Tire size & gear ratio
 

I need to change tire size and gear ratio on my 2003 ECM 5.3 4L65E, what is the easiest way.............least expensive?

Re: Tire size & gear ratio
 

I did mine when I mailed the ecu off for tune

Re: Tire size & gear ratio
 

Cheapest way is probably also the easiest. Give a local tuner like $20 for 15 minutes of his time to change it. (assuming your already using HPTuners and the ecm was unlocked).

Otherwise you've gotta mail-order it back to who tuned it for you, if the tune is locked.

You may be able to try a flash tuner like an SCT or Diablo, but many of them also "lock" the tune.

If you have HP Tuners yourself, you can just edit it in 5 minutes. Sure, $320 ain't cheap, but how many times do you have to pay someone a fee before you've paid yourself back?

Re: Tire size & gear ratio
 

Brew - Quick question. I have my tune licensed through my HPTuners software, if another tuner were to plug his laptop and HPTuner interface into my ECM, would he be able to tune it without having to purchase a new license?

Re: Tire size & gear ratio
 

+1 on buying the software. It will pay for itself very quickly, plus give you a really good troubleshooting tool.

Brew - Quick question. I have my tune licensed through my HPTuners software, if another tuner were to plug his laptop and HPTuner interface into my ECM, would he be able to tune it without having to purchase a new license?

Re: Tire size & gear ratio
 

All of the info is stored in the INTERFACE BOX, not in the laptop, or the ECM. Take YOUR interface to his shop, and he SHOULD be able to tune it without applying extra cost.

If HIS shop doesn't already have the "unlocks" for your year, then technically, he may ask you to pay. Some shops give a flat hourly or per-tune rate, regardless of if they have to gain a license (cost of doing business), others charge you for that service.

Re: Tire size & gear ratio
 

How far are you moving the gearing/tire size? Longhorn

Re: Tire size & gear ratio
 

The old gear is a 3:42 and the new is a 3:25, tires are not selected yet but I am trying to stay within a 1" to 1 1/2 shorter

Re: Tire size & gear ratio
 

Depending what tire size you are switching from, you probably won't affect the computer to much.

Check this site and plug in new gears/tire size and old gears/tire size. You're RPM doesn't change much.

http://www.ringpinion.com/Calculators/Calc_RPM.aspx

Re: Tire size & gear ratio
 

When you say will not affect much, do you mean the speedometer function?

Re: Tire size & gear ratio
 

Looks like your new gear choice will offset your new tire choice.

Re: Tire size & gear ratio
 

Thanks then I will run the computer tune that is in it now

Re: Tire size & gear ratio
 

Sounds like you are "good to go".... thanks for the calculations Hart rod ;) I went from 3.42, to 3.73's on my 02, did not mess with anything. The speedo is 4-5 mph fast on the read @ hyway speed.....that will just keep me out of trouble :lol: Longhorn