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Ok to drive in 4 wheel?

Nothing Special

Sr. Member
Joined
Nov 25, 2016
Messages
804
And even with the slightly mis-matched ratios it really doesn't amount to much. Tire rolling diameters aren't always right on, making a perfect ratio match not perfect anyway. And going around any corner or curve also changes the match.

Probably the biggest reason an empty pickup deals with 4WD on hard surfaces so well is that it's so easy to scuff back tires. A loaded pickup in 4WD is going to be harder on the equipment (in 4WD on hard surfaces). A Bronco will be somewhere in-between (but as a relatively light weight truck on relatively tough axles, it's probably closer to the unloaded pickup).

And you typically won't damage any metal parts by smooth operation in 4WD on hard surfaces. The breakage typically comes when you put shock loads on the drive train, like when you lose traction and then abruptly regain it while under power. This happens in tighter turns (the crow-hopping), but not typically at any other time when driving in 4WD on pavement.

All of that said, it's still a bad idea to use 4WD on hard, good traction surfaces. If nothing else, it wears your tires and uses more fuel. But also, even without the shock loads, the higher forces on the drive train will cause some fatigue, which typically won't come around to bite you, but it isn't doing your axle shafts and U-joints any favors.
 

blubuckaroo

Grease Monkey
Joined
Jun 11, 2007
Messages
11,795
Loc.
Ridgefield WA
I have noticed that higher gearing in front is more forgiving than lower gearing in front. Mine had 3.54 front/3.50 rear when I bought it. Gear binding is a lot easier to live with 4.09 front/4.11 rear now. I don't seem to get that shift-bind anymore where I'd have to back up sometimes.
I think it has something to do with stretching the chassis rather than crowding it.
 

Nothing Special

Sr. Member
Joined
Nov 25, 2016
Messages
804
I have noticed that higher gearing in front is more forgiving than lower gearing in front. Mine had 3.54 front/3.50 rear when I bought it. Gear binding is a lot easier to live with 4.09 front/4.11 rear now. I don't seem to get that shift-bind anymore where I'd have to back up sometimes.
I think it has something to do with stretching the chassis rather than crowding it.

Two things that make 4.09 front / 4.11 rear easier than 3.54 front / 3.50 rear. One is that there's not as much difference. 3.54 is 1.1% lower than 3.50 while 4.11 is only 0.4% lower than 4.09. So the taller gears have almost 3 times as much difference as the lower gears.

Also on average the front tires have to go farther than the back (taking the longer outside track around curves). Having higher gearing in the front can help make up that difference on turns while lower in front makes the difference even larger.
 

74 Bronco Billy

Contributor
Sr. Member
Joined
Jul 4, 2016
Messages
775
It’s raining here a lot. I want to run the 4WD HI in these weather conditions, that’s why I went with Trac Locs in both differentials, 4.56 front and rear. Around turns no binding since they have a limited slip capability, but off road I can tap the brakes and get them to lock up, right? Am I missing something?


Sent from my iPad using Tapatalk
 

Nothing Special

Sr. Member
Joined
Nov 25, 2016
Messages
804
It’s raining here a lot. I want to run the 4WD HI in these weather conditions, that’s why I went with Trac Locs in both differentials, 4.56 front and rear. Around turns no binding since they have a limited slip capability, but off road I can tap the brakes and get them to lock up, right? Am I missing something?


Sent from my iPad using Tapatalk

Sorry, but you're not going to like what I have to say here. Tapping brakes with limited slip differentials does not make them lock, and TracLocs get very little, if any benefit from applying brakes.

Truetracs, which are completely different fromTrac Locs, will transfer more torque to the tire with traction if you apply a little brake, but even with Truetracs it really only helps on the rear axle where you can apply the emergency brake to only the rear wheels (applying the foot brake to transfer torque in the front gives you a little more power to the front tire with traction, but it means you're driving with all 4 brakes on, so it's often a net loss).

Also the clutches in Trac Locs need to slip to allow the differential to work in a curve. So on slippery surfaces you are much more likely to start to skid a tire (or more) going around a corner with Trac Locs than any other type of diff (open, Truetrac or automatic locker). The only thing that's worse for stability in a corner on slippery surfaces is a spool (or a locked selectable locker).

I know a lot of people like Trac Locs. I'm not one of them. I really think they are the worst of both worlds. Not much help when you need better traction to be able to keep moving, and significantly worse stability on slippery surfaces. Of course they can be set up very tight, making them good for traction (but worse for stability). Or very loose (or just worn out) making them not as much worse for stability (but even less helpful for traction).
 

Projp

Sr. Member
Joined
Nov 14, 2004
Messages
503
What kind of truck does he have Projp?
Reason I ask is if it's got matching front and rear axles, then the ratios match exactly.
In our case the ratios don't match exactly, so it's more of an issue.

I agree though that it won't always cause dire issues, as even on hard surfaces the tires will sometimes be the first to give. In that case nothing is harmed other than some extra wear on the tires like you said.
But it's definitely different for a truck with, for example, two Dana axles, or two Ford axles, than it is for a mixed set.

Paul

He has been absent minded for years.
He usually drives a fairly new ford F150 or half ton chevy.
I am not sure how the ratios match up on front vs rear on the newer trucks.
I usually don't work on axles that are less than 40 years old.:)
Variations of tire diameter involving tire pressures, mismatched tires, or tire wear could more of a factor than small ratio differences.
 

sprdv1

Contributor
REBEL
Joined
Mar 8, 2007
Messages
81,734
4 wheel drive in a driving rain is OK. Also, being from LA, I remember when it rained even lightly after a period of no rain the water would raise the oil on the road and make for slippery conditions. As stated earlier if you think the road is slippery then it's probably OK for 4 high. Also as Blubuckeroo pointed out, it's a good idea to keep the hubs locked during inclement weather so you can switch between 2 and 4 high as needed.

Agreed.... Just use your best judgment depending on the weather..
 

Broncobowsher

Total hack
Joined
Jun 4, 2002
Messages
34,833
It’s raining here a lot. I want to run the 4WD HI in these weather conditions, that’s why I went with Trac Locs in both differentials, 4.56 front and rear. Around turns no binding since they have a limited slip capability, but off road I can tap the brakes and get them to lock up, right? Am I missing something?


Yes. No center differential. You might have limited slip at each axle, but you have a locked spool in the middle. The front axle assembly is binding against the rear axle assembly. In a turn there IS binding, there IS tire slip, or you have broken parts.
 

Broncobowsher

Total hack
Joined
Jun 4, 2002
Messages
34,833
With something that close, the amount of tire wear would come into play. How much squirm is in the tread blocks is another factor.

That ability to blip the throttle while driving in a straight line to get out of 4WD, that is the tread blocks flexing back and forth (from blipping the throttle) that takes the load off the shift collar so you can shift.

Even tires of the same size can be a different size depending on who made them.

Don't forget there is even things like tire pressure that will change the rolling radius of a tire and how far it goes per revolution.

All of this is driving in a straight line. Turn the steering wheel and it all goes out the window.

It's really simple. In 4WD you are going to have tire slip no matter what. That is a factor of life with a part time transfer case (no center differential). To run in 4WD you need to be on a surface that lacks traction. Have traction, be in 2WD. Want to ignore this advise, go ahead, but don't argue about it. Want full time 4WD like a new car, go get a new car. But a Bronco isn't full time 4WD and does not have the ability to drive in 4WD without spinning tires on the pavement.
 

Scoop

Contributor
Have Bronco, Will Travel
Joined
Feb 1, 2006
Messages
10,580
Loc.
Cuchara, CO
I was just wondering if anyone has run different front/rear tire sizes to compensate for their gear ratio difference?

One of the 2017 Jeep concept vehicles "Quicksand" is built that way.

2017-03-31_Jeep_Quicksand_Concept_02.jpg


Quicksand Article

From the article:

"The Quicksand concept is also the first Jeep concept to ever run a staggered tire setup. A staggered setup means the front and rear tires aren’t the same size. In this case, the front tires are 32 inches tall, while the rears are 37 inches tall. BFGoodrich Mud-Terrain T/A KM2 tires are used at each corner, mounted on custom 18-inch “kidney bean” alloy wheels with a center knock-off hub."

I think it's a cool concept. I'd love to see a Bronco built in a similar style. I can't find where they've disclosed the gear ratios used to run 37's and 32's. It would be interesting to find out.
 

sprdv1

Contributor
REBEL
Joined
Mar 8, 2007
Messages
81,734
Oh my... :)

One of the 2017 Jeep concept vehicles "Quicksand" is built that way.

2017-03-31_Jeep_Quicksand_Concept_02.jpg


Quicksand Article

From the article:

"The Quicksand concept is also the first Jeep concept to ever run a staggered tire setup. A staggered setup means the front and rear tires aren’t the same size. In this case, the front tires are 32 inches tall, while the rears are 37 inches tall. BFGoodrich Mud-Terrain T/A KM2 tires are used at each corner, mounted on custom 18-inch “kidney bean” alloy wheels with a center knock-off hub."

I think it's a cool concept. I'd love to see a Bronco built in a similar style. I can't find where they've disclosed the gear ratios used to run 37's and 32's. It would be interesting to find out.
 

Scoop

Contributor
Have Bronco, Will Travel
Joined
Feb 1, 2006
Messages
10,580
Loc.
Cuchara, CO
For 37's and 32's, using a gear ratio calculator, 4.10 rear and 3.55 front should work well.
 

blubuckaroo

Grease Monkey
Joined
Jun 11, 2007
Messages
11,795
Loc.
Ridgefield WA
Wow!
That's a really cool solution for someone with mismatched axle ratios. I you were already in the market for wheels and tires, this could be the "free" option.
 
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