. Take a step back and think. IT's JUST A POINTER...
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Toolman
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Re: (jasonvibe)

Post by Toolman »

The only way to be 100% sure is to borrow a friends GPS, that is how I found out that my GTO is about 2% fast.
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jasonvibe
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Post by jasonvibe »

I did a basic check on my speedo...yes it reads high. similar to yours. somewhere between 6-8% maybe as high as yours = 10% I will be doing further checks. What this does allow, is for larger tires and no worry about the accuracy. But 10% is quite rediculous. I also got similar mpg on the highway. I am in a hilly area. So I don't expect more than 30mpg. 31 is EPA
2005 AWD PlatinumAlloys, Moon & TunesPower group...just enough to be fun
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