2005 Z71

First of all, hello all.  I'm new here and I have a few questions about my 2005 Silverado.

Currently, I have a 6" BDS IFS suspension and 3" BDS body lift on my truck.  I currently run 35x12.50s and want to go to 37s.  I have 17x9 wheels and I wanted to know if going 37x13.50 will be much wider than 37x12.50.  12.50s are anywhere from $50 to $75 cheaper than 13.50s depending on the brand.  My fear is that I'll get 37s that look too thin.  Any thoughts on this?  

On the same note, I talked to BDS directly and they said that I shouldn't have to change the axle ratio if I don't plan on seriously beating on this thing off-road.  Any thoughts on that and if I need to regear, who should I go through and what kind of price am I looking at?

2ndly, I get a shake when I get too around 35mph and it goes away at about 42mph.  I have dual stabilizers on my rig and have had the truck aligned and the tires balanced.  Any thoughts on what could be causing this?  The tires are slightly cupped, but not enough to make the shake that I'm getting.

Any help would be appriciated.  Thanks!!!  
____________________
2005 Chevy Z71
6" BDS Suspension and 3" BDS Body Lift
35" Cooper STT M/T
17" Rockcrawler Wheels
AIRAID Intake
PowerAid TB spacer
Flowmaster 40 series Cat-back exhaust
Hypertech "HyperPac"
________________
2001 Jeep Wrangler Sahara
3" Rubicon Express Suspension lift
33" Mickey Thompson MTZs

This thing has got to be a slug at times if you have not regeared it. First, the shake is likely from alignment issues. (some call it Caster death wooble) Stabilizers only try to mask the problem, you need to get to cause of it. Next, 35 are  really at limit for axles and front end here (33's is a better limit for hard play as those axles are not very strong) With 37's you will have even shorter front end life and asking for axle failure even more (and tranny failure too if you have not regeared axles) Sorry if I sound a bit harsh here but I am not going to sugar coat it and tell you it is okay.  

As far as the shake, I'm running rockcrawler rims which I do not believe are hubcentric.  Could this be the cause of it?

Ok, so if I stick with 35s and regear the axl, then I should be alright?

I'm very ignorant when it comes to gearing, so what sort of ratio would I be looking at?  What sort of parts are involved with it?  
____________________
2005 Chevy Z71
6" BDS Suspension and 3" BDS Body Lift
35" Cooper STT M/T
17" Rockcrawler Wheels
AIRAID Intake
PowerAid TB spacer
Flowmaster 40 series Cat-back exhaust
Hypertech "HyperPac"
________________
2001 Jeep Wrangler Sahara
3" Rubicon Express Suspension lift
33" Mickey Thompson MTZs

WIth big tires that have a different load center relative to tire and hub, they place more strain on front end alignment. OEM/stock specs are for stock tires, rims and offsets. You likely need to dial in additional positive camber and a bit more caster and make sure toe in is about 1/64 to 1/32 max, You get front end dialed in correctly and shake will stop and it will extend you front end life a bit (as far as ball joints and bushings which have been shortened with lift) On axle ratio, you have a 4L60e which has a pretty tall OD gear in it and about a 4.88 minimum is what you need here. Even this is pretty tame on the road with 35's in OD. (about 2100 RPM @ 65 MPH in OD) You need new ring and pinion gears for front and rear axles. You do not need a bearing kit which many will try to sell you if axles are in good health otherwise. Figure on about 300 for gears for both axles on line and about 500 to 700 labor  to have them installed. Do not buy gears locally unless you have no problems with paying a lot for them.  

My ratio is 3.42.  I called my dealership and asked them my gear ratio. When I am pricing new ring and pinions, its saying that it will only fit a 4.10.  4.88 Will Work In 8.6in. With 35-2022 Master Kit/Will Not Fit 2.56 Carrier.

I have no idea what that means.  Is there a place that I can go on the net to find out what type of transmission I have, etc.  I'm in Iraq and do not have the ability to look at the glovebox.

You are making me think that I've f'd up my vehicle by lifting it and putting the 35s on it.  The last thing I want is a money pit.  I've been driving it with 35s for over a year and a half.  Other than the shake, I haven't had any problems with it.  To me, it doesn't even seem to be sluggish.  Don't think that I'm getting upset, just confused more than anything.  I appriciate the info you've given so far.  
____________________
2005 Chevy Z71
6" BDS Suspension and 3" BDS Body Lift
35" Cooper STT M/T
17" Rockcrawler Wheels
AIRAID Intake
PowerAid TB spacer
Flowmaster 40 series Cat-back exhaust
Hypertech "HyperPac"
________________
2001 Jeep Wrangler Sahara
3" Rubicon Express Suspension lift
33" Mickey Thompson MTZs

Your limiting axle is front as it can "only" go to a 5.13, the rear axle to a 5.57 for a 4.88 is not a issue. You do not buy these gears at a dealer for two reasons, one they are limited to 4.10 because GM never offered anything deeper in those axles and two you will pay about 3x the after market price too. Look for some Motive, Precision or Yukon gears.  

I've done the formula to figure out the new gear ration that I would need for 37s.  Everything I came up with says 4.10.  Is there any reason you are suggesting 4.88?  Also, the ring and pinion of a 4.88 will fit my case/carrier without modification?  
____________________
2005 Chevy Z71
6" BDS Suspension and 3" BDS Body Lift
35" Cooper STT M/T
17" Rockcrawler Wheels
AIRAID Intake
PowerAid TB spacer
Flowmaster 40 series Cat-back exhaust
Hypertech "HyperPac"
________________
2001 Jeep Wrangler Sahara
3" Rubicon Express Suspension lift
33" Mickey Thompson MTZs

masterfoxscout:
I've done the formula to figure out the new gear ration that I would need for 37s.  Everything I came up with says 4.10.  Is there any reason you are suggesting 4.88?  Also, the ring and pinion of a 4.88 will fit my case/carrier without modification?

I do not know what "formula" you used but your truck was geared to tall from factory to begin with and lifts ads drag so do not think that to can match effective ratios and be good to go as you will not and OD performance will be poor and it will shift up and down a lot. 4.88 would be a good match here, 4.10 a poor one.  

4.88 it is then.  I've checked around and found it to be right on par with what you've said price wise.  Out of Yukon or Precision, which would you recommend?  
____________________
2005 Chevy Z71
6" BDS Suspension and 3" BDS Body Lift
35" Cooper STT M/T
17" Rockcrawler Wheels
AIRAID Intake
PowerAid TB spacer
Flowmaster 40 series Cat-back exhaust
Hypertech "HyperPac"
________________
2001 Jeep Wrangler Sahara
3" Rubicon Express Suspension lift
33" Mickey Thompson MTZs

They are both good gears. I would go with best price and vendor support. (if I had to choose it would likely be Precision because they have been around a lot longer) Motive is good too.  

Alright, so now that I've answered the regearing question.

So if I regear and actually replace the OE axles with maybe some Motive rear axle shafts and new IFS axle shafts, then I should be able to run this thing up and down the road with 37s?  
____________________
2005 Chevy Z71
6" BDS Suspension and 3" BDS Body Lift
35" Cooper STT M/T
17" Rockcrawler Wheels
AIRAID Intake
PowerAid TB spacer
Flowmaster 40 series Cat-back exhaust
Hypertech "HyperPac"
________________
2001 Jeep Wrangler Sahara
3" Rubicon Express Suspension lift
33" Mickey Thompson MTZs

Nope. Not unless you want a parking lot queen. Your truck is pretty solid with 33's so so with 35's and over loaded with 37's. Front end is not strong from pig to knuckles and suspension and even if you baby it, 37 place a lot of stress on front ball joint and bushing which will have a short life and then brakes will not work well either as they are not sized for big tires. If you want to try to push something that much you should at least start with a 3/4 ton. Unlike older truck of years past, modern 1/2 tons are more car than truck and pretty lightly built.  

I KNOW your truck HAS to be sluggish with 3.42's and 35" tires. I had 3.73's and it was a dog with 35's on my 2006! I stepped up to 4.10's and it's still not very impressive. Also, Your front end is at it's absolute MAX with 35's! I just yesterday replaced my right front hub assembly which wound up costing me over $500 by the time I got the allignment I went in for! OUCH! I have 68000 miles on my truck and when I gave the tire a spin it sounded like "wheel of Fortune"!
ps: I would usually NEVER pay someone to fix my vehicle, but it was already on the allignment rack when we found the problem and I needed it done ASAP so I could drive to Michigan next week.  

Any way I can get 16" rims on this thing?  I know that in 2005 they changed the OE brake assembly requiring 17" rims.  Is there anything aftermarket I can do to get 16 inch rims to fit?  Since I'm going to stick with 35s, I'd like to get something a little more beefy like a 16x10 or wider rim.  
____________________
2005 Chevy Z71
6" BDS Suspension and 3" BDS Body Lift
35" Cooper STT M/T
17" Rockcrawler Wheels
AIRAID Intake
PowerAid TB spacer
Flowmaster 40 series Cat-back exhaust
Hypertech "HyperPac"
________________
2001 Jeep Wrangler Sahara
3" Rubicon Express Suspension lift
33" Mickey Thompson MTZs

Again you should reconsider on rims because a wider rim has to use a different offset relative to load center of tires which places more stress of front axle suspension. So what this means is that a truck with 16x10 rim will tend to place more stress on front end than 16x8 rims because 16x8 will not have to have as much offset. As you increase width of rim you must increase offset because inside of rim/wheel must still be maintained at a minimum distance for chassis which means tire and wheel center is moved out from chassis which increase the leverage of it on front suspension and the stress it induces on it. Sorry if I sound like a downer or negative here but you are pushing your front ends with 35's and you do not need to push it further with bigger offsets and rims if you want best possible front end life, tire wear and handling/tracking.