2026-01-08

Last modified: 2026-01-08 22:07:56

Car

I've mocked this up in FreeCAD:

Does that look reasonable? I don't know.

The engine model is based on rough perpendicular outlines of a ZS190 intersected with each other.

The wheels are 600mm OD, so for example 19" wheels with 2.5" tyre thickness, or 17" wheels with 3.5" tyre thickness.

Wheelbase is 2.0m and track is 1.4m.

It looks to me like there is plenty of room for everything. The engine is so small that there won't be any trouble accommodating a fuel tank, oil cooler, chain, sprockets, reversing gearbox, etc. in the same compartment. Plenty of room above the driver's feet for the brake master cylinders. Plenty of room for wheels to turn and suspension to move up and down.

The only thing that is tight is shoulder space in the cockpit, and it's not even that tight.

I kind of wish I'd taken a tape measure to the Haynes Motor Museum to see how big the Haynes Austin 7 Special is. In fact, let's look up wheelbase and track for a standard Austin 7, it's probably the same.

From https://en.wikipedia.org/wiki/Austin_7 :

• Overall width: 1.2m
• Overall length: 2.8m
• Wheelbase: 1.9m
• Track: 1.0m

So actually my wheelbase and track are both larger than an Austin 7! That won't do at all. I've been overly conservative here. Let's make it just slightly smaller than the Austin 7 in both dimensions and call it good?

I'm not sure these dimensions are accurate. I find that a 1.0m track is too narrow to fit two people inside without them overlapping. Were they just very tight to fit 2 people in? And the overall length of 2.8m seems much too long?

To start building this I'm going to need to acquire:

• ZS190 engine: £900 from ooracing but currently out of stock, £670 from Parker Racing but missing some sundries and potentially not checked as thoroughly
• 75mm by 25mm thin-walled (how thin?) steel box section for chassis: £60 for 6m length in 1.6mm thickness from themetalstore, perhaps just one piece would do it, check first in CAD
• 4x wire wheels, in 2 matching pairs, 17" to 19", preferably with discs on at least 2
• 4x tyres, worry about them later, expect £250 for all 4
• go-kart reversing gearbox: £80, eBay
• half-elliptic leaf springs: £160 from Cyclekart Workshop, currently out of stock
• fuel tank: £20, eBay
• sheet aluminium for bodywork: £120 for 2.5m by 1.25m sheet in 1.2mm thickness from themetalstore - unclear how many sheets required
• battery: maybe £50 depending on how fancy

And there would obviously be sundries like lights, wiring, chains, sprockets, nuts and bolts, mirrors, other odd bits of metal for axles etc.

But so far this comes to £1640 assuming engine comes from ooracing and only one sheet of aluminium required. Of which more than half is the engine.

I ordered the engine from Parker Racing on eBay with a £20 off coupon, so came to £650. May need to check it thoroughly based on the ooracing YouTube videos though. In particular:

• grease the starter chain
• check that the decompression lever works

And in fact it does come with the sundries that I thought it was missing, including gear lever (needed for the splines) and oil cooler.

From a quick estimate in CAD I think I'll need more than 6m of box section. Imagine 2x 2.4m long rails, that only leaves 2x 0.6m horizontal rails, and I think I'd want more than that. So maybe a 6m and a 3m length.

Bot has told me that to suit a 17x3.50 tyre I want a 17x2.15 rim, possibly up to 17x2.50, or for a 3" tyre you want about 1.6" or 1.8" rim.

A CG125 rear wheel is 17" x 1.6", so would take a 3" wide tyre. Also comes with convenient holes to bolt a disc or hub to.

OK, I got a matching set of 4 wheels in the end that were described as "HONDA CB125S CG125 H100 MT50 CL100 SCRAMBLER 17x1.60 REAR WHEEL RIM DOT 70-85 OE" - but I doubt they are truly rear wheels because there is nowhere for the sprocket to attach. They were £45 each, so £180 for the 4, and they are relatively tatty. I considered buying brand new ones at nearly twice the price but decided against, maybe I will regret that. The brand new ones came with sprocket carriers.