Speedo correction question
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Junior User
Joined: Jun 2007
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From: Newark, DE
thanks, i just called them...88 dollars! a full hour of labor my ***... i just figured that with my stock tires, to go 70 mph, my speedometer will pretty much have to read 75 mph...good enough for govt work, good enough for me.
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Originally Posted by jeffisjacked
thanks, i just called them...88 dollars! a full hour of labor my ***... i just figured that with my stock tires, to go 70 mph, my speedometer will pretty much have to read 75 mph...good enough for govt work, good enough for me.
I got pulled over doing 86 in a 55 when the speedo indicated 65 with 33" tires. I had to get the speedo checked, and at something like 35mph it was 7mph off. So I figured the percentage, went to court, and they shut the door on my percentage variation argument. I guess a law degree and years of "experience" count for more than empirical proof.
ANYWAY, I did the cypherins and gizintas and came up with a 20% offset (or so) and learned what each speed indicated actually equated to in real road speed.
[all the numbers above are estimates only as this happened in 1991 and my memory is only certified to 2 minutes]
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From: Nottingham, MD
Originally Posted by jeffisjacked
I have a 2007 F150 with larger aftermarket wheels and tires on the truck, however I want to revert back to my stock wheel/tire combo when I tow my car home. I know I can buy one of those 500 dollar power programmers to correct my speedo, but there has to be a cheaper way of doing this, anyone have any good info?
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Originally Posted by puppypower
How did you correct your speedo when you put on the aftermarket tires? And why can't you revert back using the same method?
I was thinking that, but I assumed he didn't have a stock speedo calibration or the question never would have come up.
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From: Nottingham, MD
Gotcha! Well if that's the case I would just switch to the OEM tires and drive under the speed limit. It's only for a short time and you will be towing. you shouldn't be trying to break and speed records anyway.
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From: Newark, DE
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From: Mirror, Alberta
Originally Posted by jeffisjacked
I have a 2007 F150 with larger aftermarket wheels and tires on the truck, however I want to revert back to my stock wheel/tire combo when I tow my car home. I know I can buy one of those 500 dollar power programmers to correct my speedo, but there has to be a cheaper way of doing this, anyone have any good info?
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Originally Posted by bigdavewilson
The simplest way to calculate your speedo error is with a GPS!
Then again, the error offset should be a constant, so that a moving average would be fairly accurate. By Dave, I think you've got it!
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From: Mirror, Alberta
Originally Posted by Big Daddy 18C
Isn't the GPS error greater than the 5% difference of tire sizes? I have an older Garmin eTrex, but the limitation of the system is the spacecraft. Those things directed bombs randomly all over Afghanistan, so I wouldn't trust them to keep me from getting a speeding ticket.
Then again, the error offset should be a constant, so that a moving average would be fairly accurate. By Dave, I think you've got it!
Then again, the error offset should be a constant, so that a moving average would be fairly accurate. By Dave, I think you've got it!
Your bomb reference reminds me of a friend who is an armorer in the Canadian Air Force. He always used to kid the pilots that their target was the ground and that they hardly ever missed.
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From: Copperas Cove, Tx
Since we are on the subject, when I change my Edge to my new tire size will it change my speedo, and odometer or do I need to keep my Edge on the speedometer setting to read an accurate speed? Tire Rack also has where you can type in old/new tire sizes to see the speed fluxuations at different speeds.
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