I've been thinking about upgrading my rims and tires with some 33x12.50 17's. I really want to make sure I'm doing everything right to make sure I will not be adding any extra added stress or opening myself to extra bills for repair. During my research, I've found some truck owners saying to regear the truck. What does this mean? I have the 2004 2WD QC with the Hemi. Would regearing be a must in this situation? How do I get my truck regeared if indeed this needs to be done? Thank you any suggestions or comments would be appreciated.

 

the main thing that would be done is chainging out the rear differential and puttin in one that has a higher gearing. since your wheels are going to be larger it takes fewer rotations to go the same distance, this will cause your spedo to be off. to counter act this you change the gearing in the differential.

I'm sure someone here knows a good bit more than I do, but I would think the drive train is stout enough to handle the larger tires and all you would need to do is to get your computer reprogrammed so the spedo reads properly due to the increase in tire size.

 

Well, first of all everything Drew said was correct. But the main reason for regearing is to get the engine back to the proper RPM at normal driving speeds. Because the tires are larger in diameter, you go the same speed at lower engine RPM. If it's too low, it'll be shifting in and out of overdrive often, causing wear to your transmission and killing your gas mileage. The engine will also have to work harder to overcome the higher final gearing (which includes transmission gear ratios, axle gear ratios, and tire size), the heavier tires, and the increased air resistance of the added width. This all adds up to a lot of stuff changing that your motor has to work against.

Second, I really doubt 33x12.5 tires will fit on a 2wd. I could be wrong, but I've got a set I tried on my 4x4 3/4 ton and they rub. That was with 10" wide wheels too though. Check to make sure they'll fit with your height and wheel backspacing before you buy anything and make a very expensive mistake.

 

Wow all that just for bigger tires. Don't a lot of people upgrade to bigger tires? I though all I would have to do was get my computer re-programed. I was wanting to put 33's on my truck too, but you make it sound like it's really bad for it. How much would it cost to get it re-geared?

 

The bigger tires can be compensated for by changing the computer tire size factor, but you will loose performance when going to a bigger, heavier tire set-up.

 

Well I happen to have some feedback on this issue.

I have a 2004 Qcab 2wd and just got my diff regeared.

I have a 7" lift and 35's on it before the regear I took my truck on a long drive, it was horriable it was down shifting ALL the time. I could tell it was putting alot of pressure on the trans.

When I got back from Vegas I went to have it regeared from a 3.55 to a 3.92 its is almost back to stock driving now well worth it imo. I have a friend who has a Chevy and he has a 10 inch lift and 37's and has not got it regeared you can acutally hear the diff. struggle.

Total I paid for the regear was $808.00 with the lift and tires/wheels I think my total would be around $3800.00


Also 33 will only fit if you get a front end lvling kit and 35 will fit if you get a 7 inch lift and 37 will fit if you get a 7 inch and a body lift.

 

I am changing my 3.92 LS for 4.56 LS. Don't know where you live, but in North Texas you can have that done for $425.

 

Reorg: Do you have a 4X4?

 

No, I have a 4X2 3.92 LS. I am changing out to 4.56 on 10/12/04 for $425 in DFW.

 

Here are some formulas that i got from some truck mags.

((((width*(ratio/100)/25.4)*2)+rim size))= tire height in inches

265/65R17=30.563"
35X12.5=35

(New Tires size/Old Tire size)*current gear=new gears.
(35/30.563)*3.55=4.0671