Randy_medion

the speedo of my 2007 C6 is off by about 3-5 mph when I drive 60mph, I have a coupe withe the stock Supercar tires with 60% tread left, a friends c6 is accurate with the gps what's wrong with my car?

BSSN

What is the margin of error at 20 and 100mph? (not that I advocate that...)

If it stays the same, meh. But if the margin of error increases proportionately, that's kindof a big deal.

Randy_medion

increases the faster I go

wera32

My cars are pretty close but my bikes are 10% off. I put a Black Robotics Yellow Box on my Honda to correct it. Love it. I haven't checked to see if they have one that'll work on the Corvette but I'd be surprised if they don't. yellr.com

FortMorganAl

Mentioning this on a 4 year old car indicates you probably aren't the original owner. So... Original owner had different wheels/tires and had a tune to "correct" the speedo? Or maybe you don't have the original gearing? The speedometer is just displaying a digital signal from the ECM. If the display doesn't match actual speed then there must be a physical difference from the drive shaft to tire contact patch.

Tweeter

Almost every car I've owned (including my 2009 Vette) is off by 2 mph (fast) exactly according to roadside radar signs and my 9500ix. Almost seems intentional by the manufacturer to me but 5 mph is a different story.

CodyC6

If you get a ticket for speeding, have the speedometer tested, then when you show the judge your speedometer calibration was found to be wrong (regardless of which way), you'll probably have the ticket thrown out. I've seen this happen. Worth a try.

tlcj

8850

I had to change my ECM indicated tire diameter to correct my 08. Easy fix with HP Tuner.

Daekwan06

My 07 C6 had the stock tires replaced by Michelin AS+ and I was shocked to see that the speedometer was dead on correct by GPS standards. Using the TomTom navigation app on my iPhone I drove 1100+ miles and never saw a difference of more than 1mph between the speedometer, HUD and Nav app. Speeds were between 1-90mph.

florida john

If my memory serves me well, speedometers are required to be accurate within plus or minus 5%. I am sketchy on the 5%, but there is a % limit for new unmodified cars. Obviously, changing tire size or rear gears can significantly change accuracy. May be worth an inquiry regarding a warranty fix, even beyond normal limits.

jackcasa

After checking the speedo on my '10 GS using two (2) different GPS units I found it to be "spot on" as was my '05. Your problem is puzzling.

Randy_medion

I suspect the previous owner changed the tire size, maybe with a tune, my car also seems a tad faster than the average LS2's so I'll buy a hypertech tuner, see if that fixes my problem

Randy_medion

does it affect the abs or a/h or something else like performance when you change your tire size?

JScottH3

Above 45, my speedo and HUD are 1-2 mph apart (HUD is always lower). I've had times where my speedo, HUD, and GPS all show different speeds. I figure I'll just live with it.

mforman42

My previous 3 C6s always had pretty good agreement between the HUD and speedo, but my '09 Z06 is like yours - the HUD reads lower than the speedo, and the speedo is spot-on.

I measured my speed by the old measured mile time-to-distance method at 60 MPH...

Gearhead Jim

Three Corvettes-
2001 (sold), 2006 (sold), 2009 (now).

On all of them speedo was accurate within 2 mph up to 150 as measured by multiple GPS units. Most of the time, accurate within 1 mph.

Somebody been messin' wit you ride.

8850

Changing the tire diameter on mine disabled the TC but don't know about the others. I went ahead and disabled it in my tune file so I wouldn't have a power loss around 90-100 mph.