Ducati Sporting Club UK > Model Specific - Discussion, Technical Problems and Help > 999 / 749 > Suspension set up help

[Gizmo]

Originally Posted by Felix

Don't know who said that but that's utter ********. The spring is directly dependant on the load transfer under acceleration and the amount of static weight on the rear wheel. The only difference horsepower makes is the amount of load transferred to the rear. If the bike wheelies, for instance, the entire bike/rider weights is transferred to rear wheel.

The forces acting on the swingarm are actually a pulling force from the the front chainwheel to the rear sprocket, the pivot position influences what effect they have on the suspension. this technique is used on Full sus mountain bikes to stop pedal induced bob, the pull counter acting the downward pressure, thats bit over simplified because i can't really explain exactly what happens for each pivot option but what important is where the pivot is in relation to sprocket, on a motorbike it gives squat typically on an mtb it counteracts squat but i agree horsepower just alters the amount of load.

spring weight is critical, if you are heavy you need heavier springs, compression damping ( depending upon adjustor range) has hardly any impact ( less than 10% of spring) rebound has more effect. adding clicks of compression is a placebo, i doubt many riders can actually tell 4 - 5 clicks and if the spring is way out its pointless anyway. K tech can explain all of this and adjust your shocks damping to match the spring, you may need shim changes if the spring alters by a large amount, a stiffer spring needs more rebound damping to control it and you may go beyond the adjustors range.

I added a tech article to upnorth on this based upon stuff i'd found it is quite complex but worth a read
http://www.ducati-upnorth.com/tech/suspensionspring.php

[Felix]

Yes, the pro or anti-squat forces do come into play, but on most sports bikes the are designed to cancel themselves out to a large extent by an appropriate swinging arm pivot location. The maximum contribution of additional load on the rear suspension due to squat forces are roughly 10%.

If you really want to confuse yourself, have a read of this book:Motorcycle Handling and Chassis Design. I've made extensive use of his design analysis software in my own bike project. Seems to work alright.