Speedometer Accuracy... or Inaccuracy
03-01-2003, 08:07 PM
#1
Speedometer Accuracy... or Inaccuracy
I recently purchased a Garmin GPS V, to add a navi to the car that was very simple. One of its features, of course, is to tell you your speed and direction. This evening I left the screen up the whole time which shows your compass direction and speed. First off all, the compass showed that my Mirror compass was off by 45 degrees! Then, the speed... At 20 or so it was dead accurate. However, 50 on my speedometer was 51 to GPS, 60 was 61.6 to the GPS, and 70 was 72 to the GPS! My usual 74 cruise setting was acutally 76.3 MPH! When I opened her up 100 it was really 103.9!
I have a 2k3 6speed with 4k miles.
Just letting you know, I constantly cruise at 74 and was dismayed that I was in the 10+ ticket category. Anybody else notice any inaccuracies?
I had gone by one of those radar things in town and was always dead on, but of course I was only going 30 or so. Gave me a safe feeling that it was accurate. I was wrong...
I have a 2k3 6speed with 4k miles.
Just letting you know, I constantly cruise at 74 and was dismayed that I was in the 10+ ticket category. Anybody else notice any inaccuracies?
I had gone by one of those radar things in town and was always dead on, but of course I was only going 30 or so. Gave me a safe feeling that it was accurate. I was wrong...
03-01-2003, 10:06 PM
#3
yeah, I've got a GPS V as well (and a Vista), both my Pathfinder and Maxima show 68 on the GPS while 70 on the GPS. However, I recently put 2k2 rims on my GLE that came with the 5 spoke 16's. Now in the max, I read 70 on the speedo and right under 72 on the GPS. :/ Thats hard getting used to as I was padding my speed alittle. If you are on a perfectly flat, straight road and have a good lock, you can pretty much trust the GPS. Garmin uses an averaging algorithm that will be very accurate. As for my rim change, that was pretty much what the tire calculator said it would be.
Most Nissans I have been in read 2 mph too fast. I assumed it was a liability thing, better to read alittle fast than alittle slow. I've been in other cars where they had changed rims and couldnt figure out why they were getting stopped so much, when in fact they were as much as reading 6mph too slow
The worst was an SUV, you'd probably notice a 6mph diff in most cars.
I'm kinda surprised yours is reading too slow.
Most Nissans I have been in read 2 mph too fast. I assumed it was a liability thing, better to read alittle fast than alittle slow. I've been in other cars where they had changed rims and couldnt figure out why they were getting stopped so much, when in fact they were as much as reading 6mph too slow
The worst was an SUV, you'd probably notice a 6mph diff in most cars. I'm kinda surprised yours is reading too slow.
03-02-2003, 04:28 AM
#4
Senior Member
Join Date: Dec 2002
Posts: 448
Originally posted by TimW
yeah, I've got a GPS V as well (and a Vista), both my Pathfinder and Maxima show 68 on the GPS while 70 on the GPS. However, I recently put 2k2 rims on my GLE that came with the 5 spoke 16's. Now in the max, I read 70 on the speedo and right under 72 on the GPS. :/ Thats hard getting used to as I was padding my speed alittle. If you are on a perfectly flat, straight road and have a good lock, you can pretty much trust the GPS. Garmin uses an averaging algorithm that will be very accurate. As for my rim change, that was pretty much what the tire calculator said it would be.
Most Nissans I have been in read 2 mph too fast. I assumed it was a liability thing, better to read alittle fast than alittle slow. I've been in other cars where they had changed rims and couldnt figure out why they were getting stopped so much, when in fact they were as much as reading 6mph too slow The worst was an SUV, you'd probably notice a 6mph diff in most cars.
I'm kinda surprised yours is reading too slow.
yeah, I've got a GPS V as well (and a Vista), both my Pathfinder and Maxima show 68 on the GPS while 70 on the GPS. However, I recently put 2k2 rims on my GLE that came with the 5 spoke 16's. Now in the max, I read 70 on the speedo and right under 72 on the GPS. :/ Thats hard getting used to as I was padding my speed alittle. If you are on a perfectly flat, straight road and have a good lock, you can pretty much trust the GPS. Garmin uses an averaging algorithm that will be very accurate. As for my rim change, that was pretty much what the tire calculator said it would be.
Most Nissans I have been in read 2 mph too fast. I assumed it was a liability thing, better to read alittle fast than alittle slow. I've been in other cars where they had changed rims and couldnt figure out why they were getting stopped so much, when in fact they were as much as reading 6mph too slow
The worst was an SUV, you'd probably notice a 6mph diff in most cars. I'm kinda surprised yours is reading too slow.
I've timed it, compared to those roadside radar signs, and used a GPS.
03-02-2003, 09:50 PM
#5
Supporting Maxima.org Member
Join Date: Oct 2002
Posts: 1,042
Re: Speedometer Accuracy... or Inaccuracy
Originally posted by number2jcb
I recently purchased a Garmin GPS V, to add a navi to the car that was very simple. One of its features, of course, is to tell you your speed and direction. This evening I left the screen up the whole time which shows your compass direction and speed. First off all, the compass showed that my Mirror compass was off by 45 degrees! Then, the speed... At 20 or so it was dead accurate. However, 50 on my speedometer was 51 to GPS, 60 was 61.6 to the GPS, and 70 was 72 to the GPS! My usual 74 cruise setting was acutally 76.3 MPH! When I opened her up 100 it was really 103.9!
I have a 2k3 6speed with 4k miles.
I recently purchased a Garmin GPS V, to add a navi to the car that was very simple. One of its features, of course, is to tell you your speed and direction. This evening I left the screen up the whole time which shows your compass direction and speed. First off all, the compass showed that my Mirror compass was off by 45 degrees! Then, the speed... At 20 or so it was dead accurate. However, 50 on my speedometer was 51 to GPS, 60 was 61.6 to the GPS, and 70 was 72 to the GPS! My usual 74 cruise setting was acutally 76.3 MPH! When I opened her up 100 it was really 103.9!
I have a 2k3 6speed with 4k miles.
Criminy (can you say that on the .org?), at 130 it must be out by...0.5 - or even 0.6!!!
sorry, BTW - not sniping at you, just minor residual annoyance from the previous threads.
03-02-2003, 09:55 PM
#6
Senior Member
Join Date: Aug 2002
Posts: 1,067
Keep in mind all of you that radar is innacurate like this also. It all depends on the car. You may look down and say, ok I'm going 45 in a 40, and then the cop pulls you over for doing 48 or 49 saying his radar said 49. Just because ur speedometer says 45, doesn't mean your speedometer could be just a bit off. I wouldn't really worry about it though...
03-02-2003, 10:16 PM
#7
Senior Member
Join Date: Dec 2001
Location: Charlotte, NC
Posts: 1,687
Mine is a minimum of 6 MPH slow. So when I'm going 40 MPH on the speedometer, I'm really going 46 MPH. I got pulled over by a cop who said I was going 52 in a 35 when I was driving at just a hair over 40. It seems that it gets worse the higher up I go. I took the car to the dealer, and they ordered me another speedometer. I'll get it put on this week and see if it changes any.
03-02-2003, 10:49 PM
#8
Senior Member
Join Date: Feb 2003
Posts: 217
i can't remember which one, but one of the car mags did an article about this, comparing actual speed vs. speedometer measured speed, and most of the car companies read about 1 or 2 mph fast at 70 mph, and bmw led the pack with around 3.5 mph fast i belive. maybe to help keep us safe and save on tickets?
03-02-2003, 11:19 PM
#10
Senior Member
Join Date: Nov 2001
Posts: 355
Originally posted by thrasher
i can't remember which one, but one of the car mags did an article about this, comparing actual speed vs. speedometer measured speed
i can't remember which one, but one of the car mags did an article about this, comparing actual speed vs. speedometer measured speed
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