Gears and tires advice please

[uberbeans]

I'm presently running 12 bolt/detroit/3:73 rear 10 bolt/3:73's/e-locker front with 33 bfg mud terrains/sm465/205/383/6 inch lift. I am upgrading to 37" IROC radials and am not sure which gears to change to. Presently living in Florida I am not doing much rock crawling just mud and trail stuff and general off roading though the truck was built when I lived in Washinton as a rock/trail rig. I am moving back but I will focus on a 14 bolt/d60 swap the for the rocks. Presently, I am keeping the 12 bolt/10 bolt, I am getting the 37's. I need to know what you guys (and gals) think I should run for gears. I heard something about not being able to use my current detroit on certain gear sets (4:56's and above?) also I am worried about strength of my front and rears if I go to the 4:56's. There is a guy I know here that is running a k-5 with 44's on 10-bolts front and rear with a 450+hp small block (all high rpm power as opposed to my all low end torque) and he has NEVER broke his front/rear ends and he is running lock-rights. Remember I am mostly mud and offroad now with rocks later (no problem with switching, later). I won't go to a gear set that doesn't allow me to use my current detroit. I have the "granny-low" 465 so I was wondering if that would make up for the lack of 4:56's if I went to 4:11's. I respect this forumsknowledge base I would really love some level headed advice. Later.

 

[BranndonC]

you sound like your right on track, I was thinking 4.56 throughout the post but if that does mean you cannot use your locker, 4.10's it is, but with the added cost of regearing, you probably could put some work into the engine and get the same feeling. that way you would still have the extra kick when you upgraded to 1 tons later. Hopefully someone here can confirm weather or not you can go 4.56's

 

[uberbeans]

So I guess the real questions are whether or not 4:56's will work with my present detroit that is attached to my 3:73's and if it will I will have a lot of breakage problems when I am mostly running mud and trails for now. I am running a really strong 383 with 37's.

 

[BranndonC]

breakage comes from traction and power, in soft mud you should be ok but if you jump a little or get traction all of the sudden you could brake things. I have no experiance with that though, only what i've read here over the past few years. I'm sure someone else with experiance will help more than I am

 

[MUDSTEADY]

I am running 4.88's on a 12 bolt. With a 3.08 factory gov-loc set-up using a Mr. Gasket ring gear spacer. I had to grind like 1/16" off one tooth on the ring gear to get the pin in not to worried about that the patter isn't even close to it. Haven't run it yet this weekend will be the test I am a little worried about the ring gear spacer it was 12 bucks and a detroit which I want is 600 just don't have the cash right now.

 

[71 Blazer]

If your just running through mud what is wrong with 3.73's? I have those gears in my 71 Blazer with stock axles, 35" tires and don't have any problems in the mud. If you plan on upgrading later, save your money, do it right once. For now just take it easy, roll into the mud slow and hit the gas as you get stuck. You don't have to break a land speed record to make it through a mud pit.

 

[mr_blasto]

the carrier break for 12 bolts is 3.73 and up. I tought that maybe it was different with the detroit locker, but then I went to this site:
http://www.detroitlocker.com/images/LTPCAGweb91305.pdf

There is also looks like the carrier break for detroit lockers is 3.73 and up. If you want a similar setup to stock with 3.73's you can run 35 inch tires with 4.56's or 37 inch tires with 4.88's. If you want lower RPM's, adjust accordingly. There are some good links on ck5 for gearing calculators and the like if you do a search.

If you are interested in Yukon gears for a 12-bolt axle for the 3.73 and up carrier, I have some new in box 4.88's with the master install kit for sale that I am trying to sell.

 

[K5MONSTERCHEV]

Well, lets see. Assuming you had 31's stock and are going with 37s thats a 19% change. If you re gear to 4.56 thats a 22% change, so itll give you a little more then stock, where as 4.10s is only a 9% change over stock. I say 4.56s.

 

[jekbrown]

answer to ALL non-rockwell gear questions: 5.13s.

j

 

[mr_blasto]

Well, lets see. Assuming you had 31's stock and are going with 37s thats a 19% change. If you re gear to 4.56 thats a 22% change, so itll give you a little more then stock, where as 4.10s is only a 9% change over stock. I say 4.56s.

I don't mean to pick a fight, but according to tirerack.com his blazer either came with 225/75-15's or 235/75-15's, which is a lot different than a 31" tire. The first would measure 28.29 inches while the second would measure 28.88 inches. Going to 35's from the larger size would be a 21.2% change, and going from 3.73 to 4.56's would be a 22.3% change, which is pretty close, like I said. Going from the larger of the stock sizes to a 37 inch tire would be a 28.1% change and going from 3.73's to 4.88's would be a 30.8% change, again pretty close like I said.

I am not trying to peddle something just because I have it. I was going to run 4.88's with 35's on my DD, but for the price of having the gears installed I picked up some 1-tons (which happen to have 4.56's which I will be running a 37" tire). If I were picking gears for 37" or taller tire, I would go with 5.13's or numerically higher, but that is just me.

I recommend using a calculator and playing around with it to see what combination works best for you.

 

[K5MONSTERCHEV]

I don't mean to pick a fight, but according to tirerack.com his blazer either came with 225/75-15's or 235/75-15's, which is a lot different than a 31" tire. The first would measure 28.29 inches while the second would measure 28.88 inches. Going to 35's from the larger size would be a 21.2% change, and going from 3.73 to 4.56's would be a 22.3% change, which is pretty close, like I said. Going from the larger of the stock sizes to a 37 inch tire would be a 28.1% change and going from 3.73's to 4.88's would be a 30.8% change, again pretty close like I said.

Thats why I said "assuming". IN anycase, even with 28.5" tires stock, and going to 37s, thats a 29% change. So he would actually need 4.88s because that would be a 30% change whereas 4.56s would only be 22% change. Basically were on the same page.

 

[Masiony]

...There is a guy I know here that is running a k-5 with 44's on 10-bolts front and rear with a 450+hp small block (all high rpm power as opposed to my all low end torque) and he has NEVER broke his front/rear ends and he is running lock-rights...

that one is just a matter of time. if he has never broke it, he has never wheel'd it.

...I have the "granny-low" 465 so I was wondering if that would make up for the lack of 4:56's if I went to 4:11's...

this would only be something that would affect you if you were worried about your crawl ratio. most people choose their gears by their tires vs. highway speed. unless you cruise the freeway in first gear it does not affect it. i have ran 4.56 and 35's with a 4 speed. it was a bit too short. 4.10 would have been better. but with 37's you would probably be right on the money with 4.56's. and you can probably get "thick" gears if they make them for a 12 bolt.

 

[Masiony]

I don't mean to pick a fight, but according to tirerack.com his blazer either came with 225/75-15's or 235/75-15's, which is a lot different than a 31" tire. The first would measure 28.29 inches while the second would measure 28.88 inches. Going to 35's from the larger size would be a 21.2% change, and going from 3.73 to 4.56's would be a 22.3% change, which is pretty close, like I said. Going from the larger of the stock sizes to a 37 inch tire would be a 28.1% change and going from 3.73's to 4.88's would be a 30.8% change, again pretty close like I said.

I am not trying to peddle something just because I have it. I was going to run 4.88's with 35's on my DD, but for the price of having the gears installed I picked up some 1-tons (which happen to have 4.56's which I will be running a 37" tire). If I were picking gears for 37" or taller tire, I would go with 5.13's or numerically higher, but that is just me.

I recommend using a calculator and playing around with it to see what combination works best for you.

my "stock" K5 came to me with 31's.

 

[uberbeans]

So with 37's and 4:88's sound like it is pretty close to the stock set up for the ratio between tire size to gear number. It really is at a high rpm on the highway already since it isn't a overdrive transmission (higher than most other vehicles, anyway). I was mostly concerned about strength and if my detroit could be used with the new gears. Any more advice?

 

[wayne]

that one is just a matter of time. if he has never broke it, he has never wheel'd it.

I have to laugh at this statement. I know a lot of guys running the mud boggs and using half ton axles and 44's. A friend of mine is running an 87 K5 with a 10 and 12 bolt both with spools and 4:56's turning 44's behind a built smallblock and the axles held up fine all last season. The only one I saw brake last season was a 10 bolt front that the knuckle broke off when he hit the side of the pit going full bore.

 

[ZooMad75]

4.88's with 37's and a sm465 non-od trans would put your cruise RPM at 65 mph between 2800 to 3000 rpm. 75 mph would come it at around 3300 rpm. The big tires give a natural overdrive effect since each revolution of the tire takes you further down the road than a smaller tire would.

If you plan on switching to a D60/14b combo soon, money spent now to regear the 1/2 ton stuff just seems like a waste of money to me. Without adding the cost of the D60/14b axles, you end up spending more money to change the 6 lug wheels for 8 lug and then you sould still have to regear the D60 and 14b to 4.88's.

I defineatly know why you want to change gears now. Heck I've got almost the same setup (465/D44/12b with 3.73's) but with 35's. And you bet it's a dog down low but I know I will be at least swapping a 14b (and 8 lug rotors for the D44). I don't know when, but I'm saving my money for the swap and don't plan on spending money on the 12b to regear or upgrade with a locker. I guess I'm crazy that I don't like to do things twice. It's still driveable on road and off road I've got enough gearing choices between 4lo and granny gear to still get through well.

 

[jekbrown]

I have to laugh at this statement. I know a lot of guys running the mud boggs and using half ton axles and 44's.

this prolly works because mud bogging is the least abusive terrain you could ever have. Without much traction, its hard to break things. Seriously, assuming you keep mud/water from getting inside the axle, agressive driving on the street probably abuses axles more than bogging does.

Most of us do trails and/or rocks though. In that terrain, where there is plenty of traction to be had sometimes, 44s will absolutely destroy 10 bolts. Possibly in the staging area before actual wheeling even starts. lol!

j

 

[uberbeans]

I really appreciate all of the advice. I am going to be staying in the area for probably another 4 years or so and will keep the 12/10 combo for now with probably 4:88's and the 37's. I mostly wasn't sure about the compatibility with the detroit. Those gear tire calculators are very handy! It's funny having a "rock rig" in Florida. I've got the tube wraparound bumbers and the rock sliders and all of the mud guys are really bare, running 10 inches of lift and 44's! I've got only 6 inches and 37's. (and no rebel flag) All of these guys think that it's puny!

 

[wayne]

this prolly works because mud bogging is the least abusive terrain you could ever have. Without much traction, its hard to break things. Seriously, assuming you keep mud/water from getting inside the axle, agressive driving on the street probably abuses axles more than bogging does.

Most of us do trails and/or rocks though. In that terrain, where there is plenty of traction to be had sometimes, 44s will absolutely destroy 10 bolts. Possibly in the staging area before actual wheeling even starts. lol!

j

I know why they last, it's just the statement that I have to laugh at.

 

[Masiony]

So with 37's and 4:88's sound like it is pretty close to the stock set up for the ratio between tire size to gear number. It really is at a high rpm on the highway already since it isn't a overdrive transmission (higher than most other vehicles, anyway). I was mostly concerned about strength and if my detroit could be used with the new gears. Any more advice?

get thick gears. if you are below the carrier break.