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Unread 09-28-2013, 08:50 AM   #1
Goldenknob
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Speedo wrong? vs. gps & scanner

I hooked up a bluetooth obd II scanner and was checking my speed digitally, with app on my phone. My speedo was showing I was going 70, but the scanner app was showing 67-68. I thought the app could be wrong so I turned on gps speed app and it also showed 67-68.

I am at a loss. My tires are at proper pressure, and are factory size.

Maybe the previous owner had different tires and rims and had the speedo geared? (I've only had the WK for 5 weeks or so.)

Any ideas?

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Unread 09-28-2013, 09:01 AM   #2
modernblueWK
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What size, brand, condition tires do you have? Your tires appear to be undersize.
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Unread 09-28-2013, 09:10 AM   #3
Goldenknob
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The tires are new. less than 3k miles on them 245/65/17.
wp_20130928_001_vga.jpg

wp_20130928_002_vga.jpg

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Unread 09-28-2013, 11:24 AM   #4
yzjwk
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Quote:
Originally Posted by Goldenknob View Post
I hooked up a bluetooth obd II scanner and was checking my speed digitally, with app on my phone. My speedo was showing I was going 70, but the scanner app was showing 67-68. I thought the app could be wrong so I turned on gps speed app and it also showed 67-68.

I am at a loss. My tires are at proper pressure, and are factory size.

Maybe the previous owner had different tires and rims and had the speedo geared? (I've only had the WK for 5 weeks or so.)

Any ideas?
Just about all factory speedos (every one i've had anyways) will read a little highter then actual speed .
It may just save you a ticket if your doing 10 over and the cop's radar shows your really only 7 over . the speedo's are calibrated digitally in a wk , so you could have a dealer check if you want or buy a programmer like superchips and set it yourself . you can also go up one size in tires and that will even it out as well .The last option may be why jeeps and SUV's may be a little further out then a car for example , because alot of jeep/suv owners want at least slightly larger tires.
good luck
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Unread 09-28-2013, 04:59 PM   #5
Zlartibartfast
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I have seen the same thing - my speedo read high when I had stock size tires on it. Now my tires are 5% over stock diameter and the speedo read approx 2.5% low. I rely on my GPS speedo to give me an accurate indication. When I compare that to those roadside radar thingys they have around here, it (the GPS) almost always matches
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Unread 09-28-2013, 08:33 PM   #6
tjkj2002
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I just reach down in my center console and either hit the "UP" or "Down" buttons to adjust my speedo to match my GPS while I'm driving.
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Unread 09-28-2013, 09:39 PM   #7
Goldenknob
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Originally Posted by tjkj2002 View Post
I just reach down in my center console and either hit the "UP" or "Down" buttons to adjust my speedo to match my GPS while I'm driving.
could you better explain how you do that?
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Unread 09-28-2013, 10:01 PM   #8
tjkj2002
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Originally Posted by Goldenknob View Post
could you better explain how you do that?
You can't since you have ABS(not safely) and I went back to mechanical speedo drive with a electric interface to operate the OEM speedo and ODO.
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Unread 09-30-2013, 07:27 AM   #9
Radcrd
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They are all off, even my previous Liberty was off. Run bigger size tires to compensate next time you change tires. Based on my calculations you would need to be around 30.5'' Diameter to read close to accurate. Stock is 29.5'' Diameter.
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Unread 10-03-2013, 10:08 AM   #10
tibo4wd
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2007 WK CRD QDII, GDE HOT tune. 275/55/18'' on Sahara's, SRT8 suspension.
2000 Jetta TDI (hers)
2006 Liberty CRD (sold)
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Radcrd, like diesel much?
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Unread 10-03-2013, 12:02 PM   #11
Radcrd
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Quote:
Originally Posted by tibo4wd View Post
2007 WK CRD QDII, GDE HOT tune. 275/55/18'' on Sahara's, SRT8 suspension.
2000 Jetta TDI (hers)
2006 Liberty CRD (sold)
3 VW TDI's (sold)

Radcrd, like diesel much?
Just a bit addicted
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Unread 10-04-2013, 03:31 PM   #12
Walt
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Quote:
Originally Posted by Goldenknob View Post
I hooked up a bluetooth obd II scanner and was checking my speed digitally, with app on my phone. My speedo was showing I was going 70, but the scanner app was showing 67-68. I thought the app could be wrong so I turned on gps speed app and it also showed 67-68.

I am at a loss. My tires are at proper pressure, and are factory size.

Maybe the previous owner had different tires and rims and had the speedo geared? (I've only had the WK for 5 weeks or so.)

Any ideas?
My speedometer reading is several mph different than the DashDAQ XL GPS mph reading. At highway speeds, the speedometer is 1-3 mph higher than the GPS. It reads 70 mph and the GPS reads 67-68 mph. When I get the GPS to read 70 mph, the speedometer reads ~73 mph. Less difference at lower speeds.

[Tires are new and stock size. Inflation at 35 psig. Alignment is good.] As the tires approach end-of-life and the tread wear indicators show, there will be a smaller tire rolling diameter and the indicated speedometer reading will be higher than actual, but not much..........

I believe the speed signal from the WK 545RFE xmission is electrical, not mechanical. To change its input to the dash module, it would take a device with re-programming capability. DashDAQ XL doesn't have that (as far as I know).

That's my story & I'm sticking to it...
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