6 cylinders. Big
AO Silver Member
Join Date: Jun 2009
Location: United Kingdom
County: West Midlands
Larger wheels = more accurate speedo?
I thought it was odd that the GPS in my Blackberry never matched the speed of the car speedo. When on cruise control at a speedo showing 70mph constant, the GPS would read 67mph.
Now I have read that the GPS will never be spot on, but found it odd that is consistently under judged the speed in comparison with the car readout.
Today I went for a drive with the wife and kids, with the SmartNav on my Blackberry directing us. I noticed that the two speeds now match perfectly.
The change has been in wheel size, previously ran the 215/55/16 alloys, and am now on 235/45/18s.
So the question that comes to mind is, which is the true readout? Was it that the smaller wheels threw the computer out and it over read the speed, or are the larger wheels under reading the speed? Hmmm. As the GPS is now a match for the car read out, I am inclined to think the larger wheels are giving a truer picture.
I knew the larger wheels would make a difference to the speedo, but not to the extent it seems to have.
Moved over to the dark side
And loving it