9500ix GPS Speed Accuracy
I have been noticing a discrepancy between my speedometer, diagnostic scan tool and the GPS speed on my 9500ix. Typically the RD reads 1-2 MPH slower than the speedo, and the scan tool reads 2-3 MPH faster than the speedo. Last night on a run from Crossville, TN to Nashville, TN on I-40 I became keenly aware of the differences, but thought it might be the heavy cloud cover, hilly terrain and scattered rain degrading the GPS reception.
So, this afternoon I went out and did a timed test on a straight, level 5 mile stretch of highway. Weather was mostly sunny.
For the first test I set the cruise control to 60 as indicated by the scan tool (since I thought it was probably the most accurate of the three), which was 58 on the speedo and 57 on the 9500ix. Mileage is from the highway mile markers, time is in decimal format not seconds, ie 1.05 is 1 minute 3 seconds not 1 minute 5 seconds.
Test 1
Speed:
Speedo Scan Tool 9500ix Mile Time
58 60 57 1 1.05 min
2 2.10
3 3.16
4 4.21
5 5.26
Average time per mile was 1.052 minutes. 60 min/hr / 1.052 min/mile = 57.03 MPH.
The 9500ix was correct.
Test 2
Speed:
Speedo Scan Tool 9500ix Mile Time
72 75 71 1 .85
2 1.70
3 2.53
4 3.38
5 4.23
Average time per mile was .846 minutes. 60 min/hr / .846 min/mile = 70.92 MPH.
The 9500ix was correct.
FWIW, the tires on my truck are LT 265/75-16, and I think that stock was 235/85-16, which might be why the scan tool is off.
I wasn't expecting the speedo to be right on, but I was expecting the scan tool to be correct.
I guess I'll have to start driving faster. :p
Re: 9500ix GPS Speed Accuracy
Speed display is one of my absolute favorite features of the 9500ix. I rely on speed display more than my speedometer. I knew when I first drove the Altima home from the lot it felt like I was going slower than it said and sure enough, the speedometer in my 06 Altima is off by 3-5 mph (too high).
Re: 9500ix GPS Speed Accuracy
My cavalier's speedometer reads about 2 miles per hour faster than my 9500ix as well.
Re: 9500ix GPS Speed Accuracy
I'm not sure of the accuracy of the IX, but I'd trust the GPS accuracy more than Speedo or scan tool. Speedometer error is pretty is a given Your scan tool will be getting its speed from the ABS sensors for wheel speed. This will be different for Full tread versus bald tires, so therefore won't be as accurate as a well calibrated GPS (which I can't say if the IX is or isn't). If you can get PIDS (Dataloger, or whatever it may be called in your scan tool), you should be able to pull up all 4 wheels independantly and you may find a small difference from wheel to wheel due to tire diameter caused by tread depth and/or tire pressue.
Re: 9500ix GPS Speed Accuracy
i also use the gps more than my speedo. I know its 3-5 mph depending on the speed. I love the gps speed tool haha
Re: 9500ix GPS Speed Accuracy
Quote:
Originally Posted by
Clay_in_Nashville
Speed display is one of my absolute favorite features of the 9500ix. I rely on speed display more than my speedometer. I knew when I first drove the Altima home from the lot it felt like I was going slower than it said and sure enough, the speedometer in my 06 Altima is off by 3-5 mph (too high).
X2. Amazing feature. Spec mode and Speed Display FTW.
It's especially nice to look up and see your speed right when your detector displays a threat.
Re: 9500ix GPS Speed Accuracy
Most car speedo's are off, especially the faster you go. My S2K for example is fast about 2 MPH at 80 compared to the 9500ix. Tire wear will also impact most cars speedos. I would think some cars must have GPS speedo's built in by now ... not sure though.
I trust the 9500ix, although it does have an annoying lag.
Re: 9500ix GPS Speed Accuracy
Quote:
Originally Posted by
Obsidian
Most car speedo's are off, especially the faster you go. My S2K for example is fast about 2 MPH at 80 compared to the 9500ix. Tire wear will also impact most cars speedos. I would think some cars must have GPS speedo's built in by now ... not sure though.
I trust the 9500ix, although it does have an annoying lag.
The lag on mine isn't that bad? Maybe I just drive a slow car. :o
Re: 9500ix GPS Speed Accuracy
Quote:
Originally Posted by
Clay_in_Nashville
Quote:
Originally Posted by
Obsidian
Most car speedo's are off, especially the faster you go. My S2K for example is fast about 2 MPH at 80 compared to the 9500ix. Tire wear will also impact most cars speedos. I would think some cars must have GPS speedo's built in by now ... not sure though.
I trust the 9500ix, although it does have an annoying lag.
The lag on mine isn't that bad? Maybe I just drive a slow car. :o
LOL. I don't know. Mine takes about a one half to one second to catch up or slow down. Even coming to a red light or something it will show 3-4 mph for about a half second after I stop.
Re: 9500ix GPS Speed Accuracy
Quote:
Originally Posted by
Obsidian
Quote:
Originally Posted by
Clay_in_Nashville
Quote:
Originally Posted by
Obsidian
Most car speedo's are off, especially the faster you go. My S2K for example is fast about 2 MPH at 80 compared to the 9500ix. Tire wear will also impact most cars speedos. I would think some cars must have GPS speedo's built in by now ... not sure though.
I trust the 9500ix, although it does have an annoying lag.
The lag on mine isn't that bad? Maybe I just drive a slow car. :o
LOL. I don't know. Mine takes about a one half to one second to catch up or slow down. Even coming to a red light or something it will show 3-4 mph for about a half second after I stop.
Oh yeah, mines about that lagging. No big deal to me, I guess. So are you running Speed Display and Spec Mode?
Re: 9500ix GPS Speed Accuracy
Quote:
Originally Posted by
Clay_in_Nashville
Quote:
Originally Posted by
Obsidian
Quote:
Originally Posted by
Clay_in_Nashville
Quote:
Originally Posted by
Obsidian
Most car speedo's are off, especially the faster you go. My S2K for example is fast about 2 MPH at 80 compared to the 9500ix. Tire wear will also impact most cars speedos. I would think some cars must have GPS speedo's built in by now ... not sure though.
I trust the 9500ix, although it does have an annoying lag.
The lag on mine isn't that bad? Maybe I just drive a slow car. :o
LOL. I don't know. Mine takes about a one half to one second to catch up or slow down. Even coming to a red light or something it will show 3-4 mph for about a half second after I stop.
Oh yeah, mines about that lagging. No big deal to me, I guess. So are you running Speed Display and Spec Mode?
Yeah, maybe it's not too bad. The satellites are in outer freakin' space after all. :D
I run speed display (but not speed alerts) and spec mode. I sometimes switch to expert since every CHP is running 34.7 anyway.
Re: 9500ix GPS Speed Accuracy
Every one of my vehicles is off per my 9500i speed display. My freakin truck is off by 10 mph at 65! ( I am actually only going 55) Once you use the speed display, it's hard to live without.
Re: 9500ix GPS Speed Accuracy
Quote:
Originally Posted by
Obsidian
Quote:
Originally Posted by
Clay_in_Nashville
Quote:
Originally Posted by
Obsidian
Quote:
Originally Posted by
Clay_in_Nashville
Quote:
Originally Posted by
Obsidian
Most car speedo's are off, especially the faster you go. My S2K for example is fast about 2 MPH at 80 compared to the 9500ix. Tire wear will also impact most cars speedos. I would think some cars must have GPS speedo's built in by now ... not sure though.
I trust the 9500ix, although it does have an annoying lag.
The lag on mine isn't that bad? Maybe I just drive a slow car. :o
LOL. I don't know. Mine takes about a one half to one second to catch up or slow down. Even coming to a red light or something it will show 3-4 mph for about a half second after I stop.
Oh yeah, mines about that lagging. No big deal to me, I guess. So are you running Speed Display and Spec Mode?
Yeah, maybe it's not too bad. The satellites are in outer freakin' space after all. :D
I run speed display (
but not speed alerts) and spec mode. I sometimes switch to expert since every CHP is running 34.7 anyway.
Same here. Speed alert makes it take longer to display the frequency.
