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Those with 38"+ tires and non-OD trannies...

heavy4x4

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Those with 38\"+ tires and non-OD trannies...

1) What the heck gear ratio are you guys running. I never really punched in the numbers until a day or two ago, and with a non-OD tranny (1.00 final gear) and 39.5" tires, the engine will be turning about 2200 rpm at 70 mph (which sounds ideal to me) with 3.73's for a gear ratio!

2) Here's the reason I'm asking...I'm trying to figure out what tranny and gear ratio I want to use with 39.5's
These are the choices I'm thinking: (the truck will be mainly off-road, but some road use including freeway)

TH700R4 - 5.13 (good, but not sure about the strength of the tranny with the larger tires)

NVG4500 - 5.13 (probably one of my best options)

SM465 - 3.73 (should still have decent crawl/low gear and be able to travel on the freeway - and I wouldn't have to change my gear ratios /forums/images/graemlins/woot.gif - but I would be going D60)

TH350/400 - no idea (thinking 3.73's for freeway driving, but then the low gear is gonna be really lacking)

What would you do? /forums/images/graemlins/ears.gif
 

84_Chevy_K10

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Re: Those with 38\"+ tires and non-OD trannies...

I am running 4.10 and I'm perfectly happy with the way it cruises.

4.56 or 4.88 would still be ok for highway cruising, 5.13 would be pushing it.

3.73 would make for a gutless truck that had to use granny gear to take off most likely.
 

mudhog

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Re: Those with 38\"+ tires and non-OD trannies...

i have the sm465np205 4:10 39.5 combo and i really wish i had 4:88's-5:13's
 

dhdescender

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Re: Those with 38\"+ tires and non-OD trannies...

I have 4.10's with 42" TSL's. It also does have a 472cid, so its not exactly a smallblock.

I took advantage of dual cases to offset the gear ratio. I think thats pretty much mandatory if you want a decent crawl ratio and still be geared for highway use.
 

FWP

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Re: Those with 38\"+ tires and non-OD trannies...

Damn, I'm lucky if I can hit 70 at all /forums/images/graemlins/rotfl.gif /forums/images/graemlins/rotfl.gif

38.5/14.5 SX, TH350, 4.10
 

m j

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Re: Those with 38\"+ tires and non-OD trannies...

sm 465 4.88s 39"s
2700-3000rpm and still the slowest thing on the hiways
tall gears and a reduction box is the way to go
 

mofugly13

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Re: Those with 38\"+ tires and non-OD trannies...

Damn, I was thinking of going 4.10 to go with my new 35", but that sounds like I will be geared too low for my DD. I'm gonna be taking a trip up to central Oregon this summer, so the ability to cruise 70-80 at decent rpms is important. [darn], I may have to go 3.73 or think of stepping up to 37" tires. It would be a no brainer if there wasn't such a price jump from 35" to 37".

Sorry for the hijack.
 

shane74

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Re: Those with 38\"+ tires and non-OD trannies...

5.13's and 38's is what you need to run with a TH350/400. That puts your gear/rpm ratio back to what the truck was stock. DO NOT I REPEAT DO NOT RUN 38's and 3.73's! You'll burn up your auto tranny real quick...ask me how I know /forums/images/graemlins/whistling.gif I will be running 5.13's very soon. /forums/images/graemlins/waytogo.gif They ARE NOT too much for the freeway. In fact, they should put your rpms back into the "peak power" range for the freeway. You rig should run better and get MUCH better milage than if you went with 3.73's. Do some research on your own. There are many opinions floating around out there and not all of them are correct.
 

Bhintz

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Re: Those with 38\"+ tires and non-OD trannies...

I agree with shane
 

jakeslim

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Re: Those with 38\"+ tires and non-OD trannies...

i run 4.10's and 38. Would be nice if i had 4.56's. Current set up does seem to put some stress on engine and trani when driving 60+.
 

shane74

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Re: Those with 38\"+ tires and non-OD trannies...

Nope, you'll still be geared too tall. Go with 4.56's for 35's.

Here is a bit of a comparison for you all using 3.73 gears. They are from trips I took over the last couple years in my /forums/images/graemlins/k5.gif

Trip 1 - Vancouver,WA to Bakersfield, CA pulling 19' camp trailer
3.73's and 33x12.50's
Mileage = 15-16 mpg

Trip 2 - Vancouver, WA to West Glacier, Montana again pulling 19' camp trailer
3.73's and 35x12.50's
Mileage = 12-14 mpg

Trip 3 - Vancouver, WA to Libby, Montana Pulling NOTHING
3.73's and 38x12.50's
Mileage = SUCKED ASS!!! 9-10 mpg /forums/images/graemlins/eek.gif /forums/images/graemlins/angryfire.gif

Stay with the 4.56's dood.
 

Bhintz

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Re: Those with 38\"+ tires and non-OD trannies...

[ QUOTE ]
Nope, you'll still be geared too tall. Go with 4.56's for 35's.

Here is a bit of a comparison for you all using 3.73 gears. They are from trips I took over the last couple years in my /forums/images/graemlins/k5.gif

Trip 1 - Vancouver,WA to Bakersfield, CA pulling 19' camp trailer
3.73's and 33x12.50's
Mileage = 15-16 mpg

Trip 2 - Vancouver, WA to West Glacier, Montana again pulling 19' camp trailer
3.73's and 35x12.50's
Mileage = 12-14 mpg

Trip 3 - Vancouver, WA to Libby, Montana Pulling NOTHING
3.73's and 38x12.50's
Mileage = SUCKED ASS!!! 9-10 mpg /forums/images/graemlins/eek.gif /forums/images/graemlins/angryfire.gif

Stay with the 4.56's dood.

[/ QUOTE ]like I said I agree with you but the drag issue is going to kill MPG
 

GMC

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Re: Those with 38\"+ tires and non-OD trannies...

I have 4.88's in a D60/70 setup running 38" Boggers with a healthy 350 and a T-350. Since 39.5's are quite a bit bigger than 38's and running 1 ton axles and other heavier equipment on a vehicle I would for sure go with 5.13's all the way. You could still go on the freeway with that set-up as I do with mine.
 

FWP

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Re: Those with 38\"+ tires and non-OD trannies...

Shane, What RPMs are you running at say 65-70 MPH, just curious...
 

MTBLAZER89

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Re: Those with 38\"+ tires and non-OD trannies...

Hijack
[ QUOTE ]
Trip 3 - Vancouver, WA to Libby, Montana Pulling NOTHING
3.73's and 38x12.50's

[/ QUOTE ]

/forums/images/graemlins/eek.gif I'm from Libby, MT thats not a town I ever expected to be mentioned on here /forums/images/graemlins/waytogo.gif

end hijack
 

heavy4x4

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Re: Those with 38\"+ tires and non-OD trannies...

Thanks for the ideas, all, but geez...sounds like you guys have no problem with running an engine at 3,050 rpm on the freeway (1.0 tranny gear, 5.13 axles, 39.5" tires).
Personally, I'm not comfortable doing that, I'd rather be below 2500. (With 4.10's I'd be at 2400)

Looks like right now I should be thinking about the 700R4-5.13 or NV4500-5.13 setup.
 

shane74

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Re: Those with 38\"+ tires and non-OD trannies...

[ QUOTE ]
What RPMs are you running at say 65-70 MPH, just curious...

[/ QUOTE ]

Right now I turn about 2200. When I get my 5.13's in it'll jump to about 2800.
 

Muddytazz

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Re: Those with 38\"+ tires and non-OD trannies...

Right now I'm running 4.10's and 33's /forums/images/graemlins/thinking.gif /forums/images/graemlins/doah.gif
 

Ryan B.

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Re: Those with 38\"+ tires and non-OD trannies...

TH350, 4.56's and 38's i spin 2800 at 65 on the freeway.
I switched to 35's for the street and now i'm at 3000 at 65, 3200 at 70. /forums/images/graemlins/dunno.gif /forums/images/graemlins/doah.gif
 

tRustyK5

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Re: Those with 38\"+ tires and non-OD trannies...

You'll be turning 3350 rpm at 70 with 5.13's and 38's...

I run 4.56's with 39.5's an SM465 and a 6.2 diesel. 2550 rpm at 65 mph...at 70 the tires start to shake so I just don't go there LOL. The combo I have would be perfect if I had another gear after 4th, around town it's perfect. With an auto tranny I'd have to say deeper would be better though. A manual tranny rig seems to tolerate slightly taller gearing better than the auto rigs do.

Rene
 
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