speedometer calibration

[cosmo]

I bought a 1998 NB and the speedo is off a bit. i am running 205/55-16 on it which i am positive is the stock size. made sure the tire pressures are all at 35 psi. set the needle at 70 mph. and verified by tom tom and Garmin the car was only doing 67 mph. now when i had my 2005 mustang i used a diablosport predator to change the revolutions per mile thru the obdII. do they make a tool to do this for NB or not should i just get larger tires? does anyone else have this problem running stock size and being off by 2-3 mph?

[raff]

My speedo is off by the same amount -- after awhile you automatically adjust your speed accordingly.

Almost forgot -- Welcome to the org and when you get a chance post some pictures of your NB.

[FarrisK]

Mine did the same thing. It was off by the same amount at lower speeds, too (35 mph indicated meant ~31 to 32 actual)

[Yello_jellybean]

Mine is off also. I am not sure if that excuse would get me out of a speeding ticket though. I am betting I would have better luck batting my eyelashes and pointing to my firefighter sticker. (kidding- for the record I have NEVER played that card)

[DZLBUG]

205/55/16 is stock size. The speedo error is normal. VW has done this on purpose for some reason, probably to avoid litigation due to incorrect speedometer readings. If they're going to be wrong...might as well be wrong on the safe side.

You can calibrate it via VCDS, but then your odometer will be off as it is calibrated correctly. Best just to live with it and adjust your speed accordingly. I'm surprised it was only that much...some have found them to be as much as 6-7% off where yours is slightly less than 5% off. Some of that difference can be in GPS units as well...and they aren't completely accurate for speed anyways.

Note that the error is proportional. So at 30 indicated you're going about 28.5, 60 indicated = ~57 and so on.

[cosmo]

thank you for the quick response. i will try to get some pictures up here at least one in the signature.

[Ol' Timer]

Originally Posted by DZLBUG

The speedo error is normal.

Right. About the ONLY car(s) you will find that have the correct speed readouts, are the guys that stop you for exceeding the legal known speed limits. Their speedometers are always "Certified" to be accurate.

[Fowvay]

It is supposed to be off exactly 4mph from 30mph through the end of the range.

Some show 5mph some show 3mph there is enough variance in actual tire size and wear that a built in cushion helps protect Volkswagen and it's owners. If you set it to exactly 60mph at 60mph with let's say an RSA and then you switched to brand X which has a slightly smaller diameter and then put on 40,000 miles. You could actually be doing 63 or 64 mph by the end of the tire's life cycle.. better safe than sorry I say.

I've just gotten into the habit of setting the cruise 4mph over the speed limit or must times 9mph over and still be with in a safe margin of not being pulled by the law.

[Scorpius]

I seem to have the opposite problem then listed, I was driving home my New (used) 2000 New Beetle GLS when I noticed I was passing drivers like crazy on the interstate, check and was going 70 MPH. Then next day I hooked up my TOMTOM GPS and sure enough @ 70 I wsa going 80 MPH, testing this it seems its always 10 MPH more then what the Speedo is reporting, until you get in the 30's then its about 5 off.... I would not mind actually going slower then recorded, but faster and that much faster is a problem, we plan to give this car to outr daughter in a year or so, and would like to see it more accurate then it is now.... Any guidance to calibrating it closer???

[D2Beetle]

IMO this seems "picky", don't you think? As long as you can go, legally from Point A to Point B on time and in a nice NB ride at a decent speed, does it really matter if your speedometer reads +/- 5 mph off.

[lkchris]

Yes, it's pretty much a German (probably EU by now) legal requirement for speedos to be calibrated in this fashion. Manufacturer must essentially guarantee the speedo will never read slow, and this can be a problem because not all brands/models of tires marked with the same size are actually the same size.

[FarrisK]

Originally Posted by Scorpius

I seem to have the opposite problem then listed, I was driving home my New (used) 2000 New Beetle GLS when I noticed I was passing drivers like crazy on the interstate, check and was going 70 MPH. Then next day I hooked up my TOMTOM GPS and sure enough @ 70 I wsa going 80 MPH, testing this it seems its always 10 MPH more then what the Speedo is reporting, until you get in the 30's then its about 5 off.... I would not mind actually going slower then recorded, but faster and that much faster is a problem, we plan to give this car to outr daughter in a year or so, and would like to see it more accurate then it is now.... Any guidance to calibrating it closer???

What size tires do you have on the car? My guess is that they are incorrect.

[Fowvay]

If the amount is off by an exact number and not a percentage then it sounds a lot like the needle has been removed from the face and put back in the wrong position. When I installed an led I had to remove the needles and accidently put them back in the wrong position. It took seemingly forever with me fiddling with the ignition on/off and repositioning the needle to get them exactly right.

[SMG]

Originally Posted by Fowvay

It is supposed to be off exactly 4mph from 30mph through the end of the range.

Some show 5mph some show 3mph there is enough variance in actual tire size and wear that a built in cushion helps protect Volkswagen and it's owners. If you set it to exactly 60mph at 60mph with let's say an RSA and then you switched to brand X which has a slightly smaller diameter and then put on 40,000 miles. You could actually be showing 63 or 64 mph by the end of the tire's life cycle.. better safe than sorry I say.

I've just gotten into the habit of setting the cruise 4mph over the speed limit or must times 9mph over and still be with in a safe margin of not being pulled by the law.

Incorrect actually... The smaller the tire wears the higher the indicated speed will be. A smaller tire would turn more times per mile and indicate a higher speed. Hypothetically if a 205-55-16 read dead-on 60MPH on the speedo, the same car running a 205-50-16 would actually only be travelling 58MPH when the speedo indicates 60.

[Benderbeetle Rodrigues]

Check out this link, that includes revs per mile and spedo error.
Tire size calculator

Cheers.

[Duffy]

I have been told that most manufactures calibrate the speedo 3 mph over actual speed. This is intended to keep the actual speed down and avoid a ticket.

[dmbluebeetle]

Originally Posted by Benderbeetle Rodrigues

Check out this link, that includes revs per mile and spedo error.
Tire size calculator

Cheers.

Nice find

This should be used by those who wish to change rim and tire sizes. then you can see what will happen before you do anything.

[Scorpius]

Originally Posted by FarrisK

What size tires do you have on the car? My guess is that they are incorrect.

205/55-16 and they are fairly new. I did notice today that @ 30mph on the speedo I was going 35-37 MPH, and after 40-45 on the speedo it jumped to 8-10 MPH over, 10 mph over seems to be the constant.

I might try to move the needle as suggested or take it to a dealer and see if they can calibrate it... at 10 MPH over I do not want my daughter or wife to jump in and get a ticket, not remember to drive 45 when speedlimit is 55 MPH.

on another note I also notice the odometer is slow by .8 or so then my GPS, my trailblazer was right on both speed and mileage with the GPS, would the speed being slower on the speedo then reported effect my odometer, I thought I read these are separate.

[Scorpius]

Originally Posted by D2Beetle

IMO this seems "picky", don't you think? As long as you can go, legally from Point A to Point B on time and in a nice NB ride, who cares how fast or slow you are going.

UMMMM. Johnny Law might care, if I'm driving 60 in a 55 and I'm actually doing 70 in a 55, can you say Ticket, increased insurance rates, etc....

[SMG]

Scorpius: The speedo error is built in so the car is ALWAYS travelling slower than the speedo indicates as long as you're not running oversized tires. No worries about a ticket as long as you and your family obey the speed limits.