Axle Mounted Shocks Help

[Carnaw]

Tossing around the idea of making my bomber into a true 4 link setup and ditching the TA's.

As of now I have Wraith length arms and uppers, if I am not mistaken I should just be able to get wraith length lowers and be set? But my main issue is the shocks.

The shocks are still the stockers. Plan on mounting them right to the axle on the mount right above the lower links and leaving the highest mounting point for the antirock. If I were to replace the shocks what's a solid length to go with? No u4 stuff just crawling for my bomber.

Is there anything else I need to do to make it set right. From what i've read this is going to lower my rear as well?

So what's the best way to lower the front with out loosing travel my just getting shorter shocks?

[MAC FAB]

Shock lengths will go like this: Without shocks on your rig, at full compression measure the distance between shock upper and lower mounting points. (This dimension makes or breakes the world for you) then lift it up to what it would be when topped out, take a measurement again. Your problem is by mounting on the axle your leverage ratio is now 1:1. Whatever the stroke is of the shock, that is your wheel travel. Stock is somewhere around 2 to 1, meaning a shock with 1-1/4" stroke gets you 2-1/2" travel. Where this is potentially a problem is by having limited travel also translates to minimal articulation (flex, twist, whatever you want to call it), if that matters to you. You will also need softer springs, thinner oil because of the reduced leverage ratio. HPI Savage shock is 6" eye to eye open and 4" compressed if that fits the space criteria, giving you 2" of travel. Yeti rear is about 5-1/2" eye to eye open with about 1-5/8" stroke. Stock setup is somewhere around 3" travel, I believe. As for fixing the front, perhaps soft or dual rate springs that drop your ride height without losing overall shock stroke.

[Carnaw]

Originally Posted by MAC FAB

Shock lengths will go like this: Without shocks on your rig, at full compression measure the distance between shock upper and lower mounting points. (This dimension makes or breakes the world for you) then lift it up to what it would be when topped out, take a measurement again. Your problem is by mounting on the axle your leverage ratio is now 1:1. Whatever the stroke is of the shock, that is your wheel travel. Stock is somewhere around 2 to 1, meaning a shock with 1-1/4" stroke gets you 2-1/2" travel. Where this is potentially a problem is by having limited travel also translates to minimal articulation (flex, twist, whatever you want to call it), if that matters to you. You will also need softer springs, thinner oil because of the reduced leverage ratio. HPI Savage shock is 6" eye to eye open and 4" compressed if that fits the space criteria, giving you 2" of travel. Yeti rear is about 5-1/2" eye to eye open with about 1-5/8" stroke. Stock setup is somewhere around 3" travel, I believe. As for fixing the front, perhaps soft or dual rate springs that drop your ride height without losing overall shock stroke.

That is a lot of helpful info and a great help.

So if its less leverage what's the benefit of axle mounted shocks vs trailing arms. From what was explained to me trailing arms handle a bit better with speed but overall crawling the geometry of a 4 link performs better?

[Brake Weight]

The stock rear Bomber springs have a much higher spring rate compared to the front shocks. They're also a little longer. By using Wraith length links your rear axle will articulate like a Wraith. But the shock mounting will be higher up on the chassis. You'll need to sort the shock lengths out after mounting up the rear 4 link. The front and rear will likely be different lengths. There's a couple of 4 linked Bombers here but you'll have to look for them. I can't remember the usernames but one is in Hawaii. He's got probably the coolest crawly spots on the planet.

[MAC FAB]

I don't know why anyone hasn't done a new skid to relocate the pivot locations and/or to allow for a rod end that is wider in the misalignment for closer to 30 degrees of movement. Also, what makes the 4 link better than properly set up trailing arms?

[Carnaw]

Originally Posted by MAC FAB

I don't know why anyone hasn't done a new skid to relocate the pivot locations and/or to allow for a rod end that is wider in the misalignment for closer to 30 degrees of movement. Also, what makes the 4 link better than properly set up trailing arms?

Yeah that's why I was thinking of changing it up. I know trailing arms handle great with speed but that's not the route I'm running lol


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[Brake Weight]

I'd considered doing mine with links instead of TA. I would think it'd be no longer as stable at speed but would be more apt as a crawler.

Custom bent links would be the optimum route to take for the rear due to the higher mounting points.

[altd896]

Changing to axle mounted shocks & plain lower link alone, once you dial in the spring rate, should make no noticeable difference to the handling.
The actual linking system, plain link or trailing arm (both are a 4 link), makes very little difference. It's where it's mounted on the chassis that changes the performance.

The wide, parallel mounting of the lower links in the Bomber (& Yeti & Losi trucks) improves it's high speed handling, in my U4RC truck I found mounting the lowers parallel from originally triangulated reduced the chassis roll in cornering. It also noticeably decreased the articulation of the rear axle.

Changing to a Wraith skid, along with plain links & axle mounted shock should increase the axle articulation. Wraith skid will bolt straight into the chassis but will need some mods to suit the Bomber trans.
It looks to me as if an axle mounted shock could mount to a point in chassis where the fuel cell mounts (see pic) with the use of a longer screw & maybe a small spacer behind the top ball end. It does however look like it would interfere with the stock style sway bar.

[MAC FAB]

Good info altd896. I've always thought of 4 link in the hot rod sense. So narrow on the skid is the ticket for a crawler? Weak link then, is the rod ends. Is a sway bar really necessary on a crawler only rig? Lack of wheel travel is the big gremlin I see here. Wouldn't be the first time I was out in left field either.

[Brake Weight]

Wraith length rear links would shorten the wheelbase. It'd bring the axle forward 16mm. Using the existing upper mounting location would have the shock laid down a good bit. Using the stock rear shock would lower the stance and negate some of the higher spring rate. Some have used the Twin Hammer TA which are 26mm shorter. These rigs are aesthetically good looking and performance is changed. So a shorter linked rear would put the shock more vertical.

[MAC FAB]

Twin Hammers are 1" shorter, wow. How long are the stockers, 6"? Having the shocks at 90 degrees to the TA at full bump makes for progressive suspension, not sure that matters on a crawler. I get the short wheelbase for being nimble, however, is short wheel travel more desirable than long? If so, I'm going backwards on my build. I'll have at least 4" at each corner, figuring the tires will always ltouch the ground for traction. Bad for weight transfer?

[Carnaw]

Originally Posted by Brake Weight

Wraith length rear links would shorten the wheelbase. It'd bring the axle forward 16mm. Using the existing upper mounting location would have the shock laid down a good bit. Using the stock rear shock would lower the stance and negate some of the higher spring rate. Some have used the Twin Hammer TA which are 26mm shorter. These rigs are aesthetically good looking and performance is changed. So a shorter linked rear would put the shock more vertical.

Ive seen the TA and was debating it as well. Im at the wraith length for now and going to test it all out and maybe move to the TA length next. Im also trying to figure out if I should try and lower my stance a bit as well.

[Carnaw]

Originally Posted by altd896

Changing to axle mounted shocks & plain lower link alone, once you dial in the spring rate, should make no noticeable difference to the handling.
The actual linking system, plain link or trailing arm (both are a 4 link), makes very little difference. It's where it's mounted on the chassis that changes the performance.

The wide, parallel mounting of the lower links in the Bomber (& Yeti & Losi trucks) improves it's high speed handling, in my U4RC truck I found mounting the lowers parallel from originally triangulated reduced the chassis roll in cornering. It also noticeably decreased the articulation of the rear axle.

Changing to a Wraith skid, along with plain links & axle mounted shock should increase the axle articulation. Wraith skid will bolt straight into the chassis but will need some mods to suit the Bomber trans.
It looks to me as if an axle mounted shock could mount to a point in chassis where the fuel cell mounts (see pic) with the use of a longer screw & maybe a small spacer behind the top ball end. It does however look like it would interfere with the stock style sway bar.

See thats the info I need to know i its not as simple as just switching the mounting points.

This is my first crawler so its a lot of figuring out and trying to under the geometry of everything. and understand what to do in general. haha

[am4x4]

I just did this mod but I have not had a chance to test it yet.

For shocks I used bomber rear shocks (they have black plastic parts but they are bomber body, shaft, and length) with softer springs, they are axial springs, grey with purple marks on the end, not sure what they are off but they are softer. The shocks were way to short to just bolt up so I shaved the upper eye off, drilled a hole in the cap, and screwed on a long rod end.

I made my own links but they are about wraith length

This setup did lower the rear some, which I wanted. With the rear at mid stroke on the shock the front was almost completely bottomed out. My solution was to cut the shock mount and battery hold down crossbar off the hood pivot crossbar then make a new battery hold down crossbar out of 1/4" delrin rod. This allows me to mount the shocks close to 1/2" higher using the screws for that crossbar. Now I have a low ride height and great up travel at both ends.

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[am4x4]

Just a couple of notes. You will loose some travel and articulation with this mod and you will need softer springs. When the shocks are mounted to trailing arms they are leveraged. This means that you need heaver spring rates with TA's and it also means that you get more wheel travel than the shock travel you use. When I mounted my shocks they ended up at a pretty good angle. This will also affect the motion ratio and actually give you a little bit of the same leverage effect but no where near as much as with TA's.

Regarding wraith versus bomber skids. The wraith has more triangulation on the lower links. This will in no way affect the amount of wheel travel or articulation when the shocks are mounted to the axle. It will help narrow up the links so you don't hang up on them as much and it will reduce or eliminate axle steer on articulation but it won't change the amount of articulation. The only things that can do that are shock length and shock mounting locations. The one exception to that if you ran a wraith skid with TA mounted shocks you would see a slight increase in articulation but it is because the shock mount location on the TA's are closer together so they have less vertical movement for a given amount of articulation. This would be a similar effect to moving axle mounted shocks inboard (closer to each other)

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[Carnaw]

Originally Posted by am4x4

I just did this mod but I have not had a chance to test it yet.

For shocks I used bomber rear shocks (they have black plastic parts but they are bomber body, shaft, and length) with softer springs, they are axial springs, grey with purple marks on the end, not sure what they are off but they are softer. The shocks were way to short to just bolt up so I shaved the upper eye off, drilled a hole in the cap, and screwed on a long rod end.

I made my own links but they are about wraith length

This setup did lower the rear some, which I wanted. With the rear at mid stroke on the shock the front was almost completely bottomed out. My solution was to cut the shock mount and battery hold down crossbar off the hood pivot crossbar then make a new battery hold down crossbar out of 1/4" delrin rod. This allows me to mount the shocks close to 1/2" higher using the screws for that crossbar. Now I have a low ride height and great up travel at both ends.

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Originally Posted by am4x4

Just a couple of notes. You will loose some travel and articulation with this mod and you will need softer springs. When the shocks are mounted to trailing arms they are leveraged. This means that you need heaver spring rates with TA's and it also means that you get more wheel travel than the shock travel you use. When I mounted my shocks they ended up at a pretty good angle. This will also affect the motion ratio and actually give you a little bit of the same leverage effect but no where near as much as with TA's.

Regarding wraith versus bomber skids. The wraith has more triangulation on the lower links. This will in no way affect the amount of wheel travel or articulation when the shocks are mounted to the axle. It will help narrow up the links so you don't hang up on them as much and it will reduce or eliminate axle steer on articulation but it won't change the amount of articulation. The only things that can do that are shock length and shock mounting locations. The one exception to that if you ran a wraith skid with TA mounted shocks you would see a slight increase in articulation but it is because the shock mount location on the TA's are closer together so they have less vertical movement for a given amount of articulation. This would be a similar effect to moving axle mounted shocks inboard (closer to each other)

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Your rig was the reason I looked into it even more lol. Caught your post on FB as well haha.

I'm fine with leaving the bomber skid don't plan n changing that as of now, eventually switch to the smaller trans though.

What was our main reasoning for going axle mounted from the TAs then. Since from how I understand it ti seems to be a pain to set it up right and you lost certain pros.

[am4x4]

Originally Posted by Carnaw

Your rig was the reason I looked into it even more lol. Caught your post on FB as well haha.

I'm fine with leaving the bomber skid don't plan n changing that as of now, eventually switch to the smaller trans though.

What was our main reasoning for going axle mounted from the TAs then. Since from how I understand it ti seems to be a pain to set it up right and you lost certain pros.

I have been crawling a yeti for the last year and one of the biggest hang up points is the trailing arms. When I first started this project I was going to add tabs to the top of my links to make them straight tube trailing arms (versus the stock style which hangs down) I never did try it but I think it would have been tough to get the ride height as low as I wanted it. This thing is a trail rig/crawler so I don't really have much need for trailing arms. I am not saying I have all the answers but I can tell you that it seems very well balanced on the bench top twist test

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[Carnaw]

Originally Posted by am4x4

I have been crawling a yeti for the last year and one of the biggest hang up points is the trailing arms. When I first started this project I was going to add tabs to the top of my links to make them straight tube trailing arms (versus the stock style which hangs down) I never did try it but I think it would have been tough to get the ride height as low as I wanted it. This thing is a trail rig/crawler so I don't really have much need for trailing arms. I am not saying I have all the answers but I can tell you that it seems very well balanced on the bench top twist test

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As for the rear looks easy as just getting longer shocks, or like you did get a rod end on top. You wouldnt happen to know that length eye to eye?

As for the front, was there any other options besides fabbing up the delrin bar? know where near that skilled to make something like that haha

[am4x4]

Originally Posted by Carnaw

As for the rear looks easy as just getting longer shocks, or like you did get a rod end on top. You wouldnt happen to know that length eye to eye?

As for the front, was there any other options besides fabbing up the delrin bar? know where near that skilled to make something like that haha

That really is the best way to deal with the front. You might be able to find a suspension link for an ax10/scx10 that is close enough in length to make it work using some spacers or something.

My rear shocks are about 117mm extended length so 120mm would probably be perfect

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[Carnaw]

Originally Posted by am4x4

That really is the best way to deal with the front. You might be able to find a suspension link for an ax10/scx10 that is close enough in length to make it work using some spacers or something.

My rear shocks are about 117mm extended length so 120mm would probably be perfect

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I guess the shocks are 110 stock then you got the extension on there. Ill have to mess with the stock ones for a bit. I need new shocks soon so test these first.

After reading your right up again doesn't sound to hard. Basically cut out the flap/battery hold down thing and make a new link to cross between the body under the hood. probably use some threaded rod and cut to size.