2026-09-10

Last modified: 2026-09-10 21:14:57

Cyclecar

I've welded on the leaf spring mounts:

And I'm pretty sure this gives enough clearance between the spring and the chassis rail for the axle to be mounted on top of the spring instead of underneath, which then means the uprights for the steering don't need to come up so far.

And copied into CAD:

Update: looking at the picture in CAD it is clear that the shackle angle is much too shallow. I think the shackle gets fully horizontal long before the spring is flattened out, probably I need a longer shackle. Probably I should have welded the mounts further back.

I think the shackles want to be 80mm long instead of 60mm long.

I'm going to bring the pit bike wheel geometry into CAD and have a go at the uprights.

This guy has a CAD model of a pit bike wheel hub! This may save time. https://www.cyclekartclub.com/forum/cyclekart-tech-forum.2/pit-bike-17-wheels-cad-drawings-analysis.68720/

Annoyingly it doesn't seem to be available on grabcad any more.

Shopping list:

• 35x20x10 (or 9? or 11?) front wheel bearings
• 20mm EN8 steel for front spindles
• 4mm flat bar for making new shackles
• HDPE or something (Acetal?) for making bushes for the rear spring mounts
• longer rear axle shaft (how long?)
• 2x pit bike wheels
• 16mm EN8 steel for kingpins, or alternatively M16 bolts with sufficiently-long smooth shanks
• 80mm box section, 6mm thick, >= 50 mm wide, for steering yokes

Todo is:

• make 80mm spring shackles
• fit new bearings to new pit bike wheels
• make bushes for rear spring mounts
• CAD front axle, uprights, kingpins, etc.
• make the front uprights etc.?

Front axle could be a bit like this?

The yoke on the end is 5mm thick in that pic, seems a bit thin.

I wonder if I will be able to bend the axle tube myself? Imagining a 3d-printed die and some means of pressing the tube into it? Doesn't sound impossible?

Looking at something like this for the kingpin/upright arrangement:

The yoke is to be cut out of a piece of 6mm box section, 80mm tall. Kingpin is 16mm. There is room for a thrust washer at the top, and (not modeled) the vertical piece of tube should have enough clearance to put a HDPE sleeve or something inside it for a bearing.

Bot suggests Acetal aka "POM" aka "Delrin" is superior to HDPE because it is stiffer and doesn't creep.