Gear ratios

[Nick]

Post up what you have.

My last bronco i ran 4:56's with 35" tires. In hard pack it worked well, but in the sand i felt like i needed some thing more. I considered going to 4:88's but scrapped the bronco before i had a chance.

[SteveG]

3.55 all the way. It's perfect because it's just low enough that I still get shitty fuel economy on the freeway (C6 trans) and just high enough that it's gotta be wound up to make power in the sand.

If I ever switch to an overdrive trans I'll use 4.10 gears with 33" tires.

[tcm glx]

4.10s on 35s, Love on the road, 75-80 mph on the hwy feels awesome.

On the dirt, pop it into second gear, and it pulls great!!

In the sand, do not know yet, probably will be lacking.....

[PBR]

i think with an o.d. trans that 4.56 is a great way to go. but as a d.d. you are better with 4.10's for it's hwy mannors, and if it was a trailer queen, then go 4.88's.

[philofab]

I have 4.56 and I love them... I can still drive it on the freeway. I have a 302 & M5R2 (5 speed manual).

If I need more power I will build a 427 Windsor.

[denhabr]

4.56's with 35x12.50R-15 Goodyear Silent Armors...and a TrueTrac in the rear to boot (open in front.)

Not sure how this performs, as it is still in the shop being built (Utah Broncospeed).

My $0.02 anyway...

UPDATE @ 11-15-2011: I've had the Bronco on 35's and 4.56's for close to 2 years now, and I'm very happy. Not sure what RPMs I'm turning on the highway (as I have an XL w/o a Tach), but it sounds very 'normal' as far as how fast the engine is turning. Climbing Parley's Summit (Eastbound I-80 out of Salt Lake City) forces me to turn off O/D, but other than that, the 4.56:1 gears seem just right.

Performance also just increased this last month seeing I had to address a CEL that appeared in late August. I pulled 2 codes for Lean Condition Left Bank and Right Bank...and it turned out to be a bad fuel pump. Best fuel pressure was was 25 psi (regardless of RPM,) and it should have been 35-45 psi! Once fixed, the little 302 has been running MUCH better (CEL is gone), and has been working with the 4.56's in a much more responsive way. Since this is a Daily Driver, the 4.56's work the best for me. Had it out on a U4WDA/RME4x4 Trail Clean Up this weekend, and it was playing well with all of the rock crawlers!

[PaulW]

35s, 4.56, E4OD, and stock 5.8-Mine
35s, 4.10, C6, and built 414 Windsor-Chris
Mine seems sluggish. I have not driven Chris'
Compare with the wifes Jeep LJ: 35s, 4.88, OD auto, stock 4.0. Horrible. The thing should have 5.13 gears because of the lack of power.

Wimpy motors need more gears.
PW

[bajascott]

4:88 35's. aod.302is what i am going to use
right now 3:50 35's crappy milage and not able to use overdrive untill i am doing 80+mph down hill with a tail wind.

[PaulW]

35 Krawlers, 4.88, AOD with (car gear set), stock 5.0-HO. Result sluggish even on the much lighter 72 EB
I wish I had both the truck lower AOD gear set and 5.13 gears.
-Sigh-
Another lesson - darn
PW

[Nick]

My rear end is already loaded with 4:10's, and i have a set of gears for the front. But i just know that i'll hate life running the 4:10's with 35" tires.

I'll just keep on saving my pennies and go with 4:88's.

[magic carpet XLT]

i've run all the following ratios over the years, drivetrain has always been stock 351W and C6
3.55 + 33" tires: stock, couldn't light the tires from a stop even in the wet, 18-20 mpg on the freeway
3.55 + 35" tires: worse acceleration than above but nice on the freeway
4.10 + 35" tires: mathmatically equivalent to stock, but seat of the pants felt better than stock, excellent combo in dirt, snow, sand and rocks and for a rig with no OD
4.10 + 37" tires: personally, my favorite combo, but spent lots of time in first gear and low range, ok mileage
4.10 + 40" tires: complete dog off the line, but great in low range or on the flat freeway, terrible mileage
5.13 + 40" tires: will spin the tires thru second gear in the rain (most fun setup), but winds out on the freeway (3k rpms for 60 mph), excellent power in the dirt, sand, rocks and snow. mileage comparable to 4.10s and 37s but much improved around town.

OD is really your deciding factor, IMO if you have OD you can basically gear your diffs 15-25% deeper for better power but still get decent revs and freeway mileage. my ideal setup would be something like: 351W, C6 with low 1st gearset, 4.88 gears 40" tires. i also think its more important to gear a little lower if you run an auto tranny, gotta keep the heat down.

[baja-chris]

Nick, do you have an overdrive?

[Mike]

Gears depend on the health of the motor.

When I built my 5.0 and converted to MAF and a nice cam it would light up 37" MTR's with 4.10's. Now that the motor has 75K on it it feels like I need 4.88's.

I miss that fresh motor.

[westco]

I'm running 4:88's, 35"s and a C6, but my Bronco is pretty much for the dirt only, I drive it into town occasionally and my wife drives it out the the desert following me, towing our trailer...so slow ride. It's great for launching and I drive it in 2nd in the sand, i hardly ever need to use 4wd.

[Nick]

Nick, do you have an overdrive?

Yes i do. It's an e4od

[Rednek Renegade]

i've run all the following ratios over the years, drivetrain has always been stock 351W and C6
3.55 + 33" tires: stock, couldn't light the tires from a stop even in the wet, 18-20 mpg on the freeway
3.55 + 35" tires: worse acceleration than above but nice on the freeway
4.10 + 35" tires: mathmatically equivalent to stock, but seat of the pants felt better than stock, excellent combo in dirt, snow, sand and rocks and for a rig with no OD
4.10 + 37" tires: personally, my favorite combo, but spent lots of time in first gear and low range, ok mileage
4.10 + 40" tires: complete dog off the line, but great in low range or on the flat freeway, terrible mileage
5.13 + 40" tires: will spin the tires thru second gear in the rain (most fun setup), but winds out on the freeway (3k rpms for 60 mph), excellent power in the dirt, sand, rocks and snow. mileage comparable to 4.10s and 37s but much improved around town.

OD is really your deciding factor, IMO if you have OD you can basically gear your diffs 15-25% deeper for better power but still get decent revs and freeway mileage. my ideal setup would be something like: 351W, C6 with low 1st gearset, 4.88 gears 40" tires. i also think its more important to gear a little lower if you run an auto tranny, gotta keep the heat down.

Ever run 3.73's with 33s?

[SandStallion]

Im currently running 3.55:1 w/ 33in. BFG AT's and Steel rims. It wont light them up from a dead stop, but It runs about 1800RPM between 65-70 on the freeway and im only gettign about 16-17mpgs at best w/ the E4OD. In 4-low however i can hold it in second and it takes off like a rocket in the sand. I like it for smokin the blazers up Comp @ pismo.

[ntsqd]

My suggestion would be to first play with what rpm range the engine likes to run at (assuming no dyno graph). You're looking for the rpm that the engine delivers the best cruise mileage at. One of my non-Fords has 285's & 3.73's. It wants to run above 65 mph in OD or the engine lugs and the mileage plummets. Badly plummets. Below 65 I pull it out of OD and the engine is happy again.

What knowing that rpm is does for you is tell you roughly where the Torque Peak is. The BSFC always happens at the torque peak. However/wherever you drive the truck, gear to run that rpm in the trans gear that you normally use.

Failing that, or with a stock engine you can use the stock tire & gearing to find the best match. This is when there is no experience or RoT available to sort out the best ratio, and is my preference over those two methods. For instance, I'm in the middle of an engine swap (an SOB engine into an SOB vehicle), no way to drive the donor so I looked up it's axle ratio & tire size. Plugged into Excel and got an rpm for 60, 65, & 70 mph. Then I plugged in my desired tire size and solved backwards for the axle ratio that gave me the closest rpm's. Turns out that 4.10's are a near perfect match for the 33's.

[SteveG]

35s, 4.10, C6, and built 414 Windsor-Chris

Chris, didn't you use the same gears with the stock 5.8L? Did you ever tow with it? How was it?

[PaulW]

35s, 4.10, C6, and built 414 Windsor-Chris

Chris, didn't you use the same gears with the stock 5.8L? Did you ever tow with it? How was it?

=
Back then, Chris' stock setup was always faster than my stock setup before my stretch. He has never towed.
Back then both with 33s his with C6/4.10, mine with E4OD/4.56. Mine always got better mileage. desert & highway. My engine was tighter than his high mileage unit.
His is better now with the new motor but uses the same gears.
Paul