5 replies to this topic

[beakerthemuppet2]

Hi

 

I am looking at making up some custom rear radius arms for my hill climb mini with the intention of losing a bit of weight and moving to a beam axle.

 

So I am not too worried about making up the beam axle as that is quite straightforward.

 

The radius arms and how the mate to the beam is something i have some quires about.

 

the first job is to make up a Jig to get the angles all correct prior to welding, I was thinking of building a couple of degrees negative camber into the rear arm but I think I will just take care of this with some adjusters on the beam axle. I will be making them up from CDS steel which will accept the standard rear hub assembly though I am not yet decided on the method for mounting to the beam… I have seen people use the standard radius arm pin or a setup with rose joints

 

I believe other people have done something similar? If anyone on here tried this then any pointers or words of warning/wisdom would be appreciated!

 

[nicklouse]

well you seem to be all over the place here.

 

so what does the rule book say you can do?

 

if using the radius arm pin I guess you will be using the radius arm.

 

if using rose joints you will be using constructed radius arms.

 

both require different thinking. toe in and out can be sorted with the rose joints. on the standard arm then have the inner mount bolted so you can pack it out to add toe.

 

camber. have that adjustment on the out side or none and have it preset. (how straight is the car). and what tyres and how much body roll you think you might get.

[beakerthemuppet2]

Yeah I have only just started thinking this through with any seriousness this weekend.

 

As for the rule book, well I am running Mod prod, so I believe I need to keep some form of the rubber cone in there, though it can be a drilled out piece of Swiss cheese that does nothing. Plenty of guys in my class run beam axle’s so should be fine. I will clarify this with a scrutineer at the next event.

 

Kinda leaning towards using the “constructed” radius arm with rose joints over the conventional radius arm with the pin. Mainly because I think it’ll be simpler to implement.

 

But it should be an interesting project for over the winter.

[nicklouse]

come on read the rules. "springs are free"  if you had to keep some form of rubber cone then you could not use a beam.

 

using the standard arm is the easier option by a LONG LONG way. but a little heavier.

 

see my build thread for a beam.

[beakerthemuppet2]

MSA bluebook states for mod prod:

 

"The original type of suspension must be
maintained (e.g. twin wishbone set-up cannot replace a
single wishbone suspension; a sliding pillar cannot be
replaced by a MacPherson strut; a trailing link cannot
be replaced by wishbones or coaxial springing)"

 

I took it that you can add a strut in to “assist” the original suspension but the original suspension must remain in some form.

 

Though it may be that I am misinterpreting it… it’ll still be a swinging arm after all and i have never ever actually had a scrutineer look under the back of the car so they might not even be bothered.

 

anyway thanks for the advice, i'll have a look at your build thread, might clear the fog a bit.

 

thanks

[nicklouse]

You missed this bit.

12.8.1. Additions and modifications to springs, shock

absorbers or suspension height are free.