Erroneous speed indicator?, Speed Indicator Options

[Maverick]

3km difference speed indicator

Hello, I have an 2009 Sedan Elantra, and was wondering if anyone experiened a 3km difference with the speed indicator. I plugged my GPS and noticed that there was a 3km difference with my car's indicator and what the GPS was indicating. I installed the GOS in my husband's Mazda 3 and it was dead on! If his indicator was showing 100km so was the GPS, or 110km so was the GPS there was absolutely no difference. My Elantra has an approximate 3 km difference. When I drive at 100km the GOS tells me that my speed ins 97km... and this happens all the time.

Did anyone hear of anything, did this happen to anyone. At this point I am wondering that if I drive 3km faster, then perhaps my odometer has a 3% higher mileage than it actually does, which then makes it harder to sell, and you reach your warranties faster then you should.

Looking forward to your discussions / opinion on this issue.

[a_v]

This is normal. Speedos aren't perfectly accurate, but they'll never give a reading less than your actual speed (unless you screw around with wheel sizes, that is). In Australia at least, the speedometer is allowed to be out by up to 10%.

[2001VE]

How accurate are $99 GPS units. I think the units pilots have are super accurate and some require background screening to purchase them for military reasons. There are some pilots on this site that could confirm that in US. I know Canada has some restrictions on them.

[streetfighterguy]

I have a 230 dollar gps that works very well and yes mine is showing a difference of about 3 mph on mine as well.

I am running 17's with 40 series tires so that doesn't help though.

[mtlelantra]

How accurate are $99 GPS units.

They're extremely accurate. Prior to 10 years ago US military required selective availability which doped accuracy so it was 30-100 meters off at best. This requirement was removed in 2000, so accuracy is generally less than 5 meters, and speed (for that of cars) is extremely accurate.

Yes, there are restrictions, but the restrictions are built into the GPS units- i.e. not supposed to operate at >10 miles off the ground and >500 meters/second. Good luck getting your car running at 500 meters/second = 1800 km/h = ~1120 mph i.e. the GPS programming is restricted to prevent registering that sort of speed. It's not that inaccuracies are being built into a GPS unit, it's that capabilites are restricted.

My 04 is off about 4%... so at lower speeds the difference is smaller (2 kph slower at 50, but 4 kph slower at 100)... I thought I heard there was a TSB for earlier years...

[Blupupher]

Yea, speedometers can be off up to 5% and not be considered an issue by auto makers.

3km/h is what, like 1.5 mph? My Elantra is off by 2 mph @ 65mph, my wife's van is almost 5 mph off at 65 (shows 65 on the gauge but 60-61 on GPS, but I do have different size tires that stock).

I niotice that the speedo thens to read higher than actual, which helps keep you from getting speeding tickets, yet actually makes your warranty run out sooner, since your actually traveleing fewer miles than what the speedo says (by maybe 3-4000 miles on the 100,000 miles warranty)

[Bobzilla]

^ 7% for Honda. No lie.

[Neanderthal]

3 KPH is IMO pretty accurate. Is this at all speeds or a particular speed?
Mine if off by about 5 MPH @ 80 MPH, it shows 75. I believe most makers put in some errror, on the shy side meaning it will indicate a slower than true speed.

http://www.elantraclub.com/forum/index.php?showtopic=27161

[natesi]

I don't think my speedo is off, although I'm not sure.

But I know my odometer is dead on -- checked it many times on the freeway -- at those official odometer check mile posts.


I thought I read somewhere that manufacturers intentionally make the spedo read higher but the odometer records mileage correctly.

[zirconx]

3 KPH is IMO pretty accurate. Is this at all speeds or a particular speed?
Mine if off by about 5 MPH @ 80 MPH, it shows 75. I believe most makers put in some errror, on the shy side meaning it will indicate a slower than true speed.

http://www.elantraclub.com/forum/index.php?showtopic=27161

My GM and Ford cars have always been dead on, according to my GPS. I think your mostly correct, most foreign car markers put in some error so it reads high. Not sure why, it might have to do with import regulations. I hate this problem, I'm always studying my speedo trying to calculate my actual speed on the highway. I've pretty much resorted to always using my GPS for a speedometer when traveling.

As others have mentioned, the ODO is accurate, so there is no reason they can't make the speedo accurate also, if they wanted to.

[zero10]

I tested the speedometer on my ET about 2 weeks after buying it. I found the speedometer is approximately 5-6% higher than my actual speed as verified with 2 different GPS units.

I test every car I have owned and have found the following (sorted by year of car not by order owned)
2010 Elantra Touring: 5-6% high
2008 Chrysler 300: exact
2005 Golf GLS TDI: 5% high
2002 Ford Focus ZTW: exact
2000 Chrysler Neon: exact

I also tested a couple of my relatives cars and found the following:
2003 Dodge Ram 1500: exact
2007 Mazda 3: 2-3% high

On all of the above cars I have been able to verify the odometers are accurate to within 1%, which is about as precise as I feel confident I can measure.

This post has been edited by zero10: Jan 18 2011, 05:30 PM

[Vampyrate]

So why has no once challenged this on court? I could see this as an easy win for those that can prove it.