Spedo calibration

[Munch]

Wondering how much changing tire size changes your spedo reading.

Also how is the spedo set in the computer? Do you just plug in your tire size and gear ratio to some table or what??

[Y2Kvert4me]

Gear ratio does not affect speedometer reading on a C5, since the VSS senses on the output side of the gearset (senses axle speed). Rear tire height is the only variable.

Tire size data can be easily changed with tuning software to correct the speedometer/odometer, but unless you made a radical change in rear tire height, the error is usually quite slight.

Post your current size rear tires, I can tell you how far off the speedometer will read compared to the stock rear tires.

[Munch]

Running a 295/35/19 on the rear. Yesterday I saw 4 "Your speed is" signs, I had the cruise set at 60 and each sign said 58. Not a big difference but made me wonder.

[Y2Kvert4me]

It should actually err the other way, since your tires are taller than stock.

When your speedometer shows 60mph, you would be traveling an actual 61 mph. (going faster than you think you are).

Like you said, not a big enough difference to really worry about.