Hey guys. I have a 2010 Harley Davidson model and I upgraded my tires from 275/45r22 to 285/45r22. I took it to the dealer to get the speedometer calibrated. Well its still reading 8 mph fast and they told me they can't get it any closer... Any ideas on what to do?

 

Try different shop. With something so simple this shouldn't be an issue.

 

Yeah its just strange that the dealer can't get it closer...

 

how are you checking your speed? gps is best, i usually set cruise on 40-50-60 and 70 and compare to my garmin. most speedometers read fast from the factory sowill think you are getting better mileage and get out of warranty quicker.

 

I don't understand how your getting out of warranty faster. If you drive 100 kilometres at 160kmh or 60kmh it's still 100 kilometres. ?

 

I use a gps to check it. I have no warranty on the truck anyways

 

Cause if you drive 100km but the speedo is reading fast and the truck thinks you went 110km...

You're now 10km closer to no warranty than you should be.

 

Im not a tire expert but isnt a 275 45r22 to 285 45r22 just a wider tire. I thought first number was width, wouldn't the tire still be same height since 45 hasnt changed nor the 22. Therefore your speedometer wouldnt change. I thought second number changing is what would through off speedometer.

 

As you can see the difference in tire height is like .01, its just a wider tire. Unless you ment to type in a different size tire then what you did. scroll down to 285 45 22, its just wider. I cant see .01 in height difference making you off by 8 mph.

 

The second number is a percentage of the width. In this instance....

275/45/22

275*.45 = 123.75mm height of sidewall or 4.872"

4.872*2 (have to count both sides of sidewall)+22"= 31.744"

Using the same math, a 285/45/22 is 32.01" tall

Just over 1/4" difference but it makes a difference on the ole' speedo and odometer.