VW Speedometer off by almost 10%

[max_boost]

I have a 2010 GTI and I matched the speedo to my GPS and it's close to 10%.

Now is it because I switched to 16" winters instead of the factory 18" wheels? I know there are a lot of VW guys on here so just wondering if you have the same issues and whether the dealer fixed it or not.

I did a google and was surprised to find that this is a rather common issue? I kind of figured it out after the first week of driving, the speeds just didn't feel right. LOL!

[spike98]

Mine is ok. Ive matched it to the GPS in my car. I believe you can use vag-com to adjust it.

[colinxx235]

what size tires are the 18's running vs the 16's ?

[soloracer]

Probably is your tire size causing a little part of the issue. However, your speedo is also most likely not correct either. I was issued a nice pink invitation from the mounties to attend a function at court one time for failing to honor a posted road sign. Long story short, had to get my speedo tested to see if it was off by 3%....it was off but the wrong way. So I had to buy the biggest sidewall tire possible and retest which gave the desired 3% result in my favor. The verdict was I had to go to Honda and get the speedo replaced. Turns out the factory only guarantees that they will be within 10%. I had to put a goofy sized tire to get the +3% to -3% swing (6% overall change). I doubt your tire change resulted in more than a minor change in speed accuracy.

[JordanAndrew]

my winter is off by about 3-5% versus normal stock size tire. I don't quite remember how much it is off by but around that number. 10% is quite a bit of a difference though.

You can use this tire size calculator to see if it helps.

http://www.miata.net/garage/tirecalc.html

That's how I know mine is off by a certain percentage.

Edit:

BTW, my winter is also 16's and my stock ones use to be 18's on my mazdaspeed3. I still use the same winter tires on my normal mazda3 but the stock on this is 17's.

[dj_rice]

Yes it is because of the size change, when changing from 18 to a 16" you should of chose a tire size that will be equal or close to the same as your 18" diameter I think is how to word it. When changing tires, its best to stay within 3% or lower. But yeah as stated, its just affecting your speedometer readings and fuel efficiency. So try getting wider rubber or bigger sidewall to match it up to 18" specs.

Heres a good calculator

http://www.1010tires.com/tiresizecalculator.asp

[benyl]

What is more important is the odometer. I know the BMW is about 8%+ off, but the odometer is dead on.

Manufacturers do this all the time. Ask anyone with a sport bike. Going 200 km/h on a sport bike is really on 175-180 km/h.

[Kloubek]

Originally posted by benyl
What is more important is the odometer. I know the BMW is about 8%+ off, but the odometer is dead on.

Really? I would have figured the speedo and odo would use the same measuring mechanisms... hence, both be out by the same ratio.

...the more you know...

[2002civic]

some models allow you to adjust your spedometer through the MFI, see if there is a winter tire setting on there...

[2EFNFAST]

I agree, could be the tires.

Also, some manufacturers up-rate the speedometer by +5% for legal reasons. (atleast in Europe - maybe they're getting lazy and doing that in north america?)

[soloracer]

One thing we haven't questioned is the validity of his GPS speed check. Does the GPS do instant reports like the speedo or is it averaged over a certain distance? (ie: do you need a steady state velocity for it to be accurate?)

[sloan]

I've been reading about this on the the VW forums. Seems to be "normal" from VW.

[max_boost]

Yeah my GPS is a bit slow in getting the speeds but I've used it in my 06WRX and it's bang on so I know the GTI is definitely off.

My stock tires are 225/40/18 and I know I switched to 16"wheels but they are OEM replica wheels with the proper alternate sizing for tires 205/55/16

I used that 1010 site and it says it should be "Speedometer Difference: 0.844% too fast" haha

This is the first time out of all the cars I've owned that I had this happen so I was a bit surprised.

[Aleks]

It's not the tires it's the VW speedo. It's a built in ticket preventer.

I had the same thing on my car. There should be an option in the MFD to adjust +5 and +10% IIRC. I never bothered to do this, just got used to it after a while.

[cocoabrova]

You could always sell the winter set and get 225/40R18 winters but yeah none of our customers seem to care about the speedo diff as 18" winters on their stock wheels are usually not a popular option

[picmerollin]

Originally posted by 2002civic
some models allow you to adjust your spedometer through the MFI, see if there is a winter tire setting on there...

gf's new jetta has this feature, + OR - 5% depending on if you upsize or downsize.

[max_boost]

Thanks gang!