Ulitimate Fixie coming soon. Guy Martin Speed

Wouldn't a longer wheelbase / longer trail give you more stability?
What impact would the width or the tread of your tyres have?

Yes it has as long a back end as I could make for this reason. Wide tyres roll and work far better for this type of thing, big strong solid wheels was even more important, bigger, skinny road wheels would flex to much under load and speed. The reason we go wider tyres will become apparent on the show.

it already have a longer wheelbase, relative to traditional stayer/speed record bikes.

getting the overall handling including wheel and tyre size to be as close to a TT motorbike is propably a good idea.

I never imagined guy martin could pedal that well. did it take a lot of training?
No he had to train for fixed, infact he now owns the Hope/Rourke bike I built. He loves fixie now, won't ride anything else.
He is a proper qulaity bike rider, I was stunned he is a very strong cyclist