Taller tires - computer recalibration

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Gm only gives the dealer the ability to program the truck with the possible tire combinations available for that truck... meaning is it possible to get
a truck with that engine and chassis with that size tire?? if not , then gm cannot program the vehicle... you also have to program the abs and pcm separately... some dealers just program the abs, which is much more lenient, and the shift points and Speedo are still wrong...If you find someone who deals in tires, you may be able to find a match of circumference of tires between what you have and what is available.... as for aftermarket, I don't know how they do it... must kinda be like hacked firmware for a dvd player or something....probably works, I just have no experience with it... Bobo
P.S. If you plan on leaving it as it is... I would try to have the dealer program the abs for the brakes.. the small change in speed may have a dramatic effect in how the abs works... I know it's a small speed change, but with thousands of pounds here it wouldn't take a lot to throw a monket wrench in the works....

the
difference,
more
the
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On Wed, 26 Nov 2003 12:52:03 +1300, rnf2 wrote:

Fun, yes. Especially when your formula calculates area.
Circumference = PI times diameter
Complicating things a bit more, the rolling circumference of a tire is not the same thing as one would calculate based on "tire size." The rolling radius is shorter because the tire deflects under load. However what you suggest is a good approximation especially when looking to approximate the differences between two different tire sizes.
Best thing to do is to consult the tire manufacturer's specs. Should be able to get a very accurate rolling circumference. Is usually pre-calculated and stated in revolutions per mile.
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many
OOPS!!
My bad. still you get the idea.

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managed to spout out:

half ton or three-quarter ton truck?
the dealer I bought both my trucks from told me that GM won't release the codes to the dealers to reprogram three-quarter ton truck computers, stating that a 285/75/16 does not come in a load range E, thereby decreasing the capacity of the vehicle. supposedly the dealer will reprogram half ton trucks though.
I bought the power programmer, then switched from 245s to 285s and did the reprogram myself. the heck with the dealer. buy the programmer for your truck, there's plenty of other things you can tinker with in addition to tire size. to me, it was worth the cost of the handheld.
Mike `02 Silverado 2500HD
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1/2 ton truck 265/75/16 to 285/75/16 - all 3 dealers said they can't help me what power programmer did you buy? how much if you don't mind me asking?
Thanks Danno

hand
impossible.
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me
You could ask around and see if theres anyone within a short drive who you could go visit with a crate of beer and use theirs. then have a go swapping offroad yarns and tall tales with after.
rhys
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Somehow,on Wed, 26 Nov 2003 18:35:53 +1300, "rnf2"

according to the instructions for the Hypertech Power Programmer, you can only use the unit on one vehicle at a time. it is possible to use it on more than one, but if for any reason you should ever need to return the second truck back to it's stock programming, you can't.
Mike `02 Silverado 2500HD
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managed to spout out:

Hypertech Power Programmer III. ordered it on-line from Stylin' Concepts, $349.95. here's the link: http://www.stylinconcepts.com/parts.cfm/partfamilyid/135/CategoryID/28/SubCategoryID/220 at the time I ordered mine(May 2003), they had the best price.
the only thing I had the dealer do for me was crank up the torsion bars so the front of the truck sits level with the back. I had them do this on two trucks when I picked them up new...
Mike `02 Silverado 2500HD
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says...

Okay, does raising the torsion bars change the alignment or not? I've heard opinions both ways. I have an 04 2500HD 4x4 and would like it to ride more even front to back like a Ford 4x4.
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Any change from 'factory' will alter alignment..
-- History is only the past if we choose to do nothing about it..
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"Randy Howard" wrote

Let's put it this way: the opinion that says raising or lowering front ride height by adjusting the torsion bars will "not" change the alignment is wrong.
Inversely....the opinion that says that raising or lowering front ride height by adjusting the torsion bars "will" change the alignment is correct.
Ian
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well, this probably doesn't do you any good with your chevy, but on a dodge, they can recalibrate for any size tire that was available on the truck as an option... otherwise, they just tell you that you're on your own.. i guess certain sizes are programmed in and that's the choices?

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Leaving it as is will affect your 'perceived' gas mileage and distances traveled along with a speedometer correction.
As I mentioned, I went one size over anything that was a dealer option for my Jeep and when I checked the speedo out with a GPS unit, it turned out to be right on exactly.
They usually calibrate the speedo from the factory to be slightly over with the largest 'factory option' tires so when the speedo says 65 mph, you are 'really' only going 63 or 64 mph.
I would just ask the dealer to dial the speedo for the biggest tire they can and see what the result was.
Meanwhile, all us Jeep folks with really large tires usually just get paced to find out where the speedo should be and judge the speed accordingly. It wouldn't hurt my feelings to know I have to be at 63 mph on the speedo to be doing the legal 65 mph. My CJ7 was way off when I got it with 31" tires on, it read 65 and I was only going 60 before I went up to 33x9.5 tires. So I just drove at '70 mph' to keep up the speed limit.
Mike 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's
mxz1972 wrote:

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hand
impossible.
tires
================================No big deal, your speedo will be off a little, and odo too. big woop. :) Hell when it comes time to sell it, it will show less miles than it actually has! :) Or you could buy a programmer for about $400 to change it.
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Approximately 11/25/03 14:07, Jason Cothran uttered for posterity:

Whats the increase in circumference? Ignoring the fact that unless you know the brand and model of tire, you really don't have anything more than a general idea of the actual tire diamters involved...
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Jason Cothran wrote:

Yo bud, don't know what the heck you are measuring, but in the BFG line, a P215/75/R15 has a diameter of 27.8".
The P235/75/R15 has a diameter of 29.0"
Just a wee bit more than a 1/2" eh....
http://www.bfgoodrichtires.com/assets/pdf/radial_long_trail_ta.pdf
Mike 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's
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on.
Think again. that is .6inches (just a wee bit bit over 1/2 inch) per side. It is simple math. The aspect ratio is simply a percentage of the total width. E.G., a 215/75 is 215mm*.75 inches tall (per side =*2, add rim diameter). a 235/75/15 is 235mm*.75 inches tall (per side =*2, add rimdiameter), so yes a 235/75 is, like I said, just a wee bit over a 1/2 inch (per side, but since we are all assuming, I thought you knew that) taller than a 215/75. You even showed it yourself off the chart (29-27.8=1.2 / 2 = .6 inches per side (radius)).
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Approximately 11/26/03 14:38, Jason Cothran uttered for posterity:

Ah, but what is the circumference difference little grasshopper?
87.3 compared to 91.1 inches, or a 3.8 inch difference in circumference, or just a tad over 4%, not enough to get you a speeding ticket unless you urinate on the ossifer's foot just before you beer barf on his nicely pressed uniform, but still enough to bring a slightly out of true speedometer into line.

Only for a pure and hypothetical tire, little grasshopper. Real tires are spec'd to the closest standard value and grasshoppers are encouraged to consult the actual manufacturer's data for the real tire dimensions. And recall that the difference in diameter is multipled by 3 in Kentucky and 3.14 elsewhere.
--
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right
the
how
line,
side.
Ah yes, the make it any size you want to rule lol <wink>. Where an inch equals a mile and pi is forgetten :-D.
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Jason Cothran wrote:

Huh???
I really don't get what you are saying....
The damn tire is over 1" taller. Period. Put the two against a wall and compare, one 'will' be 1.2" taller than the other on the same rim.
In my book that makes it a 'lot taller'. A 'lot taller' enough that it won't fit on some vehicles too.
The radius has no bearing on this, nor is it what I said in the first place.
Now if I wanted to figure out how much more ground clearance I would get, I would divide the diameter in half. In my case on my CJ7, I got 1" more ground clearance by changing from 31's to 33's. I got 2" more diameter which is the number needed to figure a speedo.
On my Cherokee I only got .6" more ground clearance changing from P215's to P235's.
If I am figuring out the speedo, I want the diameter measurement to get the circumference difference.
If you can't understand this simple math, then I give up on you.
I have no urge to argue with someone that wants to talk in circles.
Bye now....
Mike 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's
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