LatrobeHO

Awesome replies!!!

Thank you all very much!

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Question: Would the speedo/odo need recalibrated to display properly?

Rameister

How can I find out the gear ration on my 2003 3500?

doug

yea, always use revs/mile if you have it. or my formula if all you have is the tire size.

ah, yes, tires are definatly better than gears -- you get no visual improvement out of a gear...! thats why I actually like the 3.73s now on the 3rd gens over the 3.54 gear on the 2nd gens. its about the same change as moving to a 285 tire -- so my 04 with 285s will spin about the same as an 02 with stock tires. I happen to think that the BFG 285s look very nice on the 3rd gens, especially with an american racing wheel. and my dealer supports it as well.

bulabula

[quote author=LatrobeHO link=board=20;threadid=17922;start=45#msg170065 date=1060367515]Question: Would the speedo/odo need recalibrated to display properly?[/quote]I "think" they can go into the ECM and change it. Try a search here, this has been discussed.

I always did the math in my head when going to different size tires - close enuf for govt work.

doug

[quote author=LatrobeHO link=board=20;threadid=17922;start=45#msg170065 date=1060367515]
Awesome replies!!!

Thank you all very much!

===

Question: Would the speedo/odo need recalibrated to display properly?

[/quote]

yes. the speedo, odo, mpg, DTE, and all of that will be off by the same percentage. if you dont' re-calibrate, and then you sell the truck, some savy **** guy might try to accuse you of odo fraud.

for small changes (265 to 285) I personally don't think its worth a re-cal. But 265 to 315's is near 10% change and thats pretty big.

bulabula

[quote author=Rameister link=board=20;threadid=17922;start=45#msg170066 date=1060367624]
How can I find out the gear ration on my 2003 3500?
[/quote]Didn't it say on the window sticky where all the std and options are listed?

If not, how may rpms are you doing at (pick a speed, any speed) in high gear?

doug

[quote author=Rameister link=board=20;threadid=17922;start=45#msg170066 date=1060367624]
How can I find out the gear ration on my 2003 3500?
[/quote]
a number of ways:

- read the sticker on your door. at least I think its there, along with GVWR, GCWR, etc.

- read the original factory sales sticker

- call DC and give them your VIN

- prop the rear end up on jack stands and count driveshaft and tire revs! seriously, its the ultimate authority, and on an open diff (not anti-spin) it is is easy. rotate one wheel exactly 3 times around and count the number of driveshaft revs associated with the 3 wheel revs. chalk helps. If you get ~11 driveshaft rotations you have a 3.73. If you get ~12, you have a 4.10. Not sure if you can do this on an anti-spin axle; I've never tried.

bulabula

Here are some old posts concerning 35" tires (some have pics):


https://www.dieseltruckresource.com/...7509#msg137509

https://www.dieseltruckresource.com/...5453#msg125453

https://www.dieseltruckresource.com/...=12890;start=0

https://www.dieseltruckresource.com/...1440#msg111440

LatrobeHO

I am guessing the height of the truck would increase if I put 315's on there, correct? It looks like it might increase by 2 inches in height?

I have a garage to fit it into

erics76

The height of the truck will increase by half of the difference between the difference in height of the old tires and new tires.

doug

[quote author=LatrobeHO link=board=20;threadid=17922;start=45#msg170092 date=1060369989]
I am guessing the height of the truck would increase if I put 315's on there, correct? It looks like it might increase by 2 inches in height?

I have a garage to fit it into


[/quote]

the increase in truck height is exactly equal to the increase in tire radius. And we already know the radius of each tire from the previous exercise:

radius of the big tire = 17.2"
radius of the little tire = 15.8"

so the increase in height is 17.2 - 15.8 = 1.4"

and now you know the rest of the story :P

Rameister

Thanks Doug,
I called DC and they gave it to me over the phone.
Easy.

Gerry

doug

ok! well, what do you have? ;D ;D ;D

Rameister

It's a 3.73.
I had been wondering about it because the rev's seemed higher at 75 mph than what I remember of my 2500 1995 Cummins.
It was an automatic, as this one is.
The dealer info on my 3500 HD 2003 indicated 3.73 but there was an error on the sheet and that lead me to suspect the other info.
My fear was that I'd received a 4.11 although I'd wanted a 3.73.
Having confirmed it as what I wanted, all is well.
The revs are what they are.
Thanks again.

Gerry

doug

cool. the 3.73 and auto is a good combo. you running about 2100 at 75 mph?