for all of you math types

OceanCityGirl · Post by **OceanCityGirl** » November 18, 2006 12:13 am

I drive a mustang gt. We've been having some gas consumption issues with it and had some work done. But we've been monitoring the mileage and gas useage.
While doing this things seemed odd. We found that when we drive a mile we are really only going 8/10ths of a mile, maybe less. Also if I ride beside my husband and he is going one speed my speedometer is quite a bit different. Now for the math stuff. I don't know if i'm going to put it in the shop over this so...
Does my car actually have less miles on it then it says? Is my actual gas mileage better or worst. Are my two 19yo sons telling the truth when they say they've been pulled over and clocked going faster then the speedometer says?
Can the wrong sized tires, smaller or larger do this to a car?
We've suspected the speed thing for awhile so it's likely been doing this since I bought it a year ago.

ragtopW · Post by **ragtopW** » November 18, 2006 12:17 am

Tire size can have do it depends on how much off the size is.
I would have it in the shop..

OceanCityGirl · Post by **OceanCityGirl** » November 18, 2006 12:23 am

I"m getting new tires this weekend and I was putting it in for an allignment and a look over of the suspension because of the miles I have on the car. But if they say to me this won't hurt anything I'm not going out of my way to spend a ton of money to fix it.
The tires might be slightly off, but not that much. They're the right sized tire but not the profile size that is factory.

Desdamona · Post by **Desdamona** » November 18, 2006 12:37 am

Assuming that your odometer really has been registering 125% of the
distance you've actually been traveling, your gas mileage (miles/gal)
is also proportionately less than you've been calculating. In other words,
subtract 1/5 off that mpg amount (ex. it's not 20mpg, but really 16mpg).

Based on that same assumption, your speedometer is also reading 1/5
too high. Yours will show 40mph when you're actually only doing 32mph.
Is this what your driving side-by-side comparisons are showing?

If the answer is "yes", then your boys are telling a bigger story than they
even know. When they think they're doing 80mph, they'll be clocked at
only 64mph (which probably would get them stopped in a 55mph zone.)

And the tires can be the culprit, but only if their circumference is 20%
smaller than the odometer & speedometer are set up for. Or it could be
a problem in those measuing devices. Get the shop to check it all out.

OceanCityGirl · Post by **OceanCityGirl** » November 18, 2006 12:44 am

I'm not sure I was clear. When driving down the highway I'll get my odometer to start a mile and then watch the mile markers until I travel an actual mile. When I have driven an actual mile my odometer is registering only 8/10ths of a mile and that's generous. I think it's more like 7/10ths. When I drive beside my husband and my speedometer reads 55 he is going around 70. At lower speeds when I go thru one of those speed check things I''m generally off by around 8mph. My sons aren't the only ones who have thought the speedometer was off. I've suspected it as well.

fishinthepilins · Post by **fishinthepilins** » November 18, 2006 6:06 am

OceanCityGirl wrote:I'm not sure I was clear. When driving down the highway I'll get my odometer to start a mile and then watch the mile markers until I travel an actual mile. When I have driven an actual mile my odometer is registering only 8/10ths of a mile and that's generous. I think it's more like 7/10ths. When I drive beside my husband and my speedometer reads 55 he is going around 70. At lower speeds when I go thru one of those speed check things I''m generally off by around 8mph. My sons aren't the only ones who have thought the speedometer was off. I've suspected it as well.

In this case, it sounds like the opposite of the above explaination. Either your tires are too big (not too small), or there's a calabration problem in the speedometer/odometer. It sounds like your car actually has more miles on it than what it reads. Your gas milage is unusually poor, right? I agree with have a pro check it out. Hope you get to the bottom of it without much trouble!

12vmanRick · Post by **12vmanRick** » November 18, 2006 9:23 am

you knew this was coming

MATH SUX

pirate@43 · Post by **pirate@43** » November 18, 2006 9:38 am

Don't worry to much about it, just change you driving habits. Think of it in the long run for every 7 or 8 hundred miles you show on the car there is actually a thousand. so when it's time to get rid of the car it will show less miles on it and be worth more

it's not really worth spending the money to fix it now

PJ · Post by PJ » November 18, 2006 10:35 am

On most (if not all) vehicles, the speedometer and odometer are driven by a cable that is attached to a gear on the transmission. Thus the speed and distance shown are based on the number and speed of turns of the driveshaft.

These gears may not be all that accurate coming from the factory, and if you change wheel size or gear ratios without changing the pinion gear that drives the speedometer/odometer you can get very innacurate readings. The pinion gears can be replaced to dial in the accuracy, you just have to find a shop that will test it for you.

aeroparrot · Post by **aeroparrot** » November 18, 2006 10:38 am

It also depends on the traffic too. If you have heavy traffic in your area, you will use more gas waiting in traffic.

jimolliemom · Post by **jimolliemom** » November 18, 2006 10:43 am

Hubby's car has issues like this. His tires are not the original size and his odometer says 300,000 miles (yes rreally) and it's more like 320,000. (And it's a 1994 Suzuki Swift!)

aeroparrot · Post by **aeroparrot** » November 18, 2006 10:46 am

Don't know if anyone brought this up but was your car bought used? If so, how trustworthy was the person/dealer you bought it from? They could have done a few things to the car. Don't know if they could have done something to the speedometer but you never know.

Skibo · Post by **Skibo** » November 18, 2006 12:50 pm

Get a GPS and check your speedo. If the speedo is close, the odo is probably ok

Desdamona · Post by **Desdamona** » November 18, 2006 1:56 pm

fishinthepilins wrote:
OceanCityGirl wrote:I'm not sure I was clear. When driving down the highway I'll get my odometer to start a mile and then watch the mile markers until I travel an actual mile. When I have driven an actual mile my odometer is registering only 8/10ths of a mile and that's generous. I think it's more like 7/10ths. When I drive beside my husband and my speedometer reads 55 he is going around 70. At lower speeds when I go thru one of those speed check things I''m generally off by around 8mph. My sons aren't the only ones who have thought the speedometer was off. I've suspected it as well.
In this case, it sounds like the opposite of the above explaination.

Yeah, just go with the opposite of what I said before... but let the boys
know that the error in the speedometer is still no excuse.
And it does sound like a good way to keep your true mileage off the
odometer. Hope you didn't buy the car from a relative or "friend".

parrotpartygod · Post by **parrotpartygod** » November 18, 2006 4:49 pm

12vmanRick wrote:you knew this was coming

MATH SUX

but I'm damn good with figures

thebeachbumm33 · Post by **thebeachbumm33** » November 19, 2006 10:03 am

parrotpartygod wrote:
12vmanRick wrote:you knew this was coming

MATH SUX

but I'm damn good with figures

Arrrgh

12vmanRick · Post by **12vmanRick** » November 19, 2006 10:56 am

thebeachbumm33 wrote:
parrotpartygod wrote:
12vmanRick wrote:you knew this was coming

MATH SUX

but I'm damn good with figures
Arrrgh

that makes me want to plunder the booty

bravedave · Post by **bravedave** » November 19, 2006 11:12 am

Nice

Wanna see my

?