Gearing
Post Fiend
Joined: Dec 2002
Posts: 6,245
Likes: 1
From: IL, USA
A few things:
4.10s will push more RPMs at any given speed vs. 3.73s. They will make it easier to get the truck and any cargo moving off of the line, and will keep you in the power band.
Gear change DOES NOT effect the speedo reading at all. Only thing that does is tire size....the VSS takes it's reading off of a tone ring that is on the carrier...the only thing that effects how fast that carrier is spinning at a given speed is tire size. Gears only effect how fast the motor is spinning at a given speed.
If you need to correct your speedo...have the dealer reprogram it or get a Superlift truspeed.
4.10s will push more RPMs at any given speed vs. 3.73s. They will make it easier to get the truck and any cargo moving off of the line, and will keep you in the power band.
Gear change DOES NOT effect the speedo reading at all. Only thing that does is tire size....the VSS takes it's reading off of a tone ring that is on the carrier...the only thing that effects how fast that carrier is spinning at a given speed is tire size. Gears only effect how fast the motor is spinning at a given speed.
If you need to correct your speedo...have the dealer reprogram it or get a Superlift truspeed.
FTE Leadership Emeritus
Joined: Sep 2003
Posts: 12,246
Likes: 761
From: Houston, Texas
Originally Posted by DCSpecial
A few things:
4.10s will push more RPMs at any given speed vs. 3.73s. They will make it easier to get the truck and any cargo moving off of the line, and will keep you in the power band.
Gear change DOES NOT effect the speedo reading at all. Only thing that does is tire size....the VSS takes it's reading off of a tone ring that is on the carrier...the only thing that effects how fast that carrier is spinning at a given speed is tire size. Gears only effect how fast the motor is spinning at a given speed.
If you need to correct your speedo...have the dealer reprogram it or get a Superlift truspeed.
4.10s will push more RPMs at any given speed vs. 3.73s. They will make it easier to get the truck and any cargo moving off of the line, and will keep you in the power band.
Gear change DOES NOT effect the speedo reading at all. Only thing that does is tire size....the VSS takes it's reading off of a tone ring that is on the carrier...the only thing that effects how fast that carrier is spinning at a given speed is tire size. Gears only effect how fast the motor is spinning at a given speed.
If you need to correct your speedo...have the dealer reprogram it or get a Superlift truspeed.
Okay, so what you're telling myself and Storm is:
The only reason we don't have as much mileage as we did (given the heaviver parts and bigger tires) is because our speedo is way off, and when we're doing 65 we're actually doing about 75+?
Also, what you said about the whole motor spinning at a certain speed thing, 4.10s will raise, but at the same time lower rpms and give a better start off the line, especially if and when towing is involved.
Lastly, I understand that my truck probably won't run like it did or give me the same power and mileage it did before the lift, what I'm trying to do is recover some, if not all, the power and mileage I had before. In conclusion, I need to have my truck reflashed for the bigger tires AND I need to regear to a 4.10 LSD if I'm to make my drivetrain's job a little if not all whole lot easier.
Correct me if I'm wrong to think this...........
On edit, I've had a few brews in light of the holiday, so forgive me if none of this makes sense.
Post Fiend
Joined: Dec 2002
Posts: 6,245
Likes: 1
From: IL, USA
Lower gears (higher numerically) will always increase RPMs at any given speed.....they won't lower it.
They make it easier on the drivetrain to get the vehicle and cargo moving.
If you want it to perform like stock, then yes 4.10s with a reprogrammed speedo is the route to go.
MPG....well, taking a heavy vehicle with the aerodynamics of a brick, making it taller and putting larger/wider tires on it isn't exactly the formula to keep good MPG.
If you do a lot of highway driving you'll actually see better MPG with 35s and 3.73s since you will be pushing lower RPMs on the highway.
My best MPG on my 7.3 was with 35s, 3.73s, a chip, intercooler, turbo, intake and exhaust, and of course a Superlift Truspeed to correct my speedo. I would see 20+ mpg (hand calculated) if I cruised around 75ish mph.
As for gears and MPG.....here's an example from my trucks...all stock height, stock tires, bone stock, etc..
3.73s stock: 15-17mpg
4.10s stock: 13-15mpg
4.88s stock: 9-12mpg
This is what I see with a combination of empty driving, loaded, and towing.
To see what gears do to rpms at highway speeds with different tires and gear ratios:
http://www.FTEs diesel forums.com/fo...ead.php?t=2896
They make it easier on the drivetrain to get the vehicle and cargo moving.
If you want it to perform like stock, then yes 4.10s with a reprogrammed speedo is the route to go.
MPG....well, taking a heavy vehicle with the aerodynamics of a brick, making it taller and putting larger/wider tires on it isn't exactly the formula to keep good MPG.
If you do a lot of highway driving you'll actually see better MPG with 35s and 3.73s since you will be pushing lower RPMs on the highway.
My best MPG on my 7.3 was with 35s, 3.73s, a chip, intercooler, turbo, intake and exhaust, and of course a Superlift Truspeed to correct my speedo. I would see 20+ mpg (hand calculated) if I cruised around 75ish mph.
As for gears and MPG.....here's an example from my trucks...all stock height, stock tires, bone stock, etc..
3.73s stock: 15-17mpg
4.10s stock: 13-15mpg
4.88s stock: 9-12mpg
This is what I see with a combination of empty driving, loaded, and towing.
To see what gears do to rpms at highway speeds with different tires and gear ratios:
http://www.FTEs diesel forums.com/fo...ead.php?t=2896
Lead Driver
Joined: May 2007
Posts: 5,613
Likes: 9
From: Flagstaff, Arizona
another thing to consider about figuring your mileage with bigger tires and lift. Since your speedo is affected by the tires (if you haven't re-calibrated it) another thing is the actual miles shown. So.......it will show that you have driven LESS miles then you really have, therefore.....if you use the mileage shown on the odometer to figure the MPG.....it will come up less, a LOT less. If you know the mileage from point A to point B....use that, and how many gallons used and that'll give you a true mpg, rather then trusting your odometer.
FTE Leadership Emeritus
Joined: Sep 2003
Posts: 12,246
Likes: 761
From: Houston, Texas
Ok, this is all coming together now and from what I gather, I can save myself about $1100.
So my speedo is obviously off, that's why it seems like I'm getting crappy mileage, but chances are I'm not and the overhead liar (as it's name implies) has me fooled.
So technically, I should just have my truck reflashed, stick with my 3.73s, and maybe look into a good limited slip setup instead of regearing to a 4.10........?
So my speedo is obviously off, that's why it seems like I'm getting crappy mileage, but chances are I'm not and the overhead liar (as it's name implies) has me fooled.
So technically, I should just have my truck reflashed, stick with my 3.73s, and maybe look into a good limited slip setup instead of regearing to a 4.10........?
Senior User
Joined: Nov 2006
Posts: 241
Likes: 0
From: Southern California
thats exactly what I would do... but for now, you can always figure out how off your speedo is by dividing the old diameter of the tires by the new diameter... OR to make things easier, divide the new diameter by the old diameter then multiply by how many miles the "overhead liar" says you've traveled and thats the actual number of miles you've traveled... then proceed to calculating your MPG normally...
For example, the old diameter of your tires are 31.6" and new diameter is 34.9" (roughly stock vs 35's)... so new/old is 1.1044... say the computer says you've traveled 250 miles... multiply 250 x 1.1044 and you get 276 miles... normally on my truck, it takes 25 gallons for 250 miles (damn V10, lol)... by simply correcting the miles, I gained an extra mpg! wooohooo!!! haha...
Joey
For example, the old diameter of your tires are 31.6" and new diameter is 34.9" (roughly stock vs 35's)... so new/old is 1.1044... say the computer says you've traveled 250 miles... multiply 250 x 1.1044 and you get 276 miles... normally on my truck, it takes 25 gallons for 250 miles (damn V10, lol)... by simply correcting the miles, I gained an extra mpg! wooohooo!!! haha...
Joey
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