265 Tire Calibration test

[Paintdude]

Here is a Email I got today...


I would appreciate it if you
would
post it as I think it is valuable info for the forum.


I planned on having the "Stealership" recalibrate my 2002 Chevy 2500HD
D/A
when I replaced the Firestone 245.75.LT16 tires with Michelin MX M/S
265.75.LT.16 tires a few weeks ago. In the meantime, I did a couple
tests to
see just how far off my speedo was really reading with the new tires.
It is
reading dead on accurate with no recalibration! The details of the
tests are
below but, my point is, the dealership is ready to charge for a
recalibration that may not be required. This would also mean GM sold
the
truck already calibrated for the 265 tires!

The tests indicated the speedo is accurate at all speeds from 30 mph to
80
mph with the new 265 tires in place and with no recalibration!
I don't know what affect the new tires have on the anti-lock brakes. I
can
tell you, I will not be having a recalibration performed.
I knew my speedo was reading a mile or two high (with my old 245 tires)
based on the readings from those stand alone radar warning gizmos the
police
provide for you entertainment.

Here are the tests I performed with the new 265 tires installed:

Test 1:
Drive 60 mph on level ground, wait for the clock to click over to the
next
minute, reset the tripometer asap counting the three seconds it takes
to
reset. Now watch the clock and the tripometer. When the clock ticks to
the
next minute, watch the tripometer and count the three seconds again,
bingo,
the tripometer hits the one mile mark right on time! Repeat this test
doing
30 mph,.. I hit .5 miles at the one minute mark. Right on the money.

Test 2:
Driving at 60, 70 and 80 mph on I-25 South of Castle Rock, CO, I hit
the
reset button on the tripometer just as I passed a mile marker. Once
again,
counting the three seconds it takes the tripometer to reset. As I
passed the
next mile marker the tripometer would roll over to the next mile right
on
time (allowing for the three seconds it took the tripometer to reset).

I love my truck. 43,000 in 15 months. I wonder if GM sold the truck
knowing
most owners would upgrade to 265s or larger when the OEMs wore out

[mackin]

Paintdude

Not trying to be a spoiler ,just my observations.....
I went from a 215/85 to a 235/85 on my dually and the speed-o is right on as I have gone through those stationary Radar units myself......This is important to me as 1 or 2 ticks could mean the difference in a ticket or not around here.....

So I don't think GM anticipated anything....

I just think do to tire inflation and actual roll out varies so the difference when just stepping up a couple sizes doesn't throw it off that much.....Or from what I've seen in most Magazine test GM speed-o seems to be a little light by a mile or two in most cases.....This may attribute to the new found accurate speed.....

As far as counting to three man is that open for fluctuation....For what I've seen some here may need there fingers to get there .....LOL tongue.gif Me included, depends what time it is,what day it is, especially this time of year !!!!!! :D

MAC

[ 12-16-2002: Message edited by: mackin ]</p>

[Paintdude]

I just posted it for someone else..I have aways to go before I am gonna buy tires.

[KompressorMan]

I just installed a set of Michelin 265 Load E tires and was also thinking about getting the computer upgraded. I've also gone past the radar gizmos, speedo 65, actual radar speed 67. This is not far enough off for me to want to spend the money. I also know that for the first 36,000 miles, the speedo read a little fast. Now I might be able to get even on the rest of the warranty.
Herb

[Skinny Blinky]

With My BFG 285 my speedo is off buy 6 mph
and the milage is off by 1/10 of a mile.
My brother & I did the side by side test yesterday
with his 2003 HD all stock to see how much my stuff was off by.Those 03 are real niced inside...
Very upset that GMC can make so many changes in 1 year. My BRO just tells me to break down & buy a new one, HA...It only took him 13 year to do so,been one week for his new ride,still can't get that smile off his face... :D :D smile.gif smile.gif

[NeverForget]

You cannot use your own odometer to check your speedometer.

After going from 245s to 265s, my speedometer was only off by 3 numbers. But, my mileage dropped from 19 mpg to 16 mpg. I install the electronic box called "Truespeed" from Superlift to correct the electronic signal from the transmission to the computer under the hood. My speedo is correct and my mileage is back up to 19. So, it will pay for itself. I also don't have to worry about the ABS being off.

[Wally]

NeverForget,
Why not?
My odo error exactly matches my speedo error.
Odometer error, checked against Interstate mile markers, is exactly 7 miles off over a hundred mile check.
My odometer error, checked with GPS, is exactly 7 percent off.
Take this into account when figuring fuel mileage. Just add the 7 percent to the miles before you divide the gallons into it. Can be as much as 1.5 mpg.
285/75s on 16X8 wheels.