Speedometer 9% fast Odometer 9% too far

[whywhyzed]

My GPS says 91 km/h, speedo is reading 100 km/h
So, I know now why I haven't got any speeding tickets...

Dealer service advisor gave me some b/s line that the GPS is not accurate in a car due to the metal of the vehicle..... (he's an old guy, must think GPS is a compass)...

Is there any way the guy ISN'T blowing smoke out his hole?

I want them to extend my warranty.... I bought a car with 100K bumper to bumper, not 91K.
Car is at 62K now.

Explains why this car appears to be getting better gas mileage than the last one I had (identical design of car with same engine)

 

[JB]

Re: Speedometer 9% fast Odometer 9% too far

Since I started using GPS I haven't had a vehicle that the speedo was accurate at all speeds.

The problem is that most speedos are analog devices and nonlinear. If you check, you will probably find some speed at which it agrees with the GPS.

At 61mph (GPS) my speedo reads 63mph and at 70mph (GPS) the speedo reads 74.5mph. When the speedo reads 120mph the GPS says 112mph.

GPS is digital, linear and more accurate than any mechanical analog device.

 

[whywhyzed]

Re: Speedometer 9% fast Odometer 9% too far

Do you think we're uncovering a conspiracy here?

I can think of 4 reasons auto manufacturers calibrate speedos to the fast side.

1. Customer drives car out of warranty sooner.
2. Customer figures out gas mileage and is impressed.
3. Customer thinks the car accellerates faster than it does.
4. Customer drives car slower and it's less "abusive" to the vehicle.

 

[tommays]

Re: Speedometer 9% fast Odometer 9% too far

I believe most modern cars can have adjustments made from the speed sensor (its nessary for different size tires)to get the speed correct


Tommays

 

[JB]

Re: Speedometer 9% fast Odometer 9% too far

Yes. Speedometers can be calibrated, but only for a certain speed. Above and below that speed they may be inaccurate.

I think police vehicles are calibrated at 65mph.

 

[Pony]

Re: Speedometer 9% fast Odometer 9% too far

I don't think there is any conspiracy theory 8). At highway speeds mine is off by 3-4mph vs gps. Like JB said its calibrated at a certain speed, and varies by a bit slower or faster than that................

At least it keeps my lead foot a little lighter in my head.

 

[Vlad D Impeller]

Re: Speedometer 9% fast Odometer 9% too far

Do you think we're uncovering a conspiracy here?

I can think of 4 reasons auto manufacturers calibrate speedos to the fast side.

1. Customer drives car out of warranty sooner.
2. Customer figures out gas mileage and is impressed.
3. Customer thinks the car accellerates faster than it does.
4. Customer drives car slower and it's less "abusive" to the vehicle.

Perhaps one ought to inform Oliver Stone.d

 

[ZmOz]

Re: Speedometer 9% fast Odometer 9% too far

The speedometer in my Jeep was about 5mph fast when I got it with stock size tires...now that I put bigger tires on it, it seems to be within 1/2mph at all speeds...at least up to 85 where my needle stops.d

It's weird, my old Jeep was a few years older but almost exactly the same. It's speedo was about 3mph slow with the same size tires.

 

[jimr]

Re: Speedometer 9% fast Odometer 9% too far

Yes. Speedometers can be calibrated, but only for a certain speed. Above and below that speed they may be inaccurate.

I think police vehicles are calibrated at 65mph.

On Crown Victoria Police Interceptor the speedo is calibrated up to 140 mph. +/- very little but.....if you check them with radar they are still a little off.

 

[whywhyzed]

Re: Speedometer 9% fast Odometer 9% too far

Does anyone have any knowledge of whether the metal car could legitimately throw off the GPS instrument?

I have the original factory tires on the car. The 9% is across the board. 9% off at 20 km/h, 9% at 40k, 9% at 100k.

It looks to me like a great way to reduce the bottom line on warranty costs. Anyone EVER seen one that read slow???? Anyone have one that doesn't read fast?

It's a safety concern as far as I'm concerned. I frequently drive the busiest highway corridor in North America in this car. If you don't go 115 in the 100 zone it can be dangerous. It's tough psychologically to look down at the speedo and crank it to 123 or 125 in the slow lane.

 

[Bob_VT]

Re: Speedometer 9% fast Odometer 9% too far

Nothing throws off a gps signal except loss of satellite contact. As far as metal doing it it is semi right, it will block a signel however it is reading the signals through the glass.

I can see why you are so upset....9% is alot. I would get a consumer advocate involved and have the car tested by a police laser radar gun. Of course the only thing this will accomplish in the end is a 9% extension on your warranty.

I would contact the car's manufacturer, consumer advocates, lawyers just raise some typical hell.

 

[funpilot]

Re: Speedometer 9% fast Odometer 9% too far

As long as the GPS reports that it is receiving enough satelites, and especially with WAAS I would hang my trust on the GPS. Unfortunately, while you can verify that your car is reading incorrectly now, you can't verify that it has been incorrect for its entire use.

My TrailBlazer reads abut 1 mph low up and down the range, compared to my GPS. With more conventional (read older) cars, you can have speedometers recalibrated. Often we find that odometers read right, and the dial is off, then a cleaning and adjustment is made. If the rear end is changed or tires drastically changed some guys will have a compensating gear made for the end of the cable.

Some additional info can be had at gaugeguys.com. I use them frequently for my auto restoration fun.

fp

 

[ZmOz]

Re: Speedometer 9% fast Odometer 9% too far

Often we find that odometers read right, and the dial is off

That's what my Jeep did too...the speedometer was slow but the odometer agreed with my GPS. Now that I have bigger tires and the speedo is accurate it's probably the other way around, but I haven't checked.

 

[PuddleJumper]

Re: Speedometer 9% fast Odometer 9% too far

Had same issue with 2002 Sienna. Speedometer 60 mph gps 56.5 mph Was told by factory rep that us gov't allows 5% variation in spec.
OBTW my odometer checked spot on with the gps.
Go figure.)

 

[bjcsc]

Re: Speedometer 9% fast Odometer 9% too far

Isn't there also a number of years stated in the warranty? Only car manufacturer I know of with a 100K warranty is Hyundai, and it is advertised as 10yr/100k warranty. Average driving (15K/yr) would make your issue work in your favor. Right?

Not to mention, if it is a Hyundai, they are basic cars. Designed to get from a to b. There have been a lot of adjectives used to describe their cars over the years and "precision engineered" is not among them. (and there's nothing wrong with that, my point is to have realistic expectations)

edit: I don't know what I was thinking. Certainly it is whatever comes first. I wouldn't worry about it. Most of what those warranties cover probably won't apply if and when you have a problem anyway...

 

[DJ]

Re: Speedometer 9% fast Odometer 9% too far

GPS is far more accurate than ANY police radar.

You say the tires are the original size. Are thjey the originals? I doubt it, at your distance. If they are, they are more than 9% worn.

Remember, as your tires wear, your wheels spin faster.

 

[JasonJ]

Re: Speedometer 9% fast Odometer 9% too far

"GPS is far more accurate than ANY police radar."

No its not, but that's a nice try..

One thing to remember too is the amount of air in the tire. On my Ford, I can change the speedo calibration through the ecm. I aired my tires to the appropriate amount, drove the truck to heat the tires and get the air to expand, and measured from the axle centerline to the ground. Using this, I entered the true tire diameter into the ecm, and my speeds are spot on, as measured with police radar, and gps. improper tire inflation can affect accuracy, but not 9%. That is pretty bad. I think boat pitot systems work better than that...

BTW, the only way the radar is inacurate is if it isn't used properly of there is a problem with the unit. At the beginning of shift, the unit is self-tested, and the radar calibration is confirmed with two tuning forks set at different speeds. You tap the tuning fork and hold it in front of the gun, and it reads the "speed" of the fork. Then, if you issue a speeding ticket, you retest the unit again with the self test and the tuning forks, to confirm the system is still functioning properly. If a gun says you are going a certain speed, you are going that speed, plain and simple.

 

[puddle jumper]

Re: Speedometer 9% fast Odometer 9% too far

If im right you can check you speedo on the highway the same way the aircraft patrol does.You will see the white line across the highway and it should be 10 seconds to the next line at the correct speed limet.Depending on your tires i think there is a 7 mile anhour difrence form new to worn out.Becouse of this the police will let you get away being a little over the speed limet.
PS not like i never speed.

 

[ZmOz]

Re: Speedometer 9% fast Odometer 9% too far

If a gun says you are going a certain speed, you are going that speed, plain and simple.

That is completely false. Proper calibration is just a small part of making sure a radar reading is accurate. There are many, many reasons why a radar gun being operated by a competent officer could be totally wrong.

http://www.ibiblio.org/rdu/a-btrust.html
http://www.radarbusters.com/support/choosing-detector/mistakes.asp

It is estimated that over 25% of all radar tickets are in error.

Search google for "police radar accuracy" and you'll find about a billion different pages describing exactly how inaccurate they are...

 

[JB]

Re: Speedometer 9% fast Odometer 9% too far

Even if you were correct about a stationary radar (which you are not), Jason, there are several additional reasons why a measurement from a moving cruiser may be off by as much as 10%.

I ditto what DJohns said: GPS is more far accurate than any police RADAR.

Just one: What happens to a tuning fork when the temperature changes?