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 Post subject: Rod Ends vs Poly Bushes
PostPosted: October 14, 2020, 4:37 am 
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Joined: October 1, 2020, 3:22 am
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Hey all, Just wondering what these cars are like with 100% rod end suspension? is the ride quite harsh or since everything is so light is it not really an issue?

Conversely are Poly bushes or similar much different? how much give do they actually have? I would not have thought they would deflect that much at all? or is it surprising how much they actually flex under load.


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PostPosted: October 14, 2020, 9:00 am 
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My opinion, and it is just that, an opinion, is that there is little to no difference between the two options in the Locost. The benefit of the rod ends is that there is some adjustment range to do some fine tuning to the wheel geometries. IMO poly bushings are originally intended to replace rubber bushings in factory-built cars.

I built my car with rod ends and the car rode very comfortably on both highway and country roads. It was not harsh at all, but still very responsive. FWIW, it had IRS so that was also some help. Depending on the style of ride you want, it could be harsh if you use high rated springs and a high adjustment on the shocks.

IMO, adjustment is very desirable. So that tilts the decision to rod ends. I highly recommend Rod Ends from Jack at Kineticvehicles.com if possible.

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PostPosted: October 14, 2020, 10:39 am 
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Joined: October 24, 2008, 2:13 pm
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Location: Carlsbad, California, USA
Somewhere along the line, when I was asking the questions you just asked, a builder here (sorry, memory fails me, I can't remember who) suggested there was a hybrid solution as well. That was, rod ends on the suspension side, bushings on the chassis side. That's what I elected to do.

Here's a photo of the components from my rear 40 link setup.
Attachment:
File comment: Hybrid setup. Mixed bushings and rod ends.
Rear-4-Bar-Components.jpg
Rear-4-Bar-Components.jpg [ 124.64 KiB | Viewed 502 times ]


I'm not saying all rod ends is an issue, just that there are alternatives to it. I'm building a street car, so comfort was more of an issue than absolute performance, and I chose the hybrid solution.

Cheers,

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PostPosted: October 14, 2020, 10:43 am 
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Joined: January 11, 2017, 11:06 pm
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Location: Alberta
That basically looks like how I did my rear trailing arms, except the bushing end was not adjustable (I didn't see it as being necessary and was fabbing my own anyway). My front end is all rod ends, and I have no complaints.


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PostPosted: October 14, 2020, 12:11 pm 
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Joined: December 4, 2010, 1:53 pm
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Location: Edmonton, Alberta, Canada
This is just my experience. I built my car with rod ends on both ends. The rear springs are 180#. I found the rear suspension to be really harsh. I was going to put softer springs in, 140 or 150# but I decided to build new links with poly bushing first. The difference in my case was incredible, so much so that I won't be changing to softer springs.
FYI, I used poly bushings meant for the lower front control arms for a Triumph TR6. The bolt size is 1/2", the same as the rod ends that I replaced.

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PostPosted: October 14, 2020, 2:15 pm 
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Joined: July 17, 2006, 3:09 pm
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Location: Holly, MI
I have a couple of questions before answering:

1. How is your engine mounted?
2. What is the use of the car?
3. What kind of seat are you using and how is it mounted?
4. Manual or power steering and how is the rack mounted?

Lots of questions, but all of those will play a part in what you feel. I just replaced the stock rubber bushings with new control arms using rod ends. My car is strictly for the track, so I have different priorities than a street car. I still care about harshness, because I can feel vibrations. I didn't feel an increase in harshness. What I did feel was a massive change in the feeling when getting the car moving. The rod ends remove the "give" the rubber bushings did. It feels like the car got rear ended, because the acceleration is immediate. I would describe it as a jerky feeling; it will take some getting used to.

As for the movement, there are some great videos on YouTube showing how much the non-metal bushings deflect under load. I was surprised by how much it all moves. When you see how precise people try to get on their alignments, and then you see this movement, it gives you a new perspective.

Ken


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PostPosted: October 14, 2020, 4:37 pm 
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1. How is your engine mounted? That was going to be one of my future questions haha, pros/cons of both. but ill make another thread for that... so label that as undecided for now

2. What is the use of the car? 80% Track, 20% street

3. What kind of seat are you using and how is it mounted? Fixed back racing seat bolted to the floor

4. Manual or power steering and how is the rack mounted? Manual steering, rack ahead of axle, likely solid mounted


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PostPosted: October 14, 2020, 6:03 pm 
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Joined: June 21, 2010, 9:02 pm
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Location: Spencer WV
This is probably just tangential, but I'll mention it because I came across these and don't recall seeing info on this forum.

There are, what I'd guess you'd call cartridge spherical bearings, unless I'm mistaken as to what they are. They incorporate a boot to keep debris out. I believe MB uses them, and probably others. I think they're OEM in some cases, but I could be wrong.

In theory, you could build a control arm with a tube receiver that was capable of using these but also being able to have them swapped out for poly or even rubber bushings. Then you'd have the ability to tune it if you didn't like the results.

https://www.amazon.com/dp/B008MCZT2C/?c ... _lig_dp_it
https://www.amazon.com/dp/B0031GZ6JK/?c ... _lig_dp_it
https://www.bimmerworld.com/Suspension- ... rsQAvD_BwE

Image


If they are what I think they are, I plan on incorporating them into my project because I'm going to be operating in a very dirty environment but still want precision.

Of course, you could also swap rod ends with bushinged (is that a word?) ends as well. I don't think most rod ends have the debris protection but maybe I just haven't seen them. These also seem to be a bit more substantial which may or may not be an advantage, although I think having them inboard of the front LCA probably makes sense at least.


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PostPosted: October 14, 2020, 8:33 pm 
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Location: Sunny-Okanagan, Canada, eh?!
I initially did the solid axle in my Locost with UHMWPE bushings I machined myself (and 140# springs I did not machine). They did not have any flex at all, and contributed to some very fine snap oversteer. I changed them out to rubber, and have not regretted it.

I have found in other 4-link suspensions that I have since built, that poly bushings certainly make the axle much more rigid than it should be for a good-handling street or race car, and I would strongly recommend either rubber or spherical rod ends for the most compliant suspension. Rod ends would likely be noisier, but these are noisy cars so you likely won't notice.

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PostPosted: October 14, 2020, 8:50 pm 
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Lonnie-S wrote:
...rod ends on the suspension side, bushings on the chassis side.
A good idea that I've never implemented, would to have one rubber bushing in a four link rear suspension. It would reduce the need for perfect equality in the lengths of the top and bottom trailing arms on each side, and that bit of binding that happens when one wheel goes up and the other does not.

Frankly, I don't see why solid axles use four-link rear suspension, other that the safety advantage of having a redundant link in case somebody (cough, cough) forgets to set the jam nuts on the links and one of them wanders off.

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PostPosted: October 14, 2020, 10:55 pm 
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Joined: February 8, 2014, 10:47 pm
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Location: Cornholio OR "Where the magic happens"
Because a 3 link encroaches on the passenger seating.

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PostPosted: October 15, 2020, 12:17 am 
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Location: Sunny-Okanagan, Canada, eh?!
No reason not to put the 3rd link on the bottom.

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PostPosted: October 15, 2020, 2:00 pm 
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Location: Cornholio OR "Where the magic happens"
How does that affect the offset?

I've never considered that, or even seen one in use or a model.
Not certain it would provide the same reactions?
I think there may still be packaging issues with bar angles to get the desired reaction.

It certainly would "work" in the internet sense. (or with a stiff enough spring) :ack:

RE: compliant joints on a 4 link
It seems a minimum of 2 would needed to be used to provide symmetry (equal response turning R or L).

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PostPosted: October 19, 2020, 10:59 am 
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Joined: July 17, 2006, 3:09 pm
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Location: Holly, MI
Hermit wrote:
1. How is your engine mounted? That was going to be one of my future questions haha, pros/cons of both. but ill make another thread for that... so label that as undecided for now

2. What is the use of the car? 80% Track, 20% street

3. What kind of seat are you using and how is it mounted? Fixed back racing seat bolted to the floor

4. Manual or power steering and how is the rack mounted? Manual steering, rack ahead of axle, likely solid mounted


It sounds like most of your components are solidly mounted. When you are driving on track, there won't be the real small, high frequency, type bumps you will see on the street. In my experience, those are the ones which contribute to vibration the most. I would suggest mounting everything solidly for the track. Solid mounts eliminate the friction/stiction in the suspension and make it easier to fine tune settings and rates. For the street, you will have the wind in your face and being driving for fun. That should drown out the vibration. If you find that to not be the case, building new control arms with rubber really isn't a huge chore when you are already signed on to building a whole car.


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PostPosted: October 19, 2020, 4:35 pm 
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Yep I think your spot on BB69, Thats the plan now. thanks to all who contributed.


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