Can't change tire size.

[Frenchy]

Using 2.23 Beta.

Current says "Error." Under NEW, I enter 30 and the gear ratio (3.23), but it won't let me click Commit, to make the changes. The truck is a 5speed so it's only affecting the Speedo, but it's just bugging me. I searched and couldn't find anything. I've attatched a copy of the tune.

[waynehartwig]

Any fix to this? I've been noticing all? (say 9 out of 10 PCM's) that I've been tuning lately say 'error' in the tire size field and it can't be changed.

..I have the latest Beta as of today.

Various years, so I'm not seeing a pattern. Like right now I'm doing a 99 Silverado 5.3L and it's errored.

Any thoughts?

[fastgmc53]

anybody?? im using 2.22 and had this happen yesterday

[waynehartwig]

I'm still seeing this too with no fix...

[Chris@HPTuners]

the problem here is GM. You see, in the code that calculates the vehicle speed, the PPRev value isn't actually used and there isn't actually a tire size value in the calibration! PPRev is only used to calulate the trans output RPM for automatic trans vehicles and is almost always calibrated incorrectly for manual trans vehicles.

So what you find is that "almost all" manual trans vehicles are fitted with a 17 tooth VSS sensor but the PPRev calibration incorrectly shows 40 teeth (the usual VSS sensor for a 4L60e). To avoid this problem with almost every manual trans LS1 vehicle we have to assume the VSS Sensor is 17 teeth(even if the calibration shows it as 40).

Now, for some manual trucks they actually are fitted with a 40 tooth sensor (like a 4L60e) and our calculation breaks. There are also about 5 other stupid ways GM calibrates the speedo for LS1 trucks.

For those vehicles you'll need to scale the PPM manually.

This is one area GM is horrible at calculating, even the latest code implementation is very poor.

[waynehartwig]

the problem here is GM. You see, in the code that calculates the vehicle speed, the PPRev value isn't actually used and there isn't actually a tire size value in the calibration! PPRev is only used to calulate the trans output RPM for automatic trans vehicles and is almost always calibrated incorrectly for manual trans vehicles.

So what you find is that "almost all" manual trans vehicles are fitted with a 17 tooth VSS sensor but the PPRev calibration incorrectly shows 40 teeth (the usual VSS sensor for a 4L60e). To avoid this problem with almost every manual trans LS1 vehicle we have to assume the VSS Sensor is 17 teeth(even if the calibration shows it as 40).

Now, for some manual trucks they actually are fitted with a 40 tooth sensor (like a 4L60e) and our calculation breaks. There are also about 5 other stupid ways GM calibrates the speedo for LS1 trucks.

For those vehicles you'll need to scale the PPM manually.

This is one area GM is horrible at calculating, even the latest code implementation is very poor.

That makes a lot of sense....

[derski69]

I have a 2002 Chevy 2500 HD,and I am trying to figure out how to adjust the speedo to correct it. I put 285X75 R 16 inch tires on it and now my speedo is off. I don't understand how to change the settings. Can anybody help me?

[waynehartwig]

Post the tuen and I'll correct it for you. But you will need the Beta version to open it again/write it to yoru PCM.

But you will be able to compare the two files and see what/why I changed what I did.

[transam19]

so the only way to change the tire size is by manually scalling the ppm manually. how much can would u suggest changing at a time.

[98prblms]

I have this same problem with my 98 T/A. I'm running 26.1" tires and recently put in a new rear end w/ 3.90 gears. Can someone help break this down for me?

[fsperformance]

How big of steps do you suggest to take on the ppm at a time? Im having the same issue on a 98 gmc 1500 cant enter tire size or gear ration.

[Justinjor]

Post the tuen and I'll correct it for you. But you will need the Beta version to open it again/write it to yoru PCM.

But you will be able to compare the two files and see what/why I changed what I did.

I'll be taking you up on this tonight. I had speedo issues after my 3.90 gears were installed and regardless of what settings I used for the speedometer section, I could not get it to read correctly. I ended up just multiplying the tire size by .95 and that seems to have taken care of it. I tested the speedo at 50, 60, 70, 80mph and it was accurate.

[04colyZQ8]

How do I change from a 40 tooth T56 calibration to 17 tooth calibration? I am using a 06 SSR E40 T56 (40tooth) to run a 4.8L mated to a GTO T56 (17 tooth). When I had the stock 5 speedo meted to the 4.8L using the SSR E40 my ABS and speedo worked correctly, not that I changed to a 17 tooth T56, I get C0222 ABS code, and monitoring ABS speeds I get matched speeds from the two front sensors, they match the speedo, but the rear is way off! The rear read slower then the front. The rear uses the V.S.S. Yet my speedo is accurate according to my GPS. My truck is a 2004 Colorado, with a swapped in E40 4.8L/T56

Does the ABS get a raw signal, form the V.S.S or do I need to manually calculate the ppr, and leave tooth setting at 40 instead of 17?

[04colyZQ8]

OK I kind of fixed it! I set my V.S.S pulse per to 17, and VSS output pulses per to 40,000 and now the scanner reads same speed both fronts, and rear. No code set, no pulsating!

However under really low speeds, 1-2 km'hr I get a minor pulse! front speed sensors show, 1-2 km'hr and rear shoes zero. I think that's because of the 17 tooth low resolution. I'm not to concerned about it, since its at a crawl.

I guessed at 40,000, it was a random number kinda I thought it wants to maybe see 4000 pulses per mile, since that didn't work but it was close, just about 10 times to fast, so I times it by 10= 40000 and it seems bang on!

I'd love to hear why what I did works? And if I can improve on it to help with the low speed resolution