Andrew Ritchie, inventor of the Brompton folding bicycle, once said that the perfect portable bike would be "like a magic carpet...You could fold it up and put it into your pocket or handbag". Then he paused: "But you'll always be limited by the size of the wheels. And so far no one has invented a folding wheel." It was a rare -- indeed unique -- occasion when I was able to put Ritchie right. A 19th-century inventor, William Henry James Grout, did in fact design a folding wheel. His bike, predictably named the Grout Portable, had a frame that split into two and a larger wheel that could be separated into four pieces. All the bits fitted into Grout's Wonderful Bag, a leather case. Grout's aim: to solve the problems of carrying a bike on a train. Now doesn't that sound familiar? Grout intended to find a way of making a bike small enough for train travel: his bike was a huge beast. And importantly, the design of early bicycles gave him an advantage: in Grout's day, tyres were solid, which made the business of splitting a wheel into four separate parts relatively simple. You couldn't do the same with a wheel fitted with a one-piece inflated   tyre. So, in a 21st-century context, is the idea of the folding wheel dead? It is not. A British design engineer, Duncan Fitzsimons, has developed a wheel that can be squashed into something like a slender ellipse  . Throughout, the tyre remains inflated. Will the young Fitzsimons's folding wheel make it into production? I haven't the foggiest idea. But his inventiveness shows two things. First, people have been saying for more than a century that bike design has reached its limit, except for gradual advances. It's as silly a concept now as it was 100 years ago: there's plenty still to go for. Second, it is in the field of folding bikes that we are seeing the most interesting inventions. You can buy a folding bike for less than PS1,000 that can be knocked down so small that it can be carried on a plane -- minus wheels, of course -- as hand baggage. Folding wheels would make all manner of things possible. Have we yet got the magic carpet of Andrew Ritchie's imagination? No. But it's progress. We can learn from the text that the wheels of the Grout Portable  _  .
were difficult to separate could be split into 6 pieces were fitted with solid tyres were hard to carry on a train