Why do some bikes wobble? Why do others go in a straight line? There is absolutely no coincidence, it is all down to the physics of frame geometry and depends heavily on what is then bolted to the frame by way of suspension and wheels.

There are rules – there are very many rules – some of which contradict each other, and some schools of thought are in direct conflict, but that'll help to widen the debate. The long and the short of it is that you can make your cruiser go round corners with little more than a bit of thought, some progressive shocks, decent rubber and some sportier tyre profiles and a bit of weight shaved off here and there, but what shocks, what difference do the tyre profiles make, and where is the best place to lose weight.

With a long hard look at what Erik Buell has achieved with his range of motorcycles, and a toe dipped into the water of radical theory – and it doesn't come much more radical than vertical forks – we put the European case for tightening up the chassis to get more from the bikes we love.

If you've ever wondered why the touring Harleys have reversed yokes and extended headstocks, what difference the seventeen-inch rear wheel on the Deuce will make, why there are two Dyna frames with different steering rakes - and why the Victory's rake splits the difference between them – or even why Buells have such a steep rake, you've found the right place.