Incorrect Speedo with Chip
#1
08-14-2003, 11:39 AM
Join Date: Feb 2001
Location: Austin Texas
Posts: 120
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Incorrect Speedo with Chip
Howdy Folks, Its been well over a year since I purchased my Superchip. I bought a flipchip programmed to work with my increase in Tire size, went from stock 255-70-16 to 285-75-16. Over the course of the year, I have gone through about 5-6 of those radar deals that are used to slow people down and show you your speed. Every single one was off between 2-6 miles per hour depending on my speed. Does anyone know what I should do? Any way I can check to see if I actually got what I paid for?
Thanks,
Travis
Thanks,
Travis
#2
08-14-2003, 03:22 PM
Former Sponsor
Hi Travis,
I would never depend on those traffic radar signs for accuracy, we have them all over the place out here, too. Over the past few years out here they've taken to putting them up in many places where there is road work, for example, in an effort to get people to slow down & watch out for the safety of road workers, etc.
In my experience, they are typically about what you are seeing, a few mph off. For example, in my Lightning, whose speedo is within 1.3 mph @ 100, I typically see a speed 3-5 mph higher in the units used out here in the mountains of VA as compared to my speedo.
From what I hear, those signs aren't governed by the same accuracy requirements as police radar guns are, as they aren't being used for the issuance of traffic citations for speeding. Thus they do not get calibrated every day before use, most of them see no calibration after the manufacturer ships them, according to the highway workers that place them that I've had a chance to actually speak to about this (which isn't many, just a couple).
Now of course I have no idea as to the accuracy of the radar signs you have in your area, I can really only speak to what I have personally observed in those units compared to vehicles of ours where we *know* the accuracy of the speedometer. And in our experience, we typically see a 3-5 mph of error in the units used out here where we are. I don't think I've seen 6 mph off, but I have seen 3, 4 & 5 mph errors very commonly.
To have your program checked, contact whoever you purchased your Superchip from and they can have Superchips check the revs per mile spec in the program. That's how tire sizes are handled by the PCM, it's done by the "revs per mile" spec, meaning the number of revolutions it takes for that tire to travel exactly 1 mile. That number is simply plugged into the code, and that's it, all done.
Now sometimes we'll see that the P-metric sizing just isn't very accurate sometimes (meaning a tire that's supposed to be say, 30.8" is actually 30.4", or a tire supposed to be 35" is only 33.5", and so on), so anytime we suspect a faulty speedo calibration, we'll ask the customer to physically measure the exact tire height of the right rear tire as installed on the vehicle, on flat solid & level pavement, measuring from the pavement to the top center of the tire for an exact installed height.
Good luck!
I would never depend on those traffic radar signs for accuracy, we have them all over the place out here, too. Over the past few years out here they've taken to putting them up in many places where there is road work, for example, in an effort to get people to slow down & watch out for the safety of road workers, etc.
In my experience, they are typically about what you are seeing, a few mph off. For example, in my Lightning, whose speedo is within 1.3 mph @ 100, I typically see a speed 3-5 mph higher in the units used out here in the mountains of VA as compared to my speedo.
From what I hear, those signs aren't governed by the same accuracy requirements as police radar guns are, as they aren't being used for the issuance of traffic citations for speeding. Thus they do not get calibrated every day before use, most of them see no calibration after the manufacturer ships them, according to the highway workers that place them that I've had a chance to actually speak to about this (which isn't many, just a couple).
Now of course I have no idea as to the accuracy of the radar signs you have in your area, I can really only speak to what I have personally observed in those units compared to vehicles of ours where we *know* the accuracy of the speedometer. And in our experience, we typically see a 3-5 mph of error in the units used out here where we are. I don't think I've seen 6 mph off, but I have seen 3, 4 & 5 mph errors very commonly.
To have your program checked, contact whoever you purchased your Superchip from and they can have Superchips check the revs per mile spec in the program. That's how tire sizes are handled by the PCM, it's done by the "revs per mile" spec, meaning the number of revolutions it takes for that tire to travel exactly 1 mile. That number is simply plugged into the code, and that's it, all done.
Now sometimes we'll see that the P-metric sizing just isn't very accurate sometimes (meaning a tire that's supposed to be say, 30.8" is actually 30.4", or a tire supposed to be 35" is only 33.5", and so on), so anytime we suspect a faulty speedo calibration, we'll ask the customer to physically measure the exact tire height of the right rear tire as installed on the vehicle, on flat solid & level pavement, measuring from the pavement to the top center of the tire for an exact installed height.
Good luck!
#4
08-15-2003, 11:46 AM
Former Sponsor
