Evening people, I had the joy of some open road today, and had it up to 125MPH (on the speedo) Yet my GPS (NOT a built in model, it's a tom tom) said 133MPH. Now at 50MPH they both read within 2MPH of eachother, and at 75MPH (speedo) the GPS says 81MPH. Not sure how accurate the GPS is, BUT should i do a re calibrate (and how) or which to trust?

Bump I'd like to know about this too

I would typically say the GPS is right. Just need to make sure you're exact on the lower speeds because when you're comparing. 60mph is usually the standard comparison point (and can also be calibrated with mile markers to verify odometer as well. The numbers you're posting seem to be a little weird because usually if it's off 4% at 50mph it will be off about the same, it just seems worse at higher speeds. So at 125mph you're reading about 5% slow but at 75mph it's about 7% slow. 50mph is abotu 4% although you didn't say which way.

The GPS is more accurate. Cars are typically calibrated so the speedometer reads a little higher than the actual speed you are traveling. For instance, when I'm crusing at 70 mph on the speedo my gps usually reads 67-68. This is the case on all the vehicles I've owned with the exception of my Jeep that has 33's.

P.S. How on earth did you get to 133 mph on a Pathfinder?!?

I had this problem when I got my garmin. Its the tire size on you PF. from the factory Nissan sets the speedo for 265/75R16 for the Offroad se. but with the normal S, SE, LE our tires are 1/4-1/2 smaller allowing them to turn faster that shows 3-5mph diference. To change this you need to go to a larger tire. For me I had to put on 265/70R17,

I've actually never checked mine to my GPS. I'll take a look tonight on the way home. I'm running the 265/65-17.

skinny2 wrote:I would typically say the GPS is right. Just need to make sure you're exact on the lower speeds because when you're comparing. 60mph is usually the standard comparison point (and can also be calibrated with mile markers to verify odometer as well. The numbers you're posting seem to be a little weird because usually if it's off 4% at 50mph it will be off about the same, it just seems worse at higher speeds. So at 125mph you're reading about 5% slow but at 75mph it's about 7% slow. 50mph is abotu 4% although you didn't say which way.

That's exactly why i was so puzzled. Could it be possible the GPS didn't re calculate my exact speed fast enough, so it was showing how fast i WAS going as opposed to Current speed?

deermjd wrote:The GPS is more accurate. Cars are typically calibrated so the speedometer reads a little higher than the actual speed you are traveling. For instance, when I'm crusing at 70 mph on the speedo my gps usually reads 67-68. This is the case on all the vehicles I've owned with the exception of my Jeep that has 33's.

P.S. How on earth did you get to 133 mph on a Pathfinder?!?

Basically i had great room to get a run going up a hill, and down the other side is were i got that fast. The truck actually amazed me, Little to no steering wheel shake, and was quite stable

You are much braver than I. I don't think it would even hit that speed if you pushed it off a cliff.

Checked mine against the GPS on the way home and it's what I would expect. Speedo is 2mph slower all the way to 80mph. I didn't go further as there are horrendous winds, wet roads, and blowing snow. Not ideal for a 100+mph run

We've been having 40-50mph winds, which were conveniently a headwind for me this morning. Power was no problem but my mileage was HORRIBLE. I was watching the instant mpg and at 75mph it wouldn't go above 20mpg going DOWN hill, about 16mpg on flat, and under 10mpg up hill. Averaged 16mpg going in this morning, but average pushed up to 18mpg after the return trip. Usually average 20-21mpg round trip.

skinny2 wrote:Checked mine against the GPS on the way home and it's what I would expect. Speedo is 2mph slower all the way to 80mph. I didn't go further as there are horrendous winds, wet roads, and blowing snow. Not ideal for a 100+mph run

We've been having 40-50mph winds, which were conveniently a headwind for me this morning. Power was no problem but my mileage was HORRIBLE. I was watching the instant mpg and at 75mph it wouldn't go above 20mpg going DOWN hill, about 16mpg on flat, and under 10mpg up hill. Averaged 16mpg going in this morning, but average pushed up to 18mpg after the return trip. Usually average 20-21mpg round trip.

Damn... Pretty soon the oil companies are going to be investing in companies that make giant fans

deermjd wrote:You are much braver than I. I don't think it would even hit that speed if you pushed it off a cliff.

it was new years day (well nighttime but NYD) the roads were literally EMPTY, and i didn't hold it theres, that's the point were i hit an aerodynamic brick wall/got cold feet

UH OH... I think i may have made a big mistake by pushing the truck that far. Well more the tires than the truck. AFAIK All terrain TA's have either an R or an S rating. R is 106MPH S is 112MPH. Are those Speed ratings pretty accurate about when the tire will blowout? If they are fairly accurate then wow... What a dumbass I am for not checking first.

Well obviously they don't just blow at 112 or you wouldn't be here to write this Tirerack.com has a decent explanation of how they come up with the rating. My guess is that most tires can easily exceed that rating for a certain period of time....but I wouldn't want to do it for very long and find out.

I'm sure theres some margin in those speed ratings but I wouldn't push that far again.