I recently replaced my 16 inch stock wheels for HHR SS 18 inch wheels, great mod but my reading is now off.

I'm thinking 5+ MPH increase over what is actually showing on the odometer,
I personaly think it's because the HHR SS have wheel sensors inside each wheel and my HHR 2009 Panel doesn't.

Any sugestions.

 

Your speedo reading is off because ya changed tire sizes. Here is a handy-dandy tire size comparsion.

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

Hope this will help ya out...

Mo

 

thanks for your help, I will concider to add the odometer mod in my tune.

 

They can reflash the computer at the dealer to have it fixed. I'm thinking of having it done to mine since I just went from 16" wheels to 17"s. The dealer said anywhere from $25-50 depending on the car and what's involved on that model.

 

Your 09 Panel has to have TPMS in the rims.. It comes stock that way & the DIC will show you this.
Anyway plug your old tire size into this link, vs the new tire size & it will show you the speed-O difference at any MPH, & tire differences in precise amounts.

http://www.discounttire.com/dtcs/infoTireMath.dos

 

It will be off a little. That is why I use 215-60-16 Assurance tires in the winter. The 60's were off only 3 Revs per mile so I am almost spot on with my speedo. The 55's would be a little shorter and would read fast.

 

great info, thanks

 

If you went from a 215/55R16 to a 225/45R18 your speedo should be about 1.6 mph too slow @ 60.

Since I also went that route, I can vouch for that differance with my GPS.

 

But how do you know your GPS is right? My speedo and GPS are now right on, but the miles on the GPS and the odometer are off. And, the GPS is off 1mph in all of our cars.

 

I'd trust the GPS over any speedo anyday. Mine actually showed dead on with my GPS with the 224/40R18's I had on before, and they were indeed shorter than the 215/55R16's stock, so the speedo should have shown fast. Speedometers calibrations are just like any other guages, rarely dead on.