Speedometer Error, Way Off Options

[Neanderthal]

After purchasing a Garmin and putting the stock tire size back on, I discovered what appears to be a very big speedo error.
I'd been running 195.65.15 tires for a while, replacing the stock 195.60.15 Eagle LS.
I bought some wheels a few weeks ago, and re-installed the stock-size Altimax HP, and at 70 the speedo was showing a 5 MPH slow speed vs. the Garmin. When the speedo shows 75, the Garmin shows 70.

Is this error typical in the Elantras?

[Bobzilla]

iT'S common with ALL Asian automakers. Honda's are typically 3-4mph slower than their speedos show on average at 60mph.

[fuelrat]

Yup, like Bob said, the speedo difference is pretty common.

With the Elantra and 215/45/R17 wheels/tires I show a difference of -4mph @ 70mph.
Eg. Dash reads 70mph and Garmin reads 66mph.

[Vampyrate]

yep its a safety thing so you cant say that your speedo was way off when pulled over. Last ticket I got my speedo said I was doing 90 but I was clocked at 85 and the officer told me that is normal. 10 mph or more and then i would look into getting it calibrated

[Bobzilla]

I tried to find the bulletin (but failed) but hondar's +/- for speedo errors is 6%. that is a big number.

[Neanderthal]

Thanks for the replies.
When I put on the 65 profile tires, I was adjusting 3% for tire height/RPM. Looks like I didn't adjust enough. Is the odo off like this too? That could make your warranty expire a few hundred miles early.

[Vampyrate]

6% is a huge number when it comes to speed, but for them I guess they think that is acceptable. To me, that is not anywhere near acceptable. Personally, I would like to see a calibration between 0-3%. I think the speedo runs off of the speed of the tires spinning while a GPS uses the actual velocity of the car in relation to the satellite, which is similar to what radars use to catch speeders. With this system in place for so long, it surprises me that more people don't make more of a hullabaloo about this to manufacturers about their speed being incorrect and the method to measure their velocity is near impossible to accurately judge without computer assistance to correct the speedo readout through some mathematical equation.

[cobas]

Are you sure the GPS unit has the right tire size plugged in for its calculation? I'm sure it's under Settings somewhere.



...


I'm in a strange mood.

[Vampyrate]

Lol, I didn't know you could put tire size into a GPS, I just thought that it was something with the velocity of the car in relation to the satellite location. You know, triangulation of actual position in relation to the destination as calculated by the distance from the satellite.

[Blupupher]

GPS does not need tire size .

And yes, the speedometer being off causes the odometer to be off. So a 100,000 mile warranty is more like 95,000 miles.

My Elantra is pretty close (Speedo reads 65 mph, GPS is 63-64 mph), my wife's van is a little worse, 65 mph on speedo, 61-62 mph on GPS.

[only1db]

i havent tested with a gps unit but i know that when i had the 215/45's and going past the same radar machine i read 80mph and 80mph but now with the 210/40's my speedo says 80mph and the machine says 75mph....but techincally the 40 is a tick small for the XD

[Neanderthal]

This is the kind of thing that could create trouble with outfits like DoT, NHTSA or other fed auto-industry regulators.

If the odo is off, the official MPG rating is off by 5% or so. Which could create problems with the CAFE ratings. And defrauding people out of 5% of their warranty is, well, fraud.

From checking RPMs at Tire Rack, it looks like a 215.60.15 would get me pretty close to accurate on the speedo. I'm currently running 205.60.15 snows, which are about to be changed out because they suck (Firestone Winterforce--swapping for Blizzak W60s) and the tire place said they'd take them back, and there aren't any clearance issues with those.

Youse guys think 215.60.15 would fit with no problemo?