Lowering with 16"

[Go4th]

Originally Posted by PetersRedYaris

Try putting a GPS in your car to check your actual speed against your speedometer. I did and found I was going slower than my speedo says. It seems like all new cars say your going a little faster than you really are which means your racking up miles faster, and getting worst mileage, than you should be. If I get new tires/wheels I'll be going up 3-5% in diameter to set the speedo right.

My car: 70MPH=67 actual MPH

That don’t mean your odometer is wrong.
They may just have the speedometer calibrated a few mph off on the top end on purpose. Lots of times your dead on speed on the slower mph than the higher mph. They want you to think that you’re going that speed to help you.
Kind of like your clock. You may have it set 5 mins fast so when that alarm clock goes off you actually have five mins more.
Also I went to NC one time and the GPS said I was off route and actually I was on the exact road I was to be on per its directions. I switched lanes and it said I was going the right way. Switched lanes back it thought I was off route again. So even that GPS thing is not right sometimes. I figure it was the elevation and maybe the GPS was not updated that this is a 6 lane highway.

[PetersRedYaris]

Originally Posted by Go4th

That don’t mean your odometer is wrong.
They may just have the speedometer calibrated a few mph off on the top end on purpose. Lots of times your dead on speed on the slower mph than the higher mph. They want you to think that you’re going that speed to help you.
Kind of like your clock. You may have it set 5 mins fast so when that alarm clock goes off you actually have five mins more.
Also I went to NC one time and the GPS said I was off route and actually I was on the exact road I was to be on per its directions. I switched lanes and it said I was going the right way. Switched lanes back it thought I was off route again. So even that GPS thing is not right sometimes. I figure it was the elevation and maybe the GPS was not updated that this is a 6 lane highway.

You could be right although I think it would be rediculous if they did that??? I'll check my miles vs. the actual mile markers. Also, location of a road has nothing to do with measuring speed. Older GPS maps, and newer ones, may not be up to date, but the fact is your GPS doesn't need to know what road your on to calculate speed. They calulate speed based on a series of points and the time it takes to move from one to the next. Even the small handheld cheap ones can do that.

[PetersRedYaris]

Originally Posted by Go4th

That don’t mean your odometer is wrong.
They may just have the speedometer calibrated a few mph off on the top end on purpose. Lots of times your dead on speed on the slower mph than the higher mph. They want you to think that you’re going that speed to help you.

If your speedometer is off at high speeds, it's off at low speeds too. The reason you don't notice, and think it's dead on, is because it's "less" off.
Example: 70(speedometer)MPH=67(actual)MPH - 4.28% off

This means at 30(speedo)MPH, 4.28% off is 28.71(actual)MPH

1.28 MPH is not noticable on a speedometer but is still there and hence the speedometer is still incorrect. This is why higher speeds are required to see speedometer dicrepincies.

How does it help me to think I'm going to fast?