So I have been working at the same place for 6 years now. With my last two Rangers I would put exactly 166 miles a day door to door from my house to work and back. My wife's Tahoe shows a 167 miles round trip... My Cobalt is a different story, every time I have checked it, it says the trip is 174-175 miles... So is the Cobalt speedo off? And if so how do I check it/prove it?

And if I Google map the drive it says 82 one way and 83 the other...

 

burning rubber out of the parking lot everyday?

 

Laying 8-9 miles of rubber a day would be interesting... NJ DEP would label me an environmental hazard!

 

I've always wondered this... my ODO is saying i've driven 2500 miles since I bought the car exactly 1 month ago. Now I know i've been driving it a lot but I don't think it's that much.

 

Perhaps this is how GM gets such great gas mileage out of the Cobalt SS S/C, they increase the miles driven by 10% via a skewed OD... LOL

 

Are you on stock wheels or do you have aftermarket rims?

 

Bone stock but for I installed a Stiffy on Tuesday and have an Injen sitting in my trunk I might attempt to put in tomorrow...

 

hmm... interesting.

 

hmmm... just take it to a place you know is a mile or something and test it.

 

you mean like from the stop light to the train tracks in the fast and the furious ...

the best way would be to get on the highway watch for the mile markers on the side of the road reset your trip gauge at one, drive 50-60miles paying attention to the beginning and ending mile marker(not the 1/10mile markers the big ones that usually say mile/0), so if you start at the 40/0 marker and drive to the 90/0 mile marker your trip should read 50miles if it doesnt, take it to the deal and bitch one off

 

To start with I'm running 225/40/18's not stock size tires, however my speedo is off by atleast 5 mph @ 75 mph from the 2006 Malibu I traded in on the SS/SC. How do I know? My bro has different wheels and tires on his contour which threw off his speedo (from before and after) so I told him on the cell phone what speed I was setting the cruise at and he found ~how far off his speedo was. Well, my cobalt is off a lil more then his, and his was off by atleast 4.

I always assumed it was my aftermarket tires that threw it off that much, but it could just be they're off from the factory. As for the trip to work mileage thing, in the Malibu it was 12 mi, contour is 15, cobalt is 16 or 17. I do get real good gas mileage for my driving though

 

i know it can screw up your speedometer, but your mileage gauge too? i know for a fact my speedometer is off because of these 17s, but they came as a kit from the dealer and the dealer said they cant fix it. could this be how i have put 27000 miles in less than a year?

 

mine reads slow. I have a stock 07 LS. I have tested it against mile markers and against my mom's 99 blazer going side by side and they read 2 different speeds.

 

cant you get the speedo recailibrated somewhere?

 

if you want a rough idea of how far off your speedo/odo are due to tire change sizes, put in stock and new sizes here http://www.miata.net/garage/tirecalc.html

the important thing to remember is that the odometer and speedometer are both calculating based on the numbers of rotations of the axles. Any changes in the total rolling diameter of the tire (caused by over/under inflation, changed tire sizes) will therefore distort the accuracy of the gauges.

if i remember my bosh automotive handbook correctly, there are regulations in europe that say that no gauge can UNDERreport speed/mileage. When car and driver still did the actual/indicated speed readings, it was not uncommon to see bmws/mercedes showing 65 at 60 mph. generally, domestics tended to be closer to actual speed.

 

Calculate the diameter of your tires, the calculate the rotations per mile. Take it in and get re-calibrated.

 

lol the mileage is calculated the same way as the speedometer, so yes, if your speedometer is reading high you'll rack up miles faster.

 

It's official... I reset "Trip B" at mile 100 on the north bound GSP this morning, when I hit mile 140 Trip B read 41.1...

41.1 / 40 = 1.0275%

So I am off by about 3% or 3 extra miles on the OD for every 100 I drive...

Which almost mirrors what I have been seeing in my daily commutes:

167 * 1.03% = 172.1

I guess I need to prove this somehow to the dealer...

 

take em for a 40min ride

 

anyway to fix this by yourself? or with HPtuners? cause I think mine is off too

 

I checked the information bulletins and there is one about the speedo's being off. It says that if its within 4% than it is within specs. Yours is pretty close.





Subject: Odometer Accuracy - keywords IPC speedometer #PIC3100A - (07/11/2006)



Models: 1995-2007 All GM Passenger Cars and Light Duty Trucks





This PI has been revised to update the model years. Please discard PIC3100.



The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.

Condition/Concern:
A customer may comment that their vehicle's odometer appears to be inaccurate relative to a known distance traveled. This known distance traveled is probably based on odometer readings from other vehicles the customer has driven.

Recommendation/Instructions:
Even though there is not a federal regulation pertaining to odometer accuracy, some states do have specific laws. Generally, a tolerance of plus or minus 4% is allowed, however, it is the responsibility of each dealer to be familiar with local requirements before attempting to verify the accuracy of a customer's odometer.

To verify the accuracy of the odometer, the dealer should obtain a hand-held GPS unit to test the odometer. While driving on a straight road, over a mile long, mark the waypoint on the GPS when the odometer (not the trip odometer) rolls over a digit. When it rolls to the next digit, take a reading and compare the two for actual distance traveled versus the odometer reading.

If a hand held GPS unit is not available, the only other option is to verify the miles traveled using a surveyor's wheel or a dynamometer. Do not compare with another vehicle. Do not compare with the trip odometer. Also, mileage markers on an expressway are typically not accurate enough to perform exact measurements.

Additionally, dealers should confirm that the original size tires and wheels are mounted on the vehicle and that the axle ratio is as specified per the SPID label and have not been modified. Dealers should insure that the vehicle calibration is for that tire size and axle ratio when applicable. If correct and the odometer is beyond the required limit, consideration should be given to the relationship between the VSS and the reluctor on the transmission output shaft. Close inspection should be made of the associated wiring and any connectors in the circuits. Finally, it may be necessary to exchange the IPC with a replacement unit.

Please follow this diagnostic or repair process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.

 

Not sure about HPT, but it involves changing the wheel rotations per mile setting. Another way to fix it would be to use slightly smaller tires.

 

Well I must say I would rather have it "4%" the other way! LOL

Smaller tire would increase the revolutions per set distance and actually put more mileage on then is putting on now... You would need to increase the tire size to slow down the drive train to match the distance traveled...

 

Arg, your right. I'm having a rough "brain" day today.