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May 29, 2008 | 07:20 AM

#31

larrygranny1

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Joined: Aug 2007

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drag

it's very simple, eliminate drag......increase mpg. no tuners etc.

Sep 3, 2008 | 10:39 AM

#32

bobbyc03

New User

Joined: Jul 2007

Posts: 24

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Quote:

Originally Posted by mikejbayus

i just had them installed monday he is finishing up today i will know as soon as i have speedometer adjusted next week.

Hi,
Did you change tire/wheel size too? I thought that the speedo wasn't effected by axle ratio changes?

Bob C

Sep 3, 2008 | 12:18 PM

#33

66stang351

Elder User

Joined: Mar 2006

Posts: 516

Likes: 1

Quote:

Originally Posted by bobbyc03

Hi,
Did you change tire/wheel size too? I thought that the speedo wasn't effected by axle ratio changes?

Bob C

Changing the rear end ration will definitly have an effect on the speedo.

Sep 3, 2008 | 12:30 PM

#34

bobbyc03

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Joined: Jul 2007

Posts: 24

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Really? I had read on this forum and others that the computer calculates speed by tire revolutions... so only wheel/tire size changes effect the speedometer?

edit: I just found one of the threads that states this...

ratio change??? - Diesel Forum - The Diesel Stop.com

Some guy there switched from 4.56 to 3.73 and the speedometer didn't change at all.

Thanks!
Bob C

Sep 3, 2008 | 12:59 PM

#35

66stang351

Elder User

Joined: Mar 2006

Posts: 516

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Quote:

Originally Posted by bobbyc03

I know for a fact...I crawled under and looked...that the speedo sensor is on the tailshaft of the transmission.

Looking at the link you posted it is obvious that they have no idea what they are talking about...the guy that stated 4.56s didn't affect his speedo also put on 38" tires. Adding the 38s would have made his speedo read low then adding the 4.56 gears would have countered thatlow reading. So the end result is the speedo is correct, but only because he increased tire size with the rear change.

Sep 3, 2008 | 01:07 PM

#36

66stang351

Elder User

Joined: Mar 2006

Posts: 516

Likes: 1

Quote:

Originally Posted by dt75flh

correct on the tone ring.....however going from a 34 " ish tire to a 35.5 " tire with the stock gears....the computer reads (x) number of revolutions per mile for a given tire size that is pre programed in for the factory tire sizes.....when you put larger than stock tires on,

the revolutions per mile decrease...

so for example if the stock tire turns 675 revolutions per mile the larger tire turns less times to run the same mile like say 650.

basically it means when i was running the larger tire b-4 the gear change my speedo was reading 70 mph when in reality i was going around 77 mph..about 10% faster than the speedo was reading....gps verified....
the 4.10 ratio made up for that 10% and my speedo and odometer are correct...

this also applies to people who lift their rigs and put plus 2 or 3 size tires on without correcting the speedo...the real mileage on the truck is higher than whats reading on the odometer due to the same principle

This post exactly illustrates my point. The tire change made the speedo read low and the gear change brought it back up. He says they are correct that changing the rear has no effect then goes and shows proof that it does.

BTW, I have never seen a vehicle that took the reading off of the rearend like they are talking about...I'm sure they are out there, but not on the Ford Superduty...

Sep 3, 2008 | 03:31 PM

#37

ab257z

Senior User

Joined: Oct 2007

Posts: 159

Likes: 0

From: Poconos

Tape question

On the top grill side openings - did you tape flush with the front of the grill (taping to the chrome), or did you tape up down in the opening on top of the plastic grill work?

Sep 4, 2008 | 12:22 PM

#38

bobbyc03

New User

Joined: Jul 2007

Posts: 24

Likes: 2

Thanks for the info.

Geez I wish we bought a 3.55 LS from the get go. Ours is a job 1 3.73 open diff.

Bob C

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Sep 4, 2008 | 12:34 PM

#39

bobbyc03

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Joined: Jul 2007

Posts: 24

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edit

ops double post

Sep 4, 2008 | 03:40 PM

#40

F250Wheels

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Joined: Dec 2003

Posts: 652

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BTW, I have never seen a vehicle that took the reading off of the rearend like they are talking about...I'm sure they are out there, but not on the Ford Superduty...[/QUOTE]

All F350 and F250 have the speed sensor on top of the rear end, all the way back to 1992 that I know of. Not sure about the F450.

Sep 10, 2008 | 11:24 AM

#41

ab257z

Senior User

Joined: Oct 2007

Posts: 159

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From: Poconos

No change

Taped up the side grill openings and the tow hook openings. Went on a 2 1/2 hour trip hauling a 4,000 lb camper (half interstate, half country roads). Ran about 9.9 mpg. Noticed the fan came on a couple times when climbing a moderate hill which was unusual. Took the tape off for the trip back and got 10.4. A little more downhill on the trip back.

The tape might make a difference on unloaded highway speeds, but since I rarely run unloaded, its staying off.

I put a grill cover on in winter, and didn't get any higher mileage then either.