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Old 12/14/04, 03:01 PM   #1
Full Member
Joined: May 04
Posts: 328
Question Best gear ratio for 37 inch tires?

What gear ratio do you guys think works best for 37 inch tires?
I'd ideally like to be able to Hwy. drive my bronco to the trails, and still be able to wheel.
What do you think?
If it makes any difference, I'll have a Det. locker on the back also.

1969, 351-w,33's, np-435,
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Old 12/14/04, 03:11 PM   #2
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Southaven, Ms
Joined: Mar 04
Posts: 80
I have a 2001 SUPERDUTY with 37x12.50 17" with 4.11 gears. The 4.11 gears brought it back to a little better than stock.The bronco iI have has 38.5x14.50 15" with 4.11 I haven't drove but a few miles ,but it drove fine in that short distance.I plan on going lower with either 4.56 or 4.88.
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Old 12/14/04, 03:12 PM   #3
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Salisbury, NC
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I run 4.56 with my 36's. Turn around 2,400 at 55mph on the road. And still has good ratio for offroad with the NP435.

'72 Explorer, TBA...
'76 F250 2wd, 390, NP435, 4.10's...aka Brutus
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Old 12/14/04, 03:30 PM   #4
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Kind of seems like it comes down to 4:56 or 4:88

I have a NP435 so I'm less worried about my crawliblity. Not really sure I really want my bronco going 70 MPH but would be nice to cruise the HWy with out winding up the motor.

1969, 351-w,33's, np-435,
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Old 12/14/04, 03:32 PM   #5
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THere are a couple of charts floating around that give the optimal gear ratios for tire sizes. I would think that you would want at least 4.56 gears, if not taller. Depending on your suspension, it may not have very good highway manners; let us know what you decide and how it turns out/handles on the highway. Good luck.

Here is a prior thread where this was discussed, I believe you can find a chart here too.
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Old 12/14/04, 05:41 PM   #6
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35's at the moment, goin to 37's and staying with my current 4.56's

Red 77: SOLD
Green 77: SOLD
Looking again.
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Old 12/14/04, 06:58 PM   #7
Posts: n/a
Exclamation If you want to play, check this out....

Gear Calculator Updated Link

Let me know if you need something added.



Last edited by Miley; 02/06/05 at 11:10 PM.. Reason: Updated the URL
Old 12/14/04, 09:08 PM   #8
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Check out!

Lake Elsinore, CA
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4.88s would be the best of both worlds.

72' Sport. 302, Truck Avenger carb, NV4500, Atlas 4.3, 5.13s, detroits, 36" Iroks, Champion Beadlocks, Superiors, CTMs, F150 4x4 box, TRO. yada, yada, yada....
My RigRater Score: 1002RRv1.0 with a BOA of 28.27
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Old 12/14/04, 09:19 PM   #9
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Very cool link!
That just what I was looking for.

1969, 351-w,33's, np-435,
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Old 12/14/04, 09:26 PM   #10
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Northern California
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I run 4.88s with my 37s.

1971 Bronco & 2001 Ram 4x4 w/Cummins
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Old 12/14/04, 09:45 PM   #11
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Couer d'Alene, ID
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Miley that is a very cool link. You should put that in the tech section. You have made all our lives easier, now we don't have to do the math anymore, where were you about two months ago when I was trying to decide which tranny to go with? I had gear formulas everywhere.

Thanks again Miley very cool.

Sports is my religion, just give me a beer and prop me up in front of a TV on Sunday...Go Broncos!!!
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Old 12/15/04, 09:24 AM   #12
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Topeka Kansas USA
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Thumbs up

I would think 4:88 would be a good choice for a tire that big Good luck. Bill
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Old 12/15/04, 09:54 AM   #13
2- '70's.
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san diego
Joined: Aug 01
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i have 4.56`s with my 37" mtr`s. i would have went with 4.88`s but with an atlas and 500hp on tap i think i`ll have plenty of power to turn them.

Building 2 is a lot tougher than I think.
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Old 12/15/04, 09:59 AM   #14
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Hey Sicaz66..........Do you have any pic's of your rig? I 'm going full length axels also, and would like to see how yours came out.

1969, 351-w,33's, np-435,
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Old 12/15/04, 10:03 AM   #15
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Folsom, Ca
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Posts: 660
I have 4.88's now with my 37's. The 4.11's just were not cutting it.
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