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Old 03-06-2010, 07:10 PM   #1
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Speedo Calibration

Hey guys,

Some of you already know that I've been looking into figuring out a way to fix my speedo from being off from a range of 5mph-10mph. Quite annoying having to check the gps to make sure I'm not speeding too much!

Well, I went to the local dealer for my 20,000 mile service (damn, a year and 1 month old and i hit 20 grand!!!!), and brought up the question and was quickly answered by a firm "NO."

Well, I'm going to check another dealership and see what they say, but if there answer is the same, what should I start looking into and how much is it going to cost me!!!! Ha ha, I'd like to maybe save as much as possible due to the audio project and maybe (fingers crossed) the supercharger for out little bad boys! Thanks all!
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Old 03-06-2010, 07:17 PM   #2
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I try not to wear speedo's anymore. The wedgies are an absolute killer!
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Old 03-06-2010, 07:19 PM   #3
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Originally Posted by rb11701 View Post
I try not to wear speedo's anymore. The wedgies are an absolute killer!
alright .... actually i can't lie.... i did laugh a little bit!
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Old 03-06-2010, 07:56 PM   #5
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Well, I don't know about Tacomas, but for the Ranger's calibration, my cousin used a dyno and then also a programmer to adjust it. A SAS'd Ford Ranger with over 6in of lift and running 35's. The speedo is off by 1mph after all of this and it was set that way on purpose.
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Old 03-06-2010, 08:00 PM   #6
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Just get bigger tires, 265-75-16 ought to put your speedo right in line with the GPS
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Old 03-07-2010, 06:58 AM   #7
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Quote:
Originally Posted by Juggernaut View Post
Just get bigger tires, 265-75-16 ought to put your speedo right in line with the GPS

It's always been 2-3 mph slower than the gps stock, but when I got the 245/75/16 on there, thats when the difference was the largest. Why would going bigger increase the stock speedo?

Thanks for the brainstorming guys!
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Old 03-07-2010, 08:04 AM   #8
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Quote:
Originally Posted by C17Guy View Post
It's always been 2-3 mph slower than the gps stock, but when I got the 245/75/16 on there, thats when the difference was the largest. Why would going bigger increase the stock speedo? ...
Larger diameter tires will necessarily make the speedometer read 'lower' (than actual speed). The more you increase your tire diameter the more your speedometer will be reading 'low' (relative to actual speed).

The dealership was telling you the truth about not being able to recalibrate.

If you want your speedo to read accurately you need to look into an aftermarket speedometer recalibration unit - to be wired inline to modify the incoming speed sensor signal.
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Old 03-07-2010, 08:23 AM   #9
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The computer in the truck is set (very poorly) for whatever the stock size tire is. Putting a larger or smaller tire on the truck doesn't change how fast the truck thinks it's going but does change how fast it actually goes. With a larger tire, you will be traveling faster than what the speedometer says you are.

With our trucks already being off by 2-3 MPH, a lot of people go with a larger tire size which eliminates this error. However, from what I've been able to tell the odometer is right now with the stock tire size so going with the larger tire throws it off.

Installing a 265/75/16 tire on a Prerunner with a stock tire size of 245/75/16 takes up for a 2.3 MPH difference. On the base 2wd trucks with a tire size of 215/70/15, a 235/70/15 tire would be 2.5 MPH faster and a 225/75/15 would be 3.2 MPH faster.

Use this link (http://www.miata.net/garage/tirecalc.html) to compare various tire sizes.
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Old 03-07-2010, 08:40 AM   #10
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Quote:
Originally Posted by buyobuyo View Post
The computer in the truck is set (very poorly) for whatever the stock size tire is. Putting a larger or smaller tire on the truck doesn't change how fast the truck thinks it's going but does change how fast it actually goes. With a larger tire, you will be traveling faster than what the speedometer says you are.

With our trucks already being off by 2-3 MPH, a lot of people go with a larger tire size which eliminates this error. However, from what I've been able to tell the odometer is right now with the stock tire size so going with the larger tire throws it off.

Installing a 265/75/16 tire on a Prerunner with a stock tire size of 245/75/16 takes up for a 2.3 MPH difference. On the base 2wd trucks with a tire size of 215/70/15, a 235/70/15 tire would be 2.5 MPH faster and a 225/75/15 would be 3.2 MPH faster.

Use this link (http://www.miata.net/garage/tirecalc.html) to compare various tire sizes.

Thanks! Looks like I double screwed myself with the 16" wheels and the tires. I've been looking into the Hypertech Speedo Calibrator, but that looks like it might be a pain in the ass taking apart the gauge panel.
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Old 03-07-2010, 12:47 PM   #11
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On my 4 cyl 5 speed 5 lugger, 60 indicated is 56 or 57 on my GPS, it jumps back and forth holding a steady 60 on cruise control. So to do a true 70 it need to be reading 75 or so. My odometer error is 1.5%. To me, that is a pretty big discrepancy.
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Old 03-07-2010, 05:04 PM   #12
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I bought & installed one of THESE to correct the speedo on my old '96 Mustang Cobra almost 10 years ago when I changed the rear-end gear from the stock 3.27 to a 4.10. I don't know if anyone has used one in a Tacoma on not, but it should be possible. All you need to do is find the wire between the speed sensor and the computer. This device just splices in and adjusts the signal by whatever ratio you select. Very easy to set up (and change later if you decide to run a different size tire, rear gear, etc.).
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Old 05-18-2010, 02:06 PM   #13
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I went from 245s to 285s and the dealer got mine within 2mph at 70
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Old 07-19-2013, 09:07 AM   #14
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Tire width does not affect speedo

Quote:
Originally Posted by DWreck View Post
I went from 245s to 285s and the dealer got mine within 2mph at 70
What is the aspect ratio? Increasing width alone will not change speedo accuracy.
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Old 07-19-2013, 06:39 PM   #15
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Replaced the stock Dunflops P245/75/16's with BFG All Terrain LT265/75/16's and my speedometer is dead on with my GPS? Stock tires were 2 mph off on the slow side. Of course now the odometer is not correct. At 10,000 miles the odometer is reading actually 9600 miles.
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Old 07-30-2013, 07:46 PM   #16
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My Tacoma is fast 5-7mph what size tire would I need to fix that big of a error?
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Old 07-31-2013, 08:53 AM   #18
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Quote:
Originally Posted by camojared View Post
My Tacoma is fast 5-7mph what size tire would I need to fix that big of a error?
at what speed is it that far off? 30 mph, 60 mph?
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Old 07-31-2013, 08:56 AM   #19
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Quote:
Originally Posted by Trachito View Post
at what speed is it that far off? 30 mph, 60 mph?
3-5 off in town driving 7 off at 60- When the gps says 60 the truck says 67. I thought it was the gps at first so I borrowed two others they all say 60 and the truck says 67.
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Old 07-31-2013, 09:20 AM   #20
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Quote:
Originally Posted by buyobuyo View Post
The computer in the truck is set (very poorly) for whatever the stock size tire is. Putting a larger or smaller tire on the truck doesn't change how fast the truck thinks it's going but does change how fast it actually goes. With a larger tire, you will be traveling faster than what the speedometer says you are.

With our trucks already being off by 2-3 MPH, a lot of people go with a larger tire size which eliminates this error. However, from what I've been able to tell the odometer is right now with the stock tire size so going with the larger tire throws it off.

Installing a 265/75/16 tire on a Prerunner with a stock tire size of 245/75/16 takes up for a 2.3 MPH difference. On the base 2wd trucks with a tire size of 215/70/15, a 235/70/15 tire would be 2.5 MPH faster and a 225/75/15 would be 3.2 MPH faster.

Use this link (http://www.miata.net/garage/tirecalc.html) to compare various tire sizes.
Good advice buyo.

I wanted to run wider 16's on my 5 lug that is calibrated for stock 215/70/15 tires and wheels. So I installed 235/60/16's, because the diameter is only 1% different from stock...





Adjusting the tire aspect ratio is an easy way to compensate for different size rims.
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