portal axles

cruiseroutfit

Supporting Sponsor: Cruiser Outfitters
haven said:
Weird story -- Portal Tek took the guy's money, kept the truck for months, and didn't install the axles. Last post is in Spring 2007. I wonder how the story ends?
There are posts up to last week... still no notable progress :(


Its of my personal opinion that such axles would NOT be suitable for an overland build. There are absolutely exceptions to this rule, some of the OE portal units (Volvo and Benz) could be extremely suitable. However considering the failures and spare parts replacements... I wouldn't think extremely deep about it for my personal uses.
 

seve7

New member
boblynch said:
I know nothing about portals other than they are used on Mogs and offer great clearance with little lift. Pardon the novice questions.

Would portals be a good fit for long term overland trips? What are the down sides (higher CG, poor highway ride, less reliable, max speed limits, hard to find parts, etc.)? What type of rigs would the portal-tex parts fit on? Would they work on a larger rig (e.g., Fuso-based or Earthroamer-type camper)?
They are sweet for getting extra ground clearance, but in some cases need a torque arm attached to the axle because of the lever action of the wheel center compared the axle center (wicked axle wrap). specifically on vehicles with leaf springs. also the seals on the portals themself are prone to leaking... but if you can get past these things the extra gear multiplication, the extra ground clearance, and the cost its a pretty cool concept. but i think it would be cheaper to go with bigger tires and get heavier duty axles.
 

Martinjmpr

Wiffleball Batter
haven said:
Here's an introduction to portal axles I posted at www.expeditioncampers.com

Chip Haven

....

Several manufacturers of military vehicles employ portal axles. Best known are Unimog, Pinzgauer, and AM General's HMMWV
The HMMWV and the Pinz have 4 wheel independent suspension. AFAIK They do not have portal axles (on military HMMWVS the axle goes straight into the center of the hub.)
 
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LRNAD90

Adventurer
Martinjmpr said:
The HMMWV and the Pinz have 4 wheel independent suspension. AFAIK They do not have portal axles (on military HMMWVS the axle goes straight into the center of the hub.)
Both the Pinzgauer and the Hummer (H1/ Military) use gear reduction hubs, and have the drive axle coming into the drive wheel above the centerline. Just because they do not use solid axles, does not mean they cannot use the geared hub design, which affords both additional gear reduction at the wheel, as well as improved ground clearance from the elevated (relative to the wheel centerline) position of the drive axle. Now in the case of an Independent suspension design, it doesn't necessarily gain you ground clearance (Hummer H1 & HMMWV), but it can, as in the Pinzgauer's case. I'll see if I can round up a couple of photos if you are still in doubt..

Here is a WIKI link on Portal axles, that refernces vechicle that use Portals, and list both vehicles as well..
 
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SAR_Squid79

Explorer
I still don't understand why somebody hasn't built an IFS portal kit (based on the HMMWV design) for a Tacoma. I would MUCH RATHER have that than SAS.
 

LRNAD90

Adventurer
SAR_Squid79 said:
I still don't understand why somebody hasn't built an IFS portal kit (based on the HMMWV design) for a Tacoma. I would MUCH RATHER have that than SAS.
What is the perceived advantage? The only one I can imagine is improved CV angles with severe lift, but I wouldn't expect increases in ground clearance (still need the bottom suspension arm) and the gearing advantage is pretty much offset by having to run considerably steeper gears in the rear axle, isn't it?

A SAS has many advantages over IFS off-road, including much greater articulation, stronger components, more available differential and gearing options, etc..

This is a photo of a FJ Cruiser front suspension for reference, but I’m fairly certain it is nearly identical to the Taco’s, no?
 
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cruiseroutfit

Supporting Sponsor: Cruiser Outfitters
Best4x4xfar said:
What is the perceived advantage? The only one I can imagine is improved CV angles with severe lift, but I wouldn't expect increases in ground clearance (still need the bottom suspension arm) and the gearing advantage is pretty much offset by having to run considerably steeper gears in the rear axle, isn't it?...
While you wouldn't necessarily gain any across the board ground clearance, as you noted your lowest point will still be the bottom suspension connection at the spindle. However it does offer the opportunity to gain addition clearance in the middle of the vehicle, all while retaining a lower CV angle. With this lower CV angle comes the opportunity for increased suspension travel.

Why hasn't anyone done it in mass scale? Market doesn't demand it IMO. There have been a handful of companies toying with portal technology (Portal Tek for example), none have really hit a home run yet as to a product that really sells. Time will tell...
 

LRNAD90

Adventurer
cruiseroutfit said:
While you wouldn't necessarily gain any across the board ground clearance, as you noted your lowest point will still be the bottom suspension connection at the spindle. However it does offer the opportunity to gain addition clearance in the middle of the vehicle, all while retaining a lower CV angle.
We are kind of going off topic a bit, but I’m still not sure it would be a worthwhile project. I mean yes, you could theoretically increase the central ground clearance by tucking the center driveline components up higher, but how practical is that? I mean if you were the manufacturer doing the whole thing as an integrated design (like AM General) sure, but from the standpoint of fitting an aftermarket portal box? And if you tuck the center driveline gear higher, you are negating the advantage of the lower CV angle.

cruiseroutfit said:
With this lower CV angle comes the opportunity for increased suspension travel.
Again, I see the theory, but without considerable changes to the mounting point for the lower and upper suspension arms (allowing lengthening of them), or wide fiberglass fenders to clear lengthened arms, I think there is a very real limitation to the stock design that would make additional gains from the alleviated CV angles minimal next to what is achievable without the ‘portal boxes’?
 

cruiseroutfit

Supporting Sponsor: Cruiser Outfitters
Best4x4xfar said:
We are kind of going off topic a bit, but I’m still not sure it would be a worthwhile project...
Agreed, thats why I said the market doesn't call for it. ;)

On that note one could be designed to use OE suspension mount locations at the frame, and simultaneously provide more clearance at the spindle by designing the lower control arm to intercept the spindle/upright at a mid-point rather than the bottom such as is currently designed. The added moment would require some extra consideration when designing the control arms, but its nothing that couldn't be done. The end product would be extremely vehicle specific thus further limiting the market for said product... in a market that already doesn't exist :D
 

Martinjmpr

Wiffleball Batter
Best4x4xfar said:
Both the Pinzgauer and the Hummer (H1/ Military) use gear reduction hubs, and have the drive axle coming into the drive wheel above the centerline. Just because they do not use solid axles, does not mean they cannot use the geared hub design, which affords both additional gear reduction at the wheel, as well as improved ground clearance from the elevated (relative to the wheel centerline) position of the drive axle. Now in the case of an Independent suspension design, it doesn't necessarily gain you ground clearance (Hummer H1 & HMMWV), but it can, as in the Pinzgauer's case. I'll see if I can round up a couple of photos if you are still in doubt..
Ah, I stand corrected then. :eek:

As for why this isn't more common, my guess would be cost/complexity.

Sure, you're gaining ground clearance and/or lessening drive angles, but it seems to me you're also introducing a bunch of moving parts where before you just had a relatively simple hub and U-joint. More parts = more weight, more cost and more chances of something going wrong.

For a very few people, the cost might be worth it but for most consumers the marginal advantages wouldn't justify the significant costs.
 

Ron B

Explorer
cruiseroutfit said:
your lowest point will still be the bottom suspension connection at the spindle. However it does offer the opportunity to gain addition clearance in the middle of the vehicle.
I was curious so I just measured my hummer and from the lowest point on the a-arm to the ground, 9.5' to 10' at stock height on 37's. My friend's truck was 10.5' on 38'5 pro comps. It's about 17' to the crossmember, 15.5' to the ucp (you can see it hanging down an inch or so under the winch plate).

rb
 

rickc

Adventurer
Hi all:

I just read this thread. I think there is only one mention of the gear reduction advantage of portal hubs. In the Hummer (real one) it's 1.92:1 so there is a power/torque multiplier through the portal hub to each wheel. For those of you with IFS, you know that one wheel is often off the ground on gnarly trails. Without lockers, H1 owners (pre '99), learn to use brake throttle modulation to prevent the free wheel from spinning and transmit all the torque to the wheel that is gripping. A better description here:http://www.off-road.com/trucks4x4/article/articleDetail.jsp?id=263805

Of course a lot of serious offroad H1 owners instal lockers anyhow but this does not detract from the gear reduction and extra power at the wheels. It does make H1's slower on the highway!
 

michaelgroves

Explorer
rickc said:
I think there is only one mention of the gear reduction advantage of portal hubs. In the Hummer (real one) it's 1.92:1 so there is a power/torque multiplier through the portal hub to each wheel.
Well, of course the only inherent advantage of the hub reduction gearing is that it takes place further "downstream" than if you set up the same overall ratios in the gearbox, transfer box or differentials. And even then, it's a slightly mixed blessing: on the plus side, there is less torque being put through the diffs and halfshafts, but on the minus side, they all turn that much faster.

That was an interesting article on the Hummer - but they weren't explicit about what kind of LSD (limited slip diff) there is in the "BTM" version. If I recall, the Hummer uses some version of a Torsen diff, which allows "x" times as much torque on one shaft as there is on the other. I vaguely remember that in the Hummer, "x"=6, but I might be wrong.

A normal open differential always maintains the same torque on each side ("x"=1), so if one wheel reaches a patch of ice and only supports (say) 1000N.m of torque, then the other wheel will also only be able to apply 1000N.m of torque, which might not be enough. With "x"=6, the Torsen allows the other wheel to apply 6000N.m of torque, which probably will be enough.

But if you lift a wheel, then the torque at that wheel is zero, and so the torque at the other wheel is still zero (6x0). That's where the Brake/Throttle Modulation comes in: when you apply the brake, the wheel in the air comes under significant torque. Even though that torque is useless on its own, the opposite wheel now gets six times that braking torque. The only penalty (traction-wise) is that all the wheels on firm ground also get braked, which offsets some of the benefit.

On thinking about it, I would have thought that such a torque-sensing LSD system would be an ideal complement for the TorqTrac system, because any computerised braking on the spinning wheel would add six times that torque to the opposite wheel, without any penalty. Still not as effective as a full locker, but it seems to me it would be much more effective than a standard electronic traction control system working through open diffs.
 

Ron B

Explorer
the stock torsen diffs in the hummer were about a 4.5:1 ratio until '99, when they had to go to a 2:1 bias ratio to allow for abs. And I think because of the 2:1 ratio in the geared/portal hubs everything (driveshafts, halfshafts, t-case, diffs) is actually turning slower, not faster?

btm works extremely well, but I went ahead and changed them out for lockers (auburn elec up front, detroit in the rear) to ease some strain on the drivetrain with the crazy stuff. The '99 and later tt4 system is not very popular with most hummer owners who wheel, it's a re-active system instead of being pro-active like btm.

http://www.flashoffroad.com/features/Torsen/torsen_differential.htm

rb
 
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michaelgroves

Explorer
Ron B said:
And I think because of the 2:1 ratio in the geared/portal hubs everything (driveshafts, halfshafts, t-case, diffs) is actually turning slower, not faster?
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.


Ron B said:
the stock torsen diffs in the hummer were about a 4.5:1 ratio until '99, when they had to go to a 2:1 bias ratio to allow for abs.
Ah, ok, I've read up on this a bit now, and apparently a high bias ratio would interefere with the ABS calculations. So that seems to rule out my thought that it would be ideal to use high bias Torsen diffs in conjunction with electronic traction control!

(Also, just to clarify in case anyone misunderstands, the diff ratio itself remains unchanged (it's 2.53:1), it's the bias ratio that they changed from 4.5:1 down to less than 2:1.)

Ron B said:
The '99 and later tt4 system is not very popular with most hummer owners who wheel, it's a re-active system instead of being pro-active like btm.
I can understand that now, because they reduced the bias ratio. If they'd been able to keep the original 4.5:1 bias ratio, then the addition of traction control would have introduced no disadvantages, since BTM would work just as before, when needed.


Your vehicle must be impressive with the lockers fitted!
 
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