Can't calibrate the speedometer for new tires, but...

[hockeyman]

Has anyone come up with any type of speedometer modification idea's to let you know the speeds you're traveling with larger tires?

I've read here that I cannot reprogram the speedometer in my '03, but I'd like to see if anyone has any other easy inventions that I can try. I ask because of a few reasons:
1- Police traps, especially here in FL!!
2- If the wife uses the Envoy, I want her to have something clearly visible on the speedometer to see and use.
3- Refer to #1 again.

I'll be installing 265-70-17's and I already know what the speed calculations are going to be.

So far, I was thinking of removing the speedometer and using temporary florescent paint to make small notches at particular speed points (30-40-45-50-55...etc). Looking for other idea's though...

Heading to watch the football game now. I'll check any replies as soon as I get home later today.

Thank you for any advise given.

 

[Mooseman]

Use a GPS and pull the needle off the speedo.
or
Maybe move the needle ahead by the required amount. Not perfect but should get you in the ballpark, compare using a GPS.

 

[Sparky]

Problem with adjusting the needle position is it still won't be correct as the speed difference is a percentage, not a hard number.

On my 02 I just keep the needle no higher than the actual speed limit up until about 50mph, then above that I keep it a couple ticks below (so 70mph zone I keep the needle at 67-68). That keeps me within the 5mph range that no one will take a second glance.

 

[mrrsm]

@hockeyman This Tire Size vs. Driving Speeds Conversion Calculator can help give you a baseline to work with. Then... you might try using strips of Day-Glo Detailing Tape placed on the dust cover glass in front of your Speedometer and Tachometer Dash Panel Array, in line with your normal Target Driving Speeds vs. your own personal field of view of the Dash Panel. Make sure you are sitting exactly where you would be when driving and hold your head in such a manner that you are comfortable moving just your eyes to regularly check how fast or slow you are moving. The Tape lines will give you confidence that you are at... or under the Posted Target Speed Limits. ( I think this might be worth bookmarking):

http://www.roadkillcustoms.com/hot-...r-Calibration-Tire-Size-Change-Calculator.asp

 

[AWD V8]

I purchased a Superchips 2842 hand programmer for the '03 Envoy 5.3 for performance, and it has the option to correct for tire and gear changes.

Bonus, greatly improved shifting and performance!

Just an option.

 

[Mooseman]

I think he has an I6. Not programmable.

 

[smt 59]

When I up sized my tires I took it back to the shop that performed the PCM tune and after some basic calculations he was able to adjust the speedo, this is really the only way to do this, if you use your GPS remember that there is a delay with the signal and during this time you could get nailed for speeding.

 

[hockeyman]

I purchased a Superchips 2842 hand programmer for the '03 Envoy 5.3 for performance, and it has the option to correct for tire and gear changes.

Bonus, greatly improved shifting and performance!

Just an option.

Damn, you had my hopes up for a second there...but I have the I6 -as Mooseman mentioned.

I really do not want to always rely on a GPS for my speed, so I might just pull the speedometer off and do the paint trick with temporary translucent florescent paint. If I ever decide to go back to the stock tires or even change to yet another aftermarket size, I can quickly remove the paint and start all over again.

 

[mrrsm]

Does this After-Market Gizmo hold out any possible adjust-ability solutions?

http://www.dakotadigital.com/index....ategory_id=-1/home_id=-1/mode=prod/prd825.htm

 

[hockeyman]

Does this After-Market Gizmo hold out any possible adjust-ability solutions?

http://www.dakotadigital.com/index....ategory_id=-1/home_id=-1/mode=prod/prd825.htm

Don't know if it'll work or not, but I'd definitely like to know if someone has tried it on the I6 that's apparently non-programmable.

[edit]
The video mentions "Aftermarket Instrumentation", but I'm not electronic-savvy enough to know if it'll work with our application...

 

[Mooseman]

There's a diagram lower in the page and it mentions the OEM speedo. Why not just call them? It might mean cutting the feed from the PCM and using theirs.

 

[hockeyman]

There's a diagram lower in the page and it mentions the OEM speedo. Why not just call them? It might mean cutting the feed from the PCM and using theirs.

Actually, I sent them an email shortly after my last reply here. Although, I'm not quite sure that what they're going to tell me is completely true because essentially, they just want to sell their product. I did ask though and I will reply here once they respond.

 

[hockeyman]

Received a reply from them today and it read,
"Marc,
The SGI-5E is designed to modify a speed signal and multiply the signal up to 16x’s the input and also reduce the signal almost infinitely. You can use this with aftermarket or stock speedometers however this is not designed to work with any vehicle that has ABS nor do we support this product installed in a vehicle with ABS.

Thank you,
Cameron Anderson
Dakota Digital, Inc"

Oh well. I'll just keep my fingers crossed that someone, someday, will think of a way to reprogram the speedo for wheel changes...

 

[djthumper]

This has been a problem for everyone with a pre-06 360/370

 

[littleblazer]

There is more then likely a way to do it, as with any computer software. But since it is a foreign weird design and is no longer supported it is next to impossible. The option is there in the tech 2, but it doesn't allow for change to take place. I imagine there is some super secret top shelf gm program that can do it, but we'll never see it since it isn't well... used.

 

[Blckshdw]

It was posted in one of the tech I I threads that it can reprogram for tire sizes up to 30.6" doing that would at least reduce the amount your speedo would be off.

 

[Mooseman]

I'd have to check because I thought it was just 06+ that can be programmed for tire size using the Tech2. I saw it for my 06 but not for the 02.

 

[djthumper]

Only 06+ can have the tire sizes changed in the PCM. This has been a known issue for a while.

 

[smt 59]

Please read what I type,

It is recalibrated through the PCM.....I had it done and it works
For a minimal cost....a reputable automotive electrical technician will have the licensing from GM to perform this, it only takes about a half an hour. You are likely going to do this only once so save your money on one time use gadgets and get it done right.
(My one time rant)
Thank you...

 

[hockeyman]

Please read what I type,

It is recalibrated through the PCM.....I had it done and it works
For a minimal cost....a reputable automotive electrical technician will have the licensing from GM to perform this, it only takes about a half an hour. You are likely going to do this only once so save your money on one time use gadgets and get it done right.
(My one time rant)
Thank you...

Yes, but trying to convince an American GM Service Tech to even try it will probably be a challenge in it's own. Along with that, I'm not sure if I'll settle on that size in the future, so I do not want a "one time only" flash done to it.

I'm actually thinking of searching for someone who can custom make a Speedometer face for me. One that's already dialed-in for my tire size, if I tell them the tire calculator specs. That way, there's no need to worry about re-flashing the PCM at all. Just changing the face to whatever size tires that are installed. Good idea??

 

[Sparky]

Please read what I type,

It is recalibrated through the PCM.....I had it done and it works
For a minimal cost....a reputable automotive electrical technician will have the licensing from GM to perform this, it only takes about a half an hour. You are likely going to do this only once so save your money on one time use gadgets and get it done right.
(My one time rant)
Thank you...

Not on 02-05 i6... unless you've actually had it done. If so, I want to know who, where, and how!

 

[smt 59]

sounds like a tall challenge and not very common, sounds good though. I found a guy that does performance tunes and it is lifetime so when I want or need a tweek it is at no additional cost and he does it while you wait, not sure we're you live but I'm sure you could fine someone that is not a dealer staffer. I'v been working on cars/truckers for a long time and really not seen this type of mod not saying it can't be done but it sounds very expensive. good luck with this and if your successful post the pics, info etc. I'm interested to see the results.

 

[smt 59]

Not on 02-05 i6... unless you've actually had it done. If so, I want to know who, where, and how!

I had it done successfully just outside of Oshawa Ontario(GM) country, pm me and I will provide the info.

 

[mrrsm]

If this item is the Speed Sensor that provides the primary signal to the PCM... perhaps you can determine if it uses changes in resistance to send the data to the PCM or if it relies upon a collapsing field, such as The Hall Effect (Square Sine Wave) to do the job... Because if the matter involves or is controlled by electrical resistance...then it might be possible to get the technical readout of the Scale of Resistance at which the speedometer signals get bumped higher up the measurement scale. After all...since these vehicles no longer rely upon analog gears or Worm Drives to communicate physically directly with the Speedometer and that the NEW gauges are nothing more than common Potentiometers, then there MUST be some kind of reliable scale by which the needles change positions and provide at least a half-assed means of visual analog sensor condition communication.

And if all or any of THAT is true... it might be possible to insert an additional resistor in between this speed sensor and the PCM with just enough of an adjustment in its Micro-farad level of resistance to bump the speed up to the EXACT MPH that it should register at for a given larger OD of your particular tires. There MUST be at LEAST one Electronic Guru out in 'The Nation' with "the chops" needed to dope out a similar, simple solution to this problem. I refuse to believe that with an OBDII interface to the PCM... that the Speedometer Problem cannot somehow be "Jail-Broken". We all just have to think a little harder about it... and a solution will come:

http://www.autopartswarehouse.com/s...sor/2004/ARBC313306.html?anchor=ProductReview

 

[HARDTRAILZ]

May be able to change what the PCM thinks the gear ratio is to get you close.

 

[Mooseman]

Problem with dicking with the sensor, it will throw a code and probably disable the ABS because the sensors at the wheels won't match up anymore. And a resistor won't do it. It's a pulse signal. The PCM knows that for so many pulses with a specific tire size and gearing to show the appropriate speed. The only way is through programming the PCM in some way, which apparently is deep in the guts of this thing.

 

[mrrsm]

I know that this is yet another "Shot in the Dark" Digital, Programmable After-market Speedometer... but this one has a link on its main page to its .PDF installation manual describing many optional installation variations...and which is quite informative about how this technology works:

http://www.dakotadigital.com/index....t_id=292/category_id=240/mode=prod/prd292.htm