Does anyone know how insurance values increase / decrease?

[gorillaonabik...]

OK, insurance companies are unreasonable etc... but I cannot figure out how insurance works. This year, with an extra year of no claims, my motorcycle insurance increased by £350 TPFT. I am over 40, I have an extra year no claims, my motorcycle is simply a year older (CB1300) and yet every insurance company increased my premium.

In addition, I live in a relatively crime free area (for London) and have the usual own house etc...

As an experiment, I checked my car insurance which has been SORN'd for a year and a bit. THe insurance had decreased by £1800 TPFT!!!!! My car isn't particularly quick and is certainly not expensive so I was naturally a little puzzled.

It occurred to me I have absolutely no understanding of how insurance works from an increase / decreasing premium perspective so I thought I would find out. Does anyone know how this works?
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FZR400 (blown engine), ZXR750 (blown engine), ZX6R (accident), CBR600 which had engine issues after which I learned to change gear..., CBR900, CBR924 (stolen), CB600, CB1300 (everything blew up), BMW K1300GT (written off, hit from rear while stationary), Bandit 1250 for a couple of months, Triumph Sprint ST 1050 (nicked) and somewhere in there, I wrote off a Ducati 748 at Cadwell.

[Rogerborg]

A highly skilled and experienced insurance professional has re-classified the CB as a "sportsbike"?
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Biking is 1/20th as dangerous as horse riding.
GONE: HN125-8, LF-250B, GPz 305, GPZ 500S, Burgman 400 // RIDING: F650GS (800 twin), Royal Enfield Bullet Electra 500 AVL, Ninja 250R because racebike

[J4mes]

Depending on which company you use, the following occurs:

They throw a dart at a dart board with various prices on it.

Have a giant wheel of fortune on the wall

Pick the price out of a hat

Base the price on a pack of "Motorcycle Top Trumps"

Or other such random methods. You'll never know how they work it out!

[gorillaonabik...]