Speedo error
Thread Starter
Driver
Joined: Aug 2021
Posts: 87
Likes: 3
From: OH
Speedo error
’14 IS250…
My grandson was messing around with a speedometer app on my phone, and we noticed a discrepancy, so I researched further…
I’ve got a couple Garmin eTrexs, and set my cruise control to exactly 80 mph on level ground, no wind. Both GPSs read the same, 77.22 mph.
I do have the 18” wheel upgrade, but the tire size is speced correctly.
I might see 1, maybe even 2 mph difference from actual, but 2.78 seems a bit much.
is there any way to adjust/calibrate the speedos in our cars?
My grandson was messing around with a speedometer app on my phone, and we noticed a discrepancy, so I researched further…
I’ve got a couple Garmin eTrexs, and set my cruise control to exactly 80 mph on level ground, no wind. Both GPSs read the same, 77.22 mph.
I do have the 18” wheel upgrade, but the tire size is speced correctly.
I might see 1, maybe even 2 mph difference from actual, but 2.78 seems a bit much.
is there any way to adjust/calibrate the speedos in our cars?
Advanced
Joined: Sep 2019
Posts: 601
Likes: 290
From: Texas - DFW
Almost all cars speedometers cannot be 100% exact due to several factors and federal law allows for 5% variance. Most cars read a little bit high (to prevent speeding / tickets), if you car was reading slower than actual speed then that would be more cause for concern.
Here are some articles explaining a bit more in detail
https://www.roadandtrack.com/car-cul...ters-accurate/
https://www.foxnews.com/auto/how-fas...f-speedometers
Here are some articles explaining a bit more in detail
https://www.roadandtrack.com/car-cul...ters-accurate/
https://www.foxnews.com/auto/how-fas...f-speedometers
Thread Starter
Driver
Joined: Aug 2021
Posts: 87
Likes: 3
From: OH
How is it you’re going 145 kph, with a gate right in front of you?
Also, do you know from where each speed is referenced from?
Lastly, but not related to speed, your battery voltage seems very low. A running engine should be between 13.4 and 14.2 vdc.
Driver
Joined: Nov 2018
Posts: 64
Likes: 9
From: HU
Hi,
I've put supports under both left and right swingarms, so the running gear was in neutral position, without the wheels touching the ground.
Regarding the references the center console reading is originated from the transmission output shaft sensor. I'm just guessing in regard of the
cluster, probably it gets the reading from the CAN bus, and "distorts" the results.
The 12.6V voltage reading is normal when the battery current drain drops below a predefined threshold in this case the alternator voltage output is reduced.
When turning the headlights on the 12.6V output is instantly jumps up to 13.6V
14.4 - 14.5 output voltage is present only when the battery needs to be topped up (mostly after starting the engine).
I've put supports under both left and right swingarms, so the running gear was in neutral position, without the wheels touching the ground.
Regarding the references the center console reading is originated from the transmission output shaft sensor. I'm just guessing in regard of the
cluster, probably it gets the reading from the CAN bus, and "distorts" the results.
The 12.6V voltage reading is normal when the battery current drain drops below a predefined threshold in this case the alternator voltage output is reduced.
When turning the headlights on the 12.6V output is instantly jumps up to 13.6V
14.4 - 14.5 output voltage is present only when the battery needs to be topped up (mostly after starting the engine).
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Thread Starter
Driver
Joined: Aug 2021
Posts: 87
Likes: 3
From: OH
Regarding the references the center console reading is originated from the transmission output shaft sensor. I'm just guessing in regard of the
cluster, probably it gets the reading from the CAN bus, and "distorts" the results.
cluster, probably it gets the reading from the CAN bus, and "distorts" the results.
And just another question, how did you compare the console screen speed with a GPS if the vehicle was not moving?
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Driver
Joined: Nov 2018
Posts: 64
Likes: 9
From: HU
Basically all sensors, switches and actuators, control units are wired up to this CAN bus.
This is a standardized serial data bus for data transfer between various units in the vehicles.
So the shaft sensor output is available to all units connected to the bus (including the instrument cluster),
of course many of these units doesn't need or require that info.
The console screen - GPS compare was took place in a different round, under real road conditions.
This is a standardized serial data bus for data transfer between various units in the vehicles.
So the shaft sensor output is available to all units connected to the bus (including the instrument cluster),
of course many of these units doesn't need or require that info.
The console screen - GPS compare was took place in a different round, under real road conditions.
Last edited by Ethanol; Nov 26, 2021 at 01:18 AM.
Driver
Joined: Nov 2018
Posts: 64
Likes: 9
From: HU
From sensor point of view I'd say there's only one speed signal source exists.
Providing higher readings for the driver is supports the "to be at the safe side" theory mentioned earlier,
while the vehicle stability systems, and the transmission uses the real data.
Providing higher readings for the driver is supports the "to be at the safe side" theory mentioned earlier,
while the vehicle stability systems, and the transmission uses the real data.
Thread Starter
Driver
Joined: Aug 2021
Posts: 87
Likes: 3
From: OH
So this is your assumption, correct?
So manufacturers “add” to the indicated speed, even tho there is more accurate data available, because they want to protect us from tickets??
Maybe it’s just me, but I still don’t get this…I would prefer the accurate data to be displayed…I’m a big boy, I don’t need “help” to keep me from getting tickets.
Oh well, thanks for the replies. 👍
…supports the "to be at the safe side" theory mentioned earlier…
Maybe it’s just me, but I still don’t get this…I would prefer the accurate data to be displayed…I’m a big boy, I don’t need “help” to keep me from getting tickets.
Oh well, thanks for the replies. 👍
Driver
Joined: Nov 2018
Posts: 64
Likes: 9
From: HU
So this is your assumption, correct?
and today it is more easy (and also cheaper) to produce different readings from one signal source.
Maybe it’s just me, but I still don’t get this…I would prefer the accurate data to be displayed…I’m a big boy, I don’t need “help” to keep me from getting tickets.
if not, setting the accuracy to 100% would display the real speed.
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