User Panel
User Panel
User Panel
|
Posted: 8/29/2015 5:04:36 PM EDT
[#1]
I think speedometers tend to read a little fast. Mine is 3-4mph fast at 65-70.
|
|
|
|
Posted: 8/29/2015 5:07:08 PM EDT
[#2]
Quote HistoryQuoted:
I think speedometers tend to read a little fast. Mine is 3-4mph fast at 65-70. Speedos are normally "optimistic", in part to err on the side of caution - that is, to avoid people being ticketed for minor speed infractions despite their speedometer apparently reading at or just under. I believe that while the speedo may be calibrated to read high, the odometer may be set lower, to the expected actual condition rather than over-estimating. ETA: I guess I should have said "often" or "tend to be" rather than "normally". As noted by others, some cars and trucks these days will be pretty close (but often still 1-2 MPH over GPS or so, maybe more), while motorcycles are far more "optimistic" (often by 5 MPH, or even more at certain speeds). |
|
|
|
Posted: 8/29/2015 5:07:59 PM EDT
[#3]
In my cruiser, with the proper tires, the gps, speedometer, and radar all match.
|
|
|
|
Posted: 8/29/2015 5:08:59 PM EDT
[#4]
My cars and trucks are closer to my GPS than any of my bikes are.
|
|
|
|
Posted: 8/29/2015 5:10:01 PM EDT
[#5]
How are you calculating your tire size, but the factory dimensions?
I'm gonna bet the squish of having some load on them makes them run smaller than the published dimensions |
|
|
|
Posted: 8/29/2015 5:11:39 PM EDT
[#6]
GPS
|
|
|
|
Posted: 8/29/2015 5:14:36 PM EDT
[#7]
My truck and GPS are pretty close to each other. Within 1 mph. |
|
|
|
Posted: 8/29/2015 5:18:03 PM EDT
[#8]
I'll go with the orbiting billion-dollar constellation of satellites for $1000, Alex.
GPS is going to be pretty damn close. Your car, on the other hand, is not going to be fast. That's by design, they don't want you exceeding the speed limit when you don't think you are. The only vehicle that's ever been within a MPH or so is my Avatar, when it was sitting on 31's with the speedo gear for the stock 30's installed. That was pretty dead nuts. It's since grown up, and reads faster than the GPS again, because it has the nominally correct Speedo Gear installed. SOME newer vehicle can be calibrated, electronically, to be closer than older, mechanical Speedo vehicles. But 3-4 MPH higher than reality is pretty normal. |
|
|
|
Posted: 8/29/2015 5:27:59 PM EDT
[#9]
There are gps speedometers so that tells you what is more accurate.
|
|
|
|
Posted: 8/29/2015 5:28:08 PM EDT
[#10]
Quote HistoryQuoted: How are you calculating your tire size, but the factory dimensions? I'm gonna bet the squish of having some load on them makes them run smaller than the published dimensions |
|
|
|
Posted: 8/29/2015 5:30:35 PM EDT
[#11]
Maybe they even do it to pad the fuel economy numbers.
Posted Via AR15.Com Mobile |
|
|
|
Posted: 8/29/2015 5:30:59 PM EDT
[#12]
The speedometer is much more accurate, assuming calibrated to tire size. They do average for tire wear though so they can be off based on how new or old your tires are by as much as 2-3% either way. The GPS is using several assumptions for you speed. They also use averaging over time. Couple that with a location fix that oftern uses averaging and may be jumping around wirh in 40 feet or so.
My older GPS in the trip tic section would often say things like my max speed during a route was 150mph. Which was an indication of these errors. My newer GPS doesn't, but it isn't becuase it's reception or the actual GPS chip are better or different. It is becuase they have different software to hide these errors that areintrinsic in the system. |
|
|
|
Posted: 8/29/2015 5:34:13 PM EDT
[#13]
Trust the GPS over a speedometer.
|
|
|
|
Posted: 8/29/2015 5:34:16 PM EDT
[#14]
Quote HistoryQuoted:
How are you calculating your tire size, but the factory dimensions? I'm gonna bet the squish of having some load on them makes them run smaller than the published dimensions This. GPS can be scary accurate. Trust the GPS if it has a good fix. |
|
|
|
Posted: 8/29/2015 5:36:32 PM EDT
[#15]
My BMW is at least 4mph fast, very common complaint, my old Ford truck is dead on when matched to GPS. I drive accordingly.
|
|
|
|
Posted: 8/29/2015 5:36:35 PM EDT
[#16]
Police say my speedometer is exactly correct. Unfortunately I ignore it....
|
|
|
|
Posted: 8/29/2015 5:38:51 PM EDT
[#17]
My truck speedo is matched to the gps at 35-45 mph, but when it goes to 60 it's 4 mph faster than the gps which when measured by mile marker is correct.
|
|
|
|
Posted: 8/29/2015 5:42:55 PM EDT
[#18]
Quote HistoryQuoted:
The speedometer is much more accurate, assuming calibrated to tire size. They do average for tire wear though so they can be off based on how new or old your tires are by as much as 2-3% either way. The GPS is using several assumptions for you speed. They also use averaging over time. Couple that with a location fix that oftern uses averaging and may be jumping around wirh in 40 feet or so. My older GPS in the trip tic section would often say things like my max speed during a route was 150mph. Which was an indication of these errors. My newer GPS doesn't, but it isn't becuase it's reception or the actual GPS chip are better or different. It is becuase they have different software to hide these errors that areintrinsic in the system. I also wondered if it showed my speed as if I were on a level grade vs going up or down hills. Meaning if I was going East up a steep grade at 55 would the GPS only see my speed as a two dimensional measurement and not three dimensional. Sincerely doubt anyone will understand what I was just rying to get out of my head. Posted Via AR15.Com Mobile |
|
|
|
Posted: 8/29/2015 5:45:54 PM EDT
[#19]
Quote HistoryQuoted:
In my cruiser, with the proper tires, the gps, speedometer, and radar all match. But they go though a special calibration dont they? My brothers cruiser had a little sticker on the bottom that said Certified Calibration. |
|
|
|
Posted: 8/29/2015 5:46:08 PM EDT
[#20]
The speedometer in my Javelin along with the other gauges were all spotty when it came to proper function. I installed a modern GPS speedometer. I hope it's correct. I haven't been ticketed since I put it it.
|
|
|
|
Posted: 8/29/2015 5:47:52 PM EDT
[#21]
Quote HistoryQuoted:
My truck and GPS are pretty close to each other. Within 1 mph. Me too and Texas DPS agrees with both. 
|
|
|
|
Posted: 8/29/2015 5:49:03 PM EDT
[#22]
Quote HistoryQuoted:
I also wondered if it showed my speed as if I were on a level grade vs going up or down hills. Meaning if I was going East up a steep grade at 55 would the GPS only see my speed as a two dimensional measurement and not three dimensional. Sincerely doubt anyone will understand what I was just rying to get out of my head. Posted Via AR15.Com Mobile Quote HistoryQuoted:
Quoted:
The speedometer is much more accurate, assuming calibrated to tire size. They do average for tire wear though so they can be off based on how new or old your tires are by as much as 2-3% either way. The GPS is using several assumptions for you speed. They also use averaging over time. Couple that with a location fix that oftern uses averaging and may be jumping around wirh in 40 feet or so. My older GPS in the trip tic section would often say things like my max speed during a route was 150mph. Which was an indication of these errors. My newer GPS doesn't, but it isn't becuase it's reception or the actual GPS chip are better or different. It is becuase they have different software to hide these errors that areintrinsic in the system. I also wondered if it showed my speed as if I were on a level grade vs going up or down hills. Meaning if I was going East up a steep grade at 55 would the GPS only see my speed as a two dimensional measurement and not three dimensional. Sincerely doubt anyone will understand what I was just rying to get out of my head. Posted Via AR15.Com Mobile I follow you completely. GPS is capable of delivering either velocity measurement (surface relative including elevation or just lat-lon relative). I'm not sure which they use in the software of commercial GPS navigation systems. If they are smart it would be surface relative (same as your speedometer). |
|
|
|
Posted: 8/29/2015 5:50:40 PM EDT
[#23]
Quoted:
GPS says I'm doing 51, speedometer says 55. Programmer was set for proper tire size calibration. Change calibration to a smaller tire and the GPS is just one mph slower than speedometer. The question is which do I go with? Match the speedo to the GPS or stick with correct tire size calibration. As is it would seem that is adding extra miles on the odometer. Trust GPS or programmer? If both are calibrated, the spedo will be more accurate. Minor lag, plus accuracy being dependent on number of satellites. |
|
|
|
Posted: 8/29/2015 5:52:24 PM EDT
[#24]
My last 2 Ford 250 work trucks with factory tires read 2mph faster on the speedometer than I'm actually going.It doesn't matter if I'm going 35 or 65 the speedometer always reads faster than gps or the cops little portable radar machines read.
|
|
|
|
Posted: 8/29/2015 5:52:39 PM EDT
[#25]
Quote HistoryQuoted:
I also wondered if it showed my speed as if I were on a level grade vs going up or down hills. Meaning if I was going East up a steep grade at 55 would the GPS only see my speed as a two dimensional measurement and not three dimensional. Sincerely doubt anyone will understand what I was just rying to get out of my head. Posted Via AR15.Com Mobile Quote HistoryQuoted:
Quoted:
The speedometer is much more accurate, assuming calibrated to tire size. They do average for tire wear though so they can be off based on how new or old your tires are by as much as 2-3% either way. The GPS is using several assumptions for you speed. They also use averaging over time. Couple that with a location fix that oftern uses averaging and may be jumping around wirh in 40 feet or so. My older GPS in the trip tic section would often say things like my max speed during a route was 150mph. Which was an indication of these errors. My newer GPS doesn't, but it isn't becuase it's reception or the actual GPS chip are better or different. It is becuase they have different software to hide these errors that areintrinsic in the system. I also wondered if it showed my speed as if I were on a level grade vs going up or down hills. Meaning if I was going East up a steep grade at 55 would the GPS only see my speed as a two dimensional measurement and not three dimensional. Sincerely doubt anyone will understand what I was just rying to get out of my head. Posted Via AR15.Com Mobile We understand vectors I highly doubt the few feet elevation form the hill makes any real difference. Plus GPS can measure elevation so your slope could even be determined. |
|
|
|
Posted: 8/29/2015 6:05:06 PM EDT
[#26]
Most tires, esp. off road and all terrain tires can be pretty "off" from their advertised sizing. I know in the 33" range, some tires measured low 32s. BFG were the closest I believe to a true 33" I know my M/T Baja Radials were 32.8.
And dont forget the "squish" factor, air pressure and wear. I change tire size and gear ratio so my speedo is wayyyyyyyyyyyyy off. but ive GPS'd it and im exactly 20mph off. So if I read 75, im actually going 55mph |
|
|
|
Posted: 8/29/2015 6:18:53 PM EDT
[#27]
I'd go with GPS.
Not affected by tire size, tire wear, tire pressure/temp. Plus I doubt they calibrate car speedos at the factory |
|
|
|
Posted: 8/29/2015 6:21:41 PM EDT
[#28]
I've noticed most cars I have owned have indicated anywhere from 1-4% over actual speed. I've never had one read less than actual speed. The German cars I've owned seem to come in on the lower end of that range, and the Japanese and American cars are on the upper end of that range. |
|
|
|
Posted: 8/29/2015 6:33:43 PM EDT
[#29]
How about having someone pace you? That's what I did. My truck is 5 mph under at 65. When the speedo says 65 you're actually going 60. And 2-3 mph low at 35.
|
|
|
|
Posted: 8/29/2015 6:46:20 PM EDT
[#30]
Quote HistoryQuoted:
How about having someone pace you? That's what I did. My truck is 5 mph under at 65. When the speedo says 65 you're actually going 60. And 2-3 mph low at 35. If their speedo is a little off (all are) and yours is a little off it's not going to be accurate. GPS is the easy answer. |
|
|
|
Posted: 8/29/2015 6:48:39 PM EDT
[#31]
Quote HistoryQuoted:
If both are calibrated, the spedo will be more accurate. Minor lag, plus accuracy being dependent on number of satellites. Quote HistoryQuoted:
Quoted:
GPS says I'm doing 51, speedometer says 55. Programmer was set for proper tire size calibration. Change calibration to a smaller tire and the GPS is just one mph slower than speedometer. The question is which do I go with? Match the speedo to the GPS or stick with correct tire size calibration. As is it would seem that is adding extra miles on the odometer. Trust GPS or programmer? If both are calibrated, the spedo will be more accurate. Minor lag, plus accuracy being dependent on number of satellites. No. Even if both were perfectly matched to each other in identical conditions at the same time, the moment friction modifies the tyre temps and the centripedal forces expand the tyre the speedo will already be off. |
|
|
|
Posted: 8/29/2015 6:51:42 PM EDT
[#32]
Quote HistoryQuoted:
How about having someone pace you? That's what I did. My truck is 5 mph under at 65. When the speedo says 65 you're actually going 60. And 2-3 mph low at 35. What if the "pace" vehicle is Off? its a viscous cycle. GPS all the way....... |
|
|
|
Posted: 8/29/2015 7:12:56 PM EDT
[#33]
Quote HistoryQuoted: What if the "pace" vehicle is Off? its a viscous cycle. GPS all the way....... Quote HistoryQuoted: Quoted: How about having someone pace you? That's what I did. My truck is 5 mph under at 65. When the speedo says 65 you're actually going 60. And 2-3 mph low at 35. What if the "pace" vehicle is Off? its a viscous cycle. GPS all the way....... I didn't think of that |
|
|
|
Posted: 8/29/2015 7:17:47 PM EDT
[#34]
Quote HistoryQuoted: My truck and GPS are pretty close to each other. Within 1 mph. |
|
|
|
Posted: 8/29/2015 7:41:24 PM EDT
[#35]
My speedometer got so far off a couple of years ago that I bought a new GPS to use it for a speed indicator. $600 to replace the instrument guage vs. $150 for a good GPS...GPS won. |
|
|
|
Posted: 8/29/2015 8:16:46 PM EDT
[#36]
Quote HistoryQuoted:
I'd go with GPS. Not affected by tire size, tire wear, tire pressure/temp. Plus I doubt they calibrate car speedos at the factory They do it to police cruisers. Not sure if ford did it for the crown Vics but someone did. |
|
|
|
Posted: 8/29/2015 8:23:13 PM EDT
[#37]
My speedometer reads the same as my Gps which I did find surprising. I think the Gps would give a more accurate reading of speed of the two for the most part.
|
|
|
|
Posted: 8/29/2015 8:31:20 PM EDT
[#38]
I tested my Escort radar detector gps, Garmin gps and phone gps all at once a while ago. If recall they were all within a half mph, seems like the phone was slowest to react to changes. I concluded that they were to be trusted over my speedos.
My KLR factory speedo is 10% high, odo is correct, I have a Trail Tech Striker(gage set) that allows you to adjust tire dia., I have adjusted it to match the Escort radar detector gps(9500ix). |
|
|
|
Posted: 8/29/2015 8:36:38 PM EDT
[#39]
GPS is more accurate, but has a bit of lag.
|
|
|
|
Posted: 8/29/2015 8:37:47 PM EDT
[#40]
If you wanna get less sophisticated , use a Stop watch and mile markers on the highway.
|
|
|
|
Posted: 8/29/2015 8:39:50 PM EDT
[#41]
GPS tells you how fast you were going during the sampling period. with proper setup (tire size/inflation, no malfunctions in the device), a speedometer tells you how fast you are going.
and your speedo is not subject to reception anomalies. |
|
|
|
Posted: 8/29/2015 8:40:17 PM EDT
[#42]
Quote HistoryQuoted:
If you wanna get less sophisticated , use a Stop watch and mile markers on the highway. best way to calibrate a speedometer. |
|
|
|
Posted: 8/29/2015 8:41:48 PM EDT
[#43]
Quote HistoryQuoted:
I'd buy that. I moved down one inch in diameter to get the speedo closer to the GPS. Still I wonder if that adds extra miles on the odometer that I didn't really put on. Quote HistoryQuoted:
Quoted:
How are you calculating your tire size, but the factory dimensions? I'm gonna bet the squish of having some load on them makes them run smaller than the published dimensions You went to smaller wheels to make your speedo match gps? For real? |
|
|
|
Posted: 8/29/2015 9:04:42 PM EDT
[#44]
Quote HistoryQuoted:
You went to smaller wheels to make your speedo match gps? For real? Quote HistoryQuoted:
Quoted:
Quoted:
How are you calculating your tire size, but the factory dimensions? I'm gonna bet the squish of having some load on them makes them run smaller than the published dimensions You went to smaller wheels to make your speedo match gps? For real? No, I set the programmer calibration to a smaller size. Posted Via AR15.Com Mobile |
|
|
|
Posted: 8/29/2015 9:06:05 PM EDT
[#45]
Using the roadside radar speed readers my car and motorcycle are spot on.
I would only go by GPS if it was a high dollar unit. You could ask your local LE agency to help you out . |
|
|
|
Posted: 8/29/2015 9:07:47 PM EDT
[#46]
Quote HistoryQuoted:
GPS tells you how fast you were going during the sampling period. with proper setup (tire size/inflation, no malfunctions in the device), a speedometer tells you how fast you are going. and your speedo is not subject to reception anomalies. I set the cruise control at 55 on the highway and watched it for five miles or so until I was convinced it was steady. Posted Via AR15.Com Mobile |
|
|
|
Posted: 8/29/2015 9:08:20 PM EDT
[#47]
Quote HistoryQuoted:
Using the roadside radar speed readers my car and motorcycle are spot on.I would only go by GPS if it was a high dollar unit. You could ask your local LE agency to help you out . I would not put much faith in those being dead on. Temprature fluctuations might screw with the oscillator. |
|
|
|
Posted: 8/29/2015 9:13:52 PM EDT
[#48]
Quote HistoryQuoted:
Using the roadside radar speed readers my car and motorcycle are spot on.I would only go by GPS if it was a high dollar unit. You could ask your local LE agency to help you out . It's an older Magellan but a good one, besides roadside radars are kind of scarce around here and no telling if they've been calibrated themselves. Posted Via AR15.Com Mobile |
|
|
|
Posted: 8/29/2015 9:15:42 PM EDT
[#49]
Quote HistoryQuoted:
It's an older Magellan but a good one, besides roadside radars are kind of scarce around here and no telling if they've been calibrated themselves. Posted Via AR15.Com Mobile Quote HistoryQuoted:
Quoted:
Using the roadside radar speed readers my car and motorcycle are spot on.I would only go by GPS if it was a high dollar unit. You could ask your local LE agency to help you out . It's an older Magellan but a good one, besides roadside radars are kind of scarce around here and no telling if they've been calibrated themselves. Posted Via AR15.Com Mobile Without being in a climate controlled environment they would most likely need calibration many times throughout the day. |
|
|
|
Posted: 8/29/2015 9:17:59 PM EDT
[#50]
Even consumer gps should be accurate to less than 1/10 mph
|
|
|
Win a FREE Membership!
Sign up for the ARFCOM weekly newsletter and be entered to win a free ARFCOM membership. One new winner* is announced every week!
You will receive an email every Friday morning featuring the latest chatter from the hottest topics, breaking news surrounding legislation, as well as exclusive deals only available to ARFCOM email subscribers.
AR15.COM is the world's largest firearm community and is a gathering place for firearm enthusiasts of all types.
From hunters and military members, to competition shooters and general firearm enthusiasts, we welcome anyone who values and respects the way of the firearm.
Subscribe to our monthly Newsletter to receive firearm news, product discounts from your favorite Industry Partners, and more.
Copyright © 1996-2024 AR15.COM LLC. All Rights Reserved.
Any use of this content without express written consent is prohibited.
AR15.Com reserves the right to overwrite or replace any affiliate, commercial, or monetizable links, posted by users, with our own.
