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Reprogram Tire Size

zebra

Well-Known Member
Messages
199
Location
cold & windy
Looking around the forums, I can't find anything on folks reprogramming different tire size in the PCM so that the speedometer & odometer read correctly. Are folks not fixing this when changing tire sizes, or are they just not talking about it?

I simply want to confirm what methods are available aside from mailing the computer back to a shop (or buying a crappy handheld generic tune module). We're happy with our PCM of NC custom tune, which corrected for our current 285/75-17s (33.8"), but I'm eyeballing some 255/80-17s for our next set (32.8 to 33.3", depending on the model). Of the stealerships here in town: one quoted $110 for 1hr of computer flashing, and the other said it'd be ~$350 for GM to write a custom flash & them to download it to the truck... which is absolute horses#!t because I did my previous 99 GMC with a friend's TechII in about 5min after changing to 33s.

I obviously don't still live near that friend and ain't sure if the E38 PCM is as easy as a 0411 to update the revolutions per mile for the VSS. Thoughts?
 

zebra

Well-Known Member
Messages
199
Location
cold & windy
PS: This correction doesn't just ensure the speed & mileage shown on the dash are correct. It also affects ABS behavior (and I imagine traction control + stability control + the simulated limited-slip action) to ensure they all function correctly.
 

CaseyS

Well-Known Member
Messages
747
Location
Louisiana
1) buy what you need to do it your self
A) hp tuners
B) efi live
C) generic ??

2) pay someone to do it
A) dealer [$110 you had quoted]
B) send you pcm in to someone
C) local tuner
D) friend hookup.
 

08H3

Well-Known Member
Messages
1,349
Location
United States
I don't know if it's still the case, but PCM of NC used to offer discounted price on tunes after the initial one.
 

alrock

El Diablo
Staff member
Messages
10,540
Location
Scottsdale
PCM of NC is a terrific resource for tuning your H3. In addition to tire size you can adjust shift firmness and other driveability factors. I highly recommend contacting them to discuss options.
 

zebra

Well-Known Member
Messages
199
Location
cold & windy
PCM of NC ain't open on the weekend, but i called yesterday. as mentioned out the gate: he already tuned our truck 4yrs ago, and what he quoted for just changing tire size or even doing a couple minor updates was significantly less than i originally paid... and much less than the dealers here.

it's now the difference of affording + a week without the computer versus a local friend who thinks his scanner might do it. he's thinking it might only do OEM sizes, though. a 255/80-17 is only slightly taller than Adventures came with.


PS: no tuning will ever come close to matching the shift improvement this guy's kit made on our truck
https://core-shifters.com/products/2006-2010-hummer-h3
 

rascole

Well-Known Member
Messages
2,693
Location
Bellflower, CA
Pay for the priority 2 day shipping, they have done mine in less than a week and I live in SoCal. I haven't seen any scanners that can change tire size yet, but would be nice if it could.
 

zebra

Well-Known Member
Messages
199
Location
cold & windy
if i remember right, he had our computer in & out within a day, too... but that's still a week without a computer, and my wife does home health. GM's Tech 2 scanner definitely changes tire sizes; i'm pretty sure a couple other mechanic's shop scanners do, too - it just seems like they all might be limited in what diameters and/or revolutions per mile they'll allow.

i've also heard of folks programming custom diff ratios to get around tire size limitations in the computer.
 

crwalkerasla

Well-Known Member
Messages
344
Location
Corinth, MS
PCM of NC Has done my rig twice. 1st time with the initial reprogram going to 33's. Second time to adjust trany shift point for cruise control & going to 35's. 2nd time was only $65.
 
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