GPS speedometer ap accuracy

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Randalla
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Joined: Fri May 24, 2019 8:58 am
Location: North Scottsdale

GPS speedometer ap accuracy

Post by Randalla »

I've been wondering for some time how accurate the speedometers are on the Z and the Roadster since I have no idea if I have the correct speedo driver in each transmission, and the tires/wheels are far from factory stock. Tonight Lisa went with me to record the numbers at 50, 60 and 70 mph (on the speedos). Both cars were within 1 mph at all those speeds, prompting the question of how accurate these aps are. The one on my phone is just called "Speedometer." The ap gets 4.5 stars.
1967 1/2 Roadster- 1600 4 cyl.
1972 240Z- 280 I-6
1976 710 Wagon- L20B 4 cyl.
1977 620 King Cab - L18 4 cyl.
2003 350Z Track- VQ V-6
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Turboman280
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Joined: Tue Jun 11, 2019 8:28 pm
Location: Mesa

Re: GPS speedometer ap accuracy

Post by Turboman280 »

All my vehicles read a bit high according to the roadside radar signs. The DigiHUD GPS phone app I use has similar readings, so that would seem to be confirmation to me.

I imagine the accuracy improves at steady speed, as GPS detection and calculation takes a wee bit of time to happen.
Carl
1975 280Z restomod
Work in progress
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Randalla
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Joined: Fri May 24, 2019 8:58 am
Location: North Scottsdale

Re: GPS speedometer ap accuracy

Post by Randalla »

Thanks for responding Carl. Honestly, I thought I may have been off by as much as 5mph before checking, so I'm actually pleased it's that close.
1967 1/2 Roadster- 1600 4 cyl.
1972 240Z- 280 I-6
1976 710 Wagon- L20B 4 cyl.
1977 620 King Cab - L18 4 cyl.
2003 350Z Track- VQ V-6
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Turboman280
Posts: 171
Joined: Tue Jun 11, 2019 8:28 pm
Location: Mesa

Re: GPS speedometer ap accuracy

Post by Turboman280 »

Randalla wrote: Mon Jul 05, 2021 10:47 am Thanks for responding Carl. Honestly, I thought I may have been off by as much as 5mph before checking, so I'm actually pleased it's that close.
I'll have to ride with you some time and we can compare apps.
Carl
1975 280Z restomod
Work in progress
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Jeff G 78
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Joined: Thu Jun 03, 2021 9:15 am
Location: Sun City West

Re: GPS speedometer ap accuracy

Post by Jeff G 78 »

My 280Z with the correct OD tires reads about 10% high compared to GPS, but interestingly, the odometer is very accurate. I checked both on a road trip several years back using a GPS and the mile marker signs on a toll road. After 100 miles, the odometer was within 0.1 miles total even though the speedometer read way high. I made a speed chart to keep in the car so I know how fast I'm going compared to the speedometer.
Jeff
SCW
'78 280Z
'74.5 260Z - SOLD
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Randalla
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Joined: Fri May 24, 2019 8:58 am
Location: North Scottsdale

Re: GPS speedometer ap accuracy

Post by Randalla »

Now that's a bit of a conundrum. Weird that the two would not sync. I'm sure there must be a logical explanation.
1967 1/2 Roadster- 1600 4 cyl.
1972 240Z- 280 I-6
1976 710 Wagon- L20B 4 cyl.
1977 620 King Cab - L18 4 cyl.
2003 350Z Track- VQ V-6
User avatar
Jeff G 78
Posts: 40
Joined: Thu Jun 03, 2021 9:15 am
Location: Sun City West

Re: GPS speedometer ap accuracy

Post by Jeff G 78 »

I am no speedometer expert, but I'm guessing it proves that the mechanical part of the system is working. The speedo gear in the trans, the cable, and the odometer are are in sync, but the speedo has no direct drive. The faster the cable spins, the higher the speedo reads and I believe this is done with a magnetic pickup. I'm not sure if they degrade over time, or if the Datsun speedos were just never very accurate even when new. I've never taken the time to disassemble one to see if there is anything that can wear or become dirty leading to inaccuracy. When I made the move, I don't even think I kept any of the half dozen sets of gauges I had.
Jeff
SCW
'78 280Z
'74.5 260Z - SOLD
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cgsheen
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Joined: Sat May 25, 2019 11:34 am
Location: Mesa, AZ

Re: GPS speedometer ap accuracy

Post by cgsheen »

Jeff G 78 wrote: Tue Jul 06, 2021 12:59 pm I'm not sure if they degrade over time, or if the Datsun speedos were just never very accurate even when new.
Although they were kinda sealed up, at their age the seals aren't great and sometimes missing. They definitely crud-up (industry term) even if there aren't critters building nests/laying eggs inside. So they are both: never completely accurate (cuz era thing) AND will degrade over time.

They aren't that difficult to take apart and clean & refresh and if you repaint the inside with flat white paint, it's amazing how much brighter you can get your gauges looking even without LED "bulbs"...
260Z - L28ET - MS3X ECU, Ford COP w/ Nissan Ignitor, diyautotune optical wheel - T04e .63 A/R, Intercooled - 310cc Injectors - Ultra Heaven Fuel Rail - 14point7 Spartan2 wideband - Coilovers - Big Brakes - 304 Gold Metallic! Sakura Garage, Phoenix AZ
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Turboman280
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Location: Mesa

Re: GPS speedometer ap accuracy

Post by Turboman280 »

A place like Dick's speedo tach should be able to calibrate.
Carl
1975 280Z restomod
Work in progress
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