(updated) First impressions of 35's on my Eco Diesel

[Bulldog10]

My Cooper 35's with Mopar 2" Lift and Black Rhino 17" are to Die For!! 22mpg and still climbin!

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[Bulldog10]

Sorry if this was already answered but does anyone know the cost of having the dealership reprogram for tire size? The idea of having to remove a Tazer every time you visit the dealership sounds like a pain.

NUTHIN! Just Ask!

 

[M390]

Mopar accessories are guaranteed for 2 years unlimited mileage I believe. If you install any other random part on your vehicle which was not on it from the factory nor can be added through the Dealer Connect vehicle options area it is considered a modification. Modifications are not covered by warranty regardless who installs the part. Anything damaged due to that part being installed on your vehicle is not covered either. Gearing changes alters emissions which can be another ball of wax.

It has to be proven the additional parts caused the damage by the dealership. That’s where the Magnuson Moss Warranty act comes into play. Technically changing tire size alone changes the effective gearing of a vehicle also ”altering emissions“...

 

[cecaa850]

It has to be proven the additional parts caused the damage by the dealership. That’s where the Magnuson Moss Warranty act comes into play.

I believe that you have to prove that it didn't which can be much harder. The manufacturer can deny coverage if they think a non Mopar part caused it. They don't need to prove anything at that point. To reverse that, you'll probably need a lawyer and end up in court. Ultimately you may win but it could cost you more than the repair to do so.

 

[cecaa850]

NUTHIN! Just Ask!

Have you had that done for free? To change the tire size at the dealership I thought that you had to buy a service contract which will allow a one time change.

 

[BEERviper]

Have you had that done for free? To change the tire size at the dealership I thought that you had to buy a service contract which will allow a one time change.

I've never heard of a dealer to do this, nor anything else, for free. I had my dealer install a Mopar 2" lift and 37" tires on Mopar wheels and they "included" the tire size reprogram as part of the labor charge. Sadly I don't think they entered the correct tire size as my speedo is 1 mph off from radar or GPS.

I think the dealer is actually charged to enter the new data into the FCA/St system so they wouldn't ever do it free.

 

[cecaa850]

I think the dealer is actually charged to enter the new data into the FCA/St system so they wouldn't ever do it free.

That's correct to the best of my knowledge. It isn't cheap and it's only good one time.

 

[M390]

I believe that you have to prove that it didn't which can be much harder. The manufacturer can deny coverage if they think a non Mopar part caused it. They don't need to prove anything at that point. To reverse that, you'll probably need a lawyer and end up in court. Ultimately you may win but it could cost you more than the repair to do so.

That dealership gets a rep for doin that repeatedly and you can bet it’s gonna hurt their sales. Either way I’m not livin in fear. Gonna continue to mod mine and enjoy it to the fullest. If one is worried to death every little mod you make is gonna break something else you’re probably in a pretty low quality rig to begin with. I certainly don’t feel Jeep Gladiators fall under that category

 

[cecaa850]

That dealership gets a rep for doin that repeatedly and you can bet it’s gonna hurt their sales. Either way I’m not livin in fear. Gonna continue to mod mine and enjoy it to the fullest. If one is worried to death every little mod you make is gonna break something else you’re probably in a pretty low quality rig to begin with. I certainly don’t feel Jeep Gladiators fall under that category

Mine is not bone stock either. I have a BMW M2 that I bought new and immediately started putting performance parts on it. If something breaks, you won't hear me cry because BMW won't warranty it. I weighed risk vs reward prior to starting swapping parts on it.

 

[tcramer11]

Ahhh, I think I get your point. Thanks! I'm going to put it in my own words - and if you don't mind - correct me if I'm wrong:

(1) The stock ecodiesel gearing (3.73) is not the correct gearing for a stock tire (when you say stock tire do you mean the Rubicon 33-inch tire, of the other models which come with what - like a 29 or 30?).

(2) Because stock gearing is over-geared, moving up in tire size (to a 35?) actually results in the correct gearing (i.e. gearing that better matches the diesel engine's power band).

According to your calculations, would the following make sense in the JT Diesel?

3.73 - 35 inch tire
4.10 - 37 inch tire
4.56 - 40 inch tire
4.88 - 42 inch tire

Thanks!

Did u get a reply to ur follow up?

 

[tcramer11]

Negative. Let me explain more clearly what I meant:

The diesel has a super narrow power band. It makes peak torque at 1,600 RPM. By 4,000 RPM it's out of juice. Totally different animal than a gas engine. Completely different.

On a gas engine, higher RPM actually puts you in the "meat and potatoes" of the power band, so, gearing the axles down to raise the RPM up can be a benefit sometimes. Not always but sometimes. And that's why guys traditionally have always re-geared Jeeps. Jeeps needed more RPM to start with, so adding larger tires made a bad situation worse. Re-gearing was necessary.

On a diesel, the power band is really narrow and the sweet spot is right off idle. So your goal is to keep RPM as low as possible. Current Jeeps are coming from the factory over-geared. 3.73 is overkill. My truck has 3.92 which is overkill. So what we need is to either gear the axles UP (numerically lower), or, add taller tires. By adding taller tires you're effectively doing the same thing, i.e., dropping RPM. And that's what you want. Lower RPM.

We can see a perfect example of this in the Ram with the same engine and transmission as the Jeep. The guys on the Ram side of the forum who have 3.21 axle gears are seeing about 20% better fuel economy on average, compared to the guys with identical trucks running 3.92 gears. It's all because on a diesel the opposite is true; you want LESS RPM not more.

U reply to stixman s follow up question ? Thx

 

[Jocww]

I've never heard of a dealer to do this, nor anything else, for free. I had my dealer install a Mopar 2" lift and 37" tires on Mopar wheels and they "included" the tire size reprogram as part of the labor charge. Sadly I don't think they entered the correct tire size as my speedo is 1 mph off from radar or GPS.

I think the dealer is actually charged to enter the new data into the FCA/St system so they wouldn't ever do it free.

Gupton charges 150 to do this. I asked them not to and will put it towards the tazer

 

[BEERviper]

Gupton charges 150 to do this. I asked them not to and will put it towards the tazer

Yep that's the right idea, I wish my dealer gave me that option.

 

[Jocww]

Yea, Matts been pretty cool with the parts. Im wondering if I should do the Fox steering stabilizer for 170? If its needed or not. He says the adjustable track bar is not needed, but if i wanted to i could do the steering stabilzer. Is this a good price and should I do it? Im going to 37s right off the bat so I wont know what I am missing in terms of performance. And so I could roll it into financing.

 

[mrmo]

I don’t get your argument. You say diesels have a narrow power band, so don’t regear. Isn’t that even more of a reason to regear if you put on bigger tires? The larger tires will throw off the factory designed gear ratio, so the narrow power band of the diesel makes it even more important to get back to the intended ratio, hence, you need to regear. If the power band was super broad, regearing would be less crucial.

I agree, putting 35's on my diesel Willys and swapping out the 3.73 to a 4.11 will essentually return to the same affective gear ratio within about 100 rpm. That plus the GDE tune i will be set

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