pfouche's blog

Another GPZ FF - gets a new rear end

Last September I had a shake-down run to Monty's place in York, across to Kirby Lonsdale and home. Apart from learning a few things about chain maintenance, that trip reinforced the need to sort the rear end. To make space for the lowered seat, the rear wheel had been moved back. This was done by adding bolt-on swingarm extensions. Extending the swing arm messes with the suspension, so it felt a bit soggy at the back. The effective spring rate changes with a square rule, meaning that the response time to any bump was loooooong.

Another GPZ FF

With the t-max project slowing down and the prospect of another summer coming and going without an FF to ride – and that summer being in the south of France, I decided it was time to build something – anything (with a low COG and seat-back) – to get me on the road.

When we left Ireland and the truck came to take our stuff to France, I had been planning to sell the GPZ that I had been riding while the T-Max was off the road being FFed, but at the last minute there was room for it, so to France it came.

Mallory Approacheth

On the last Saturday before the Festival of 1000 Bikes at Mallory Park, this is what the bike looked like. Naked and lying in the sun - a good way to enjoy summer in Provence.

What you can't see is the closed fuel tap. I found that on the main highway.

Somewhere to sit

After initially building a seat mock-up to check ergonomics, I designed the seat sub frame in two parts.

Mating Hossack to T-Max Lump

Here the Hossack front end it being held up while the first pieces of the frame are fitted between it and the engine. The rear suspension has been disconnected to allow the lump down to ride height un-laden. The engine is supported by four temporary legs with adjustable feet. These allow the lump to be levelled. The bottom of the sump is set level and the ground clearance set to the T-max quoted ride height. As shown the wheel base is exactly as per standard. You can see that there is room to reduce the wheelbase.

The new front end interferes with the standard location on the air-box. You can see is sitting on top of the engine. The radiator is unsupported - the lump of wood fell over.

Actual Progess

A lot has happened since my last post. The first thing that happened was that I got actual prices for the billet forks. It turns out that CNC is not that much cheaper in Thailand than in Europe. I guess that makes sense as the point of CNC is to remove most of the labour which is the element that is cheaper in Thailand.

After going through the designs with Royce Creasey and faced with an imminent departure from Thailand, I redesigned the forks from 50 x 25 x 3 mm rectangular section steel.

Ready to cut steel (and aluminium) hopefully!

Ok this is the 'final' design - ready to go to the builders. The forks have been pared down to 3.6kg for the pair. They are 6061 – T6 alloy. FEA has been done assuming a 1 G stoppy with a 300kg all up weight all on the front wheel.

Hossack is not always as simple as it looks!

My first attempt at a Hossack front end was designed to be built as much as possible out of stock material - tube and box section - as possible. The ball joints were bought from a friendly neighbourhood motor factor for the princely sum of 600 baht (about €12).

ThaiMax - The story so far - Design Evolution

It started with a tape measure. That didn't get me too far, so I got a friend to photograph me on my T-max from as far away as possible with maximum zoom. It wasn't nearly far enough, but the results are acceptable.

ThaiMax - The story so far.

Since the re-build of BikeWeb has killed my links I am going to build this as a blog, rather than a book

I had been keeping this under my hat until such time as it appeared it would actually going to get off the drawing board.

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