I wonder how many people when faced with 2 products, one with an A rating and one with a B rating ever ask, what’s the actual difference between them? I’m sure most people’s thought processes are that A is obviously better than B so that’s what I should go for. It’s exactly the same with spin speeds, 1600 rpm is faster than 1400 so it must get laundry dryer and it must be better ..

I share your suspicion of the spin ratings. As with ‘efficency’ they don’t tell you anything very useful unless you know how they are arrived at.

If one machine extends the spin for several minutes, it will presumably get a higher rating, but will leave your clothes more creased! The force involved, as I indicate above, is a straightforward calculation based on diameter and rpm, the more the merrier in both cases.

I think A,B,C ratings are generally pretty useless – for instance, A-rated ‘low-energy’ lightbulbs produce an entirely different quality of light to their D-rated counterparts, and use far more energy in manufacture, are transported from China and create hazardous waste!

Just linearly, but they do go up, so all other things being equal, the bigger the drum, the better.

The centrifugal force (centripetal, if you’re being pedantic) does follow a square law, so doubling the speed quadruples the force. This is not trivial – clothes spun at 1200 rpm experience an eye-popping 386G, while 800 rpm gives a more relaxed 171G (these all assume a drum diameter of 48cm). I bought a 1600 spin machine because, nerd that I am, I did the maths and discovered that the extraction force would be nearly 700G, assuming it really did go at the advertised speed. Note that this is nearly twice as much as the force at 1200 rpm, so I maintain that speed is the important thing, although a big drum will help as well.

I found a nifty on-line calculator here: http://www.centrifuge.jp/cgi-bin/calc-e.cgi

If you do some research on commercial washing machines and extractors, you will see that they use a G-force rating. This is a simple algorythim based on RPM and drum-diamator.

The sales-folks like to use spin-speed but it would be more realistic if the industry setteled on G-force rating which allows buyers to compare machines of different drum-diamators and spin-speeds with a common numerical factor.

As drum-diametors get bigger, the G-forces go up exponentially. I would not be surprised that at some point, the G-forces of 1600 RPM and large drums start to breach some safety-factors. (Not to mention bearing-limits!)

I expect that there is not much more to gain from spinning faster than about 1200 RPM with todays larger-diametor drums anyway.