Tire size speedometer issue

Hi,

My 2013 TDI Passat came with all season tires 215 60 r 16. 2 years ago I bought used rims/tires 215 55 r 17 from another Passat TDI owner. Ever since my speedometer has been over indicating my speed by about 10%. The faster I go the wider the gap. For instance, If I am travelling at approx 120 kms h my Speedometer indicates 135 kms h.

I am about to buy new all season tires for these 17 rims. I used an online tire calculator and th difference with the speedometer should be about 0.06% between these 2 rim/tire sets. Any idea why the gap 10% speed when I switched rims tires 17 size?

Looks like you get 795 revs/mile from the stock tire size. With the 17" tires you have listed then give you 790 revs/mile

The difference is 0.58% So you speedo will read 61.77 mph when your car is actually moving at 60 mph.

I am trying to find the new tire that is close to my stock settings and it is very challenging to get one that is close to stock.

In am going from 16" to 19"!

Hope this helps.

Most clusters you can adjust the speedo through adaptations. Not sure about Passat NMS, never tried one.

actual tire sizes fluctuate as well. Those two tires might be much farther apart in dimensions than their sidewall sizes indicate.

This is very apparent with high performance tires and their listed tread width. You stack a set of two different brands, but the same sidewall listed size and one will be considerably taller than the other.

That might be accounting for the greater difference as well

VW's also over estimate the speed greatly compared to other companies. Most indicate at least 5% above actual when comparing speedo speed to GPS for example. So 5% is normal. Your 10% seems a little out of whack though.

Wingnut said:

VW's also over estimate the speed greatly compared to other companies.

Click to expand...

My BMW speedometer is more optimistic than my VWs. Has stock diameter tires.

Uberhare said:

Most clusters you can adjust the speedo through adaptations. Not sure about Passat NMS, never tried one.

Click to expand...

I adjusted my Passat and Golf through adaptations. Instructions are in the forum but you need a Vagcom.

It bothered me that my GPS and traffic app showed a different speed than the speedometer.

My understanding is that if you change via adaptations your odometer won't be correct.

If you want to find out the real difference between different brand and model of tires then you need to get the manufacturer's data sheet and compare the actual OD of each brand/model tire. THEN you can accurately figure out the difference between them. Also, as the tire wears, the OD changes so make sure to include that into your calculations too when comparing old and new tires.

On my former 2002 Jetta I went from the stock 195 to 205 tires. The speedo now read the same as my GPS.
Did the same last year when I junked the crappy Passat Hankook tires, up one tire size.

I think it also changes the odometer reading, but who cares! Maybe if you're leasing and have a kilometer limit.