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+--- Thread: Determine gear ratio (/thread-1665.html)
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Determine gear ratio - chuzie - 07-12-2009
The question of my actual gear ratio was brought up yesterday and now I am seriously wondering what I have in there. I have always assumed it was 4.11 because that is what the previous owner told me but now I am not so sure.
Most guides tell you to jack up and rotate the wheel once if locked and twice if not locked to determine the ratio based on the rotations of the driveshaft.
I have a lockrite so just because I jack up the rear does not necessarily mean both sides are going to turn but it is not a spider gear setup either so I assume I still apply to the 1 tire revolution rule, right?
If that is the case I got about 3.50 driveshaft turns out of a single turn of the wheel. YIKES! 4.11 my butt! That explains a LOT.
Guess I have something else to add to the list.
Determine gear ratio - bucketobolts - 07-12-2009
Have you looked up the axle code on the VIN tag to see what was factory? Then you never know what a previous owner may have installed.
The 4.10/11's would be nice. If you ever decided to go lower like 4.56-4.88's you wouldn't have to replace the front carrier. Some brands make thick gears that will work with the 3.50 carrier. I have installed these for other guys. Never had a set myself. And never heard anyone complain about them.
Determine gear ratio - chuzie - 07-12-2009
I haven't yet. This is not the original axle, that was made clear to me when it was purchased.
What are you running?
I definitely want to get 4.11 or 4.56. Here are the numbers I crunched (35" tires w/C4).
3.54 - 60 MPH - 2000 RPM 3.52 - 70 MPH - 2400 RPM.
4.11 - 60 MPH - 2400 RPM 4.11 - 70 MPH - 2800 RPM
4.56 - 60 MPH - 2600 RPM 4.56 - 70 MPH - 3100 RPM .
I need to retain the ability to drive this puppy to events since I don't have a trailer. The question now will be is 2600, 2700, or 2800 RPM considered OK for extended periods like highway driving? Also, are 4.11 suitable for crawling considering I am running 302/C4/D20/35"tires?
Chuck made the comment yesterday that having brakes that work are nice but using gears to crawl down a hill is nicer. I don't even know if that is possible with what I am suggesting but something to consider.
Determine gear ratio - Timstrk - 07-12-2009
If you're running 35s you will like 4.56s much better than 4.11. Trust me on this one. 4.88 might be a little steep for the street but if you don't drive it much, on the street, then that gives you more options later if you want even bigger tires. Been there, done that. Its easy to see the mistake looking back.
Tim
Determine gear ratio - chuzie - 07-12-2009
I don't see myself going larger than 35" for the sole reason that I want to be able to park in the garage and I clear by less than an inch right now.
4.88 - 60 MPH - 2800 RPM
4.88 - 70 MPH - 3300 RPM
What ratio are you running Tim?
Determine gear ratio - bucketobolts - 07-12-2009
I ran 4.56's with 36" tires. It ends up close to the factory final drive. I didn't have to touch my speedometer gears and it was correct.
If your going to drive instead of towing to the trail, a set of low transfer case gears or something like an Atlas may be worth the money. You would have your highway gears for daily driving and the super lows for trails.
Determine gear ratio - chuzie - 07-13-2009
Good idea. Maybe it is time to start saving up for an Atlas. I think I am going to go with 4.56 as you and Tim suggested. Now I just have to find some $$$ to pay for it. Pretty sure no one is going to buy used 3.54s.
Determine gear ratio - johnpaulgolf - 07-13-2009
chuzie Wrote:Pretty sure no one is going to buy used 3.54s.
Well ya never know that maybe one Bronco brother(me) could possibly maybe break some 3.50's and might need a backup set !!! just a thought
cratchhe:NOW post some Video :biggthumpup: :biggthumpup:
Determine gear ratio - SC74 - 07-13-2009
Don't rule out the 4.30 gears either. I have 4.11 with 33's and sometimes wish I had gone lower, but I think 4.56 would have been TOO low without stepping up tire size. 4.30 is a good medium.
Determine gear ratio - chuzie - 07-13-2009
Hand not thought about 4.30s. I will have to run in through the calculator.
JP, you're running 3.54s? I had no idea. That transfer case really does a lot for you huh?
Hey Bucket, I found a Richmond Gear 4.56 (9") set on Ebay for 100.00 but who is making sets of 4.56 that will fit on 3.54 carriers that you had mentioned?