2026-09-18

Last modified: 2026-09-18 09:48:31

Cyclecar

How long does the tube for the beam axle need to be?

• 650mm straight section in the middle
• plus curve of 200mm radius for 50 degrees, x2
• plus 90mm straight section at the end, x2

So about 265mm per straight section. If I want to have excess tube so that I can mess up a bend and still have another go, then I need at least 650 + 265 * 3 = 1445 mm.

Annoyingly Rapid Metals don't have any 36mm round tube.

The Gemini Karts ad says they use "1 3/8″ x 14 SWG CFS 3 BK drawn tube" https://www.geminikarts.co.uk/product/cyclekart-front-axle/

• 1.375" = 34.925 mm
• 14 SWG = 2.03 mm thickness

So I guess 35mm tube is fine, given that I measured the clamping bolts as suitable for 36mm.

Rapid Metals do have 35mm tube, but only 2mm wall thickness and I was hoping for 3mm. But maybe this is a good opportunity to use 2mm instead and save 1/3 of the weight.

If it's 1.15m long then it will be about 1.9kg with 2mm walls and 2.7kg with 3mm walls, so saves nearly 1kg.