Soap Box Suspension Set Up

[Brucey]

O.k, I've spent way more than I ever intended and have now aquired the following for my Soap Box Racer.

 

4 x Kart steering arms, bearings and chassis brackets

2 x 20" BMX wheels (36 spoke) with discs and cable operated calipers

2 x 20" BMX wheels (42 spoke)

1 x Kart Steering column, track rods and rose joints.

 

Lots of square hollow and round hollow steel.

 

I intend to have front wheel braking and adjustable tracking on the rear wheels (the tracking and steering arms are similar to Graeme Smith's soap box).

 

I have cut off the kart stub axles and adapted them to accept the M14 x 1 BMX wheel axles and mounted this assembly to the steering brackets (usually a fixed part of a Kart chassis)

 

My questions are:

As I don't have suspension (similar to a kart), should I put camber on the front and rear wheels? I can't think of an easy way to make this adjustable so was thinking about fixing 2 deg negative camber per wheel to allow for tyre movement.

 

What effect does castor angle have on steering (self centering?) and what would be considered a good value?

 

Please bear in mind I want minimal drag and rolling resistance at all times.

 

Any advise would be appreciated before I start cutting metal!

 

Bruce.

 

 

[myothercarsa2cv]

Argh Brucey, still have that Julie brake. Also found an HS33, could probably get a pair of those... (hydro rim brakes, but couldn't let them go for free!).

 

No expert on setups, but any camber on bike hubs would probably not do the bearings any good as they aren't exactly heavy duty, and will have relatively a lot of leverage acting on them - they're big wheels, 20". Bike wheels will have least rolling resistance with no camber - least tyre contact, and least load on bearings. Get the tyre pressures right too, 30 psi max I would say...

 

I *think* you need the castor to be leaning back, so to speak, to get self centering. Not too much mind, my 2cv snaps due to it's mad castor. Have you got the Ackerman effect dialled? That could really do the biz for the steering. A touch of toe out might also be good on the fronts.

 

John

_________________________

 

Bugsy: '82 2cv6 (Back on the road!!! 😬)

Talloulah: '08 1.6K Classic (Grubby )

[Brucey]

Cheers John

 

My Son is picking up a Trials push bike for me tonight (in an attempt to improve my poor motorcycle trials riding!) so may be interested in the HS33's anyway! At 50, I may find I'm getting too old to learn this bunny hopping stuff!

 

My fear with having the wheels dead vertical is the way the side forces will act on the wheel (which doesn't usually take anything like the force I will be subjecting them to)

 

Also, when I watched The Gadget Show, (with Gail Porter 🥰), the front wheel rim wobbled like mad under hard cornering. I recon this was a geometry problem caused by no camber. I was working on the principle that a 2 deg camber should have little affect on a road going BMX tyre footprint. I have also pumped the tyres up to 80psi . That should keep the rolling resistance down!

 

Bruce.

[peterg]

with Gail Porter 🥰

 

surely you mean she's one of the most irritating women on TV at the moment and we skip through all her bits on the Gadget Show (thank god for PVRs)

[u01rsb]

Cut the nobbles off those tyres like the old chap in the World's Fastest Indian (great film to watch for speed freaks) to cut down rolling resistance.