Im going to start out with some good wide needle bearings and see what happens. Assuming I ever get that far
Just looking at some rocking arms for a new suspension set-up.
What sort of bushes would you recommend for the pivots?
In my mind I've got something like metro radius arm bushes or a similar OE manufacturers bush, Polyurethane bushes or taper roller bearings.
Any thoughts on the pro's and con's, or any other suggestions?
cheers
Chris
1980's Nissan Lemans sports prototypes used 5/8" sperical bearings, they were using something like 2000lb springs, with loads of
downforce.
Paul
[Edited on 18/8/07 by Cousin Cleotis]
Interesting.
Presumably the joints were placed vertically with the pivot running between 2 or 3 joints?
Before throwing out the whole rocking arm idea as a waste off effort, I looked at this quite a lot. Basically as the shock to wheel movement ratio
will inevitably be reduced any movement in worn or compliant bushes is amplified.
So as a result it looks to me to be necessary to go to metal or possibly nylon bushes of some sort so as to eradicate the compliance issues.
I've not actually worked on one of these systems first hand so this is from my research and calcs.
People who've actually built cars with this system may have a different view...
My riot uses standard mettalastic bushes as per the book. The motion ratio is 1:1 and the compressability of the bushes is low- I would have thought
much stiffer than the stiffness of the springs and I admit I don't see Dougs point for a non aero car.
Having said that racing Strikers which use the same system of top rocking arms use taper roller bearings I presume it is to reduce stiction in the
bearing rather than a compliance issue.
There are a couple of sites showing the system try Googling Striker
What it comes down to is that there is no perfect option for this application. Rubber will add a spring to the rocker which reduces the shock/springs
efficiency. Solid bushings will wear, and bearings will brinell from the shock loads.
Im going to start out with some good wide needle bearings and see what happens. Assuming I ever get that far
didn't one car use mini rear radius arm thingys.
errm, radius arm bush? you know the large thing that bolts onto the sub frame and the rear suspension arm.
(ok, i know thats a terrible description, just back from watching the mighty wigan althetic play a great game of footy, we're top of the league
and my brains stopped working)
Do you mean Lotus 33 style rocking arms ? They look good and have aerodynamic advantages but when you start looking are the structural issues they
become a little less attractive.
If I were doing it I would use the needle rollers and pivot pin from either BL Mini or an old Jag rear suspension.
Or if its is a rising rate rocker set as per current single seater practice some guys on the forum have tread that road already, some are truly
excellent some less successful, again a lot of structural issues involved but at least it by-passes the problem of wishbone flexing.
[Edited on 18/8/07 by britishtrident]
Yes, I guess I assumed you were talking about push/pull rod rockers and not a rocking upper a-arm. Which are you using?
Im using a pushrod setup because of how wide my front track is. There is no viable way to mount the coilover to both the control arm and frame.
Found this on the Fisher sports Car site
"Fit the rocker arm first, this pivots on an M12 x 225 bolt, using tube ferrule and nylon tophat section bushes. These bushes will be a tight
fit in the rocker arms, the tube ferrule must be 0.5mm longer than the bushed arm and must be able to move freely. If the ferrule is too tight in the
nylon, ream out with an old bolt slotted and fitted onto a drill with emery cloth. Some resistance is acceptable – too loose and you will have slack
suspension!"
To get good mechanical grip from the suspension I have 300lb springs on the front (40/60 f/r weight) and I just went out to the garage and jumped up
and down on the car. Rocker arms moved a lot but I coulden't see any deflection in the metalastic bushes.
quote:
Originally posted by MikeR
didn't one car use mini rear radius arm thingys.
errm, radius arm bush? you know the large thing that bolts onto the sub frame and the rear suspension arm.
(ok, i know thats a terrible description, just back from watching the mighty wigan althetic play a great game of footy, we're top of the league and my brains stopped working)
Sealed needle bearings
quote:
Originally posted by chrisg
anyone know the diameter of the mini/metro bushes?
I think I might go for needle bearings, the car is very light in weight and you wouldn't get any "sticktion" with those.
cheers
Chris 
Chris,
Let us know how you get on with sourcing bearings the arguement has convinced me to change to roller bearings. I disconnected the springs and there is
quite a bit of resistance to movement through the metalastic bushes and as you say with a light car, the riot has only 100kg on the front wheels, it
may well be noticable on the road. There is a bonus that the caster would be dead easy to adjust.
David
Chris , I think the formula27 used Metro radius arm repair kits rather than Mini ones . The Mini ones only have one needle roller bearing, the other end uses a bush that needs reaming to size
I'll let you know and Rusty - yes you're right I've just looked out my old F27 plans and they are the Metro bushes.
Cheers
Chris
I'm using poly bushes on my setup. A friend of mine who's building a menace (mid engined fury) was told by fisher that they switched from
bushes to needle roller bearings in their pivots, but then switched back to bushes as people complained the ride was too harsh with the bearings. I
expect racers would use bearings though.
Liam
That's interesting.
I wouldn't have thought that the pivots would have had any bearing(geddit!) on the ride quality.
I mean one end up the other end down via the coilspring/damper, if the pivot is having an effect on ride quality wouldn' t that mean that the
bush was flexing?
And if it is, is that a bad thing?
Shouldn't ride compromises be taken out in the spring/damper?
I've been regarding the pivot as purely that - a fixed point.
I'll look in to it!
Cheers
Chris
Using metallic bearings will effect harshness and noise transmission but much less on ride quality.
These are the bearings I used. They mainly take radial load but also except a small amount of lateral, I cant remember the exact terminoligy of the
bearings.
I used Loctite 638 to hold them into the housings.
Remember that the pivot sees twice the force compared to one end.....
John
PS Just found this on my website....
I chose NJ type cylindrical roller bearings. They give the major load rating in the radial direction with a small amount in the axial direction.
[Edited on 23/8/07 by JB]
[Edited on 25/8/07 by JB]
quote:
Originally posted by chrisg
I wouldn't have thought that the pivots would have had any bearing(geddit!) on the ride quality.
Hi sorry i forgot all about this discusion and the other related one.
In the other post i refered to problems accuring with the setup. This comment was aimed at the issue of the pivots and all the asosiated problems.
At the end of the day the only way ST got it to work better was to use needlle roller bearings.
But the big problem is the loads placed into the chassis. and how you go about sorting that without ending up with a chassis that needs replacing
every time you give the wheel a knock.
I had typed a long post detailing all the problems that the various manufacturers have had with this setup. But i think it would of just upset to many
people.
But one thing to remember is that if going with the rocker arm setup is that you will also require your dampers to be valved to suit that application
IE not off the shelf items. But Have any of the manufactureres done that and supply them with there kits ?.
cheers matt
most bearing dealers / stockists should be able to help, with regards load ratings suitability etc
on our rockers we run 2 cassete needle roller bearings inboard and and two needle radial thrusts outboard per rocker,
best regards
marc
quote:
Originally posted by marc n
most bearing dealers / stockists should be able to help, with regards load ratings suitability etc
on our rockers we run 2 cassete needle roller bearings inboard and and two needle radial thrusts outboard per rocker,
best regards
marc
quote:
That may not be so locost...
I would think that tapered roller bearing would be good for this application as long as the correct ones are chosen. Quite a few cars use trb's on rear radius arms as the basic design copes with radial and thrust loads which would also exist in a top rocker arm. Take a look at the old 1100/1300, Citroen XM, all variations of the Fiat Tipo chassis and a few others I can't remember.