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Shock internals and Top Out


rocky2
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Lets take a look at the internals of basic shock/strut/damper design and discuss "Top Out"

 

The optimal position of the rod piston "B" should be in the center of the stroke when the vehicles weight is loaded on the suspension system. ie. spring

shock_zpsb86e5a4d.jpg

 

 

 

The available stroke in a R50 front strut is approximately 7" that's 3.5" in either direction if rod piston is centered. With a longer coil spring of lets say 2" the stroke is diminished to approximately 1.5" in the upward travel of the rod.

 

2012-11-29132043.jpg

 

If you put a longer spring in place, the stroke will be affected thus decreasing the upward movement/travel of the rod. In other terms, the articulation of the wheel in its downward motion will be limited and the shock absorber will reach the end of its travel commonly known as "top out". Now this may change over time and/or after the springs settle/relax or are weighted/loaded with accessories, more weight ie. bumper, winch or whatever. Obviously, if left unaddressed damage may occur to the shock/strut, a loud noise will be heard when the wheel travels through the available range and articulation is decreased. This is easily addressed on solid axle design by installing a longer shock that matches the spring length. But IFS axle design demands alternatives.

 

Several remedies are available and are not limited to:

 

1) Limiting straps

 

strap_zps9e363595.jpg

 

 

2) Rod extensions

 

rodext_zps03ab8970.jpg

 

Rodext2_zps168eaec7.jpg

 

 

3) Strut modification

(this is one possible design modification,the strut internal mechanism is being spaced upwards in the strut housing)

 

2007-01-01000000-9.jpg

 

2007-01-01000000-2.jpg

 

Another possibility

 

ORIstrut_zps50433826.jpg

 

ORIstrut2_zps30489279.jpg

 

Coilover possibilities are endless

Coilover_zpsb604a507.jpg

 

:deadhorse:

 

Please comment to this post

Edited by rocky2
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That's my old college roommate's rig with the ORI struts (Methfinder). I really like the idea, but they cost a fortune. If anybody knows a similar version, even if its the most basic design (CHEAPEST) I would be all ears.

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maximum motorsport coilover strut kit gotta love em rocky whats the strut housing diameter if u have that u can just order a coilover sleeve kit and weld it up with a good spring and your golder or am i off by something.

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As rocky2 plainly and clearly pointed out using easy-to-understand language and excellent diagrams, the stock strut with stock springs allows for an equal ratio of compression and extension (50:50, or 3.5" in either direction, for a total of 7"). With different coil springs, whether for lifting or for lowering, the ratio of compression:extension is different. For our purposes, we are addressing lift springs. With a 2" lift, the compression is increased to [a little less than] 5.5", while the extension is reduced to just [a little more than] 1.5". If you wanted to restore the compression:extension ratio back to 50:50, you would need to add a 4" extension to the strut. But for practical purposes we only want to get the extension back to the stock length of 3.5", so only a 2" extension is needed.

 

Double-wishbone IFS designs, such as on the Nissan WD21, WD22, and many Toyota vehicles, the suspension extension is limited by bump stops or other methods that are disassociated with the shock or spring. However, on a suspension design that uses MacPherson struts, the suspension's maximum extension is limited by the maximum length of the strut.

 

On a RWD vehicle, the only practical limit on the stroke of the strut is determined by the suspension geometry. The lower A-arm can only swing downwards so far before the suspension geometry is severely compromised. However, on a 4WD vehicle, in addition to preserving suspension geometry, the stroke of the strut is limited in order to prevent the front CV axles from operating at excessive angles when the suspension is fully unloaded.

 

As mentioned above, if the "at rest" position of the suspension is 2" higher than stock, not only is the suspension geometry (camber and toe) altered - requiring corrective countermeasures, but the "at rest" position becomes too close to the maximum travel. So, lengthening the strut to provide it more extension seems like a good solution.

 

The problem with lengthening the strut is that it can no longer prevent the CV axles from operating at excessive angles. Note that under normal use, this isn't an issue because the suspension will rarely be fully unloaded. However, when driving on uneven terrain, this could be catastrophic, resulting in destroyed CV joints.

 

No matter which type of suspension lift components are selected (strut spacers, coilovers, stiffer springs, strut inserts, strut rod extensions, etc.) the maximum CV angle must never be exceeded.

 

For this reason, it is inadvisable to lengthen the struts (simply to avoid "top out") without ALSO installing additional hardware on the lower suspension components or other means of limiting the downtravel. This is why a subframe drop is also an important thing to consider.

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You're right XPLORx4 and I appreciate your insight. I think that we all can agree.

The maximum CV angle should not be overly exceeded for prolonged periods of time and/or usage.

 

But as the "theexbrit" has stated: "As for the CV angle, I measured the angle with the wheel off the ground & with the 2" AC lift my maximum angle was about 25 degrees, still well within OEM specs (33 degrees max I think) so you'll be fine" Of course I have no pictures at full wheel articulation and therefore, empirical knowledge of supposed excessive CV angle is as yet unverifiable to the skeptical.

 

As you state: "So, lengthening the strut to provide it more extension seems like a good solution. The problem with lengthening the strut is that it can no longer prevent the CV axles from operating at excessive angles"

 

I am stating and visually representing that the strut assembly overall has already been lengthened by using a longer spring. I am advocating lengthening the rod, Not the strut assemby, so as to return the compression/extension ratio back to 50:50 and addressing the "top out" issue. I do not think that using or allowing the "top out" of the shock is an acceptable means of preventing excessive CV angles and posssible catastrophic and destroyed CV joints, as I am sure you would agree!

 

Theoretically, lengthening the strut rod to match what the spring has already extended and returning the compression/extension ratio back to 50:50 in its travel range does not exceed the recommended CV angle at full articulation.

Angle measurements will be taken and posted at a later time.

 

Exclusively yours

Rocky

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("it is inadvisable to lengthen the struts (simply to avoid "top out")

 

I couldn't agree more, but this has already present (lengthened strut) when using longer springs. I am only advocating centering the rod in its travel. I think you believe that this will allow for even more downward wheel travel and exacerbate the problem and ruin the CV joint or am I mistaken.

Maybe I am wrong, but I just can't get my head around using the "top out" as a means for limiting the travel and CV angle.

 

Gotta go eat and will be back soon.

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Hi rocky2,

 

I think I'm not understanding your terminology, so I'm getting confused. From what I can observe, replacing the coil spring in a stock strut will not lengthen the distance between the strut tower on the body/chassis and the ball joint on the A-arm when the wheels are off the ground. In fact, you can completely remove the spring from the strut altogether, reinstall the strut, and the distance between the chassis' strut tower and the ball joint will still be the same as when the spring is installed.

 

However, if you increase the distance between the chassis' strut tower and the ball joint, whether by lengthening the strut rod OR by installing a spacer between the strut assembly and the tower, the distance is increased.

 

It is this increased distance that can compromise the integrity of the CV axles. It only takes 1/3 of a rotation to bind and potentially break an overextended CV joint.

 

As long as the overall distance between the strut tower and the ball joint is the same as factory specs when the wheels are off the ground we can assume that the CV joints are operating within specified tolerances.

 

I have never been an advocate of any kind of suspension modification that increases the maxiumum distance between the strut tower and the ball joint, thereby increasing the maximum CV angle, because I believe the risk of breaking a CV axle is too great while driving off-road, where there is a high likelihood of having no weight on a front tire that is also fully turned right or left. There may be some users on the forum who have successfully installed 1" spacers between the strut tower and the strut mount ("top hat") but I have doubts about whether they have hung one or both front tires in the air while off-roading without a front sway bar.

 

Therefore, I could become an advocate of increasing the distance between the strut tower and the ball joint only if there is a similar increase in distance between the chassis and the centerline of the front differential output flanges (aka subframe drop).

 

By no means am I advocating "topping out" as a means for limiting suspension travel. I'm just stating that this is what happens already. With longer/stiffer springs, this just happens more frequently and with more force (due to the higher spring rate) when the wheels are ON the ground. By the way, I bet this pheonomenon would be far less prevalent if the rebound valving of struts made for the R50 was a lot firmer. That is, the compression valving could be high-speed, while the rebound valving could be very low speed. Unfortunately, I think the more popular struts, such as the KYB GR2, are gas-charged and have faster rebound valving than compression valving.

Edited by XPLORx4
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By the way, we both 100% agree that while there is weight on the front suspension on level ground, the best place for the shock/strut piston to be is centered in its stroke.

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I'm glad that this thread got started! The points being made are really helpful & are being made in an explanatory & understandable manner, especially with the excellent illustrations.

 

There is not enough being made of the fact that the 2" lift can give you problems. Like most people I was so excited about getting my lift that I just went ahead & did it without much research, I also used the NX4 spacers. Result = horrible positive camber & topping out badly. Sure some people have done the lift, spacers, etc, with no problems but this thread is a must for anyone contemplating a lift on an R50. I hope it gets pinned.

 

When my KYB's collapse after topping out so much, I'm getting Konis, a rod extension & a SFD :itsallgood::jig:

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I think I'm not understanding your terminology, so I'm getting confused. From what I can observe, replacing the coil spring in a stock strut will not lengthen the distance between the strut tower on the body/chassis and the ball joint on the A-arm when the wheels are off the ground.

Yes it will, if the strut is longer or shorter but depending on "top out" or "bottom out" for that matter to prevent excessice CV angles seem disingenuous at best.

In fact, you can completely remove the spring from the strut altogether, reinstall the strut, and the distance between the chassis' strut tower and the ball joint will still be the same as when the spring is installed.

 

I think we are considering two different scenarios. You are taking only into account strut length when the wheels are off the ground. I'm talking about centering the strut rod piston in the shock body when using longer springs.

You are right, if no spring is present the rod will only allow so much articulation downward between the top hat and ball joint. If I lengthened or shorten the rod now, with no spring, then yes further or decreased articulaion is present. But, I contend, is CV angles dangerously increased and at what point of length.

 

I am postulating that when using longer coil springs, say 2" longer and lengthening the rod in an equal amount you're center the piston in the shock body and YES the strut can now travel further before "top out" when unweighted that it will not create damaging CV angles when, YES the wheels are off the ground.

 

"However, if you increase the distance between the chassis' strut tower and the ball joint, whether by lengthening the strut rod," the distance is increased

Not so at all,

 

Lengthening or shortening the rod itself does not affect strut assembly length only rod piston centering.

 

Lets say you use the stock spring and only lengthen the rod with an extension, you are pushing the piston at the end of the rod in the shock body in deeper, please refer to the first pic in my thread. This would create "bottom out" early. So it would be necessary to shortening the spring in this scenario. Would you not agree?

 

"By no means am I advocating "topping out" as a means for limiting suspension travel. I'm just stating that this is what happens already"

How does the factory/stock set-up prevent excessive CV angles and or "top out" when the wheel is off the ground?

 

By the way, we both 100% agree that while there is weight on the front suspension on level ground, the best place for the shock/strut piston to be is centered in its stroke.

How is this achieved when using longer springs, without correcting the length of the rod?

 

I guess it's six of one or a half dozen of the other. Ruin the strut with "top out" or destroy the CV joint with angle. But I have to reiterate that correcting the rod length when using longer springs will not create overly excessive CV angles of 33%.

 

Please enlighten me !


Edited by rocky2
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i'm pretty sure the total extension of the McPherson strut will be extended with a longer rod as it relies on the rod length to stop it from extending too far. If you increase the length of the strut with an extension I'm willing to bet that the spring will push all the rod out of the strut when off the ground with no load.

 

Now whether or not it exceed the 33% maximum angle would have to be verified.

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Dear rocky2,

First, I will take you at your word that you genuinely want to be enlightened.

You wrote, "I think we are considering two different scenarios. You are taking only into account strut length when the wheels are off the ground. I'm talking about centering the strut rod piston in the shock body when using longer springs."

First, I would like to remind you that we agree that we are not talking about the same things. I understand that what YOU are talking about is centering the piston in the available stroke of the strut while the suspension is supporting the static weight of the vehicle. This is actually an excellent solution, except in your example of the Pathfinder strut stroke being +3.5"/-3.5" (total of 7"), with the AC 2" coil spring lift added, the stroke would then be +1.5" [extension]/-5.5" [compression] (total of 7"). In order to center the piston in the strut, the rod extension would need to be 4", not 2": +5.5"/-5.5" (total stroke of 11").

A 2" strut rod extension to a 7" long strut rod will yield only 9" total stroke, and will not achieve centering the piston, for the result would be +3.5"/-5.5".

When you measure the AC coil springs while they're sitting on the ground all by themselves, just removed from the shipping box, they are pretty long. If I recall, they're probably at least 16" or 17". The stock springs, when sitting on the ground all by themselves are somewhere around 13" or 14". Note that both the stock springs and AC springs are too long to fit inside the original 7" strut or even an elongated strut with a stroke of 11".

This is why in order to install any kind of coil spring into a strut, you need to use a coil spring compressor or strut compressor. If you don't compress the spring, it will be exceedingly difficult, if not humanly impossible to assemble the strut. If the uncompressed spring is too short to fully extend in the strut, it will dangle around and fall out of place during suspension movement when reinstalled in the vehicle.

OK, for argument's sake, let's assume that you've managed to install AC 2" lift coil springs into a strut whose total stroke is 11", so that when the static weight of the vehicle compresses the suspension, the piston is centered in the stroke. At the moment, everything works great (except for alignment issues caused by the altered suspension geometry). You won't ever get the topping out problem. Problem solved, right!?

Perhaps, but if you drive the truck on uneven terrain that might possibly allow the suspension to fully unload and extend to its maximum length of 11" (remember how long that strut was before you reinstalled it in the truck?), the suspension A-arm will drop 4" lower than it did when Nissan assembled it in the factory, the CV angle will become greater than its design tolerance, and I guarantee you that something will break. If not the CV joint itself, the boot will tear. Or perhaps even the ABS sensor cable or brake fluid line will overstretch as the A-arm drops below its design tolerance.

I will remind you again that you are taking about STATIC LOADED COMPRESSED SUSPENSION, while I am talking about FULLY UNCOMPRESSED SUSPENSION. So, we are metaphorically defending two different things: you're defending apples, and I'm defending oranges.

I will reiterate my firm position that I cannot and do not advocate to any Pathfinder owners the use of any type of device that alters the overall distance between the chassis strut tower and the ball joint while the suspension is uncompressed, UNLESS such a device is accompanied by other hardware that also lowers the center of the differential output flanges by the same amount. Installation of such devices (not SFD) carries risks that may result in driveline failure.

I take this position because I believe that the risk of binding a CV axle is too great when the knuckle/hub drops lower than its intended design, which is common when off-roading, and even more so without a swaybar. However, I am sure the forum members, including myself, would be greatly indebted to any owners who have installed strut spacers, strut rod lengtheners, or other devices that increase the strut tower-to-ball-joint distance (without any kind of subframe drop) to get their trucks up on a lift or jackstands (under the frame, not under the suspension), lock it in 4WD, crank the steering wheel full left or full right and videotape the CV axles in action while someone else applies the accelerator. If the CV axle doesn't bind or the boots don't split, then I would change my position and would confidently support such a device, bearing in mind that the positive camber issue is not fully addressed except by camber bolts or elongating the upper holes in the lower strut mount.

Edited by XPLORx4
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O.K.

Let me get my head around your hypothesis. Because I think you are being argumentative.

We both agree that lengthening the strut is not optimal for an IFS and/or R50 Pathfinder. But we both have lengthened the strut assembly by using AC coils. Can we agree on this?

I assume, cannot be absolutely certain, that the length of the entire strut assembly has been increased by 2", when using AC coils. Now the static weight of the vehicle and/or sag has at this point not been considered. Perhaps once the vehicle has been put back on the ground this is not exactly accurate. I am simply proposing that the rod now needs to be centered in the shock body in order to prevent "top out" and/or shock failure. I think you are commenting that this modification is inadvisable because excessive articulation, when unloaded, due to this mod will create CV failure. Am I correct?

 

As to the comment:

A 2" strut rod extension to a 7" long strut rod will yield only 9" total stroke, and will not achieve centering the piston, for the result would be +3.5"/-5.5".

It certainly will center the piston if the rod has been stretched by using a 2" longer spring.

 

My mathematics puts this at centered rod. If you pull the rod out by 2" by putting 2" longer springs on then I assume we need a 2" rod adjustment in order to center the rods piston.

 

In order to center the piston in the strut, the rod extension would need to be 4", not 2": +5.5"/-5.5" (total stroke of 11").

I think your math is wrong here. The rod can only be extended to its 7" max with or without an extension or longer springs. I don't know where you are getting this 11" total stroke. This assertion, I certainly need enlightenment. 2+7= 9

 

I will reiterate my firm position that I cannot and do not advocate to any Pathfinder owners the use of any type of device that alters the overall distance between the chassis strut tower and the ball joint while the suspension is uncompressed, UNLESS such a device is accompanied by other hardware that also lowers the center of the differential output flanges by the same amount. Installation of such devices (not SFD) carries risks that may result in driveline failure.

 

So, if I get your drift, you are saying go for a SFD don't use the AC coils or if you do just deal with the "top out", please clarify.

 

Strut rod lengtheners do not make the overall strut assembly longer!! The springs are making it longer. I can't stress this enough!!

The rod extension can only change the realitive position of the rods piston in the shock body and change the "top out"or "bottom out"

 

O.K. I will concede that the articulation has increased with a rod extension and will increase the angle of the CV joint when unloaded. But I cannot and do not believe that this angle is severe enough to damage the CV joint and that "top out" should be ignored. Let me get the video camera out or you can too. Don't forget the scientific process. You can prove me wrong anytime you want.

 

Did you look at that kid "snow4me" who just posted his lift pictures. His camber angle, assumed CV angle and one can only imagine "top out" issue is proof in the pudding. Get a SFD and don't mess with the springs.

 

So, apples and oranges. Sacrifice the shock or the CV

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i'm pretty sure the total extension of the McPherson strut will be extended with a longer rod as it relies on the rod length to stop it from extending too far. If you increase the length of the strut with an extension I'm willing to bet that the spring will push all the rod out of the strut when off the ground with no load.

 

Now whether or not it exceed the 33% maximum angle would have to be verified.

Soooooo, do you advocate allowing "top out" or correcting it ?

 

Does it really rely on rod length to stop it from taveling too far ?

Edited by rocky2
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So i have been following all the threads concerning strut top out, and/or modifying them to correct it.

 

I just want to say congrats to rocky2 as he has done a good job working on modifying struts to try and fix the top out issue.

 

I also feel that not everybody has as severe of an issue as others.

 

When i first installed my lift about 2 years ago, it did top out alot for the first couple weeks. Since then it might top out once every month or two. So personally i see no need in trying to modify the struts. And if you drive more carefully it shouldnt top out at all.

 

When i measured my new AC springs compared to the factory ones, there was less then an inch difference.

 

Pezzy has been running her lift for how long, 5 or 6 years with no issues?

 

I see no way to extend the length of the strut to get rid of top out without it affecting the CV angle or balljoints or anything else in the front suspension that would lead to premature wear.

 

Im sure this post will open a can of worms hahaha

 

Debate on my friends!!!! :)

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Soooooo, do you advocate allowing "top out" or correcting it ?

 

Does it really rely on rod length to stop it from taveling too far ?

I'm positive it relies on the rod length to keep it from travelling too far.

 

As for "correcting it", the ideal solution would be to first measure the CV angle with a longer strut rod (whether it's a strut extension or a longer strut) and see if it goes over the specified 33% (assuming this is the right number). If it doesn't, all is well. If it does, then I would say limiting straps would be the best option to stop the strut from extending past the CV's maximum angle.

 

I'm running OME HD in the front and I haven't had any top out issues with KYB struts. My previous R50 had OME MD in the front with the occasional strut top out over speed bumps. I understand that you're trying to prevent strut failure but in the 2 years I drove my previous R50, I had no strut related issues even while offroading. I would say strut top out is something most can live with, especially since there hasn't been much reports of strut failures.

 

Overall I feel safer knowing my strut can only extend so far without destroying my CV while offroading. I'd much rather drive out of the trail with a dead strut than a broken CV. ;)

Edited by projekz
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Hey projekz

 

"I'm positive it relies on the rod length to keep it from travelling too far"

 

The ball joint is what it relies on, you didn't think that the engineers at Nismo would rely on strut "top out" for articulation control now did you? The control arm can only go down so far before the maximum angle of the ball joint is reached. Not the CV joint or the strut rod. Anything else you want to know just ask.

Once you start accepting inherent problems without finding solutions, you are taking the apologists approach to logic.

balljoint_zps912cb435.jpg

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Dude

 

I see no way to extend the length of the strut to get rid of top out without it affecting the CV angle or balljoints or anything else in the front suspension that would lead to premature wear.

 

You have already extended the strut assembly by putting a longer/stiffer spring in the system. I am not advocating making the strut longer, just centering the rod in its travel range. In the preloaded position.

Of course,as XPLORx4 so eloquently points out, the CV angle could possibly be exceeded when at full droop or when the wheel is off the ground if a rod lenghtening device is incorporated. Which is yet to be determined.

 

:deadhorse:

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O.K.

XPLORx4 is right

 

Don't lengthen the strut

-if you do by using AC coils-which does lengthen the strut!

Don't even think about lengthen the rod in order to center the piston in the shock body, just deal with the "top out", because this can only increase the articulation of the suspension and CV angles when the wheel is off the ground and possibly cause CV damage and/or failure. Even though the ball joints limitation will prevent this from happening.

 

As Phantom10Pathfinder says, "I see no way to extend the length of the strut to get rid of top out without it affecting the CV angle or balljoints or anything else in the front suspension that would lead to premature wear." "The rod not the strut" Oooops I'm sorry

 

I most humbly retract everything that I have posted in this regard.

 

I can't bring you kicking and screaming into the light, you'll have to get there on your own.

 

I'm going skiing before I go to work.

Ciao Huevones

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Hey projekz

 

"I'm positive it relies on the rod length to keep it from travelling too far"

 

The ball joint is what it relies on, you didn't think that the engineers at Nismo would rely on strut "top out" for articulation control now did you? The control arm can only go down so far before the maximum angle of the ball joint is reached. Not the CV joint or the strut rod. Anything else you want to know just ask.

Once you start accepting inherent problems without finding solutions, you are taking the apologists approach to logic.

balljoint_zps912cb435.jpg

 

 

So, you're saying that if the strut was removed from the front, the suspension would sit at the same level as when the strut is in and extended all the way? Only the ball joint would make the suspension stop from going further down?

 

I'll have to check this out myself. I can't picture it in my head right now.

 

I'm hoping to get down to Utah in May for GoneMOAB. If I do so I'd love to have a beer with you. :beer::beer:

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So, you're saying that if the strut was removed from the front, the suspension would sit at the same level as when the strut is in and extended all the way? Only the ball joint would make the suspension stop from going further down?

 

I'll have to check this out myself. I can't picture it in my head right now.

 

I'm hoping to get down to Utah in May for GoneMOAB. If I do so I'd love to have a beer with you. :beer::beer:

 

 

 

Beers yes. :beer:

Edited by rocky2
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