Choice of spring rates is an interesting topic. All this talk of 90N springs got me thinking�

80N/mm = 8.2Kg/mm at the spring

Approximate linkage rate = 3:1 (3x the movement at the wheel compared to spring compression)

Rear wheel will roughly compress by 1mm for every 2.7Kg of weight added (we�ll use 3Kg to keep the maths straight forward.

Let�s assume the rear half of an unloaded bike is 100Kg so this will give you about 33mm of static sag. Add a rider of 100Kg, whose weight (for arguments sake) is split 30/70 front/rear, then there�s an extra 70Kg acting on the rear spring bringing the total to 170Kg. This will give a dynamic/rider sag of 57mm. Not quite the ideal third of suspension travel which would be around 65mm.

You would need to add approximately a further 25Kg of weight on the rear to reach the theoretical ideal of 65mm dynamic sag. This would equate to roughly an extra 35Kg of rider weight if you assume a 30/70 split.

Very roughly, based on a number of assumptions, an 80N/mm shock spring (zero preload) will be suited to 195Kg weight at the rear, 100Kg is the bike and 95Kg (70%) of the rider�s weight. Therefore this spring would suit a rider who weighs in at 135Kg (or a 90Kg rider with 32Kg of luggage).

A 90N/mm (9.2Kg/mm) will give 65mm of dynamic sag with 215Kg of weight at the rear, 100Kg being the bike and 115Kg (70%) of the rider�s weight. This equates to a rider weighing 164Kg (or a 90Kg rider and 52Kg of luggage).

All the above is based on no preload, so dialling in a bit will increase the payload further yet maintaining the same sag. 10mm of preload for example on an 80N/mm spring will buy you and extra 25Kg of luggage, or 37Kg or rider. On this basis, I would suggest that an 80N/mm spring is more than enough for any rider up to 120-130Kg (18-20 stone) in weight and certainly too much for a sub 100Kg (<16 stone) rider on an un-laden bike (who would need the 70N/mm standard option). Remember, you can always dial in preload, but you can�t take it away � you�re always best erring on the side of a lower rate than a higher one when selecting a spring. There�s probably a good reason Ohlins don�t sell a 90N/mm spring anymore� and that�s because hardly anyone actually needs one!

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