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Author: Subject: To rose joint or not to rose joint??
J666AYP

posted on 4/9/19 at 04:51 PM Reply With Quote
To rose joint or not to rose joint??

Gents,

I know this has been touched on in the past. I'm ready to start building my rear wishbones but I need to decide on either bushings or rose joints, anyone have any insight into this? I have worked out all the options in my head along with pros and cons of both set ups but I'm left wondering if rose jointed wishbones would be too harsh for road use?

The way I see it:

Pros to rose joints...
Much finer adjustment
Less movement in the whole system
Fewer squeaks and noises
Probably more predictable handling
The coilovers do all of the work
More connected feel to the car and what its doing

Cons...

More uncomfortable
Little to no adjustment with bushes
More wear/stress on other components
Price
more fabrication work

Anything I have missed?

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jelly head

posted on 4/9/19 at 05:53 PM Reply With Quote
i think you've nailed it there.

i found ride quality to be fine on the road with rose joints but personally i wouldn't have them again on a pure road car as they wore out pretty quickly (maybe they were crap qality), and they're not cheap to replace.

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melly-g

posted on 4/9/19 at 07:53 PM Reply With Quote
I've got 4 of them, some poly bushes and metalastic bushes on the rear of the Avon.
I've only had to replace 1 rose joint in 12 years! Non of the others though?
More than happy with that!

Not harsh at all, but as I said I've got a mix of all types of bushes.

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coyoteboy

posted on 5/9/19 at 08:05 AM Reply With Quote
I don't really see why, if designed correctly, it would be any significant amount more harsh or fast wearing. I've been in fully rose jointed cars that were super supple and lovely. If they're sized right they won't wear out early.





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peter030371

posted on 5/9/19 at 08:10 AM Reply With Quote
First Striker had metalastic bushes and was a handful on the road (fine on track) as the suspension tried to control the car on less than perfect roads, bushes all had to be replaced every 6 or 7 years (I had it 18 years in the end so replaced them twice) as the rubber had perished from age. Adjusting the dampers one or two clicks had a different impact on the handling as the bushes aged (I didn't realise this until I built the second car, see next paragraph)

Second Striker is fully rose jointed, the suspension is now only controlled by the dampers/springs which makes road use sooooo much smoother (smooth track is still great). With the car on stands and the dampers disconnected the wheels can be lifted up and down smoothly and with ease over the full range of travel...just seems to 'feel right' IMHO. Adjusting the dampers a few clicks has a consistent effect even to this amateur driver

When fitted correctly metalastic bushes have a rising rate effect and I am not sure that is right on a light weight 7 style car. You can measure this and tune the suspension to 'cope' with this but why should you need to? How many well sorted 7 cars do you see with rising rate springs?

Including build time the joints are now 5 years old (only down 1000 miles, similar to the old Strikers use though) and they are all still in A1 condition. If they had been metalastic bushes I would be thinking about replacing them all in the next year or two due to age

To me:

Pros of rose joints
the suspension just works so much better
Cons of rose joint
they cost more (but then I would cut back in other areas to cover this cost if need be)

Pros of metalastic bushes
cheaper initial outlay
Cons of metalastic bushes
will wear out, even if not used
do not allow proper suspension control

Never used poly bushes so can't comment on them.

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davew823

posted on 5/9/19 at 10:36 AM Reply With Quote
rose joints

A good compromise is a combination of both. Use the rose joint on the axle attachment side and the rubber bush on the chassis side. This allows axle adjustment and isolates the frame from the noise and vibration. Also install "Seals-it" on the rose joints. This can easily extend the life of the rose joint by 2 or 3 times. davew823
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MikeRJ

posted on 5/9/19 at 11:44 AM Reply With Quote
quote:
Originally posted by peter030371
When fitted correctly metalastic bushes have a rising rate effect and I am not sure that is right on a light weight 7 style car. You can measure this and tune the suspension to 'cope' with this but why should you need to? How many well sorted 7 cars do you see with rising rate springs?



The force required to twist the bushes is a tiny fraction of the force required to compress the spring. Remove the shock and you can move the bottom arm up and down by hand, put the shock back on and you'd struggle to move it more than a few mm.

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coyoteboy

posted on 5/9/19 at 01:39 PM Reply With Quote
Guess it depends on the bush, I can barely move the arm on one of my cars without the spring, but by the same token, deflection in any of the other axes is relatively easy too, making them a bit miserable from a control perspective. A swift pull and I can deflect my tin-top contact patch 10mm backward.





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peter030371

posted on 5/9/19 at 02:05 PM Reply With Quote
quote:
Originally posted by MikeRJ

The force required to twist the bushes is a tiny fraction of the force required to compress the spring. Remove the shock and you can move the bottom arm up and down by hand, put the shock back on and you'd struggle to move it more than a few mm.


When I was young free and single and had nothing better to do at weekends I did measure the force on one corner of the car and although I don't recall the figures (it was nearly 20 year ago) I remember it was a few % of the spring rate on the same corner. Maybe the ones JP fitted on my Striker were different (he never did follow anyone else). By 'feel' the amount changed with the ageing of the rubber in the bushes, hence I replaced them all twice during my ownership.

Use rose joints and its a few more % that doesn't change/ is controlled and is in your favour when it comes to predictable handling over time

Obviously if the cost of new rose joints when (or if) they wear out is an issue to you then accept the compromise of the cheaper bushes. They clearly do work as many, including me on my old Striker, use them but rose joints just seem better in so many ways/ Personally its a choice I made and has given me a car that is better for my use

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Bluemoon

posted on 5/9/19 at 02:15 PM Reply With Quote
^^ Poly bushes and metalastic bushes are different... Poly bushes also come in different hardness to add to the complication. If poly bushes require much force something is wrong and should be investigated.

Metalastic are more compliant, poly bushes can vary from compliant to rock hard, Rosejoints are rock hard. Some suspension geomterys rely on the "compliance" to stop binding and would lockup with rose joints...

As usual, there is no "correct" answer, just different compromises.

Dan

[Edited on 5/9/19 by Bluemoon]

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JimSpencer

posted on 6/9/19 at 06:59 AM Reply With Quote
quote:
Originally posted by davew823
A good compromise is a combination of both. Use the rose joint on the axle attachment side and the rubber bush on the chassis side. This allows axle adjustment and isolates the frame from the noise and vibration. Also install "Seals-it" on the rose joints. This can easily extend the life of the rose joint by 2 or 3 times. davew823


This or a variation thereof

But not because one is 'better' than the other.

But because it allows you to align / set up the car properly once it's built, shimming brackets or worse still cutting them off and moving things (Got that T shirt ) is a right PITA, build adjustability in at the design stage and then 'make it as straight as you can' gives you a solid foundation to get a good handling car IMHO.

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Oddified

posted on 6/9/19 at 06:44 PM Reply With Quote
Assuming the car is to be more performance orientated, then any bushes would be fairly stiff any way so the difference between a few bushes and rose joints is negligible. As Jim mentioned above, making the suspension adjustable is also far far easier with rose joints.

Ian

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J666AYP

posted on 7/9/19 at 12:29 AM Reply With Quote
Thanks for all the info gents, has been very helpful.

Right I have started building again (sigh). I am in the process of building my rear uprights/hub carriers then I can start on the wishbones. I'm going to be using polly bushes on the car end and rose joints/spherical bearings or whatever they are called on the spinny rubbery end. Will alow for some dampening of vibration and at the same time be easier to adjust.

This leads me onto my next question... I have started my uprights and it's going very well so far, the only issue I have is that the rear lower wishbones wont be horizontal to the ground without some complicated changes that have there own problems. Would it be a real issue to have the lower wishbones angled up towards the hub by a little bit? Probably a 3/4"-1"from inner mounts to the mounting on the upright?

I guess this is the price for doing things a little bit differently

[Edited on 7/9/19 by J666AYP]

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J666AYP

posted on 7/9/19 at 04:32 PM Reply With Quote
Ok scrap the 3/4"-1" its 10mm that the lower wishbone is raised by towards the hub. Is this going to be a problem?
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Oddified

posted on 7/9/19 at 09:40 PM Reply With Quote
quote:
Originally posted by J666AYP
Ok scrap the 3/4"-1" its 10mm that the lower wishbone is raised by towards the hub. Is this going to be a problem?


Short version of effect is a lower roll centre, but that's only a part of the overall picture and without knowing other factors such as weight distribution and cg i wouldn't say good or bad.

Ian

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J666AYP

posted on 8/9/19 at 10:25 PM Reply With Quote
Cheers mate, have got the gap down to +/-3mm now so fingers crossed...
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