Why are front rims positive offset?

[Unforgiven]

On large trucks such as the Deuce or any other big truck the front rims are always positive offset (as opposed to negative "deep dish" offset).

I am a novice to large truck design. I'm just curious why every large truck has positive offset on the steer axle? Is it simply to aid steering or is there a safety issue involved?

Smaller "regular" trucks often run deep dish rims all the way around to widen the stance.

Positive offset:




Negative offset:


I'm just curious why large trucks never have negative offset tires up front.

 

[doghead]

The fronts need to steer(turn). They pivot at the kingpin. If you had dish out, the distance from the pivot point to the center of the tire would be greater. The shorter, the better, to lessen the force needed to steer.

That's just one reason.

 

[armytruck63]

Plus, the wheels are the same as the duals in the rear. That means you can move the wheels anywhere on the truck, and the spare tire goes on anywhere.

 

[Unforgiven]

Aha, that makes sense. But the kingpin is strong enough to take the load, correct? Otherwise the 4x4 guys running big deep-dish tires would be shearing the pin during hard turns right?

 

[B3.3T]

Doghead and armytruck63 are both exactly right. With all that weight on the front, unless the tires match the pivot point steering would be really difficult, even with power. Its all in the physics...

 

[KsM715]

Run them dish out for a while and report back with your findings.

 

[cjtroutt]

The fronts need to steer(turn). They pivot at the kingpin. If you had dish out, the distance from the pivot point to the center of the tire would be greater. The shorter, the better, to lessen the force needed to steer.

That's just one reason.

Ditto

 

[ODdave]

Aha, that makes sense. But the kingpin is strong enough to take the load, correct? Otherwise the 4x4 guys running big deep-dish tires would be shearing the pin during hard turns right?

Any time you move the tire further from the king pin / ball joints you increase the loads tremendously. It is not a good idea as they WILL FAIL when you need them most, think of all those 90's style chevy 1500's with 3 in body lifts and 33's with the wrong offset, those ball joint wear out incredibly fast.

 

[Flyingvan911]

Run them dish out for a while and report back with your findings.

Be sure the tires have enough clearance before you drive the truck. It would suck to turn the wheel and tear something up.

 

[Alredneck]

Ummm, hmm,! Doghead and Army truck are correct.

However running dished out in the front, I dont believe would cause the accelerated wear as stated. It would wear more but if kept up should be feasible. ( Now why would you want to, is another question ) See during time of war, in mucky environments, soldiers would mount 11s on the inside and 9s dished out in the front to help the heavy fronts of these trucks float better. There was no official report ( somebody have one, I cant find it ) on extra maintenance being required from such hard use. These axles are built tough, and should not be compared to a normal half ton drive axle.

Also dished out in the rear, I have many miles on my turck with no adverse side effects. Reason being the weight of the wheel and tire is still basically center between the bearings of the hub. Then also if you look at the weight comparing capacity of these axles, bearing life should remain close to normal. With bigger tires ( 395s for example ) you are going further faster at a lower rpm which will reduce wear, reduce heat, all extending service life of the bearing set!

 

[ODdave]

Ummm, hmm,! Doghead and Army truck are correct.

However running dished out in the front, I dont believe would cause the accelerated wear as stated. It would wear more but if kept up should be feasible. ( Now why would you want to, is another question ) See during time of war, in mucky environments, soldiers would mount 11s on the inside and 9s dished out in the front to help the heavy fronts of these trucks float better. There was no official report ( somebody have one, I cant find it ) on extra maintenance being required from such hard use. These axles are built tough, and should not be compared to a normal half ton drive axle.

Also dished out in the rear, I have many miles on my turck with no adverse side effects. Reason being the weight of the wheel and tire is still basically center between the bearings of the hub. Then also if you look at the weight comparing capacity of these axles, bearing life should remain close to normal. With bigger tires ( 395s for example ) you are going further faster at a lower rpm which will reduce wear, reduce heat, all extending service life of the bearing set!

how would it not cause acc. wear? hes not talking about running duals in the front. With a single flipped it would place the centerline of the tire OUTSIDE of the bearing's !!!!! The wear being addressed is not the tires but the kingpins,

As far as comparing them to half ton trucks, yea these axles are big, but pound for pound they are NOT remarkably strong! think of the comparison i made, K1500 weight 6,500lb's (roughly), Deuce 14,000lb's, Its the weight to strength ratio i was compairing, not the axle to axle strength.

Of corse you have no problems with your rears, your hubs are not flipped so as you stated the tire centerline is still between the bearings........

 

[Alredneck]

I partially agree the front will wear a lil more. But would think other compents in the steering, ball joints/kingpins would wear faster than the bearings in the hubs on the front. I may have misunderstood but thought we were discussing bearing wear on the front.

Im still not understanding why the OP would even want to consider running them dished out on the front! Cool factor, not really in my opinion. After market wheels with more offset are available but still safer to use than saving money and flipping the fronts.

 

[Kohburn]

while running a dish out increases bearing and joint load that is not that actual reason for the deep offset. The real reason has to do with suspension geometry and scrub radius. the higher the scrub radius the harder it is to steer and the more feedback you get from everything. Scrub radius is essentially the distance between where the center-line through the kingpin intersects the ground and the center-line of the tire.

automobiles with a steeper kingpin angle can have less backspacing on the front wheel.

 

[Squirt-Truck]

All above is correct, but primary reason is to keep the load between the bearings, also mentioned above.
Look athe difference in the hub length on the front vs the rear. If you will check you will find that the centerline of the tire is right in the middle of the front hub and the centerline of the rears (Dual) is in the middle of the rear hub.

 

[Unforgiven]

I partially agree the front will wear a lil more. But would think other compents in the steering, ball joints/kingpins would wear faster than the bearings in the hubs on the front. I may have misunderstood but thought we were discussing bearing wear on the front.

Im still not understanding why the OP would even want to consider running them dished out on the front! Cool factor, not really in my opinion. After market wheels with more offset are available but still safer to use than saving money and flipping the fronts.

I totally understand now, thanks to Doghead & others.

The reason I asked is because I'm new to large trucks. I've been around 4x4's for ages but have only had a Deuce for a year.

I'm making mine into an off-road RV. I'm a geologist, occasional fossil hunter, and avid outdoor enthusiast. I go places that I shouldn't go. But I go there anyway for days on end.

So I want to build a more comfortable "expedition" vehicle based on the Deuce.

I've watched every Deuce video available on YouTube. For the money, I think this truck is an awesome platform to start from. But, like anything in life, there is room for personal improvements to suite your needs.

One thing that I noticed on the YouTube videos is the Deuce's front tires seem too narrow in stance on hummocky, downhill rough trails. This may not necessarily result in flipping the truck. But lodging it sideways on a rock & catching a fender is not a joyful scenario either. It would be nice to have a slightly wider stance up front.

In my state the maximum width is 102" with an extra 3" for pneumatic tires & mirrors. So, 108" is the state vehicle width. Some municipalities have a 96" restriction. To make a long story a little shorter, I was curious if the front stance could be widened to aid in stability. The truck is going to be lifted to accommodate larger tires. That will put the center of gravity higher. A wider stance would be beneficial.

Also, I've had a wild-hair-up-bum idea if it's possible to have tandem-rear steer axles. My projected wheelbase using an M36 frame is about 240". That's almost identical to a 40' motorhome. While certainly drivable, I can already well imagine off-road situations where a 240" wheelbase could be, shall we say, less than optimal. But if a stock bogie-axle setup is used, the leaf springs would not allow the rear tires to turn much before rubbing. Deep dish rims on rear-steer axles would allow front axles to be used in the rear without rubbing issues. Now, I'm not saying that I'm going to do this. But I like to investigate all possible permutations before I start modifying things.

Short story:

Truck is getting lifted w/ long wheelbase. I want to widen the stance slightly for better off-road stability.

Doghead answered my question.

Can the front hubs be flipped?

 

[jimmcld]

Go to a five ton. You can put 16.00x20's on it without lifting. It will be more stable and it includes power steering.

 

[mckeeranger]

Can the front hubs be flipped?

No. The part of the rear hub that is flipped, does not exist on the front.

 

[KsM715]

You can run larger tires and custom wheels with a different offset. Lots of guys running bobbed trucks run the modified HMMET wheels.

Look through this thread for all the different wheels that can be used on the front of a Deuce.

http://www.steelsoldiers.com/deuce-...deuce-picture-thread-if-not-here-post-em.html

 

[mudguppy]

there is an official name for this: it's called 'scrub radius' and it's the distance of the center of the tire/wheel from the steering knuckle joint (kingpin or ball joint). ideal setup is zero scrub radius as this would eliminate any forces exerted by hitting a bump/pothole while moving and reduces steering effort to minimum.

this is why such a positive offset is used in OTR and other heavy trucks, in attempt to minimize or reach zero scrub radius.

'deep dish' is a pizza crust style.

 

[mudguppy]

... Can the front hubs be flipped?

actually, technically you can. however, you have to remove the brakes completely.

i have two steer axles that i have done this to for a mud truck - the drums were ditched, hubs flipped, and pinion brakes were added. i had to machine the rotors some so that the lugs would clear the spindle stud nuts.

so, yes you can flip the front hubs, but i don't think there's a feasible braking solution in a deuce or similarly sized vehicle.