Portal vs Straight Axles

[stigno]

I used to run vehicles with ordinary axles (mostly Axial SCX 10 II), but have moved to portal vehicles (TRX-4 and Vanquish Ultra).
I love portals for their excellence in the rough terrain and would never go back.
Just lover the centre of gravity a bit, and enjoy

 

[MOguy]

the top picture is a Brazin with a TGH2low trans
the second is a stock TRX4 chassis WITH the ESC on top of the transmission.

The TRX DOES NOT have a high center of gravity.

https://i.ibb.co/1shgPRc/2lo.jpg

https://i.ibb.co/xH2jFVK/trx4.jpg

 

[Phildirt]

It’s the design of the axle, not the height of the vehicle, the skid, or how flat the links are. CG and ride/skid height are not necessarily synonymous, at least not as it pertains to this thread. With a portal axle the diff and axle tubes are higher than a straight axle where the tube is in line with the center of the wheel. That is what is meant by ‘higher center of gravity”, there is more weight above that imaginary line.

It’s probably not enough to amount to a hill of beans on these trucks because they are already so light. But if you had a 1:1 application it would probably be very noticeable.

Yes there are other ways to move the center of gravity upwards (accessories, longer shocks, lower shock mounts etc).

You can make any rig sit low, but no matter what the axles and diffs are higher on a portal rig as they relate to the wheel hub.


Sent from my iPad using Tapatalk

 

[MOguy]

It’s the design of the axle, not the height of the vehicle, the skid, or how flat the links are. CG and ride/skid height are not necessarily synonymous, at least not as it pertains to this thread. With a portal axle the diff and axle tubes are higher than a straight axle where the tube is in line with the center of the wheel. That is what is meant by ‘higher center of gravity”, there is more weight above that imaginary line.

It’s probably not enough to amount to a hill of beans on these trucks because they are already so light. But if you had a 1:1 application it would probably be very noticeable.

Yes there are other ways to move the center of gravity upwards (accessories, longer shocks, lower shock mounts etc).

You can make any rig sit low, but no matter what the axles and diffs are higher on a portal rig as they relate to the wheel hub.


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If you took everything the same but the axles (portals up a fraction of an inch) and the got smaller tires on the portals (fraction of an inch) you clearance would be the same but you could lower the rest of the vehicles because you are running smaller tires. That could change how gravity affects you rig.


But Portals may not turn as well

But portals have less torque twist

But portals aren't scale.

But But But.

What may be advantageous over one obstacle may do you in on the next.

Best thing to do is to learn the strengths and limitations of what you are running and try to pick a line where you strengths will shine and you limitations won't screw you over.

 

[WHITE-TRASH]

An issue that isn't mentioned much if at all is the knuckles getting caught on things with portals, namely trx4 being the worst offender. The distance from the inside of the tire to the knuckle or portal box can be a big issue.

 

[Phildirt]

If you took everything the same but the axles

Kind of proving my point I think. If everything was identical on 2 rigs, except the axles, the one with the higher axle tube/differential would technically have a higher center of gravity. It's unsprung weight is higher than on the straight axle rig. Yes it is only a tiny bit, but that is a "scale" tiny bit.



As mentioned though in a rig where everything is measured in oz instead of lb I don't think it's going to be a dramatic enough difference to manifest itself physically. It just happens to be compounded on some of the portal rigs because they lend themselves to accessories or have big bodies (Defender being the usual suspect).

I don't think anyone is saying portals are at a disadvantage here, or will make a rig more likely to tip (opinion/drama) but a portal axle does have a higher center of gravity just by design/physics (fact). And for the record I do agree everything has a drawback. Usually that is driver skill, not weight distribution. My daughter can flip a rig on a flat surface lol.

 

[ferp420]

on alot of runs ill.take a rig with 10.2 axles and 1.9 tires and a 2.2 on portals the 10.2 will go everywere my other rig with portals on 2.2s will go
i dont think it makes enuff of a diffence from a drivers perspective to worry about
run them and have fun

 

[MOguy]

An issue that isn't mentioned much if at all is the knuckles getting caught on things with portals, namely trx4 being the worst offender. The distance from the inside of the tire to the knuckle or portal box can be a big issue.

This definitely could be an issue with smaller tires.

 

[MOguy]

Kind of proving my point I think. If everything was identical on 2 rigs, except the axles, the one with the higher axle tube/differential would technically have a higher center of gravity. It's unsprung weight is higher than on the straight axle rig. Yes it is only a tiny bit, but that is a "scale" tiny bit.



As mentioned though in a rig where everything is measured in oz instead of lb I don't think it's going to be a dramatic enough difference to manifest itself physically. It just happens to be compounded on some of the portal rigs because they lend themselves to accessories or have big bodies (Defender being the usual suspect).

I don't think anyone is saying portals are at a disadvantage here, or will make a rig more likely to tip (opinion/drama) but a portal axle does have a higher center of gravity just by design/physics (fact). And for the record I do agree everything has a drawback. Usually that is driver skill, not weight distribution. My daughter can flip a rig on a flat surface lol.

yep, if you take advantage of the higher diffs and run smaller tires MAYBE by lowering everything else you come ahead????

I think the trx is good for side hill because of how the engine and trans sit low BUT then you have the higher diffs to probably negate that.

On a slanted board my TRX will take more slant than any of my other RTRs maybe by a degree or two but that is a static board. Even that little bit of higher diff could though it off it the weight shifts on a real course or trail.

I have my trx setup so I can open and close the diffs independently. Unlocking the front diff helps with side hill. The top front tire stays light and the power goes to it helping to pull it up as opposed to a locked rig (esp with overdrive) having the front end pull you down.

 

[furadi]

An issue that isn't mentioned much if at all is the knuckles getting caught on things with portals, namely trx4 being the worst offender. The distance from the inside of the tire to the knuckle or portal box can be a big issue.

In 2 years of crawling that has never once happened to me. The pumpkin on my Enduro gets hung up way more than anything on my TRX4.

 

[furadi]

So since I first posted in this thread I've done a lot more tuning indoors due to the snowpocalypse.

I've since added SSD brass all around on the Enduro, went to softer springs and thicker shock oil. Both trucks are in the 5lb range. With the addition of Brass the enduro is much more planted but it still is higher CG than my TRX4 in real world use. These trucks have all the same mods for the most part and the same wheels. I also have some brass +3 wheel hexes and shock keys coming for the Enduro which should put it on level ground with the TRX4.

So they'll have equal climbing / sidehill ability but the TRX4 will just have more ground clearance.

The idea that having portals in itself = high CG is just incorrect. At least in the case of the TRX4 because the entire chassis is designed around the portal axles.

 

[furadi]

Visually the biggest difference between the Enduro and the TRX4 that would effect CG is the transmission. On the Enduro it's above the frame rails. On the TRX4 it's right smack in the middle of the frame rails. I think if the Enduro had a flat transmission
like the TRX4 it might not even need brass.

 

[MOguy]

The center of gravity is higher then the diffs so in theory portals vs non portals will not affect the COG but any weight that is higher could through the balance of when moving over an obstacle.

The problem with the COG and the Enduro is the shocks sit it too high, the trans is also taller and does sit higher than the TRX.

I run TRX shocks on my element and it is able to sit lower and does much better. The axles on the Enduro are also less than wonderful. (but that wont affect the COG). By changing the axle ( I have axial AR44s) and socks on the Enduro it rocks and can compete with other RTRs.

 

[durok]

Another thing that helps in the Traxxas TRX-4 is the added weight inside the portal boxes at the end of each axle - this is weight at the best place possible:

 

[furadi]

The center of gravity is higher then the diffs so in theory portals vs non portals will not affect the COG but any weight that is higher could through the balance of when moving over an obstacle.

The problem with the COG and the Enduro is the shocks sit it too high, the trans is also taller and does sit higher than the TRX.

I run TRX shocks on my element and it is able to sit lower and does much better. The axles on the Enduro are also less than wonderful. (but that wont affect the COG). By changing the axle ( I have axial AR44s) and socks on the Enduro it rocks and can compete with other RTRs.

Oh that's why I got the softer springs for the enduro to allow it to droop. Once I get the shock keys it'll be as low as it can be.

 

[Phildirt]

Oh that's why I got the softer springs for the enduro to allow it to droop. Once I get the shock keys it'll be as low as it can be.

I took a different approach, I guess just based on my driving style. I found that firmer springs with lighter shock oil worked better for me than softer springs, not enough rebound after they were compressed. With the firmer spring the rig feels more stable/sold/planted as the axles 'fall' into low spots. It felt mushy before I did that. Don't forget the lower you go the more contact you are going to have with your skid/arms/pumpkins. Kind of a point of diminishing return there.



I think the best thing you can do for an Enduro just based on my limited experience is add weight down low, I have heavy knuckles/brass c-hubs/metal bead locks/metal axle tubes and lockouts, metal diff covers and it has no problems side hilling. The biggest improvement with that setup that I noticed is the front end stays planted going uphill, it used to want to sit on it's ass a lot.

 

[furadi]

I took a different approach, I guess just based on my driving style. I found that firmer springs with lighter shock oil worked better for me than softer springs, not enough rebound after they were compressed. With the firmer spring the rig feels more stable/sold/planted as the axles 'fall' into low spots. It felt mushy before I did that. Don't forget the lower you go the more contact you are going to have with your skid/arms/pumpkins. Kind of a point of diminishing return there.



I think the best thing you can do for an Enduro just based on my limited experience is add weight down low, I have heavy knuckles/brass c-hubs/metal bead locks/metal axle tubes and lockouts, metal diff covers and it has no problems side hilling. The biggest improvement with that setup that I noticed is the front end stays planted going uphill, it used to want to sit on it's ass a lot.

I mainly went to the thicker shock oil to counter the torque twist which seems to be working out ok.

I also find that the lower the ride the better the climbing ability. Currently my Enduro can climb a 58 degree traction board. That's with the soft springs and using rubber bands to pull the axles up.

 

[Phildirt]

I mainly went to the thicker shock oil to counter the torque twist which seems to be working out ok.

I also find that the lower the ride the better the climbing ability. Currently my Enduro can climb a 58 degree traction board. That's with the soft springs and using rubber bands to pull the axles up.

Never heard of using rubber bands. Interesting. Seems like they would get snagged on something and shoot you in the eye lol.


That's a pretty controlled environment, I have not had an opportunity to do something like that, most of my observations are made in the woods. Might need to build a test ramp haha

 

[furadi]

Never heard of using rubber bands. Interesting. Seems like they would get snagged on something and shoot you in the eye lol.


That's a pretty controlled environment, I have not had an opportunity to do something like that, most of my observations are made in the woods. Might need to build a test ramp haha

Yep yep it is controlled which is a great way to test and tune any changes. As an example I can move my rear shocks one hole and fail @ 60 degrees on the traction board when I just made it 10x in a row. It's a must for tuning IMO.

As an aside without the rubber bands I would have to lower the board to like 50 degrees.

 

[WHITE-TRASH]

In 2 years of crawling that has never once happened to me. The pumpkin on my Enduro gets hung up way more than anything on my TRX4.

The c hubs on my trx4 axles rigs are beat up from rocks bashing them constantly. Those rigs lives on 2.2s with narrower (.350) hubs as well so they aren't hanging out there in the breeze but tucked in reasonably.

I probably have a much different approach as I tend to use my inner sidewall to pull up on obstacles since I'm more of a comp driver than scaler. Capra axles are built with clearance in mind so they don't get hung up nearly as bad.