Using some sort of device to get actual MPH readings? - Page 2 - PeachParts Mercedes-Benz Forum

phantoms · #16 10-27-2004, 10:13 PM

You might consider a Gtech performance meter. It will tell you much more than mph.

http://www.gtechpro.com/

MTUpower · #17 10-27-2004, 10:26 PM

Even the cheapest handheld GPS units are very accurate, and they will update within a second if you have multiple satelites to pull data from. The SOG (speed over ground) can be averaged to whatever you would like basically- every second, every three seconds, every 10 seconds. every minute-etc. I have a unit that hooks up to my laptop that has a chart plotting program which allow me to pinpoint my position on a e-chart to within a few feet while underway in the ocean. I passed on the map feature- roads have road signs- but the ocean doesn't. I changed my '80 wagon to 15 inch rims and lower profile tires and the speedo read 79.6 and the GPS 80.

tangofox007 · #18 10-27-2004, 10:29 PM

A good GPS will update the speed faster than your speedometer. It will also show minor changes that would be impossible to see on the speedometer. Using GPS will be beat any other method hands down.

tenknots · #19 10-28-2004, 07:39 AM

At the speeds we're talking about, a GPS is very accurate and typically updates more than every second. WAAS GPS's are accurate to within 1-2 meters, so any variations in accuracy are quickly averaged out.

They're not perfect though. Before WAAS, I had a GPS with me as I sailed south along the Mexican coast. For three hours, the GPS said I was travelling at 250 knots at an altitude of 25,000 feet. I kept the track to show my buddies. In that vein, I would assume if you kept a running of your movement and was ever pulled over for speeding (but weren't), you'd have pretty good evidence to back yourself up. Don't know if that's been tried in court yet or not.

Alan Hamm · #20 10-28-2004, 11:24 AM

I use a GPS all the time on trips. Mine is about 4 years old and does not use WAAS. But the speed update is almost instantaneous. You can watch it accelerate right along with your speedo.

Anyone ever tried taking a GPS to court to challange a speeding ticket? I got a ticket a couple year ago and I was sure he was wrong but it was not worth it to fight it. Figured in the future if I had a GPS unit along I could download raw data into my computer and find a way to calculate the speed at any stretch of road. Might present an interesting case.

boneheaddoctor · #21 10-28-2004, 11:30 AM

Quote:

Originally Posted by Alan Hamm

I use a GPS all the time on trips. Mine is about 4 years old and does not use WAAS. But the speed update is almost instantaneous. You can watch it accelerate right along with your speedo.

Anyone ever tried taking a GPS to court to challange a speeding ticket? I got a ticket a couple year ago and I was sure he was wrong but it was not worth it to fight it. Figured in the future if I had a GPS unit along I could download raw data into my computer and find a way to calculate the speed at any stretch of road. Might present an interesting case.

thats interesting idea, problem is it would incriminate you at times the cop didn't flag you. Besides most of the kangaroo courts I've been to are more interesting in bringing in revenue than dispensing justice.

Alan Hamm · #22 10-28-2004, 11:53 AM

Quote:

Originally Posted by boneheaddoctor

thats interesting idea, problem is it would incriminate you at times the cop didn't flag you. Besides most of the kangaroo courts I've been to are more interesting in bringing in revenue than dispensing justice.

Yea, but even the threat of having some technical data to challenge their "calibration" might cause the officer to be busy that day and not show up. Last ticket I got I asked the officer to show me his readout of my speed. He said he could not do that. This in itself pissed me off. He had nothing to prove that the number he wrote on a piece of paper was based on anything.

But don't get me started. This was 18 months ago and I still feel my Blood pressure rising.

boneheaddoctor · #23 10-28-2004, 12:19 PM

Quote:

Originally Posted by phantoms

You might consider a Gtech performance meter. It will tell you much more than mph.

http://www.gtechpro.com/

oooooooooooooo, that way you can have bragging rights to 18 second zero to 60 time......

true, it gives you all that other fun stuff to let you know just how slow the car really is.

H-townbenzoboy · #24 10-28-2004, 12:53 PM

Wal-Mart has the Garmin GPS for $88.76! Now I don't need to know the exact 0-60 time with that expensive $200 gizmo, if anyone asks me, my answer is... SLOW!
-Joe

dmorrison · #25 10-28-2004, 01:13 PM

I would use the mile marker method. Do 60MPH and it shoudl take 60seconds to drive 1 mile. Adjust your speed to make the time between mile markers exactly 60 seconds. That is 60MPH on your speedometer. Of course figure it over a couple of markers.

WAAS GPS. Yes the GPS units are very accurate. Speed update displays are based on the software running the unit. Each unit will have its own criteria unless its meeting an FAA certification requirement. Then it is specified.

Understand that GPS is only as good as the number of satellites that the unit is recieving. The more satellites the better the data. The system now is very accurate. During the gulf war of 1990 the DOD eliminated the Selective Availability (SA) program. whick reduced its accuracy. They chose to keep the "system" turned off after the war. So the accuracy is very good.

The WAAS system is based on your unit recieving an update signal from one of the 25 ground based units thoughout the US. If you do not recieve the signal the acuracy is reduced.

The aviation industry will use the ground based update system to fly all our instrument approaches in the future. Some pretty neat and scarry stuff. Airliners will be able to shoot CAT IIIa approaches, IE you dont' see the runway when the aircraft touches down, based on a few satellites at 22,500 miles away and a ground based correction unit. The system is supposed to provide 6 inch accuracy.

Dave