GPS speed comparison with 285's

[BILLUA]

Just a quick note, I had Big O 285 A/T's put on yesterday to replace my stock Michelin 265's so I put the GPS in the truck to check it out. I have heard that even factory speedo's can have errors in them and am sorry I didn't put the GPS in before to compare.

At 50 mph indicated, GPS says 52. mph

At 80 mph indicated, GPS says 82. 5 mph



The error is almost identical to the percentage the new tires are to the old ones... .

That is so small that I don't have to worry about it



Always good to have hard data!!!

Bill

 

[bigbrassmonkey]

GPS measures speed as the crow flys, not speed over ground, so if you were going up a hill at 50 mph, the gps wouldnt have the data to make the correction,



it would be a longer distance to travel up a hill from point a to point b. Yet if you were air bourne the same point a-b distance would be shorter, a very small amount, but still shorter





Don't forget the Gov developed GPS for nautical navigation





JMO



Joe

 

[BILLUA]

u r correct sir

Joe, I use GPS as a airline pilot all the time..... U r Correct in the way that it calculates speed and distance. .

The error that was built into GPS signals to send out a degraded signal to civilian users was taken out 2 years ago due to the ever increasing use by said civilians. The Clinton administration had the error phased out Now potential accuracy for civilian users is plus or minus 3 meters...

I also did my testing on flat road, but if you would have to climb or descend a VERY steep hill to have the reading affect a speed calculation. .



Wow, all I was trying to do was give someone a general idea about what they might encounter switching to bigger tires...



Take care, Bill



P. S, Got a pic of the Night Train?

 

[MD500E]

I also have 285's . The truck came stock with 245's. I have used both a gps and those little trailers that the local cops park along side the road that tell your speed, to caculate the error in my spedo. truck reads 70, actual is closer to 75-76. At 35 actual is about 37-38. Just my observation.