Tubular radius arms- bearings.
Turbo Mini Forums

Hi all. I've been planning it for ages, and nearly ready to start making up my radius arms from CDS tube, I've made a channel shaped steel beam so everything is going to be custom, but just can't decide what type of bearings to use.

Anyone got any thoughts?

Easiest IMO is to use double row sealed ball bearings, very heavy duty (singles for the inside maybe), but they don't resist much end thrust, perhaps just a brass thrust washer fitted either end would provide the gap fill and side loading resistance?

Taper bearings would be best really as they resist side loading, however I don't know how you would fit them in a given gap (between mounting brackets) as they need to be torqued up which means the length has to be adjustable.

It's being built for rallying, so needs to be strong, hence why I'm not using rose joints. I'll also be making them wider than standard to give better triangulation against the heelboard/beam, for when the hydraulic handbrake is being used and the car is going sideways over rough ground.

I'm thinking just fit standard ball bearings as they are piss easy to change and will make it all a lot easier!

Cheers,
TC

www.topcatcustom.co.uk

what makes you think rod ends aren't up to the job?

I seriously doubt it!

The way they would have to be mounted, and the fact that there would probably be thread sticking out which is a weak point. Also depending on the design they may cut into valuable space between the tyre and beam (is always tight there even with standard components and big tyres).

www.topcatcustom.co.uk

I understand your concern, I thought that myself until I saw how a rod end fails. Amazingly the thread seems to be the strongest part.
What about a rose joint (without a thread) rather than a rod end pressed into your tube and maybe even a circlip for extra peace of mind like these http://www.ebay.co.uk/itm/5-8-COM-10-T-PTF...=item255be38f52

I seriously doubt it!

Guess the side loads would be an issue with ball bearings, you would need some kind of washer like on the standard radius as you said to limit this.

Maybe better off with what Paul suggested.

Edited by minivan63 on 19th Sep, 2012.

Paul, that was my third option! I am making some custom rear subby mounts for a prototype new Mini with those at the moment, but I thought to myself that with a classic mini radius arm set up, both bearings will be dead true to each other so there is no point using spherical bearings which are good for allowing mis-alignment but no real need on a "true" axle in effect.

The 2 plus points I can see with a spherical rod end is they they have a 100% contact face making them strong and are easy to install, but are not as free rolling as a ball bearing and thus the fit has to be perfect into the tube else the outside can spin instead of the centre part. The same applies with the centre fixing- fit has to be perfect to stop spinning on the shaft.

www.topcatcustom.co.uk

Just use standard trailing arms rebuild kits then, theyre well proven

I seriously doubt it!

If you use POS rod ends, then you might have problems. If you use the high quality Rod ends, then you will not have problems. If you have any doubts about the strength of rod-ends, ask yourself what is so different from a front suspension double-wishbone setup as seen on many custom race cars (aside from two, instead of one arm of course)
For example:


Take a look at the pictures in the link above - if these two wishbones are able to take a little under half of the forces from decelerating one of these cars, I think you'll find that two rose joint are ok for your rear arms.

I also suggest you head over to your local grass-track course. Rear swinging arms have been used on these for ever, and developed into what they are using today. NONE of those guys use the mini bush / thrust washer / needle roller system on custom setups - they ALL use shperical rod-ends. Why re-invent the wheel?

Edited by turbodave16v on 19th Sep, 2012.

Dave, I know what you mean, the grasstrack minis look like a decent lightweight setup, but they don't use all the available width to the ends of the heelboard like most minis do, may not matter but I'm just picturing sliding sideways into ruts etc the amount of force going into the set up, which only stage rally cars really have to put up with.

It was just the protrusion into tyre area that put me off threaded rose joints when using full width.

Paul, I may use standard bearings, but make up longer shafts so I can make wider arms, they can be lighter then and a whole lot stronger just by using more width.

Thanks for the input

www.topcatcustom.co.uk

Forget grasstrack Minis, try twin bike engined 350bhp hatchbacks that also use trailing arms with rose joints, and spend 1/2 the lap sideways over lumps bumps and ruts. Yes theoeretically rose joints have some limitations, but go up a size and they are more than strong enough for the job in hand.

TC, if you look 16 images down on my page you will see my version of this very setup. Dont reinvent the wheel one of these Autotest Car endured the greatest side load possable for a mini, these rod ends are M10 size made by SKF they are boom proof this car has done 200+ autotests with no signs of wear or brakage

http://www.turbominis.co.uk/forums/index.php?p=vt&tid=447470

Paul, I saw that build thread, very interesting. I like your use of the rod ends mounted on the car instead of on the trailing arm, it does mean having the thread sticking through the heelboard though which is why I dismissed the idea originally, however I don't see why it would be a problem actually! Will think about that, might be the best solution, I reckon a big "O" ring around the thread between the heelboard and beam would stop any shit going through into the car too.

Tom I know what you mean, and know that most single seaters are built with rod ends, but the triangulation is a lot better with wishbone type suspension than with a trailing arm, but I'm still probably worrying too much.

There's been some fantastic input in this thread cheers again people.

www.topcatcustom.co.uk

TC, We really had no problem with water or crap getting in where the holes in the Heal board are drilled just use Alloy washers instead of the standard steels ones and they will seal grand.
The pull out strength of these rod joints are amazing. During a test session of this car I over shot a throw and slid sideways into a concreter curb at +30mph the only damage done was a bent Stub axle (the only original Mini Bit I used) and a broken alloy wheel, I really would have no hesitation using them in any rally situation, One thing I will suggest tho is that you defiantly do as you say and make each arm the full with of the heal board as in my own computer modelling this transformed the load paths on the bearings to nearly 100% Compression/Tensile as opposed to the standard length witch is very Radial in its force path.
cheers
Paul.

Excellent cheers Paul, I think my rear beam may be a little overkill too now.....

4mm folded mild steel...

Hole saw to the rescue!

www.topcatcustom.co.uk

paul did you ever say what that car weighed ?

Medusa + injection = too much torque for the dyno ..https://youtu.be/qg5o0_tJxYM

Where i used to work, we used to use rod-ends on bottom arms. fitted to forest spec, pug 205 rally cars.
Often checked for wear but lasted for quite a while. They were expensive rod ends with grease nipples and also fitted with boots to stop as much dirt ingress.

David.

Robert I did not but I think its some where around 440 and 450 only weighed it on a Sand and Gravel weigh bridge so not very accurate, It just got some new alloy rear arms and front hubs as well as some split rims so we are probably near 430 now I would hope. sorry for the Post Hijack