Taller tires - computer recalibration

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2000 GM 4x4 - switched from 265/75/16 to 285/75/16. Want to reset parameters for speedo, abs etc... Been to a few dealers today and they are making it
sound like quite a process. Have to call Oshawa, Ontario (in Canada) and find out if it can be done. At least two hours time involved. Might have to burn new program in computer? Can anyone explain to me what is involved?
Thanks in advance Danno
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parameters
to
Slap a power programmer (you +about$300) or their computer (them + whatever they decide to charge) into the diagnostic terminal on your truck, inputting tire size change at appropriate prompt, wait a couple minutes, drive away calibrated.
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to
Danno,
I saw a recalibration gizmo in either Jeg's or Summit's catalogue.
Call em' and see what they can do. IIRC it was around $149.
www.jegs.com or www.summitracing.com
Doc

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I would find someone with a GPS and clock it to see.
When I went up from the stock 215's to 235's, my speedo was right on. it was off before...
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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Going up from a 215 to a 235 will not change the speedo. That is the width of the tire in millimeters. The second number is what determines how tall the tire is.
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On Mon, 24 Nov 2003 20:40:01 -0500, Jason Cothran wrote:

Going from 215/75 to 235/75 *will* change the calibration because 75% of 215 is not the same as 75% of 235.
I agree with another suggestion, find a GPS and try it before sweating the issue too much. My Toyota Avalon indicates a bit slow, my Sonoma is maybe 1 MPH fast, and I'm very unhappy my Honda GL1800 Goldwing indicates over 4 MPH fast.
About the only issue you will have with ABS is if all wheels are not of the same size, or if the size changed so much that it moved the low speed disable-ABS point.
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Maybe you should explain that the width of the tire is 235mm and that the height is an aspect ratio of 75% of that width.
~KJ~

width
tall
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width
tall
thats right, but just going the 215 to 235 will not, no aspect ratio was listed.
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wrote:

If not listed, I assume it to be the same for both 215 and 235. Same aspect ratio (say, 70%, 75%, 80% or whatever) and tire height changes when the width changes. This is by definition.
Here's a decent calculator:
http://www.miata.net/garage/tirecalc.html
--
Jukka

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I understand completely how tires are sized. I was just stating the 215 and 235 say nothing of the tire height without the profile listed.
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Jason
Taken from the original post.. '2000 GM 4x4 - switched from 265/75/16 to 285/75/16. Want to reset parameters'
I would think that a 285/70/16 would be closer to the original size..
-- History is only the past if we choose to do nothing about it..

was
and
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I am not speaking of the original post, I am speaking of one deeper in the thread. Obviously, the profile was stated in the original post
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On Tue, 25 Nov 2003 08:07:29 -0500, "Jason Cothran"

What's funny though is how everybody else knew what the original poster meant without the mention of aspect ratios........
Matt 99 V-10 Super Duty, Super Cab 4x4
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Whats even funnier is I'm not speaking of the original post. I am speaking of the one to which the response was to.
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Jason Cothran wrote:

I didn't bother to list the aspect ratio, it was the same, that's why it changed my speedo.
In order for those tires to be the same, the aspect ratio would have to be radically different, something like a 75 series and a 50 series.
If I did that, it really wouldn't make any sense to post about it would it?
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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of
In order for the heigth of a 215 and 235 to be the same, there be by no means a radical difference. Maybe 5% at most.
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Jason Cothran wrote:

It sure will unless you radically change the profile.
I went from P215/75's stock to P235/75's.
It is a lot taller tire.
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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it
width
tall
A lot taller? 15 mm (just over 1/2 inch) is a lot taller?
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Ok - so i have been to 3 gm dealers today and they all told me it is not possible to recalibrate for 285/75/16 tires. So what is the deal - the hand held aftermarket power programmer will work but the dealer says impossible. Can anyone shed some light on the topic for my feeble brain. Is it even really necessary except for the speedo and maybe the shift points? The tires are only about 1 - 1.5" larger in diameter. What are the consequences of leaving it as is?
Thanks Danno

on.
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hand
impossible.
tires
work out the Pi R squared formula from high school and work out how long the circumferance of the 285s are and the originals there will be a difference, divide the number of feet in amile by the circumferance in feet and thats how many times the wheels turn in a mile. the smaller wheels will turn more often and the mileometer will be out by however many turns of the wheel the 285s differ from the originals.
fun maths. not sure if it will help.
rhys
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