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Does anyone know the procedure or proper way to do this. I have an 05 silverado 4x4 with the 4.8l and a 5 speed. When the tune is pulled from the truck, it shows an "error" in current tire size and the size calculator will not pull up. The truck has stock 3.42 gears and I went from a 265/70/17 to a 305/70/17. Any help would be greatly appreciated.
Jack
did your actual tire diameter change? all i see is you put wider tires on which shouldn't affect anything.
The overall diamater of the factory goodyears is 31.7". The tires I put on the truck (maxxis buckshot) have an overall diameter of 33.9". The calculated height of each tire is probably less but the speedo is off enough to get me in trouble. We were kinda stumped when it wouldn't let us change the tire size and calculateQuote:
Originally Posted by Chris@HPTuners
Chris, no disrespect meant at all, but let me help you with the tire sizing. If you already know this, I apologize, just trying to help.Quote:
Originally Posted by Chris@HPTuners
Lets start with the tire size that came stock on his truck.
265/70/17
What this means is as follows.
265= The tread is 265mm wide.
70= The sidewall is 70% of 265
17= wheel size
So, his sidewall is 185.5mm. Now, you multiply that number by 2 because you have sidewall both over, and under the wheel.
So, you have 371mm of tire. Now convert that to inches.
371/25.4=14.60 inches of tire.
Now add in the wheel diameter, and you have the overall height.
14.6 + 17 = 31.6 overall diameter.
The new tires put him at a 33.81" overall diameter.
Here is a nifty online calculator that is much easier than doing the math.
http://www.miata.net/garage/tirecalc.html
In the Editor, Go to tools, unit conversion and there is a tire size calculator.
Ok, I feel pretty dumb right now.:oQuote:
Originally Posted by Rammer
Sorry for the waste of page space.:doh:
Actually, doing a roll out will give you the most exact tire height as the tire "squishes" (for lack of a better term) a little reducing the rolling radius.
HTH
EC
yeah, my bad, not enough caffeine before engaging brain into gear that day ;)Quote:
Originally Posted by BLWNGTO
so what si the solution when the stock file reads error? I have an 07 yukon I just put 26 inch wheels on, and can't recal the speedo, because the commit change button is ghosted.
has anyone solved this??
You will have to manually calculate the tire turns per mile.
1. Do a roll out in inches.
2. 63360/roll out gives you tire turns per mile
3. Apply that value to the appropriate slots in the speedo file.
4. Take old tire turns/mile divided by new tire turns/mile & multiply your shift points & TCC lock values by that.
Remember as the tire diameter goes up the turns/mile go down and your shift speeds should go up with a larger tire.
is there a write up on the best way to do a "roll out"Quote:
Originally Posted by EC_Tune
Mark the ground, rotate one revolution, mark the ground, measure the distance in inches.
I know this is an older thread...but,
Your calculation is based on a rear diff gear of 1:1. You have to multiply your sum by the ratio of the rear gear (in my example...4.88) to get the trans revs/mile...right? There isn't an area in the speedo breakout for revs/mile.
Example...315/75R16 tire = 34.6 or 108 1/2 inch roll out or 34.6 * 3.14 (pi) = 108.644.
63360/108.644 = 583.19 * 4.88 = 2845.963 trans revs/mile
Doesn't this really all depend on the number of teeth on the VSS sensor?
Yes that will give you VSS Pulses/mile
I have just found this thread, lots of good info. I have been struggling with this adjustment for some time now. I was asked by a friend to correct his speedo. He has a 02' GMC Sierra 6.6 DSL and 36" tires. I did the rollout calc. (112.5") and div by 63360. I entered this number in the 'VSS tire rev per' field and then produced a ratio of change by dividing the old and new numbers. I then changed the 'VSS pulses per" field by this ratio. The result was an accuate speedo but a constant "C0238" DTC. The "VSS pulses per mile" I came up with my way was 83578. I just did the calc. from this post and came up with 84027. The questions I have are can this small difference fix the DTC problem and if not how do I proceed?
I have noticed in my 4L80E tune I have a feature which automaticly makes this calc. and is not available for the alison.
Mark
Try this tire calculator. :D
I've put a couple hours into it so it should be right for most all tire size applications.
It's a ZIP file renamed to .txt so I could upload it.
Just save it to your drive and then rename it from .txt to .zip then unzip it.
Enjoy!
Sweet Doug!
Very nice work. I entered all of my info and came up with the same numbers I am using already!? Can you tell me how this system works? If I put in the stock numbers the speedo is off but no DTC's. If I put in my numbers then the speedo is spot on but the DTC's return. I am not totally clear on how th two numbers relate to each other.Quote:
Originally Posted by EC_Tune
Mark
What DTC's are you seeing? If it's ABS related and you have much bigger than stock tires and/or a gear swap it's simply the ABS system whining that the front and rear sensors are out by > 15%. A Tech 2 can fix that for you.
And did you enter 40 Pulses per Rev trans output? That's the number that most trucks have.
If you need to fudge the speedo you can put in the VSS Pulses per Mile that you calculated with the spread sheet.
The DTC is C0238 ( wheel speed mismatch). Yes on the 40 PPR. the speedo is acurate but still getting the DTC. Do I have to go to the dealer for the tech 2 change?Quote:
Originally Posted by EC_Tune
Mark
Yep. Tech 2 is the only thing that can reprogram your ABS module for the new tire size.
And you need them to put in a tire size close to the one you have on your truck.
The other solution is to put in the stock trans rev/mile value and make the speedo VSS Pulse/mile correct. All your shifting will be off as well as the reported speed with VCM Suite but you won't have the dash light (ABS related).
Attachment 12500 ok heres one of my tunes that i cant adjust the tire size please help my speedometer is going crazy
Quote:
Originally Posted by EC_Tune
you sir, are a gentleman and a scholar!!! thank you for your contributions
Now if I could find a setting in the Tech II for 35in tall tire :(Quote:
Originally Posted by EC_Tune
Tech 2 will only load a preexisting GM calibration - it will not modify the calibration. Changes to wheel and tires (sometimes a dealership upgrade) require a different calibration - some of these already exist - and are accessible via a VCI number.Quote:
Originally Posted by TwoFast4Lv
As an example, the same applies to upgrading some newer vehicles to allow Cruise Control to function (which did not originally come equipped with Cruise Control). You call the GM Tech Line (have never found these folks very helpful) and if the calibration exists (i.e. was an option) - they will upgrade the VIN based calibration for your specific vehicle - and issue a VCI number to access this. All for a fee of course.
I know this is an old thread, but everything points back to here and I'm not sure if I'm doing this correctly. I made a slight change of tire size, just enough to put me about 2mph out at 60mph (not a big deal, but it bugs me). I went from 255/45r18 to 275/40r18. I used the spreadsheet and you can see the differences. However I'm not sure what all to change.
Do I just change the VSS tire revs per mile?
Attachment 42358
Also, I assume I manually scale the transmission as well?
Attachment 42359
Based off the calculation in the spreadsheet?
Attachment 42360
Am I missing anything else???
I know it's a necro-thread, but here's how I've delt with the dreaded C0238 and the speedo issues with my customers:
http://www.hptuners.com/forum/showth...The-Fix-Thread
Awesome wirte-up! however ive been having an issue because my current tire size is listed as error and the gear ratio at 1 and when I enter the new values the commit button stays ghosted. Ive searched but haven't found anything useful. if I have to manually calculate the revolutions that is ok but just wondering if any one has found a fix.
I know this is old, but does anyone have this info? :worship:Quote:
Originally Posted by EC_Tune
I found an equation for number of pulses this might help you.Quote:
Originally Posted by griswold
https://www.circuitschools.com/wp-co...e-formula.webp
There is an online calculator too.
Source: https://www.circuitschools.com/pulse...ula-in-detail/