Rear Axle Ratio Questions

[Karl_in_Chicago]

The Midwest spends a good portion of the year with partial snow cover on some roads, or with bridges that freeze over when the rest of the road is just fine, or the occasional rain that turns to sleet that starts to freeze. In all of those conditions I would not be in 4H, since it's NOT meant for paved roads. I wouldn't switch into 4H before every potentially slick bridge, I wouldn't switch into 4H before hitting every drift that's blown over an otherwise dry road. But in all of those conditions, I'd DEFINITELY be in 4A, as conditions can change quickly and the ability of the vehicle to send power exactly where it needs to at exactly the right time is a HUGE confidence builder for driving in adverse conditions.

On top of that, 4A isn't just an on/off switch for 4H, it varies power transfer where it's needed. So it's still functionally superior to straight 4H, especially in conditions where traction constantly varies aka slippery paved roads.

2H/4H rules for offroad driving and in consistently slippery conditions (mud, sand, gravel, ice, full snow cover), but for the frequent traction/no-traction situations seen on midwest roads for 4+ months of the year, 4A is king.

Exactly. Chicago salts the crap out of the roads but starts with the main routes and works their way out to the smaller neighborhood streets once the main storm is over. Between that - and the wind blowing snow from parks and such back onto the roads - it's extremely common to be driving on dry then suddenly encounter snow. I'd definitely want the 4A here.

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[Laminar]

Take the xfer case apart and you will find a basket clutch and electromagnet getup that performs the exact same function as the 4 lock dog clutch. Its just a way to have a computer shift it...nothing more.

Why does the clutch have to be an on/off switch? Why can't it provide varying levels of engagement?

 

[Bmadda]

Why does the clutch have to be an on/off switch? Why can't it provide varying levels of engagement?

It will burn up the basket clutch if it does that

 

[Gamecock]

Just browsing the build tool for that RAM trx.. so it comes with 34.6” tires and 3.55 gear ratio... so why all the talk on bronco needing 4.46-4.7? What’s really needed? Is it the 700hp that eliminates the gearing need on the ram?

You're only looking at one part of 3 in the Final Drive Ratio, and each has equal weight: Final drive ratio = axle ratio x transmission gear ratio x transfer case ratio.

Like someone above said "4.xx seems to be the sweet spot for 33s"...that statement is meaningless, because he is taking anecdotes from vehicles with completely different gearing and trying to look at them in the context of a Bronco and only accounting for 1/3rd of the gearing puzzle.

 

[Laminar]

It will burn up the basket clutch if it does that

Why? Why can't the friction plates and transfer case fluid be designed to dissipate the heat generated?

 

[da_jokker]

Why? Why can't the friction plates and transfer case fluid be designed to dissipate the heat generated?

I don't know enough so I probably should just keep my mouth shut but.... ? when 2 things rub... something is wearing. So slipping the clutches would eventually take its toll.

Personally I think there should be just some basic options....

100 rear (open diff) normal driving
70 rear/30 front (open diff) dry but possible slippage like rain, snow, etc
50/50 with lockers (rear +/- front) off road or serious traction compromise.


But what do I know.

 

[Laminar]

I don't know enough so I probably should just keep my mouth shut but.... ? when 2 things rub... something is wearing. So slipping the clutches would eventually take its toll.

Sure! Can a slipping connection be designed for a lifecycle of >150,000 miles? Like main and rod bearings?

 

[da_jokker]

Sure! Can a slipping connection be designed for a lifecycle of >150,000 miles? Like main and rod bearings?

Yes they can....but they are designed NOT to grip. A better comparison would be brake pads... dissipate the heat... hell, dunk them in fluid... they will still wear because if they don't, they can't do their job.

 

[Bmadda]

Why? Why can't the friction plates and transfer case fluid be designed to dissipate the heat generated?

My guess would be because the people who write the sales brochures have families to feed also?

 

[Laminar]

My guess would be because the people who write the sales brochures have families to feed also?

You guys would poop your pants if you knew how the Twinster AWD system works in the Focus RS.

 

[cursed_hemi]

The gearing is definitely a concern for me. I'm curious to see how the manual feels with the 32"s because I really would like to upgrade to a 33". Makes it look so much beefier.
I went from a 27" tire to a 30" on my Jeep with stock gearing (manual trans) and it really killed acceleration. I pretty much never get out of third unless I'm on the highway. Really have to be careful about bogging in first gear from a stop too.

I realize on the Bronco I'll it will be a much smaller difference - 32" to 33" but it's still concerning that the Badlands comes with the 4.70 gear with the 33"s.

 

[Zeta]

So let's say someone got a Base - 2.7 - 10A setup. What would going to 32 inch tires do with the stock gear ratio? Also, same question but with Sasquatch going down from 35s to 32s? (Can you tell I want 32s?)

 

[Karl_in_Chicago]

So let's say someone got a Base - 2.7 - 10A setup. What would going to 32 inch tires do with the stock gear ratio? Also, same question but with Sasquatch going down from 35s to 32s? (Can you tell I want 32s?)

You'd want to update the system so it could recalibrate the speedo and shiftpoints. Don't know if the Bronco let's you do that yourself or if it has to be done by dealer. In time I imagine there'd be aftermarket programmers that would let you do it yourself like there are for many other vehicles, but it may take time before they figure out how for the new Bronco.

Anytime you lower the size of the tires - and presumably by extension the weight - you make it easier for the engine to accelerate and maintain speed. 33's to 32's, meh, 35's to 32's I imagine would definitely be noticeable.

 

[dgorsett]

This worry has slowly been increasing as I view the BD as having 90% of what i'd ever need/want. However, the gearing and max crawl gear ratio, plus front locker (and 210) and 33" tires only being available in Badlands might see that $6K price bump become closer to necessary..... Which sucks as i've been pricing everything out based on BD and is in-budget. Buuuuuuuuuuuut, do it once, and do it right.

(Full disclosure: The only way i'm getting a bronco is with a manual transmission and I have less than 0 reservations about the 2.3 being more than capable for Bronco as it's in the gf's Ranger and I like the motor quite a bit)

I think the 4.46 would be just right with 32-33"s. It's only 5% different from the 4.7 and tire difference is 7-8% difference, you won't even notice, especially with the manual and double especially with the crawler. With the auto you may notice some hunting on the highway but that would probably more perception than reality. Also remember that as differential gears get lower (higher numerically) the gears become weaker in the same model diff (more teeth per unit of diameter means finer teeth)

Question: does anybody know if the 10 spd is like other Ford Select Shifts, in that you can limit how high a gear the trans shifts to. On my 6 spd F250 I can limit the upper gear selection, great when towing or in the mountains.

 

[Zeta]

Thank you. I just wouldn't want to turn it into a slow accelerating dog or make it have to rev too high to maintain highway speed. I'm coming from an XJ though so I'm sure it's all better in every way drive train wise.

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