Electronically governed top speed?
#32
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#33
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I disagree with a lot of this reasoning. I do agree that the higher the speed that you go the more inaccurate the speedometer can become BUT it is relatively accurate up to a point. Good car review companies test this out by verifying the speedometer speed compared to actual speed. If memory serves me correctly they test between 60-100MPH. They will tell you how much the speedometer is off and most of the time it is correct. I also believe there are certain requirements as far as accuracy goes. GPS is not accurate compared to the speedometer. Calculation using the wheels can take in account correction factors which are easy to calculate especially for newer cars with a built in computer. If my TI-83 can do it then a car can do it. They can also calculate slip hence why we have LSD and the LSD light shows up. GPS is only accurate to point but GPS cannot give you exact positioning especially if it is a civilian GPS. How exact is GPS now? Within 10, 50, 100 feet? I will have to look that up. If it cannot pinpoint your exact location before and after then the calculation won't be exact either.
This link gives some more info: http://www.caranddriver.com/features...dal_feature__1
#34
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You are welcome to your opinions but GPS measures speed by doppler shift, not by exact position. That is why GPS manufacturers can quote accuracy of velocity measurements like .1 knots (<.1 MPH). I would take anything that eliminates sources of error, hence speed gun or GPS.
This link gives some more info: http://www.caranddriver.com/features...dal_feature__1
This link gives some more info: http://www.caranddriver.com/features...dal_feature__1
#35
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Two links to check out.. the first deals with the speed rating of tires.
PLEASE PLEASE PLEASE everyone.... for your safety.. check out the speed rating of your tires BEFORE you attempt to see how fast your car can go. You don't want to be hitting 150+ mph only to have your tires blow out from underneath you.. very messy.
Please refer to the following link:
http://www.tirerack.com/tires/tirete....jsp?techid=35
Scroll down to the Speed Rating section.
The second link deals with a good way to gauge your speed and your speedometer.
http://www.tirerack.com/tires/tirete...currentpage=35
PLEASE PLEASE PLEASE everyone.... for your safety.. check out the speed rating of your tires BEFORE you attempt to see how fast your car can go. You don't want to be hitting 150+ mph only to have your tires blow out from underneath you.. very messy.
Please refer to the following link:
http://www.tirerack.com/tires/tirete....jsp?techid=35
Scroll down to the Speed Rating section.
The second link deals with a good way to gauge your speed and your speedometer.
http://www.tirerack.com/tires/tirete...currentpage=35
#36
You are welcome to your opinions but GPS measures speed by doppler shift, not by exact position. That is why GPS manufacturers can quote accuracy of velocity measurements like .1 knots (<.1 MPH). I would take anything that eliminates sources of error, hence speed gun or GPS.
This link gives some more info: http://www.caranddriver.com/features...dal_feature__1
This link gives some more info: http://www.caranddriver.com/features...dal_feature__1
#40
Registered User
#42
Seems strange to me that the Auto version would cut out lower than the 5sp version....The gearing is certainly there to do it? It is certainly stable at speed though...My Lightning used to get a little floaty over 145...
A one time measurement of speed using GPS could have the potential to be highly inaccurate as GPS units have a spherical position tolerance (IE when your handheld unit says position quality 15' your position is somewhere within a 15' radius sphere...) You may not actually be out by 15' but the unti can guarantee that the position it is displaying for you is within that tolerance of your actual position...You can jump from one side of this sphere to the other every time it re-measures (usually 1-5 second intervals) so you can see where a one time reading could be highly inaccurate and give a massive spike of peak speed. Incidentally you will never see a low spike as it never gets recorded in peak speeds (the mistake far too many people make when using handheld GPS for top speed is to look at the peak which can record a spike)...
However a GPS unit used to average a speed (not just using individual observations) is highly accurate (and this is the display you see when it is reading out in the "speed" setting rather than the "peak speed" setting...
I am a surveyor by trade and use the stuff every day...We use survey grade equipment (errors measured in mm's vs the feet of recreational units) and still see spikes in speed measurements...
But they are correct...your speedo will always read higher than actual speed...You will usually see it be fairly accurate up though posted speed limits (70mph) but the error will grow substantially after that...
#43
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When i was cruising around at night on dry clear road i hit 151 then i had to slow down due to the turn but the car feels so smoth at that speed. Also i notice that you cant set your cruise control if you going more then 95 it wont let you.
#45
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So I guess Black Betty's avatar is a shot of "his friend's" speedo at 149mph.....
Not sure if this is relevant but GPS does take 3 satellites to triangulate a position. There are errors associated with that calculation: user range error and a type of dilution of precision (often times GDOP, geometric dilution of precision). There could be geographic errors as well, for example, if your car is in a deep canyon, but we don't really run into that scenario often. So in terms of positioning for civilian usage, there is some degree of error. I'm not familiar with how the GPS receivers calculate for ground speed but if it relies on the satellites constellation, then it's definitely not perfect.
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Not sure if this is relevant but GPS does take 3 satellites to triangulate a position. There are errors associated with that calculation: user range error and a type of dilution of precision (often times GDOP, geometric dilution of precision). There could be geographic errors as well, for example, if your car is in a deep canyon, but we don't really run into that scenario often. So in terms of positioning for civilian usage, there is some degree of error. I'm not familiar with how the GPS receivers calculate for ground speed but if it relies on the satellites constellation, then it's definitely not perfect.
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Last edited by ucla bruin; 04-01-2008 at 01:18 AM.