On Thursday, September 29, 2016 at 9:37:55 AM UTC-4, rbowman wrote:
On 09/29/2016 12:59 AM, wrote:
If someone puts on larger auto tires, than the vehicle was originally
equipped with, will the Speedometer read faster or slower than the
actual speed?

For example, Lets say a car came with 15" tires and I put on 16" tires
(and rims). When the speedometer should read 30mph (with the original
15" tires), will it read about 25 or about 35mph with the 16" tires?

I cant seem to comprehend how to determine this.....

Like Paul said, it depends on the rolling diameter of the tire. For
example 18" wheels with those rubber band tires may not have a greater
diameter than 16" wheels with a higher profile tire.

I run 15" in the summer and 14" studs in the winter and the studs show
about 10% slower. I just go by the GPS. The car's speedometer is
centrally mounted which introduces for parallax so the GPS display is
more convenient anyway.

I recently borrowed a friend's "church van" sized van to move some stuff.
50 miles from home, the speedometer stopped working. Sometimes it would
pick a speed and just sit there, other times it would bounce back and
forth over a 20 MPH range. I downloaded a speedometer app for my
smartphone and used that for the rest of the trip.

When I returned the van I told my friend about the issue and volunteered
to pay/help pay for the repair. He replied: "Oh, yeah. I guess I should
have told you about that. I always use a GPS as my speedometer."

(He also didn't tell me that the turn signals didn't work unless the
Hazard button was depressed. The Hazards didn't work at all, but they
had to be "On" in order for the turn signals to work. I stumbled upon
that one myself while checking the lights for the trailer harness.)

Hey, it was big and it was free. No complaints!