What rear axle ratio's are you running - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Paul Y · 07-18-2014, 06:05 AM

Good morning Gentlemen,

As my build is now approaching the physical rather than the esoteric, my shopping list for upgrades is becoming more defined.

So, today's series of question:-

What axle ratio are you running and what is the rest of the drive line?

Mileage?

Are you happy with your choice?

Eventually I will run a LM7, TKO 600 (road/race gearing) and a 265/65/15 tyre/tire.

My initial thoughts were to copy the Tahoe gearing (3.42-3.73- 4.11) but get conflicting reports and, as I wont be towing a 3000lb ski boat, a lot of it is irrelevant.

I will be using the truck as a DD but also for track days/autocross events.

Previous experience with a DNE 4+1 saw me use a 3.25 with 29" tyres. With a BBC I got over 18mpg and ran a very low 12second quarter.

Look forward to hearing your thoughts and comments.

P.

**Clyde65** · 07-18-2014, 07:57 AM

I run a 3.73 in my 12 bolt 71/72 rearend. I have a 4.8/4l60E. with this ratio, I feel it hits the sweet spot with the OD trans and also quick starts off the line when needed. I also use a 29" tire ( 275/60/15BFG)

Paul Y · 07-18-2014, 08:18 AM

Thanks for the reponse

What sort of mileage are you achieving?

P.

**TJ's Chevy** · 07-18-2014, 09:47 AM

I'm running 3.73 in my stock 12 bolt truck axle....30 inch tire...Feels like I need and OD trans at 65...but cruising at 55 at 2500 rpm gets me around..oh...15 mpg...my 292 is old an worn out..so once I rebuild it I'll be able to figure the mileage a little better.

vin63 · 07-18-2014, 10:26 AM

3.70 behind a 4L80E transmission and 31" tall tire.

NEWFISHER · 07-18-2014, 11:16 AM

""" My initial thoughts were to copy the Tahoe gearing (3.42-3.73- 4.11) but get conflicting reports and, as I wont be towing a 3000lb ski boat, a lot of it is irrelevant.""?"

If never towing and using as DD I would run the 3:42

Shaky · 07-18-2014, 11:35 AM

250/Richmond 5-speed/3.08

You can only expect so much mileage as you push a brick through the air...

**Clyde65** · 07-18-2014, 11:42 AM

Quote:

Originally Posted by Paul Y

Thanks for the reponse

What sort of mileage are you achieving?

P.

I have gotten 19.5 on mostly highway ( 75/25) I think if there wasnt much wind ( yeah right) I could get 20.5 on all highway.

61_FL_Apache · 07-18-2014, 07:43 PM

I have a 3.08 and 28" tall tire. I wish I had more gear.. I run 70 @ 2600 rpm.

**Palf70Step** · 07-18-2014, 08:05 PM

The original rear with 3.73 gears and 29" (275'60x15) tire. I have no clue what I get for mileage as I have not gotten the speedometer gear in the tranny replaced yet. It does wind at 65/70 on the road, but it does it well.I plan on going to a 3.08. I am running a 3 speed manual tranny. Best guess is around 13-15.

LostMy65 · 07-18-2014, 10:22 PM

In my truck at present is a 3.90 with 26" tire.
it revs way too high at only 50mph.
I'm going to swap it to a 3.08 this winter.
If it bogs it down too much, I'll put the 3.73 I also have.

Paul Y · 07-19-2014, 04:11 AM

Wow,

A lot of information! I have used an online gear calculator that shows with the .84 5th gear and a 3.73 gear 70 comes up around 2500, with a 3.42 the same rpm gives me 76mph.

I suppose my real question is where is the sweet spot for the LM7? Think I will try one of the LSx forums unless anyone knows better?

Thanks for the input.

P.

07-18-2014, 06:05 AM	#1
Paul Y Registered User Join Date: Jul 2013 Location: Essex Posts: 950	What rear axle ratio's are you running Good morning Gentlemen, As my build is now approaching the physical rather than the esoteric, my shopping list for upgrades is becoming more defined. So, today's series of question:- What axle ratio are you running and what is the rest of the drive line? Mileage? Are you happy with your choice? Eventually I will run a LM7, TKO 600 (road/race gearing) and a 265/65/15 tyre/tire. My initial thoughts were to copy the Tahoe gearing (3.42-3.73- 4.11) but get conflicting reports and, as I wont be towing a 3000lb ski boat, a lot of it is irrelevant. I will be using the truck as a DD but also for track days/autocross events. Previous experience with a DNE 4+1 saw me use a 3.25 with 29" tyres. With a BBC I got over 18mpg and ran a very low 12second quarter. Look forward to hearing your thoughts and comments. P.

07-18-2014, 07:57 AM	#2
Clyde65 1965 Chevy C10, 2005 4.8L/4l60 Join Date: Aug 2004 Location: DFW Texas Posts: 8,549	Re: What rear axle ratio's are you running I run a 3.73 in my 12 bolt 71/72 rearend. I have a 4.8/4l60E. with this ratio, I feel it hits the sweet spot with the OD trans and also quick starts off the line when needed. I also use a 29" tire ( 275/60/15BFG) __________________ Clyde65 Rebuild of Clyde http://67-72chevytrucks.com/vboard/s...84#post8338184 69 Aristocrat Lo Liner build http://67-72chevytrucks.com/vboard/s...84#post7561684 *support our troops!*

07-18-2014, 08:18 AM	#3
Paul Y Registered User Join Date: Jul 2013 Location: Essex Posts: 950	Re: What rear axle ratio's are you running Thanks for the reponse What sort of mileage are you achieving? P.

07-18-2014, 09:47 AM	#4
TJ's Chevy Post Whore Join Date: Mar 2013 Location: Southern Oregon Posts: 10,399	Re: What rear axle ratio's are you running I'm running 3.73 in my stock 12 bolt truck axle....30 inch tire...Feels like I need and OD trans at 65...but cruising at 55 at 2500 rpm gets me around..oh...15 mpg...my 292 is old an worn out..so once I rebuild it I'll be able to figure the mileage a little better. __________________ 1966 Chevy C10 "Project Two Tone" http://67-72chevytrucks.com/vboard/s...d.php?t=596643 1964 GMC "Crustine" semi-build:http://67-72chevytrucks.com/vboard/s...d.php?t=665056 My youtube channel. Username "Military Chevy": https://www.youtube.com/channel/UC_h...fzpcUXyK_5-uiw

07-18-2014, 10:26 AM	#5
vin63 It's Better With Nitro Join Date: Apr 2008 Location: Chino Hills, CA Posts: 2,262	Re: What rear axle ratio's are you running 3.70 behind a 4L80E transmission and 31" tall tire. __________________ 1963 C-10: Deluxe-optioned cab, shortbed, fleetside Pontiac 462 ci, Kauffman D-Port alum. heads 4L80E, narrowed sheetmetal Ford 9-inch Tubular front and rear suspension Custom 6-piston front disc and 4-piston rear disc brakes

07-18-2014, 11:16 AM	#6
NEWFISHER Registered User Join Date: Sep 2012 Location: Oregon Posts: 3,303	Re: What rear axle ratio's are you running """ My initial thoughts were to copy the Tahoe gearing (3.42-3.73- 4.11) but get conflicting reports and, as I wont be towing a 3000lb ski boat, a lot of it is irrelevant.""?" If never towing and using as DD I would run the 3:42 __________________ GOD BLESS AMERICA!

07-18-2014, 11:35 AM	#7
Shaky Six in a row makes it go... Join Date: Mar 2009 Location: Vacationland: Maine Posts: 1,346	Re: What rear axle ratio's are you running 250/Richmond 5-speed/3.08 You can only expect so much mileage as you push a brick through the air... __________________ 67 C20 long step resto: http://67-72chevytrucks.com/vboard/s...d.php?t=342086 66 C10 long step build: http://67-72chevytrucks.com/vboard/s...=1#post3814790 CT to Alaska in a 67 C10: http://67-72chevytrucks.com/vboard/s...d.php?t=399224 “The height of sophistication is simplicity." - Clare Boothe Luce

07-18-2014, 07:43 PM	#9
61_FL_Apache Who Me? Join Date: Sep 2010 Location: Royal Palm Beach, FL Posts: 4,067	Re: What rear axle ratio's are you running I have a 3.08 and 28" tall tire. I wish I had more gear.. I run 70 @ 2600 rpm. __________________ Steve 1997 Tahoe LT 4D 2WD (DD) 2001 Blazer 4D 2WD 1961 Apache 10 (sold) 1965 C10 Stepper (sold)

07-18-2014, 08:05 PM	#10
Palf70Step State of Confusion! Join Date: Jul 2002 Location: Gulfport, MS USA Posts: 47,468	Re: What rear axle ratio's are you running The original rear with 3.73 gears and 29" (275'60x15) tire. I have no clue what I get for mileage as I have not gotten the speedometer gear in the tranny replaced yet. It does wind at 65/70 on the road, but it does it well.I plan on going to a 3.08. I am running a 3 speed manual tranny. Best guess is around 13-15. __________________ Bill 1970 Chevy Custom/10 LWB Fleetside 2010 Toyota Tacoma PreRunner SR5 Double Cab - DD Member of Louisiana Classic Truck Club (LCTC) Bill's Gallery Life isn't tied with a bow, but it's still a gift. Live simply. Love generously. Care deeply. Speak kindly. Leave the rest to God!

07-18-2014, 10:22 PM	#11
LostMy65 But Found Her 25yrs Later! Join Date: Oct 2010 Location: Oregon City, Oregon Posts: 10,530	Re: What rear axle ratio's are you running In my truck at present is a 3.90 with 26" tire. it revs way too high at only 50mph. I'm going to swap it to a 3.08 this winter. If it bogs it down too much, I'll put the 3.73 I also have. __________________ I lost my 65 - Found it 25 years later: http://67-72chevytrucks.com/vboard/s...d.php?t=426650 66 C20 Service Truck: http://67-72chevytrucks.com/vboard/s...d.php?t=428035

07-19-2014, 04:11 AM	#12
Paul Y Registered User Join Date: Jul 2013 Location: Essex Posts: 950	Re: What rear axle ratio's are you running Wow, A lot of information! I have used an online gear calculator that shows with the .84 5th gear and a 3.73 gear 70 comes up around 2500, with a 3.42 the same rpm gives me 76mph. I suppose my real question is where is the sweet spot for the LM7? Think I will try one of the LSx forums unless anyone knows better? Thanks for the input. P.



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