OK I could be way off here but my gears were turning all day. This is somewhat loose but follow me. Looking at an old TJ speedo gear chart I looked up what 35" tires and 4.88 gears called out for 39 tooth gear. I then looked at any gear and tire combo that would beable to be flashed by a dealer and found 4.10 gears and 29" tires(stock tires on an X) uses the same tooth pattern. Like I said loose but in theory since this is all ratio's that we are changing this should work for all you guys with 4.88's and 35's. When the 08's come out and 3.73's are available it sould work for guys running 4.10 and 33's. Shoot me down if wrong but it should work. Check the chart. Remember DCX can flash for 4.10 gears soon 3.73 and a variety of tires under 32.2"

http://go.jeep-xj.info/HowtoSpeedoGears.htm

 

You are on to something. The math works out best those of us running 4.10's and 35s.

If you do the math, with 35's and 4.10 gears the new effective gear ratio is 3.75:1. So if you have the dealer flash our computer to simulate having the X package with the optional 32" tires and 3,73 gears----PROBLEM SOLVED!

THANK YOU VERY MUCH!

When will the dealers have the ability to flash for 2008 tires/gears?

- Bill

 

I found this calculator and it verified my math: http://www.4lo.com/calc/geartire.htm

- Bill

 

Too bad the speedo has nothing to do with gears since it uses a wheel speed sensor to derive vehicle speed. Speedos won't be correct until someone can flash for larger tire sizes.

 

The sppedo is being picked up by a magnetic tone ring it doesn't change regardless of gear or tire size. So if you match the same ratio it should work. The Flash essentialy represents the physical speedo gear that was in the older models nothing more.

I am going to stop by the dealership today for warranty work I will ask about 08 flashes.

 

Oh yeah the dealer flashes for gear as well since they just did my x when I put rubi tires on. There is a direct relation between gears and tires they need to flash for both.

 

My understanding is the speed is calculated off of revs\mile. There is a spot to put in gear ratio on a different "screen". The revs per mile is actually in the ABS module of the PCM. Very similar to how the speedo correction is on my Dodge truck. You change the gear ratio, then change revs\mile in the ABS ... viola ... correct speedo.

The PCM doesn't know what a 31" or 50" tire is ... doesn't care ... it only knows revs per mile. This is where you can get correction even if you don't change gear ratios. But, DCX has gotten wise. The Dodge trucks can now only be flashed to the equivilent of 285's (because that is what is on a Power Wagon) and our Jeeps to the Rubi size. And as a side note, getting the ABS part correct can save you a lot of trouble ... you nail the brakes and end up with the brakes releasing because they think they lock up and you run in to someone, your insurance company could deny the claims as you functionally altered the vehicle safety systems.

Also, Jeep could deny ALL warranty due to the increase in tire size ... so be careful ... and those of you saying "oh no they can't ... all I changed was tires" ... yes, they can ... by increasing tire size and not correcting the ABS module ... thus the speedo AND odometer are wrong ... Jeep has no way to verify the EXACT mileage of the vehicle ... and this is what ALL warranty is based off of (other than years of course). A friend in Indiana just went through this on a TJ ... 2 years in court costs over a blown tranny (granted his dad represented him) ... he was at 33xxx miles ... Jeep claimed he was over the 36000 miles even though the TJ registered 33xxx.

Outcome: Jeep won, he was fined $5000 for "knowingly altering the odometer of a vehicle", his title was converted to a salvage title due to "unknown or inconsistent odometer readings" and ordered to pay Jeep's court costs ... he is appealing that decision. Bottom line, be prepared to pay to play.

A good service manager\director is worth all the beer in Germany. I continually thank mine and ensure he is never thirsty. I have had a few claims that could have gone either way as my fault or Dodge's fault ... valid arguments both directions. I have yet to come out of pocket ... but I never ask for a free rental ... never demand it be done by x date, etc. I have been know to yell and scream at the new car sales guys ... heck, packing up and leaving is a great negotiation tactic ... but in service I am as zen as I can get.

 

Interesting... I wonder what AEV is doing to calibrate the speedo.

 

Here's my question though, if someone ha 35" tires, and asks for a speedo calibration, and Jeep is unable (or unwilling to do it) and said person's ABS fails because of that reason, could Jeep not be partially or fully liable? Especially because they are technically able to do it (AEV can) but refuse to do so possible to give them an advantage on warranty claims (which is the only reason I can see them not doing it)

 

nope ... Jeep can say "we can program up to an xxx size tire as that is what we offer". Once we as consumers chose to operate the vehicle outside of those conditions, we assume 100% liability. Now if ABS failed because the brake line coming off the master cylinder exploded .... maybe. But i guarantee Jeep would have an easier time proving the now needed higher pressure required to break due to the large tires caused it than you will be able to prove faulty metal.

Modifying vehicles is VERY much like Vegas in two ways:

1 - It is ALWAYS a gamble ... be prepared to lose, but enjoy the victories

2 - You have to pay to play