+Eric K Posted October 22, 2002 Share Posted October 22, 2002 I noticed whenever I have my GPS in my car it is always approximately 3 MPH different from my speedometer. (Of course right now I'm having a brain fart and can't remember if it's slower or faster) Anyway, what is probably more accurate. My car or my GPS? Quote Link to comment
+The Leprechauns Posted October 22, 2002 Share Posted October 22, 2002 My Garmin V is always 3 mph SLOWER than what is shown on the car speedometer. I notice this when I'm on a flat, straight stretch of interstate and have the cruise control on. I guessed that either the calibration on the car speedometer is a bit off, or that the manufacturers build in a little "cushion" just like the police give us a 5 mph margin of error before writing a ticket. After all, it's impossible for the satellites to be wrong, isn't it? x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x What if the Hokey Pokey IS what it's all about? Quote Link to comment
+briansnat Posted October 22, 2002 Share Posted October 22, 2002 I've noticed my Legend is nearly always dead on. At most its 1-2 MPH off. Flying cross country, it clocked the plane at 519 MPH. "Men don't stop playing because they get old, they get old because they stop playing" Oliver Wendell Holmes Quote Link to comment
+SimonG Posted October 22, 2002 Share Posted October 22, 2002 My GPSr often reports a speed of as much as 10mph slower than my speedometer. I remember reading somewhere that speedos are legally allowed to report too fast a speed, but not too slow a speed, so when they make them they err on the side of too fast. I think that was referring to British law, but I would imagine it's the same over there. I suspect the speed your GPSr reports is bang on. Quote Link to comment
+Jamie Z Posted October 22, 2002 Share Posted October 22, 2002 Your GPS is more accurate than the speedometer in your car. Jamie Quote Link to comment
+Stunod Posted October 22, 2002 Share Posted October 22, 2002 At highway speeds my GPS just about matches the speedometer in my Chevy, but is 5 MPH slower than my buddy's BMW. Great German engineering, huh? "Just because I don't care doesn't mean I don't understand." Quote Link to comment
+sbell111 Posted October 22, 2002 Share Posted October 22, 2002 My GPSr is always within a mile of the Oldsmobeast's digital guage. Quote Link to comment
dave and jaime Posted October 22, 2002 Share Posted October 22, 2002 tire size will affect the accuracy of your cars speedo. manufactures are required to calibrate by the stock size, if you change the size it will affect the accuracy of your speedo. the speedo gear setup is generally a set of plastic cogs which will wear over time and generally dont give good accuracy. here in nl i understand that tickets given for <15 km/hr over the limit have a 80% chance of being overturned for these reasons. also my mazda truck reads 100 km/hr when my gps say 95 km/hr. i trust the gps for accuracy. Quote Link to comment
+Geo-Johnson's Posted October 23, 2002 Share Posted October 23, 2002 Our town has one of those trailers that the police department puts out to clock how fast you're going. Our geovan says it's going 3mph faster than what they clocked us at. We also used hand held radios and compared it with a friends van....also 3mph off. In playing with the GPS speed, the GPS also says we're going 3mph slower than what the speedometer says........And since the police are always right we're going to believe the GPS is right on.......... Quote Link to comment
+BletchleyPark Posted October 23, 2002 Share Posted October 23, 2002 I made a number of passes with both my Streetpilot and my Vista at sppeds ranging from 25 mph to 45 mph. Each time the GPSrs matched the radar. BP Quote Link to comment
+Centaur Posted October 23, 2002 Share Posted October 23, 2002 In the cross country driving trip we did in September I was courious to see how the speed on my GPSV woudlrelate to the speedo in my '02 Envoy. I was surprized to find they matched exactly. I was expecting one or the other to be off. They also have matched the radar speed displays we have passed. Quote Link to comment
TriCityGuy Posted October 23, 2002 Share Posted October 23, 2002 It's like saying I find my GPS 3 mph faster than my Flinstonemobile and 2 mph faster than my Conestoga wagon. GPSr's are way more accurate than automobile speedos. Auto speedos not only are usually off a mph or two, but also off differently over their range. I have a Sonoma that's about 1 mph under at 30 mph, over 2 at 60 mph, and over 4 at 100mph. I confirmed this with airplane markers, a stopwatch, and some dusted off algrebra. Garmin specs say 0.1 mph presumably with full signal. I would guess that it's not more than a factor or two off for lesser signal strength and personally figure it's easily within 1/2 a mile an hour. Quote Link to comment
azog Posted October 23, 2002 Share Posted October 23, 2002 I have an analog speedometer in my car, so it's hard to tell, but I noticed that it's +/- 1 mph, which is close enough for government work. ---------- Do not answer a fool according to his folly, lest you be also be like him. Quote Link to comment
Dale_Lynn Posted October 23, 2002 Share Posted October 23, 2002 To really test GPS against car speedo... Find a set of mile posts (most states have them exactly 1 mile apart) get car speedo on 60 and watch GPS..... IF you are going exactly 60 mph you will do 1 mile in 60 seconds... Compare results... Dale -------------------------------------------------------- I'm Diagonally Parked, In A Parallel Universe. -------------------------------------------------------- Quote Link to comment
MTET Posted October 23, 2002 Share Posted October 23, 2002 I have a competition tow boat (for wakeboarding) with dual speedometers which allows me to be highly accurate and precise in my MPH reading. When I compared the boat's MPH reading with my GPS, both were nearly identical. A difference of .3 MPH. I'm convinced that the GPS speed is quite accurate. Quote Link to comment
+15Tango Posted October 24, 2002 Share Posted October 24, 2002 I guess I'm backwards--the speedometer in "The Millennium Falcon" reads about 2.5 mph slower than my GPS or those speed trailers--it seems like every one else's speedo reads faster. Think Globally, Act Locally Quote Link to comment
+Wadcutter Posted October 24, 2002 Share Posted October 24, 2002 I've compared my 12MAP against my radar unit, which is routinely calibrated and certified to be off no more than +/- 1 MPH. My 12MAP is always right on. Speedos in vehicles can be off a great deal depending if size of tires have changed or gear ratios. Usually a change in 1 tire size will change the speed by 3-5 MPH. Quote Link to comment
+Kite and Hawkeye Posted October 24, 2002 Share Posted October 24, 2002 We've got a Saturn with its original tires. On a long, straight stretch of freeway, we tested GPS vs speedometer, and found the GPS about three mph faster than the speedometer. Gave us pause, since we, uh, didn't think we were exceeding 80. Quote Link to comment
+culpc Posted October 24, 2002 Share Posted October 24, 2002 I've also found that not only is the GPSr more accurate than the speedo (verified by the officer who wrote the ticket), but the speed will vary quite a bit (3-4 mph) while speedo reading is the same speed. I would guess that this results from a fat needle and skinny marker lines... Children today are tyrants. They contradict their parents, gobble their food, and tyrannize their teachers. - Socrates Quote Link to comment
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