Portal vs Straight Axles

[jdss13]

I've been wondering about the pros and cons of portals vs straight axles. Portals give more ground clearance but they also increase the CG of the whole vehicle, add more complexity and a bit of weight plus the possibility for broken gears on the portals and they add more gears/friction between the motor and the wheels. What is your personal experience, are portals always better?

[Phildirt]

I think you answered your own question as far as pro/con.

I don't have a portal rig, but from what I have read in this forum there is a place for both depending on terrain and driving style. Portals would shine over obstacles but not do as well in off camber/side hill situations, whereas a straight axle would do better in those situations but get hung up more often but that depends on skill too, a good driver has a feel for where the diff is as a line is tackled.

I think it's really subjective and depends on the build, you can throw out a lot of assumptions when comparing 2 rigs side by side (what size tires? Any accessories up top? Hard bod or lexan? Buggy or truck? Crawling, trailing, or bashing?) - there are pretty much exponential combos of how you can approach a build or a line.

[furadi]

I really haven't noticed any cons to having portals. People have always claimed a portal truck would be worse at side hilling but that hasn't been my experience. In my experience side hill ability usually comes to CG and what type of foams someone is using. Even the lightest SCX10's struggle to follow my side hill lines if they don't have good dual stage foams.

You also mentioned weight which can only be viewed as a pro in this case because it gives us an easy option to add brass down low.

I actually ran up against an SCX10 on Sunday and while he did very well you'll notice that my TRX4 just kind of walks over the obstacles that he struggle with.

https://youtu.be/wMtHk4DL-KM

[furadi]

Originally Posted by Phildirt

I think you answered your own question as far as pro/con.

I don't have a portal rig, but from what I have read in this forum there is a place for both depending on terrain and driving style. Portals would shine over obstacles but not do as well in off camber/side hill situations, whereas a straight axle would do better in those situations but get hung up more often but that depends on skill too, a good driver has a feel for where the diff is as a line is tackled.

I think it's really subjective and depends on the build, you can throw out a lot of assumptions when comparing 2 rigs side by side (what size tires? Any accessories up top? Hard bod or lexan? Buggy or truck? Crawling, trailing, or bashing?) - there are pretty much exponential combos of how you can approach a build or a line.

It's not just axle clearance. You have to worry about skid clearance too.

[jdss13]

Originally Posted by Phildirt

I think you answered your own question as far as pro/con.

I don't have a portal rig, but from what I have read in this forum there is a place for both depending on terrain and driving style. Portals would shine over obstacles but not do as well in off camber/side hill situations, whereas a straight axle would do better in those situations but get hung up more often but that depends on skill too, a good driver has a feel for where the diff is as a line is tackled.

I think it's really subjective and depends on the build, you can throw out a lot of assumptions when comparing 2 rigs side by side (what size tires? Any accessories up top? Hard bod or lexan? Buggy or truck? Crawling, trailing, or bashing?) - there are pretty much exponential combos of how you can approach a build or a line.

Yeah you're right there are a lot of variables at stake here, it's not a question of one is always better than the other, I think both have their places, depending on the rig and driving style.

Originally Posted by furadi

I really haven't noticed any cons to having portals. People have always claimed a portal truck would be worse at side hilling but that hasn't been my experience. In my experience side hill ability usually comes to CG and what type of foams someone is using. Even the lightest SCX10's struggle to follow my side hill lines if they don't have good dual stage foams.

You also mentioned weight which can only be viewed as a pro in this case because it gives us an easy option to add brass down low.

I actually ran up against an SCX10 on Sunday and while he did very well you'll notice that my TRX4 just kind of walks over the obstacles that he struggle with.

https://youtu.be/wMtHk4DL-KM

That's some good driving yeah from those runs the portals just seem to have helped but some SCX10 approaches were a bit weird plus it also depends on a whole lot more that just the axles obviously nonetheless thanks for sharing the vid!

[Stormin2u]

I'm freshening up my 1.9 scale truck and one of the things I've noticed is builders using a portal axle in the rear for extra break over..

I have a Brazin Scale ATL chassis with TRX4 axles and its my first choice for an afternoon on the rocks, its a beast.

[WHITE-TRASH]

I have 4 portal axles rigs right now, 2 have trx4 and 2 have capra axles. My sportsman and pro rigs are both straight axles. For me the portal rigs are on 1.9s and the straight axle rigs are on 2.2s. 2.2s on a portal rig raise everything way up and stability becomes an issue. Anyone that knows me knows that's a big statement because I hate small tires but the narrower, taller axles need smaller tires to keep things in check. With the portals small tires have about the same clearance as 2.2s and straight axles.

[durok]

While I like both - and am not a fan of adding lots of weight to try to overcome handling issues - it's relatively simple to add brass portal covers and they add weight by default of their location to just about the best possible place - the very end of the axles, and mostly below the axle centerline, yet it's non-rotating weight.

Also, because you're driving slowly, a little added drivetrain friction is no big deal - there are still people that run worm-gear crawlers...

IMHO, have one of each and take 'em both to your favorite spot and have fun!

[Disco Stu III]

A con of portals that I am currently dealing with, is the 2.3:1 reduction in gearing. This is on a rig that didnt have portals to start with. To get a similar wheel speed (A touch faster than walking pace at full tilt) I tossed the 35 turn brushed motor and installed a 20 turn. The driveshafts now spin alot faster than they were meant to. They fly apart pretty quickly now. Not game to throw the 11 tooth pinion gear in there now (to replace the 13). Maybe I can use capra shafts?

Sent from my SM-J250G using Tapatalk

[furadi]

Originally Posted by Disco Stu III

A con of portals that I am currently dealing with, is the 2.3:1 reduction in gearing. This is on a rig that didnt have portals to start with. To get a similar wheel speed (A touch faster than walking pace at full tilt) I tossed the 35 turn brushed motor and installed a 20 turn. The driveshafts now spin alot faster than they were meant to. They fly apart pretty quickly now. Not game to throw the 11 tooth pinion gear in there now (to replace the 13). Maybe I can use capra shafts?

Sent from my SM-J250G using Tapatalk

Why would you not replace the pinion and or spur?

[Phildirt]

Stock Capra comes out to about 31:1. So something in this equation would have to change, if you can get there with spur/pinion it's the easiest change:

Axle - 30:8
Portal - 23:12
Trans - 30:54
Spur - 34t
Pinion - 14t

[Greatscott]

One GIANT pro for portals is the gear reduction at the hubs. This reduces the amount of torque through the drive shafts, which greatly reduces torque twist.

[furadi]

So this is interesting. I just got an Element Enduro kit to have as a 2nd rig for my kids. With both trucks running full droop the TRX4 actually has much lower CG. The skid is lower and the trans is flat compared to the Elements taller stacked trans.



Also the torque twist of the Element is unreal.

So really is there any downside to portals in this case?

[Phildirt]

$400+ rig versus $250 rig would be the only downside I can see. The Enduro is a very basic truck compared to the TRX4 so not really apples to apples. I like my Enduro but bought it as a 'hold me over until I figure out what I really want to buy next' option. You could throw some high clearance links on the Enduro for a better profile.

What is the difference in height from the skid to the floor on them?

[furadi]

Originally Posted by Phildirt

$400+ rig versus $250 rig would be the only downside I can see. The Enduro is a very basic truck compared to the TRX4 so not really apples to apples. I like my Enduro but bought it as a 'hold me over until I figure out what I really want to buy next' option. You could throw some high clearance links on the Enduro for a better profile.

What is the difference in height from the skid to the floor on them?

The Enduro is a kit so they actually already have about the same amount invested. (high clearance link kit is on the way)

I thought about measuring the skids but I'm trying to think of a way to do it accurately.

[Phildirt]

Originally Posted by furadi

The Enduro is a kit so they actually already have about the same amount invested. (high clearance link kit is on the way)

I thought about measuring the skids but I'm trying to think of a way to do it accurately.

If you are just wanting to measure at static height, all things being equal, just cut a strip of paper until it snugly fits between the 2 points and then measure it (if the concern is not being able to get a ruler/tape measure/calipers under it.



Remember there are other variables on the 'droop' as well such as unsprung weight, I doubt the transmissions weigh the same but may be close, and the TRX4 has an extra servo/etc. Minute differences that all add up.

[furadi]

Originally Posted by Phildirt

If you are just wanting to measure at static height, all things being equal, just cut a strip of paper until it snugly fits between the 2 points and then measure it (if the concern is not being able to get a ruler/tape measure/calipers under it.



Remember there are other variables on the 'droop' as well such as unsprung weight, I doubt the transmissions weigh the same but may be close, and the TRX4 has an extra servo/etc. Minute differences that all add up.

Oh mine is a sport so no extra servos.

[Phildirt]

I think a neat comparison that would be more 'clinical' would be a portaled SCX10iii versus one with the new straight axle AR45. Then you have the same rig with the only variable being the axle design. Run them side by side and see if any of the assumptions are correct on a consistent basis.

[TRX4ME]

Before comparing, use the same wheel/tire combo on both vehicles.

[furadi]

Originally Posted by TRX4ME

Before comparing, use the same wheel/tire combo on both vehicles.

That would only exaggerate the difference as the enduro has smaller tires currently.