# Changing Gears



## Sacmetrofire (Sep 21, 2005)

Im getting my differential gears changed tomorrow from 4.34 to 4.11. Has anyone gone that route and if so, notice any change in towing?

Tim

Thanks ahead of time.


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## 2500Ram (Oct 30, 2005)

Sacmetrofire said:


> Im getting my differential gears changed tomorrow from 4.34 to 4.11. Has anyone gone that route and if so, notice any change in towing?
> 
> Tim
> 
> ...


4:34 to 4:11 why







Did you mean 3:54? Actually I've never heard of that gear ratio but there are tons out there.

What are you trying to accomplish, better MPG, towing, top end? If any of those listed all you will accomplish is maybe better MPG while NOT towing. If you were talking about a 3:xx gear to 4:11 you will see improved towing, off the line seat of the pants feel, lower top speed but if you stay in the speed limit







you won't see much difference, just higher RPM's.

Bill.


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## oiler (Jan 5, 2005)

2500Ram said:


> Sacmetrofire said:
> 
> 
> > Im getting my differential gears changed tomorrow from 4.34 to 4.11. Has anyone gone that route and if so, notice any change in towing?
> ...


don't think there is such as a ratio. 
more than likely you've got a 3.73 or a 3.42 ratio.
4.34 to 4.11 would be a step down for towing
Jeff


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## ee4308 (Aug 23, 2005)

Must just be a typo. I noticed in the signature block that he has posted there a 3.43.


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## 2500Ram (Oct 30, 2005)

ee4308 said:


> Must just be a typo. I noticed in the signature block that he has posted there a 3.43.
> [snapback]62802[/snapback]​


That would help for towing then, minimal effects with an OD tranny for daily driving.

I should read the sig line more often









Bill.


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## Ghosty (Jan 17, 2005)

You will notice a significant difference...

According to the manual you should get about 1200 more towing capability going from a 3.43 to a 4.11 but remember this does not increase your GVWR ...

Your RPMs will increase about 1000 when comparing before and after at the same speed ...

your gas mileage should drop by about 2.0 mpg I figure ... (looking at the sticker info published by Chevy between a 3.43 rear and a 4.11)

You should also think about investing about 80.00 in a Throttle Body Intake for your carb -- will increase your gas mileage by about 1 mpg and give you about 15 more hp...


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## 2500Ram (Oct 30, 2005)

Ghosty said:


> Throttle Body Intake for your carb
> [snapback]62812[/snapback]​


What's a carb








Just funnin ya. Good advice. Also unless they adjust your spedo you will be running approximately 10% faster. So 50mph on the spedo means 55mph.

Bill.


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## PDX_Doug (Nov 16, 2004)

Tim,

You will certainly notice a difference, as the others have pointed out. Pulling power and acceleration will increase. Top end and mileage will decrease (God bless Isaac Newton, eh!).

Question, is your 'Burb two or for wheel drive? Remember that if it is four, you need to change the front differential gears as well!









Also, and with all due respect to 2500Ram, your speedo will read faster than you are actually going. Not slower. Think of it this way: Your speedo/odo reads off the output shaft of the transmission. As it is calibrated now, it expects 3.43 revolutions to cover a given distance. With the new gears, it will take 4.11 revolutions to cover the same distance, thus 3.43 revolutions using the new gears will not take you as far as it used to. Therefore, since you are covering less distance than the odo is expecting you to, the odo will read high (it will say you have gone further than you have). Since you are also covering less distance in a given amount of time than the speedo is expecting, it will read high as well (say you are going faster than you actually are).

Simple, right?









Happy Trails,
Doug


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## 2500Ram (Oct 30, 2005)

I thought that's what I said.









On edit I contradicted myself in the first sentence, running faster. PDX_Doug was correct, youâ€™re running slower on the speedo but faster in ticket time from the cops.


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## camping479 (Aug 27, 2003)

Went from 3.42 to 3.73 on our yukon, made a big difference towing.

Mike


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## 2500Ram (Oct 30, 2005)

PDX_Doug said:


> Also, and with all due respect to 2500Ram, your speedo will read faster than you are actually going. Not slower. [snapback]62827[/snapback]​


Ok, I was thinking and edited my last post but that is not correct.

Your speedo from a 3:xx to a 4:xx gear will offset the speedo slower. I have changed gears from a 3:55 to 4:56 and had a 12% difference in the speedo verified by GPS. So if I was driving @ 55 MPH I was actually doing approx 61-62mph.

Bill.


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## cookie9933 (Feb 26, 2005)

Think you mean 3.43 to 4.11 Never heard of a 4.34 ratio. Have heard of 3.43

If that's correct, you will notice considerably better pulling and acceleration. You will also notice higher engine RPM and probably less MPG.

Bill


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## Moosegut (Sep 24, 2005)

cookie9933 said:


> Think you mean 3.43 to 4.11 Never heard of a 4.34 ratio. Have heard of 3.43
> [snapback]62845[/snapback]​


You forget one thing - sacmetrofire is from California. I hear all kinds of crazy things go on out there so maybe he DOES have a 4.34 rear.









Okay, seriously, 3.43 to 4.11 is a big jump and will be quite noticeable. While we're on the subject, will I get a big enough boost in towing, to make it worth my while, if I go from a 3.55 to a 3.73?

Scott


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## PDX_Doug (Nov 16, 2004)

OK, let's take another shot at this speedo error thing. I realize that most of you probably couldn't give a rodents rump about this, but for those of you that don't really understand this, and would like to, here goes...

Let's do an imaginary road test of two vehicles, identical in all ways except for the rear axle ratio. Our test will take place in the middle of the Nevada desert, on a road that stretches straight as an arrow for 100 miles. No turns. No hills. No wind. Just a perfectly straight road. Lined up beside each other are our two Suburban test vehicles. One of the vehicles has the standard 3.43:1 axle ratio. The other has been 'upgraded' to a 4.10:1 axle ratio, but the speedometer/odometer has not been recalibrated to account for this. With me so far?

Before we start, let's take a look at how the speedo/odo work. There is a sensor (of some form or another) on the output shaft of the transmission (you can think the driveshaft if you want, the speeds are the same) that reads RPM of that shaft and converts it into speed and distance. It is important to understand that the speedo/odo does not know (or care) how fast you are actually going, or how far you have traveled. All it is doing is counting shaft revolutions, and then converting that to an 'indicated' MPH on the face of the speedo. In order to accurately display the speed, the speedo applies a conversion (or calibration) factor to the shaft RPM. In our case, we will assume that both vehicles are calibrated to indicate 60MPH when the shaft is turning 2,260RPM (no, I did not just pull that out of a hat!).

We will also assume that the standard 265/70-16 tires on each vehicle have a rolling radius of 15.3" (30.6" diameter). From that we can determine that - with a little rounding - the tires have a circumference of 8 feet. To be exact: (2*Pi*r)/12, or (2 x 3.1416 x 15.3) / 12 = 8.01108 feet. In short, for every one revolution of the wheel, the 'Burb will travel 8 feet.

So, let's hop in our test vehicles and get going! we will accelerate to an indicated 60MPH on the speedo, set the cruise control, and maintain exactly that 'speed' for exactly one hour. at the end of one hour, we will see the following:

Vehicle 'A' (with the standard 3.43 axle) will have seen the output shaft turn 135,600 times (2,260RPM * 60 minutes). Passing through the rear differential - and the 3.43 gearing - the axles (and wheels) will have turned 39,533.5277 times (135,600 / 3.43). Multiply those wheel revolutions by 8 feet/revolution, and we will have traveled 316,268.2216 feet, or 59.8993 miles. In other words, our 'true' speed was about 60MPH (59.8993 miles in one hour). Just what the speedometer indicated!

Now, let's jump in vehicle 'B' (with the upgraded 4.10 axle). As with vehicle 'A', and since we have been driving at an 'indicated' 60MPH, the output shaft will have turned the same 135,600 times. This time however, due to the 4.10 gearing, the wheels will have only turned 33,073.1707 times (135,600 / 4.10). Multiply those revolutions by our 8 ft tire circumference, and we will have traveled 264,585.3659 feet, or 50.1109 miles. Our 'true' speed works out to about 50MPH. 10MPH less than what the speedo indicated we were going.

So in summary, stock vehicle 'A' (with the 3.43 rear end) is indeed traveling at the speed that the speedo indicates it is, but vehicle 'B' (with the 4.10 rear end) is traveling 10MPH slower than what the speedo says.









So, what about that GPS verified speed increase 2500Ram was talking about, you ask? Well, there has to be something else in play here. It is pure conjecture on my part, but I am going to guess that Ram has substantially larger than stock tires/wheels mounted. Changing the tire diameter has the same effect as changing the axle gearing, and a big enough increase in diameter will not only eliminate any gain from the gearing change, but offset it the other (undesired) way. How big an increase would it take? in the case of our test vehicles, about a 10" increase in diameter.

OK, I'm exhausted! How about you?









Happy Trails,
Doug


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## snsgraham (May 18, 2004)

I can speak intelligently







about this, I did it on my old TV.
I went from a 3.55 to a 4.11 on a 4WD and it cost me about $1600 at my Ford dealer. I had a 4.6 liter V-8 on my F-150 and was looking for more "leverage" over the load I was carrying/towing. It made a significant difference in power to the ground, speedo error and a more relaxed experience while driving. Noticeably more snap when the truck was empty as well!
I needed more weight carrying ability, otherwise I would not have upgraded the TV. Definitely a good if not expensive mod IF you are happy with the rest of the TV's abilities.

Scott


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## dougdogs (Jul 31, 2004)

PDX_Doug said:


> OK, let's take another shot at this speedo error thing. I realize that most of you probably couldn't give a rodents rump about this, but for those of you that don't really understand this, and would like to, here goes...
> 
> SNIP
> 
> ...


Excellant post Doug!

Now let me throw you a curve ball. Most new cars/trucks can be programmed for gear / rim / tire size changes.

Some dealers will do these changes for free, some charge you a few bucks. I have a set of snow tires and rims for my wife's Audi, that are hugely different that her stock tires and rims. It takes my local Audi dealer service guy about 35 seconds to plug in the controller, make and save the changes. (I bring them a box of pastries each time!)

The rim/tire size doesn't make a huge difference, but the town next to us will nail you for going 26 in a 25 zone.

Some new imports also now use the sensor for ABS as a speed sensor


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## Ghosty (Jan 17, 2005)

Moosegut said:


> cookie9933 said:
> 
> 
> > Think you mean 3.43 to 4.11Â Never heard of a 4.34 ratio.Â Have heard of 3.43
> ...


NO. Your looking at an increase of a mere .18 at a cost of approx $1500 ...


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## Fire44 (Mar 6, 2005)

I just checked on the GM ordering program and in 2004, 3.42 ratio rears were not available for the 1500 Suburban (2wd or 4x4). The rear that Tim has would be a 3.73 or 4.10 from the factory. According to factory spec's a 2004 Suburban 1500 with a 5.3 liter and 3.73 rear ratio would have a towing capacity of 7,400 pounds with weight dist. If the truck had 4.10 would have a towing capacity of 8,400 pounds with weight dist.

The 2005 Suburban was offered with your choice of 3.42 or 4.10 gears. The 3.42 rear in 2005 was rated to tow the same 7,400 pounds as the 3.73 in 2004.

I don't know how they come up with these numbers.......it must be that new math!!!

Gary


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## camping479 (Aug 27, 2003)

I was told there's more involved than just changing the speedo to adjust for the gear change. When I had ours done my mechanic told me the computer needs to be reprogrammed not only for the speedometer but for shift points in the transmission. Since everything is run by the computer, if you change one element it can effect other things as well.

Any GM guys or mechanics who can elaborate since I don't know much more than that??

Mike


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## Fire44 (Mar 6, 2005)

Mike, I just checked with one of our mechanics and he said that you are right. It can also effect the ABS system if you don't reprogram the computer.

Gary


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## Crawfish (Sep 14, 2005)

If anyone plans to reprogram their computer, buy the handheld reprogramer yourself instead of letting the dealership or tech reprogram. The reason is, when you reprogram your chip and you have a problem with your engine it has to be programed back to the stock programing before it can be worked on. When the engine is worked on they are expecting to see stock settings out of the computer. Just though I would throw that in.

"*Let's Go Camping*"

Crawfish


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