I measured my swaybars, and have 26 mm front and 16 mm rear. Since torsional rigidity is proportional to fourth power of diameter, this means that the stiffness of the front bar is 7 times that of the rear. So only 1/8 of the anti-roll force is at the rear. Why is this? I have looked around, and in "sports" suspensions the rear swaybars tend to be bigger, but on the other hand some modern independent rear suspensions have even thinner swaybars that would be doing hardly anything.
Where is the majority of the weight located in a vehicle? Which end controls the vehicles direction? Which end of the vehicle needs the most control during abrupt maneuvers?
Manufacturers typically bias a vehicle's handling towards understeer rather than oversteer as it is "safer" for a less experienced driver (the correct response to understeer is to lift off the gas to try to transfer more weig ht to the front of the vehicle) and having stiffer bars in the front helps with that.
Additionally, many front-engine vehicles do not have 50/50 weight distribut ion, so even for "neutral" handling you'd still need stiffer bars (and stro nger springs) in front.
Finally, the attachment points for the bars and the length of the various l ever arms in the system can mean that to have the same effective anti-roll effect, the bars may still need to be different sizes. Since the front whe els also steer, it makes sense that the attachment points for the front bar may be farther inboard on the lower control arm than the rear bar for reas ons of tire clearance, meaning that that point may move less for a given am ount of wheel travel, meaning that a stiffer bar is required. (however, yo u also need to take into account the length of the portion of the bar runni ng fore-aft as well and also treat that as a lever arm, although it will li kely bend a little as well.)
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