Tire size adjustment

[DieselDixon]

I'm going to be putting 285's on my truck in a few weeks and wanted to adjust the speedometer. I am not interested in the extra HP that some of these programmers have, I mainly want to adjust for the tire size and get rid of the speed limiter. Which one of the kits is cheapest that will do this? Or do you know if I can take it to the dealer and have them adjust for the tire size at least?

Thanks

[Phil B.]

With my 2001, the dealer would (could?) only adjust the ABS for different tire sizes and not the speedometer. I have the Predator and it handles the re-cal nicely. Others have used a splice in product from Superlift (I believe) that only addresses the recal. Good luck.

Makes me wonder if the power boxes that re-cal the speedo also re-cal the ABS settings for tire size(?).


Phil B.

[sdaver]

I would agree the predator.........plus a scan tool and some performance settings if you changed your mind... :D dave

[DMAX Daddy]

My Predator has NOT been accurate as of late. 4 MPH off at 70MPH accroding to my watch and GPS in a measured mile.

I hope 1.07 fixes the problem. :confused:

[Phil B.]

Randy- Did you verify that the gear ratio was set correctly? My predator mysteriously was reset to 3.72 and this messed with the speed. The algorithm they have is definitely close to accurate (according to my 12 channel GPS). I went one size larger and one size smaller to see if this was more accurate but their catalog of tire sizes was right on the money (+/- 2MPH).

[Sandaholic]

I believe the cheapest way is with the Hypertech Programer. I set it to my 285/75/16 Revos, took about a minute to program. Haven't had a chance to check with GPS but looks right when compared to traffic (if that counts for anything!).

[DMAX Daddy]

Phil,

Thanks for the idea, I'll check it when I get it back with 1.07 in it smile.gif

The thing is, it was perfect when I first did it. Hopefully it was just a brain fart

[RWTD]

Originally posted by DMAX Daddy:
Thanks for the idea, I'll check it when I get it back with 1.07 in it smile.gif

The thing is, it was perfect when I first did it. Hopefully it was just a brain fart Yeah, definitely check into what Phil said, as I have seen the exact same thing.

Another thing to remember is that the Predator (as well as any other programmer for the Duramax) uses math to compute the calculations, and if your tire isn't exactly say a 32.83" tall tire (which is what a 285/75-16 calculates to), then naturally your speedo will be off if you input this into the Predator as the "Actual Tire Size". This is why the Predator gives you the ability to change your tire sizes in such minute means (280/75-16, 290/75-16, etc.), to correct for manufacturers' variations in their tire heights. What I usually do is go to the manufacturer's website and find the specs on the tire and they will list the true overall height of the tire, and then I will find a standard tire sizing measurement to input into the Predator that equals that height.

Here's an example of something to note as well:

A 330/65-16 is just *slightly* taller than a 285/75-16 (32.89" versus 32.83"), and playing with size variations such as this can really help to get that last .25 mph you've been looking for in speedo accuracy ;)

I hope this helps!

Sincerely...

[jjackson]

Since the '04's are supposed to be shipping w/265's vs. the 245's we got, I'm wondering if the dealer can re-calculate the 03's using the 04 settings. That would at least make the speedometer closer for those of us who have the 285's..? Anybody tried that yet..?

John

[Chris Strandt]

I have a question as to the ability of these programmers to change the gear ratio/tire size. I'm looking at installing a Duramax powertrain into a Hummer.

The Hummer has an effective gear ratio in the back of 5.24, with 37 inch tires.

Is it possible with the Predator to input any given tire size and gear ratio? I could figure out the gear ratio and tire size of the stock drivetrain, and just recalulate the appropriate tire size (something pretty small).

Thanks

[DMAX Daddy]

My only concern was it worked for a while then one day I was playing with the GPS and noticed it was off. I hadnt hooked up the Predator in months and had not changed anything.

[sdaver]

chris it can be done.......steve cole could with a custom ecm.......or contact johan mangs at diablosport... :D dave

[RWTD]

Originally posted by Chris Strandt:
The Hummer has an effective gear ratio in the back of 5.24, with 37 inch tires.

Is it possible with the Predator to input any given tire size and gear ratio? I could figure out the gear ratio and tire size of the stock drivetrain, and just recalulate the appropriate tire size (something pretty small).Chris, the Predator can correct from a 10 inch up to a 40 inch rim, from a 100mm width to a 400mm width, and from an aspect ratio of 5 all the way up to 125. So, mathematically it will allow you to correct up to a 79.37" overall height of a tire (is there even such a thing for a passenger vehicle? :D ), but of course the limitation is within the pcm itself.

The pcm will accept large #'s, but on most GM vehicles it will start spitting out warnings in the form of brake lights, and/or ABS and SES lights, if you input variables via the Predator into the pcm that compute out to around 36" or greater. Since I doubt you're swapping over the braking and ABS system you most likely will not have any issues with codes set or brake lights coming on because of being out of the threshold limits of the pcm.

Also, anyone who needs special needs, please contact your dealer first, or if you are my customer then please come to me first. Do not go directly to DiabloSport (unless it is a revision upgrade, which I posted concerning earlier), unless instructed to by your dealer. Even then, your dealer is the one who is suppose to service and support you, and do the communication for you. My main point here is that if you purchase through a reputable company, then they will be able to assist you best when you are requiring anything. DiabloSport is an extremely busy company, and they can't always meet the demands of dealers' customers directly when the dealer is one who should try, first.

[Chris Strandt]

RunninWithTheDevil,

Thanks for the info. I will have to do my math and see what tire size would be equivilent with the lower gearing.

You brought up an interesting point.. and maybe I should start another topic.... how does ABS work with the Duramax PCM? I will be going non-abs since I perfer that setup offroad, and it makes putting the truck together alot easier. I assume the PCM is going to require input from the boo switch... but will everything run okay w/o having ABS?

Should I really be calling someone like yourself for customer programming for what I'm thinking about doing?

Thanks,
-Chris

[Lone Eagle]

The local dealers have several 04s on the lot. All have 245s and the dealer said there is no optional tire size available. Later! Frank :mad:

[flhrciblueice]

Originally posted by Lone Eagle:
The local dealers have several 04s on the lot. All have 245s and the dealer said there is no optional tire size available. Later! Frank :mad: I just ordered my truck and the spec sheets and option list did not list 265's. I had the salesman(my uncle) check and GMC told him that they would not be offering a larger tire. :rolleyes:

[Albee]

DieselDixon, I also went to the 285 tires in the BF Goodrich All Terrain KO's. I read on this forum at one time that it changes the speedo about 7.8%. I have found this to be a little off but not much. Close enough to keep you out of trouble with the law. I have a spread sheet with the figures in it. If you would like it just let me know. Good Luck.

[DieselDixon]

Albee,

What type of modifications did you have to do in order to get the tires to hit. How many turns on the TB's and what did you have to cut in order to clear?

Thanks

[Albee]

DieselDixon, I did not turn my torsion bars at all. I did have to trim the plastic in the fender well on the drivers side in front of the tire. I trimmed it up about 2-3 inches. That is all I had to do to get the tires not rub. I have heard of turning the torsion bars to raise the front end, but also hear you have to realign the front end after you do this. I have not done this. Good Luck.

[jeff800]

Here is a cool site for figuring different tires sizes and the effect it has on the speedo and gear ratios.
http://www.dakota-truck.net/TIRECALC/tirecalc.html

Here is another tire size site, for those of you who can't visualize what effect the numbers do to the physical size of the tires.
http://www.miata.net/garage/tirecalc.html

[DieselDixon]

Hey Albee,

That is a good side shot of your truck, if the 285's are in that picture could you send me the full size picture of it? mtd@yahoo.com

Also did you leave the stock wheels on or get new ones?

Thanks

[Albee]

I tried to send you a pic this morning and tonight it came back undeliverable. Sorry.

[DieselDixon]

Sorry about, my mail box was full. Give it one more try. Thanks

[Sandaholic]

Just an update, I verified my speedo accuracy with my GPS and it was dead on. I am running the 285/75/16 Revo on stock wheels, hypertech programmer set at 32.75".

Since my speedo is now accurate, does that automatically mean my odometer is accurate?