Watts link rear suspension
- Thread starter javajoe79
- Start date
javajoe79
Fabricator
Repurposing tie rod ends gives me a simple, easy and readily available part to service. They would be the same parts in my front steering so 2 different spare parts will service all of that. My other options might be heims instead but I would say that finding tie rod ends in your average town is easier than finding heims.
I know it's not necessary but it's not that complex. I've built a few for road and track cars and it is a rather simple setup. This will just be overbuilt and use cheaper parts than your average road race watts link. I am however already rethinking the wheel bearing assembly. I think I will just machine a pivot and use readily available, sealed roller bearings.
Nothing wrong with a panhard bar but if you get down to it, it allows the axle to move in an arc as it travels up and down, especially n a vehicle with a good amount of travel. The watts link does not allow the axle to move in an arc. It also acts the same when loaded to either side, where a panhard does not. Maybe I would never feel it in this truck but you can feel it on a track car.
The other thing is being able to obtain the proper roll center and fit the linkage in between the frame rails. I could do this with either linkage but if I chose a panhard bar, it would have to be very short and that makes the arc travel much worse. I haven't plotted it out but I think I would end up with a couple inches of side to side travel with a panhard bar that short and say 12" of travel.
I know it's not necessary but it's not that complex. I've built a few for road and track cars and it is a rather simple setup. This will just be overbuilt and use cheaper parts than your average road race watts link. I am however already rethinking the wheel bearing assembly. I think I will just machine a pivot and use readily available, sealed roller bearings.
Nothing wrong with a panhard bar but if you get down to it, it allows the axle to move in an arc as it travels up and down, especially n a vehicle with a good amount of travel. The watts link does not allow the axle to move in an arc. It also acts the same when loaded to either side, where a panhard does not. Maybe I would never feel it in this truck but you can feel it on a track car.
The other thing is being able to obtain the proper roll center and fit the linkage in between the frame rails. I could do this with either linkage but if I chose a panhard bar, it would have to be very short and that makes the arc travel much worse. I haven't plotted it out but I think I would end up with a couple inches of side to side travel with a panhard bar that short and say 12" of travel.
gait
Explorer
ATW modified a few with coils and watts linkage.
mine is parabolics.
its a long time ago ....... I paid a bit of attention to roll centre, roll axis, and centre of mass during box design. The suspension travel, even with a bit extra travel with parabolics, is such that the roll steer with gusty side winds is negligible. With the 4m x 2.1m side of the box on the Canter its more stable in side wind than my '81 Merc car. Slightly related, I haven't felt the need to add steering damper and have no hint of front axle tramp. Articulation is more than adequate for my use.
Its a truck with a floppy chassis, two beam axles, and limited suspension travel.
Nice project, but I guess I'm wondering what problem you are trying to solve.
mine is parabolics.
its a long time ago ....... I paid a bit of attention to roll centre, roll axis, and centre of mass during box design. The suspension travel, even with a bit extra travel with parabolics, is such that the roll steer with gusty side winds is negligible. With the 4m x 2.1m side of the box on the Canter its more stable in side wind than my '81 Merc car. Slightly related, I haven't felt the need to add steering damper and have no hint of front axle tramp. Articulation is more than adequate for my use.
Its a truck with a floppy chassis, two beam axles, and limited suspension travel.
Nice project, but I guess I'm wondering what problem you are trying to solve.
SkiFreak
Crazy Person
I assume that you are talking about the centre bearing for the Watts link here... yes?
On my truck (modified by ATW) the centre bearing of the Watts link is a greaseable phosphor-bronze bush. I did think about replacing this with a sealed ball or roller bearing setup, but chose not to do so upon thinking about it further.
The biggest determining factor was that the Watts link had to be unaffected when being submersed in water (fording rivers). As much as you can use seals on either side of the bearings, this is one of the lowest parts on the truck and is prone to a lot of dirt/mud. As I am sure you would be aware, grit and seals are not good bedfellows. The bush solution is, in my opinion, a more robust solution in this situation. Even if the bush is badly worn, it will still function, albeit being a bit noisy.
I did end up replacing the original ATW bush with one that I machined myself. The new bush has slightly closer tolerances and better grease track grooves.
javajoe79
Fabricator
Haha! the only problem I have currently is I have nothing there. No panhard, no watts. I'm not necessarily worried about the handling being sketchy but if I have to build from scratch, I may as well make the best linkage possible. After all I have the means to do so. If I had an existing complete suspension I would probably leave it alone.
This is the truck I was referring to. My 4 link is not unlike his either. http://canter4x4.com/gallery/core-modifications-to-the-canter/#gallery[gallery]/21/
Ahh so it's you. I guess I never made the connection. I also thought about a bushing for that exact reason. Good info! I have a few chunks of bronze around and I could even machine a spare set to carry in case but you're right, it could be pretty badly worn but still function. How many miles do you have on your new bushings? Also have you had any wear issues with the heim joints? I have considered them in addition to the boots you can buy to cover them but I feel like the 1 ton chevy tie rod ends are more than strong enough and they are much cheaper than heims.
Also if you don't mind sharing, what length and rate coil springs are you running?
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whitenoise
Adventurer
If you're just doing it for the coolness factor and a "cause I can" approach, have at it. It's very clear that you have the design and build skills to make something that can be used in the truck.
I hope you take the following advice in the right spirit, I am not here to offend, argue or say that I know everything about this.
1. Be advised that the geometry is not as simple as it looks. Symmetric geometry does not equal symmetric roll center migration, or axle shift. There is much more to it than that, one of the issues being that a suspension like this cannot be analysed as a pure kinematic linkage (sorry I cannot discuss further details). The higher the total wheel travel, the more difficult it is to obtain linear characteristics - this might explain your success with track cars which see only a fraction of the travel your off-road truck will want to see.
2. This brings us to wheel travel. Unless you have over 13-14" of total wheel travel, and are using all of it (think desert race pre-running) you will probably not see any advantage from a watts link. In fact, as I have pointed out above, it is much easier to tune yourself out of the ballpark with a watts than a panhard. This is one reason why its not done on production cars (not just cost).
If I were in your position, I would build a Panhard with the following characteristics:
- as parallel to the ground as physically possible when the vehicle is at LOADED ride height.
- as long and straight as physically possible.
- place the center of the Panhard at the desired roll center height. if you're converting a leaf spring vehicle and dont know any better, this height should equal or be 1-1.5" above that of the old spring perches on the axle.
From extensive (and objective) experience, I'm willing to guarantee that a well-designed Panhard will outperform an average Watts link in terms of ride quality, handling, and of course, durability.
I hope you take the following advice in the right spirit, I am not here to offend, argue or say that I know everything about this.
1. Be advised that the geometry is not as simple as it looks. Symmetric geometry does not equal symmetric roll center migration, or axle shift. There is much more to it than that, one of the issues being that a suspension like this cannot be analysed as a pure kinematic linkage (sorry I cannot discuss further details). The higher the total wheel travel, the more difficult it is to obtain linear characteristics - this might explain your success with track cars which see only a fraction of the travel your off-road truck will want to see.
2. This brings us to wheel travel. Unless you have over 13-14" of total wheel travel, and are using all of it (think desert race pre-running) you will probably not see any advantage from a watts link. In fact, as I have pointed out above, it is much easier to tune yourself out of the ballpark with a watts than a panhard. This is one reason why its not done on production cars (not just cost).
If I were in your position, I would build a Panhard with the following characteristics:
- as parallel to the ground as physically possible when the vehicle is at LOADED ride height.
- as long and straight as physically possible.
- place the center of the Panhard at the desired roll center height. if you're converting a leaf spring vehicle and dont know any better, this height should equal or be 1-1.5" above that of the old spring perches on the axle.
From extensive (and objective) experience, I'm willing to guarantee that a well-designed Panhard will outperform an average Watts link in terms of ride quality, handling, and of course, durability.
javajoe79
Fabricator
If you're just doing it for the coolness factor and a "cause I can" approach, have at it. It's very clear that you have the design and build skills to make something that can be used in the truck.
I hope you take the following advice in the right spirit, I am not here to offend, argue or say that I know everything about this.
Thanks. No worries!
1. Be advised that the geometry is not as simple as it looks. Symmetric geometry does not equal symmetric roll center migration, or axle shift. There is much more to it than that, one of the issues being that a suspension like this cannot be analysed as a pure kinematic linkage (sorry I cannot discuss further details). The higher the total wheel travel, the more difficult it is to obtain linear characteristics - this might explain your success with track cars which see only a fraction of the travel your off-road truck will want to see.
Admittedly I am not as deep into it as say your average engineering student but I have a decent grasp on it. Help me understand better where you're coming from saying that. My understanding of a watts link tells me it keeps the axle moving up and down in a straight line I imagine until one or both linkages reaches its limit.
2. This brings us to wheel travel. Unless you have over 13-14" of total wheel travel, and are using all of it (think desert race pre-running) you will probably not see any advantage from a watts link. In fact, as I have pointed out above, it is much easier to tune yourself out of the ballpark with a watts than a panhard. This is one reason why its not done on production cars (not just cost).
My main desire for the watts link is the limited space I have to build and install a long enough panhard bar. Describe what you mean by tune myself out of the ballpark. That makes me think of a road race car and making too many changes at once and ruining the handling. It is done on production cars, I wouldn't say it's common though.
- place the center of the Panhard at the desired roll center height. if you're converting a leaf spring vehicle and dont know any better, this height should equal or be 1-1.5" above that of the old spring perches on the axle.
As the height of the original leaf spring perches is unknown to me I was shooting for having the roll center slightly above the front roll center as that is how I have know it to work best usually. That means it's in the typical spot, about 3" above the axle center line. Sounds just like 1-1.5" above the old spring padsWith a panhard bar that limits me to maybe a 24" bar as the frame is in the way.
From extensive (and objective) experience, I'm willing to guarantee that a well-designed Panhard will outperform an average Watts link in terms of ride quality, handling, and of course, durability.
Tell me in what respect it will outperform a watts link? I am not opposed to ditching the watts and I can always try it in the future but I can't imagine any drawback other than complexity.
Thanks again or your input
whitenoise
Adventurer
Glad to see you're open to going with a simpler arrangement. When I say the Watts isn't done on production cars, I mean in the past decade or so. I believe the last production vehicle with a Watts link (in NA, at least) was the PT Cruiser. Other OEMs have tried it and decided it's not worth its benefits over a track bar.
I suggest you study a bit more about the linkage kinematics as the axle goes through it's travel, either with software or a simple scale model. It's not a perfect straight line follower at all, in fact if you get the geometry wrong (which in my experience is several times more likely than getting it correct) it can be worse than the average track bar. That's what I meant by "tune your self out of the ballpark", except you would be stuck with what you build, unless you're willing to build a fully adjustable design...
All this being said, a 24" track bar sounds... Inadequate. I noticed in your Facebook link that the chassis came with duallies, any reason why you can't replace that with a super single type tire? You would have a overhung frame bracket for the track bar but I'm fairly certain it will be at least twice as long as now...
Sent from my ONEPLUS A3000 using Tapatalk
I suggest you study a bit more about the linkage kinematics as the axle goes through it's travel, either with software or a simple scale model. It's not a perfect straight line follower at all, in fact if you get the geometry wrong (which in my experience is several times more likely than getting it correct) it can be worse than the average track bar. That's what I meant by "tune your self out of the ballpark", except you would be stuck with what you build, unless you're willing to build a fully adjustable design...
All this being said, a 24" track bar sounds... Inadequate. I noticed in your Facebook link that the chassis came with duallies, any reason why you can't replace that with a super single type tire? You would have a overhung frame bracket for the track bar but I'm fairly certain it will be at least twice as long as now...
Sent from my ONEPLUS A3000 using Tapatalk
javajoe79
Fabricator
Newer Durango comes to mind
Pt cruiser huh? Weird. Never realized that.
I would do adjustable mounts for sure
I've already converted to single tires.
The problem comes under full compression, the track bar would hit the frame. Just no way around that without either putting the bar and roll center really low and or fabbing an oddly shaped bar to reach around the frame
The truck had a panhard bar when I got it but they had notched the frame to allow clearance and I'm not ok with that. It was about 36" long and bent
Pt cruiser huh? Weird. Never realized that.
I would do adjustable mounts for sure
I've already converted to single tires.
The problem comes under full compression, the track bar would hit the frame. Just no way around that without either putting the bar and roll center really low and or fabbing an oddly shaped bar to reach around the frame
The truck had a panhard bar when I got it but they had notched the frame to allow clearance and I'm not ok with that. It was about 36" long and bent
SkiFreak
Crazy Person
Yep...
Not enough miles to give you any real indication, but the heim joints on mine are humungus, so I am guessing that they will go the distance (they use a 1" bolt). Even the guys at ATW admit that these were overkill, but they are unlikely to break.
The Watts link bush I replaced showed little to no wear after about 7000KM. Not a lot, I know, but the truck is not finished yet, so it does very few miles currently.
I would think that heim joints would better suit this application, but this is definitely not my area of expertise.
Cannot tell you that either, as I did not get the specs from the guys at ATW. Should probably put that on my list, as I should have that info myself.
javajoe79
Fabricator
Yep...
Not enough miles to give you any real indication, but the heim joints on mine are humungus, so I am guessing that they will go the distance (they use a 1" bolt). Even the guys at ATW admit that these were overkill, but they are unlikely to break.
The Watts link bush I replaced showed little to no wear after about 7000KM. Not a lot, I know, but the truck is not finished yet, so it does very few miles currently.
I would think that heim joints would better suit this application, but this is definitely not my area of expertise.
Cannot tell you that either, as I did not get the specs from the guys at ATW. Should probably put that on my list, as I should have that info myself.
Thanks! Agreed on the heims. They are certainly stronger. If you should find out the coil spring specs. Please let me know
whitenoise
Adventurer
Newer Durango comes to mind
The problem comes under full compression, the track bar would hit the frame. Just no way around that without either putting the bar and roll center really low and or fabbing an oddly shaped bar to reach around the frame
The truck had a panhard bar when I got it but they had notched the frame to allow clearance and I'm not ok with that. It was about 36" long and bent
Yup, thats a 15 year old design and while it certainly worked, they went back to a panhard for the next gen Durango. Frame notches can be reinforced in other ways unless you're saying they cut off half the section, it has been done on quite a few prototypes before.... With a combination of a slightly lower roll center, i think a good panhard could be made to work.
javajoe79
Fabricator
Yup. Exactly what they did. I patched it