portal axles

[Guinness44]

During the Chile Challenge, the portals definitely were an advantage. Diffs on regulars hung up left and right in those extreme trails. Extreme buggies seem to often go that route nowadays. They are hardly expedition vehicles. .
The groundclearance gained on the H1, and the gearreduction, is what makes it the H1, with the lowrpm torque of a diesel. Like the climb to Grey Mesa on the Hole in the Rock trail: Its 7 feet wide, so there is only one line. The couple H2s that were along had some trouble clearing the diffs at that one spot, while the 1s, just went over. Even so the independant suspension is not favored by most, we have learned to drive "all over again". Coming from a TJ, where air under a tire is gonna be a unstable moment....

 

[Antichrist]

This also keeps the vehicle's center of gravity lower than it would be if using a conventional approach (big tires, big body lift) to achieve the same clearance.

I question how significant this difference really is. All the heavy stuff, diff, axle housing, frame, engine, gearbox, etc. are sill at the same height relative to the ground.

 

[Ron B]

For any given road speed, a vehicle with 2:1 hub reduction gear will have its diffs and shafts spinning twice as fast as a similar vehicle in which the same overall gearing is built into the transfer box (or the diffs). The 2:1 hub reduction then slows the wheels down to the designated speed.

Now I'm all confused (easy to do)! It just seems the halfshafts spin so slow when compared to the tires when I see videos of my truck climbing but your explanation makes sense, thanks.

here's a mid '90's dealer video that is fun to watch which talks a bit about what you have said:
http://www.youtube.com/watch?v=Yf9FPs40VUM

rb

 

[Guinness44]

I question how significant this difference really is. All the heavy stuff, diff, axle housing, frame, engine, gearbox, etc. are sill at the same height relative to the ground.

It makes a big difference in stability. Look at a Hummer with the 37 inch tires stock. Then look at a lifted Powerstroke (my friends), with 37 inch tires. To fit those, that lift is 6, 8, inches, not sure. The truck looks very nice, but bet on offcamber sections it will be a trip. And the diffs are still hanging low, so lines will be limitied by that.

 

[Antichrist]

It makes a big difference in stability. Look at a Hummer with the 37 inch tires stock. Then look at a lifted Powerstroke (my friends), with 37 inch tires.

You're comparing two entirely different vehicles. You have to compare the same vehicle, a Ford on portals with 37" tires and a Ford on stock axles with 37" tires.

 

[Guinness44]

True, then I guess you gain the clearance under the diff. Wouldnt you have less lengthy liftsprings/shoks with the axle higher than stock. When we lifted the TJ, it got very squirly....compared to stock. (it was the 90 inch WB that also didnt help there)

 

[michaelgroves]

True, then I guess you gain the clearance under the diff.

Yes, as I see it, portals have only one major benefit - increased ground clearance under the axles. It's an extremely formidable advantage off-road, but comes with some significant downside: raised C.o.G. (the axle and diffs are higher than an otherwise identical vehicle with conventional axles), complexity, and more complicated suspension and axle mounting to avoid severe axle-tramp.

The other advantages, such as hub gear reduction, can be achieved without portals, or they are necessary because of the increased ground clearance (e.g. more manageable axle-shaft angles).

 

[madizell]

Portals are also, as a rule, heavier than a straight axle. Controlling unsprung weight then becomes an issue if the vehicle is used on roads and trails as opposed to hard core off road. There is also a leverage issue because the effective axle line and the weight of the tires is so far removed from the suspension contact plane. Retro-fit portals are not suitable for higher speed vehicles because of the design compromises. Rock buggies and competition vehicles don't usually need to think about highway travel issues.

 

[Portal-Tek Axles]

We just joined Expeditionportal.com

I have to say that it is neat to see a great site dedicated to expedition vehicles. The staff at Portal-Tek has a tremendous affinity toward the expedition and overland style vehicle travel. The concept of self supported vehicle travel is definitely at the roots of where almost every member of our team comes from.

Since this is a portal axle based discussion we would like to contribute to the conversation. The last seven years of portal testing has provided us with some very interesting data and test results that we would like to make available to this community.

I have noticed a few times that 'center of gravity' has come up in this thread. To be honest before we finalized our prototype design we assumed that the COG on any vehicle equipped with our axles would be higher. One of the silver linings of our testing stage was that we found this to be grossly inaccurate. After some serious rough and angry testing we found that our design was EXTREMELY balanced and stable. We concluded that this happens because more mass is located in the center of each wheel (low and wide) with less relative mass in the center of the housing. This is one of the reasons that a Unimog, which is tall and relatively narrow, is able to be so stable in off camber situations. In comparison a similar vehicle with straight axles, running 39" tires would have to have such a tremendous amount of spring lift to clear this size of tire that the COG would definitely cause the vehicle to be very 'tippy'. In our experience a portal equipped vehicle with less spring lift will allow for more clearance and bigger tires (both positive) while providing a very stable COG. For more info on spring lift vs. true lift please visit- http://www.portal-tek.com/faq.html

-Jim Jackson

 

[Antichrist]

For more info on spring lift vs. true lift please visit- http://www.portal-tek.com/faq.html

Hmmm..I read Why are Portal-Tek Axles advantageous to a suspension lift?
While some of the information in that section is indeed factual (what would be in a FAQ), other information/terminology is vague and misleading.
You mention 10" suspension lift, but don't mention what vehicle, what size tires you'd fit with that much, what size tire you could fit with a combination suspension/body lift.
You state portals with 33" tires gives a 4.5" "TRUE LIFT" over straight axles with 33" tires. In my years of off-roading true lift (related to true ground clearance) has always been defined as the distance from the ground to the lowest point, which in the case would be the same pretty much for portals on 33" or straight on 33". True lift will always be the difference in radius for one tire to a larrger one.
Portals will get your diffs higher, true, but that's different.

 

[michaelgroves]

You state portals with 33" tires gives a 4.5" "TRUE LIFT" over straight axles with 33" tires. In my years of off-roading true lift (related to true ground clearance) has always been defined as the distance from the ground to the lowest point, which in the case would be the same pretty much for portals on 33" or straight on 33". True lift will always be the difference in radius for one tire to a larrger one.
Portals will get your diffs higher, true, but that's different.

Am I missing something? Isn't the diff usually the lowest point, in which case a portal axle's raised axle tube and diff translates into more (true) ground clearance?

 

[Antichrist]

Am I missing something? Isn't the diff usually the lowest point,

Depends on the axle/suspension design.

 

[michaelgroves]

I have noticed a few times that 'center of gravity' has come up in this thread. To be honest before we finalized our prototype design we assumed that the COG on any vehicle equipped with our axles would be higher. One of the silver linings of our testing stage was that we found this to be grossly inaccurate. After some serious rough and angry testing we found that our design was EXTREMELY balanced and stable. We concluded that this happens because more mass is located in the center of each wheel (low and wide) with less relative mass in the center of the housing. This is one of the reasons that a Unimog, which is tall and relatively narrow, is able to be so stable in off camber situations. In comparison a similar vehicle with straight axles, running 39" tires would have to have such a tremendous amount of spring lift to clear this size of tire that the COG would definitely cause the vehicle to be very 'tippy'. In our experience a portal equipped vehicle with less spring lift will allow for more clearance and bigger tires (both positive) while providing a very stable COG. For more info on spring lift vs. true lift please visit- http://www.portal-tek.com/faq.html

-Jim Jackson

It's hard to meaningfully compare portal-axle trucks with standard-axled trucks, because portal axles allow bigger wheels with less suspension lift. However, I don't really see why you'd have a lower COG with a portal vehicle, even if you raised the suspension of the other truck. Comparing them, in both cases, the body, chassis, engine, gearbox, wheels, hubs, brakes etc. all sit at the same height... The springs are longer on the non-portal truck, but other than that, the only difference is that axle tube and diff are a few inches higher on the portal truck. Not a very significant difference, perhaps, but a slightly higher COG.

The "tippiness" of the non-portal truck is perhaps due to the much longer springs, rather than a raised COG?

 

[michaelgroves]

Depends on the axle/suspension design.

Well, I asked the question specifically in connection with your objection. For normal 4x4 trucks, the differential is usually the lowest point, and is therefore the measure of "true" ground clearance.

If you raise the diffs by fitting portals, then you raise the true g/c, unless the portals introduce a new low point (which, glancing at Portal-tek's design, they don't).

 

[KevinNY]

Mog on 39s, not tippy.

http://picasaweb.google.com/VTXSVP/RokCut/photo#5240902432709821202