It has been established that trucks and SUVs handle poorly and usually have an uncomfortable ride. Those with soft rides have to be jacked up pretty high to maintain the carrying capacity with soft springs. There is a better solution:

Trucks should have car-like front tires and two sets of wheels and tires under the bed, one for no-load conditions and one for hauling conditions. The no-load tires would be lightweight, with independent suspension tuned for car-like handling and ride. The full load wheels would be mounted on a rigid axle on very stiff springs. The system would be designed such that with no load in the bed, the full load set of wheels would be 2-3 inches off the road, reducing unsprung weight. Adding weight to the bed would naturally cause the heavy duty wheels to come into contact with the road. The result is a truck with carlike ride and handling with no comprimises on load carrying capacity. This may also increase fuel mileage by decreasing tire rolling resistance under most driving conditions.

Furthermore different gear ratios could be used for each set of wheels, adding to the efficiency of the system.
-- gabe, Jul 11 2004

(?) This very capability is quite common among Swedish trucks http://gustafssonsa.../grafik/lastbil.jpg
[FarmerJohn, Oct 04 2004]

You do see 'drop down wheels' on some triple axle aric tractors, but at well over 5 tonnes, you're going to struggle to get it to 'handle like a car'. To prevent simply crushing the front tyres and ruining the roads you run on, you'd have to use twin wheels like you see on the back of transits.

HGVs also ride on 'air bags', which are only really able to adjust height, not stiffness.

Adding another comlete drivetrain could be tricky also, and add even more weight and cost!

With gears well into the double figure range, and automated manual transmissions that skip gears when able, there's not much need for different gearing. Removing the road speed governor when unloaded might make sense though.

Sorry, it's got to be a FishBone.
-- Skrewloose, Sep 22 2008



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