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Discussion Starter #1
Figured this would be good info for all the 4x4 guys out there. This is the formula that you need to use to figure out what gears you "need" to get for your truck.

New Gears = (New Tire Size X Old Gear Ratio) / Old Tire Size

Spelling it out...
Your new gear ratio equals the new tire size multiplied by your old gear ratio. Take that number and divide it by your old or stock tire size.

Here's how the formula worked out for me:

New Gears (NG) = (41x4.10) / 31
NG = 168 / 31
NG = 5.42

So by the numbers, I would have needed a 5.42 gear set to get me back to my stock performance with 4.10 gears and 31" tires. As is usually the case, the gear guys don't make EXACTLY the ratio you need, so you'll need to search for a gear ratio that's close to what you wind up with. For me it was 5.38 gears from Yukon.

There are several VERY usefull calculators under the "TECH" tab at the top of the DodgeTalk.com page, directly next to the blinking "CHAT" area. Click the "TECH" buttons, then click on the "Calculators" tab once it pops up.

Best of luck!
 

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Cool, thanks for the info. My sluggish 3.55's should be replaced with something in the neighborhood of 4.10. Just don't have the money right now :(
 

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OK I went to a site (Accuautoparts) that had 4.56 gears from three makers. They all had different prices. Is this something where you get what you pay for or are the gears just about the same quality. I'm gonna call them later this week.

Hey 01 OFF ROAD. I was looking into getting the tru trac detroit locker, and I was wondering if you drive your rig on the road or just for wheelin. My concern is with driving around town. DO the lockers make a lot of noise and are they funky in turns. Any info would be great. I'm gettin ready to spend some dough real soon, and if I change the gears I want to get the locker while the diff is open. Talk to you later.
 

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Discussion Starter #4
MUDDOG said:
OK I went to a site (Accuautoparts) that had 4.56 gears from three makers. They all had different prices. Is this something where you get what you pay for or are the gears just about the same quality. I'm gonna call them later this week.

Hey 01 OFF ROAD. I was looking into getting the tru trac detroit locker, and I was wondering if you drive your rig on the road or just for wheelin. My concern is with driving around town. DO the lockers make a lot of noise and are they funky in turns. Any info would be great. I'm gettin ready to spend some dough real soon, and if I change the gears I want to get the locker while the diff is open. Talk to you later.
My rig is my daily driver. I do 26 miles round trip. I've got a full blown Detroit locker in the rear. I decided to keep the front open. Here's the problem. My truck's in the shop and won't be done till Thanksgiving, so I can't tell you from first hand experience how the Detroit is on the street.

What I can tell you is what made me decide to go with the Detroit vs a "lunch box" locker. First and foremost, there isn't much stronger than a Detroit. I've heard about too many problems with the lunch box lockers. I don't want to have to deal with all that. Second is the traction. Boom, it's there. No buttons to push, no spinning tires for 15 minutes while the clutches spool up, etc. Finally, there's plenty of people out there running Detriots on the street right now.

Don't think you can just throw a Detroit in the rear and drive like you normally do. With a locker in the rear, you're going to have to re-learn how to drive. Any locker is going to load up when you take a turn and hit the gas. That causes tire chirp, and it can't be good for your drive line. This is where the limited slips and most of the lunch box lockers are more friendly on the streets. Think about coming to a stop at a red light, or stop sign and having to make a sharp right hand turn. You'll definitly have to re-think about how to take those turns with the locker. Not saying it can't be done (or I wouldn't be doing it), just be careful when you're re-learning how to drive.... and IF you have a significant other, make sure he/she know's what they're getting into.

You've got the right idea about doing gears and locker at the same time. MOST places won't charge you extra to do a locker while they're doing gears. I'm paying $250 per axle for gears / lockers. Plus another $500 +/- in parts. Plan on spending between $1000 and $1500 for gears and a locker.

I was encouraged to do a locker in the front axle. That's right - full Detroit! And that came strait from the guys at Randy's Ring and Pinion! Reason being is our front axle disconnect. I decided against it, because I'm not THAT hard-core..... yet.
 

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Hey thanks 01 offroad. Let me know what you think after you get your truck back. I still have a lot of meat on my MTR's (33's) so I think I have some time before I make the change. I think 4.56 gears with 33's may give me too many RPM's when I drive on the highway to work. Plus winter is coming. bbuuuuuuuuuuuuuuurrrrrrrrrrrrrr. I only go wheelin every now and then in the winter. One thing I want to do this month is get the 3'' body lift. I tried to post some pics last night of my rig but the shots were too big. I will see if I can modify the pics with irfanview.
 

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Discussion Starter #6
MUDDOG said:
Hey thanks 01 offroad. Let me know what you think after you get your truck back. I still have a lot of meat on my MTR's (33's) so I think I have some time before I make the change. I think 4.56 gears with 33's may give me too many RPM's when I drive on the highway to work. Plus winter is coming. bbuuuuuuuuuuuuuuurrrrrrrrrrrrrr. I only go wheelin every now and then in the winter. One thing I want to do this month is get the 3'' body lift. I tried to post some pics last night of my rig but the shots were too big. I will see if I can modify the pics with irfanview.
Cool. Will do. With any luck, I'll have my truck by Thanksgiving.
 

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WOW, this is tellin me I will need 5.91's...I wonder how many rpms that is on the hwy lol
 

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Well I am going from 225/75/16s to 265/75/16s according to the equation I need to change my 3.55s for 3.84s (which I guess means 3.92). So now with the bigger tires, this means it will be slower off the line, right? Will my speedo read faster or slower than actual? I think I am getting a head ache.
 

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i dont think so scooter
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I have 265/70r17, which is like a 31.5" tire and i couldn't see using more than 3.73 with these.
Yes, with bigger tires and no gearing it will have slower acceleration. 3.92's might be alright though, you'll just turn a few hundred more rpm's at high speed.
 

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Well I'll be sticking with my 3.55's for now. I really can't afford to do gears, although I will be looking into an LSD unit in the near future, so I'll probably just figure in gears then.
 

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Bayly go to TECH at the top of the page. There are a few calculators. You may have found it by now. I haven't been on this site in a while.
 

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I am getting ready to do gears using the formula of 39.5x3.55 I get 140.225 if I devide that by 31 (265 70 16) I get 4.52 is this correct? Do they make a 4.52 or what is the next steepest gear made I believ it is the 4.56. What is the best limited slip to replace the rear gears with?
 

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yes 4.56 is next steepest gearset. Go with a detroit locker. Your truck looks like a mudder...
 

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Big Green
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What does the detroit locker do this is a 75% road truck we take to the shows and hardly drive gets driven mabye 50 miles a month
 

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Discussion Starter #17
elliottcarlose said:
What does the detroit locker do this is a 75% road truck we take to the shows and hardly drive gets driven mabye 50 miles a month
I've had my Detroit in the truck for quite some time now. It's about 90% "invisible." The ONLY time I know it's there is when I'm making a sharp turn and hitting the gas. Then I'm greeted with a nice "chirp" from my tires. Once I'm going straight again, it's like it's not even there.
 

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New Gears = (New Tire Size X Old Gear Ratio) / Old Tire Size
In my opinion, this is not a very good formula to use to determine your next gear size. It leaves out too many other variables, like the weight of the vehicle involved, weight/tread design/rolling resistance/etc of the new larger tire, transmission types (auto versus manual), transmission gear ratio's, etc... I find that this formula, and most gear charts that you see, are probably about right for Jeeps and other small vehicles, but on our full size heavy Rams, they come up short. I recommend doing the calculation, then going with at least the next size up from what that shows to get back close to stock - two sizes up for more performance.

For example, when I went from 265/75/16 (31.64" diameter) to 285/70/17's (32.7" diameter), this calculator told me I needed:

(32.7 X 3.55) / 31.64 = 3.66 gear

Ignoring this result, I went with 4.10 gears instead, and they did pretty good, and could have probably even gone to something like 4.27 (if they made that for the 9.25 rear). Had I followed this formula, I probably would have just stayed with my 3.55, or else tried a 3.73 or a 3.92, and would have been disappointed. This is the same reason that when I regear for my 35's, i'm going with 4.88's instead of 4.56's like most people do. This formula says I should only need a 4.38, but I know that's bs.
 

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Big Green
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I want to do what ever takes mine back to stock where the speedo is correct I will go one deeper if necessary. I am not going to race this truck and the v10 pulls her fine now but miss the get up and go it used to have.
 

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I used a GPS to figure out what my speed was. My gauge reads 5 mph slow. I have 35's and running 4.56 gears. The tach reads 2600 RPMS at 80 mph. Another thing I will say is that my beast is a GAS HOG more than ever. My computer is saying I get 10-11 MPG, but thats probably off..........but pretty close.

What gear set do you have elliot? 3.55? If so, your truck must be a dog with 39's.
 
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