AHC + Suspension Enhancement System

[PK470]

Guys,
I recently acquired a 24’ Light Weight (Lite) Travel Trailer. Dry weight is 4,600lbs. With all the camping gear and extra stuff, I am looking at approximately 5,000lbs.

I have towed this Trailer on several occasions. Even long distance driving (over 500 miles). I have the Equalizer Weight Distribution Hitch. Trucks tows flawlessly good. ZERO sway. Level ground towing experience is a joy. However, a real pig on long high mountainous passes. Most of the time I simply find myself throwing in the flashers and getting behind the other 18-wheelers.

Anyway, other than towing I am experiencing a minor setback that I am hoping I could get your help with. With the trailer hooked up to the tongue, my trucks completely bottoms out. The AHC is forced to remain on ‘L’ no matter what.

I am looking into a permanent/ long term solution to this and it appears that I would be better off if I incorporate some sort of Suspension Air Helper Springs (Airbags).

I have searched on here but there is a lot of scattered info all over the place. Plus it appears that the OP never really provides the ultimate update and/or feedback regarding the final set up process.
That said, I have a few questions;

1) Is there a detrimental effect/ conflict that arises with AHC when airbags are in place? I mean, how does AHC really respond in relation to the spring assembly when hauling heavy loads?

2) During the installation process, I understand that I have to jack up the truck and have the axle freely suspended. What about the AHC leveling position prior to jacking up the truck? Should I have it on ‘L, N or H’ before turning off the truck and getting it up on the air?

3) Last but not least, it appears that I have two options to accomplish the task;
a. Airbags that actually fit inside the existing coil springs. This approach has an associated adjustable air pressure system. Also comes with air line and separate valves for manual inflation. http://www.etrailer.com/Vehicle-Suspension/Lexus/LX+470/2006/F4124.html?vehicleid=20061013631
b. Hollow rubber springs that sit directly on the axle. This approach doesn’t involve dismounting the existing coil springs, rather just an additional rubber cushion to help reduce the sag when carrying heavy loads. Also, this approach wouldn’t require adjusting air pressure at all. http://www.etrailer.com/Vehicle-Suspension/Lexus/LX+470/2006/TTORSEQ.html?vehicleid=20061013633

The hollow rubbers springs set up is almost twice as much as the airbags set up. However, the Hollow rubber springs seems to be ideal on a non-invasive installation and maintenance perspective.

Between the two options, which one would you recommend? Which option would be ideal for the LX set up?
I intend to provide a complete write up with installation pictures once I determine which route to go with.

In all reality, I am hoping that this thread would help any AHC Suspension Enhancement seeker find all the answers to his/ her questions.

Thanks in advance.

 

[Wilsil]

Between the two options, which one would you recommend? Which option would be ideal for the LX set up?
I intend to provide a complete write up with installation pictures once I determine which route to go with.

The best option is the one you didn't mention.
c. Swag the AHC for conventional suspension system.

 

[sonk76]

The best option is the one you didn't mention.
c. Swag the AHC for conventional suspension system.

While this seems to be the prevailing wisdom in these parts, I'm one of the few who seems to discent. I think if you can afford to maintain the AHC setup it is an excellent solution. Particularly for towing and hauling heavy loads as it allows for auto leveling of the truck--provided that it is operating within its specs.

I found that by swapping to 80 series rear coils and non-AHC torsion bars up front the system weight carrying capacity increased considerably. I'm also running the SES rubber springs in the rear. They serve as flexible bump stops rather than as constant load carrying setup (in my case)

 

[Actualeyes]

While this seems to be the prevailing wisdom in these parts, I'm one of the few who seems to discent. I think if you can afford to maintain the AHC setup it is an excellent solution. Particularly for towing and hauling heavy loads as it allows for auto leveling of the truck--provided that it is operating within its specs.

I found that by swapping to 80 series rear coils and non-AHC torsion bars up front the system weight carrying capacity increased considerably. I'm also running the SES rubber springs in the rear. They serve as flexible bump stops rather than as constant load carrying setup (in my case)

I'm also a dissenter

Do you know what the rear pressures were (in techstream) prior to changing to the 80 series coils?

Are you running standard AHC height or have you adjusted the height sensors?

I ask because I intending to try putting in stock nonAHC coils - currently running at 9.4 mPa in the rear with full LPG tank, full fuel tank and dual rear wheel carrier.

Cheers,
Andrew.

 

[tarpaigh]

I also see many disadvantages to switching to a conventional suspension. I have put Firestone airbags into my lx to assist with towing. It works well for me. I have wondered about switching coils to an air spring suspension to assist the ahc, as a mud member from Australia previously had done (?Dinibili). I was just not sure of the reliability.

 

[Actualeyes]

I did it... See post in this thread:

https://forum.ih8mud.com/100-series-cruisers/746740-ahc-lc-springs-bars.html

Can recommend it for overladen AHC vehicles...

 

[Brian Waag]

PK470 - similar to you, I pull a trailer with my 2006 LC. I have an Aliner pop up trailer with a custom Deaver suspension so I can take it offroad and keep Momma happy. With gear I'm guessing it weighs about 2000 - 2200 lbs. plus extra weight in the back of he Cruiser. It's totally stock except for the 33 inch Nittos I just put on it. I have already purchased an ARB bullbar w/winch mount and will buy a winch shortly. I am interested in putting either a Slee rear swing away or ARB swing away rear bumper on the back which combined will add quite a bit of additional weight. I tried to engage the AHC on my recent trip up in the Sierra Nevada mountains and it started to lift and then dropped down to low, bypassing the neutral position. I've been leaning towards ripping out the AHC and replacing with an OME suspension, but am now back on the fence after reading the responses to your inquiry. Anyone else out there that can weigh in on adding airbags or other equipment verses removing AHC for an OME or similar??

 

[PK470]

The best option is the one you didn't mention.
c. Swag the AHC for conventional suspension system.

Easier said than done. Anyhow, my LX currently has only 41k Miles. 100% stock other than BF Goodrich AT tires. The AHC functions perfectly well. Maybe its just me but it simply doesn't make sense to get rid of a fully non-problematic and functional AHC system (which has its advantages) for a 100 series conventional one. I would possibly venture this route if my AHC had taken a sh!t already. But not just yet.

While this seems to be the prevailing wisdom in these parts, I'm one of the few who seems to discent. I think if you can afford to maintain the AHC setup it is an excellent solution. Particularly for towing and hauling heavy loads as it allows for auto leveling of the truck--provided that it is operating within its specs.

I found that by swapping to 80 series rear coils and non-AHC torsion bars up front the system weight carrying capacity increased considerably. I'm also running the SES rubber springs in the rear. They serve as flexible bump stops rather than as constant load carrying setup (in my case)

Thank you for the eye opener post. Yes! I still believe there is a non-invasive way I could offer support to the AHC and still help in maintaining its normal operation. I understand that hauling/ towing heavy loads constantly will evidently reduce AHC's lifespan but that's why there are stuff like airbags/ rubber springs to help alleviate AHC's load.

I did it... See post in this thread:

https://forum.ih8mud.com/100-series-cruisers/746740-ahc-lc-springs-bars.html

Can recommend it for overladen AHC vehicles...

Thank you, I just read through the entire thread. Glad that the 100 series coils helped out on your case. Are you towing anything? Please provide feedback as to how this set up handles the increased weight.

PK470 - similar to you, I pull a trailer with my 2006 LC. I have an Aliner pop up trailer with a custom Deaver suspension so I can take it offroad and keep Momma happy. With gear I'm guessing it weighs about 2000 - 2200 lbs. plus extra weight in the back of he Cruiser. It's totally stock except for the 33 inch Nittos I just put on it. I have already purchased an ARB bullbar w/winch mount and will buy a winch shortly. I am interested in putting either a Slee rear swing away or ARB swing away rear bumper on the back which combined will add quite a bit of additional weight. I tried to engage the AHC on my recent trip up in the Sierra Nevada mountains and it started to lift and then dropped down to low, bypassing the neutral position. I've been leaning towards ripping out the AHC and replacing with an OME suspension, but am now back on the fence after reading the responses to your inquiry. Anyone else out there that can weigh in on adding airbags or other equipment verses removing AHC for an OME or similar??

We are on the same page. Not sure how many miles your '06 LC has. How is your AHC holding up?

 

[PK470]

Here is my progress:

I contacted Carl the other day (one of the vendors on here- justdifferentials.com). He proposed the following options"
1) Remove AHC and install aftermarket or stock LC type suspension (stock or lifted height) (starts at about $600 on up)
2) Leave AHC and Install airbags to coils ($120ish)
3) Leave AHC and Install LC type rear springs which are a bit firmer in conjunction with the timbren rubber bumpstop springs. The Timbrens could be spaced down closer to axle if necessary to limit amount of droop. $215 pair for timbren, $120 pair of stock LC type coils.

After our conversation back and forth, I made my mind to lean towards option number 3. However, I decided to opt out of the new coils for now. Will see how the ride in conjunction with Timbrens bumper stopper makes a difference then proceed from there.

If the Timbren Rubber bumpstops take a beating, I will go ahead and replace my LX rear coil springs with beefier and stronger 100's or 80's. Can anyone tell me the difference between 100's and 80's coil springs?

Also, it appears that the rubber bumpstop springs offered by justdifferential.com are made of a special soft compound. They are smaller in size and less stiffer than the original timbren rubber stopper sold elsewhere. I would like a weighed opinion from members who have ordered this.

Again, my objective is simply to find a solution for towing my Travel Trailer on normal trucks height plus without the AHC reading being on 'L'.

I will provide update as it unfolds.

Thanks.

 

[Actualeyes]

There is little published data about the LX coil springs, but here's what we know and some reading between the lines:

Stock LX470: unladen mass 2530kg GVM 3260kg
Stock TBs + FR AHC pressure 6.9mPa +/- 0.5
Stock coils: 11mm dia, 5.6 turns so I guess 15 N/mm spring rate + RR AHC pressure 5.9 +/- 0.5
(Note pressure measured with full tanks so unladen + 122kg = 2652kg)
Will carry 608kg incl ball weight of any trailer without AHC over-pressure condition

It is worth noting by comparison that:
Stock nonAHC Hundy: unladen mass as low as 2230kg (depends on model) GVM 3300kg
It has higher spring rate stock TBs
Stock coils: 14.5mm(?), ~7 turns, ~30 N/mm spring rate - similar spring height

Now OME use a 18mm, 7 turn, 43 N/mm spring rate coil to support extra 200kg or .065 N/mm per extra kg (as one point of reference)
And as if to confirm that, they also have a 56 N/mm spring rate coil to support 400kg (over stock).

So by changing the spring from stock LX to stock nonAHC 100 series I have about 15 N/mm or support for extra 231kg.

Now I have maybe extra 450kg but some of that is carried by the wound up torsion bars.

With the extra support of:
The nonAHC 100 series coils, AND
Winding up the stock Torsion bars quite a bit - maybe ten turns but I gave up counting...

My AHC pressures are now close to factory spec. Therefor it (the AHC) should support that additional 608kg easily including tow ball weight. Mind you 5 passengers x 80kg ea, a loaded fridge, recovery gear and trailer ball weight could easily blow that!

Technically then the car would be over the GVM, but I have driven 100 and 105 series trucks over GVM for 100's of 1000's of km - they did have heavier coils and shock absorbers and other beefed up suspension components but the same or similar chassis/dynamics.

Reading between the lines that 231kg was being supported by the 3.4mPa over spec on RR AHC pressure (the difference in AHC pressure between running stock LX and stock nonAHC coils).

So, I hope that removes a bit of the mystery, albeit based on my own theories and empirical evidence.

Someone in the know may know the exact spring rate of the stock LX coils.

Someone with a set of those race car scales might measure corner mass on all four corners to get an idea of how the unladen mass is distributed really (front-rear especially).

Someone might know the engineering details on LX torsion bar behavior/specs.

Someone in the US might like to do the same exercise with Imperial units and US spec'd vehicles

But in general this leads me to suggest an engineering methodology like this for AHC vehicles at risk of over-pressure AHC "limp home in L mode":

Take "unladen vehicle" with full tank - including your bars, tanks, winches etc
Measure AHC pressures
Adjust torsion bars until front pressures in spec - If you can't get the FR AHC pressure in spec replace with nonAHC torsion bars and adjust until in spec
If rear AHC pressure is about 9.4 +/- 0.5 mPa consider using nonAHC stock Hundy coils - that should give you about 608kg carrying capacity
If you need more carrying capacity than that, or have significantly higher pressures than that consider standard height extra load carrying coils like OME+200 or OME+400kg products.

Other thoughts;
* there's a hell of a lot of assumptions here - "your mileage may vary"
* this assumes AHC is in good working order
* there can be other consequences of exceeding advertised GVM including the long arm of the law, insurance caveats etc and safety
* unsprung mass is an issue as is higher COG if you have non standard wheels and tyres
* there are many more considerations if towing is part of your plans - trailer brakes, weight distribution hitches, tow ball height/position/capacity, trailer weight distribution, tow bar/hitch rated capacity, COG, oh, and legality etc
* if you think this is bunkum please say why... It's a theory that has been tested empirically once

And for the OP...

The question for the timbrens would appear to be what load are they carrying at the N height... If nothing they won't affect AHC normal performance... I.e. If the AHC is over pressure at that height it will still be over pressure with timbrens sitting there and all the timbren will do is stop it going as low in L mode, presumably.

Also, if you or JustDifferentials are not using the AHC data from the ECU you are working blind. Get the OBD-II/techstream kit and use it - it's quite straightforward.

And I think when they said removing AHC started at $600, that would be just removing it! Putting in a full set of shockers, TBs and coils is a lot more than that, even just the parts!

 

[LockedNLoaded]

Easier said than done. Anyhow, my LX currently has only 41k Miles. 100% stock other than BF Goodrich AT tires. The AHC functions perfectly well. Maybe its just me but it simply doesn't make sense to get rid of a fully non-problematic and functional AHC system (which has its advantages) for a 100 series conventional one. I would possibly venture this route if my AHC had taken a sh!t already. But not just yet.




Thank you for the eye opener post. Yes! I still believe there is a non-invasive way I could offer support to the AHC and still help in maintaining its normal operation. I understand that hauling/ towing heavy loads constantly will evidently reduce AHC's lifespan but that's why there are stuff like airbags/ rubber springs to help alleviate AHC's load.



Thank you, I just read through the entire thread. Glad that the 100 series coils helped out on your case. Are you towing anything? Please provide feedback as to how this set up handles the increased weight.




We are on the same page. Not sure how many miles your '06 LC has. How is your AHC holding up?

Personally I am a big fan of the AHC system. I currently have 161k on mine with absolutely zero issues to date. I am amazed that my LX still drives like its brand new. I know there are those on here who hate on the AHC so I guess I am in the minority. Very interested to see what you end up doing.

 

[uHu]

This thread is already very good, with in-depth discussions.
Adding one consideration into the equation:
When replacing the rear coils with something that supports more weight, the AHC pressure will go down. If the pressure is too low, the damping will not work sufficiently, like driving without shocks.
If you replace with non-ahc LC-springs, and the truck is empty, the ahc pressure will be zero, which means the shock absorber-function will be zero as well.
(In practical terms, there is a bit of damping, due to the increased pressure when compressing the springs over a bump).
(The damping in an ahc system happens in the actuators which are on the hydraulic line between the gas-sphere and the shock absorbers; and not in the shock absorber itself, which is more like a simple hydraulic ram.)

Based on this, if you don't always have an increased weight, it would work better with helper air-bags.

 

[r3run33]

no one mentioned or maybe I missed it but what about going to the stronger shocks and globes of the AHC that the armored people use when armoring up the LX! I know this has been done alot with the 200 series and maybe not that much for the 100 series. Anyone know what springs or upgrades they have used??

 

[uHu]

no one mentioned or maybe I missed it but what about going to the stronger shocks and globes of the AHC that the armored people use when armoring up the LX! I know this has been done alot with the 200 series and maybe not that much for the 100 series. Anyone know what springs or upgrades they have used??

Stronger globes??
There's no problem using stronger springs on an armored truck - the weight increase is permanent.
I can check with those doing the armoring for the Norwegian Army, but I think they only use stronger springs - or ditch the AHC.

 

[Brian Waag]

PK470, I just rolled past 107k miles and the AHC appears to work fine, when not pulling my trailer. It is pretty slick to have when it's functioning properly. I'm just not sure it would even after trying some of the suggestions in this thread as the trailer tongue weight will be all over the map when I'm doing some serious offroad towing. Then again, I'm no gear head so maybe there is a cheaper solution than upgrading to an OME. I already got a quote of $1100 to rip out the AHC and install the OME. OME kit from Slee is around $1100 so we're talking $2200, ouch.

 

[LCHardriver_02]

PK,

One thing to remember when looking to swap out springs to increase tow loading is that you will not always have the trailer connected and I am unsure how the system would work completely unloaded with stiffer springs. Sonk76 may be able to speak to this. Now, given that I do not have the AHC, so I am less familiar with it than I am with the conventional set up, I do know that my OME 863s are very stiff when I am not connected to a trailer or have at least 300lbs in the back. With that said, they were awesome on the last camping trip, where we loaded down the back of the LC with a whole bunch of weight. 4 large coolers filled, plus two plastic tubs full, plus sleeping bags.

Just wondering but would adjusting your weight distribution hitch a bit to bring the back end of the truck back up to just below non-loaded height make sense? I thought that was how the set up of those things was supposed to work. Of course, I have not set one up, so I am guessing here.

 

[Wasatch Jay]

This thread is already very good, with in-depth discussions.
Adding one consideration into the equation:
When replacing the rear coils with something that supports more weight, the AHC pressure will go down. If the pressure is too low, the damping will not work sufficiently, like driving without shocks.
If you replace with non-ahc LC-springs, and the truck is empty, the ahc pressure will be zero, which means the shock absorber-function will be zero as well.
(In practical terms, there is a bit of damping, due to the increased pressure when compressing the springs over a bump).
(The damping in an ahc system happens in the actuators which are on the hydraulic line between the gas-sphere and the shock absorbers; and not in the shock absorber itself, which is more like a simple hydraulic ram.)

Based on this, if you don't always have an increased weight, it would work better with helper air-bags.

(I don't want to hijack this thread, am generally pretty clueless about the AHC system, but do have a question...)

It seems with an AHC equipped vehicle some of the weight is carried by the torsion bars / rear coils and some by the AHC system. If one put non-AHC coils and torsion bars on an AHC equipped vehicle and then adjusted the AHC sensors so that the pressure readings were in-spec, wouldn't that translate into a taller ride height (un-laden vehicle)?

And if they vehicle were then loaded with say an extra 1,000 lbs, wouldn't the AHC system work in conjunction with the stiffer springs / TB's in supporting part of the additional load. It strikes me as a win-win. Please explain how I'm wrong.

 

[r3run33]

hey forgot to add I myself have had failures to do the AHC system having rust or corrosion issues from the stuff DOT puts on the roads here in the winter! all problems I have spoken to the lexus tech up here and he says they are either this type of problem or the actually replacement parts not working correctly. so if anyone from the forum that has had issues chime in on where you are to help out. Sorry if I mentioned the spheres I meant the pumps for the system being able to help with the weight of the loaded up armored LX's.

 

[uHu]

(I don't want to hijack this thread, am generally pretty clueless about the AHC system, but do have a question...)

It seems with an AHC equipped vehicle some of the weight is carried by the torsion bars / rear coils and some by the AHC system. If one put non-AHC coils and torsion bars on an AHC equipped vehicle and then adjusted the AHC sensors so that the pressure readings were in-spec, wouldn't that translate into a taller ride height (un-laden vehicle)?

And if they vehicle were then loaded with say an extra 1,000 lbs, wouldn't the AHC system work in conjunction with the stiffer springs / TB's in supporting part of the additional load. It strikes me as a win-win. Please explain how I'm wrong.

This would be an either-or, not both...
The stronger springs would carry more of the vehicle's weight. That could either be used to set the vehicle height higher (adjusting sensors), until the Neutral Pressure is in spec; or it could be used to keep the pressure in spec with a much higher weight.
If you first adjust the sensors to make the truck sit higher at the nominal ahc pressure, and then add weight, all the added weight would be supported by the ahc, just as if you had normal springs and normal height. Not to mention that at such a high suspension position, the ride would suffer because of the short down-travel available.

If you want to keep the AHC and not fit helper air bags, the best you could do is to have a bit stronger springs in order to keep the neutral pressure at the bottom of the bracket WITH all the normal junk in the truck (things you normally carry anyhow). That would give the ahc a slightly easier job when loading up the truck and hitching the trailer.
I could also imagine having a little cheater box between the sensors and the ahc-ecu, which would give me an inch higher Normal height (with my then reinforced springs) and then flick a switch on that box to give me a ride 1" lower than standard in order to support more weight (the coils would be more compressed and carry more of the weight). That way I would sit slightly higher for offroading, and slightly lower for the highway with all the stuff loaded, and the pressure OK in both situations.

PK470, are you OK with the development of this thread, or are we going sideways now? You need someone with first-hand experience chiming in for some of your Qs.

Re. What position to put the AHC in prior to changing springs or fitting air bags: If you keep it in Normal before jacking up, you will still have pressure in the shocks when they are fully extended. In position Low, the pressure could become negative (towards vacuum) when extending the shocks completely. That could possibly make it easier to get air into the system.

The AHC is really simple, it just adjusts the pressure until the height sensors say "zero" (equals half-way travel). If the springs are good and the weight is standard/stock, it means that the ahc-globes (nitrogen springs/spheres) is carrying about half of the weight. As long as you keep the ahc-part at the same number of pounds (or kilos if you like), the system will be happy. That means that if you add weight over the designed capacity, you have to help the system one way or another.

 

[Wilsil]

My AHC system is sort of working on my 150k miles LX.
It goes up and down on command, but struggles sometimes when the Kimberley Kamper is hooked up.
The sport/hard switch doesn't work, which I think is also part of the system.
I like the AHC concept, but don't think it is the best when offroading.