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Lowered-floor minivans are a bit of a modern marvel - push a button, and the door opens, and a ramp deploys, allowing seamless access for one to roll in using a wheelchair.  However, such seamless access isn't without its drawbacks, namely when it comes to vehicle ground clearance, where the needed lowered floor dictates a scant 5" or so between the underside of the floor and the road under no-load conditions - add a powerchair's weight and other passengers to the van, and that 5" of ground clearance dwindles to where clearing slightly raised manhole covers and driveway lips can be tough.

Indeed, ground clearance can be an issue for those who transport a heavy powerchair and multiple passengers in lowered-floor minivans.  However, for many, a simple, off-the-shelf component swap can make a meaningful difference in maintaining optimal ground clearance under load in lowered-floor minivans.

Most lowered-floor minivans feature conventional rear suspension, with leaf springs and shock absorbers.  The leaf springs handle most of the vehicle's weight, while the shock absorbers control vertical wheel movement, as in traveling over bumps.  When one places a lot of weight in a lowered-floor minivan, the shock absorbers compress, limiting wheel travel, and the leaf springs flatten - all of which lowers the entire minivan chassis, decreasing ground clearance.

Now, if the leaf springs handle much of the vehicle's weight, wouldn't adding additional helper springs stiffen the suspension, keeping the minivan from squatting under load?  Absolutely - but the entire ride quality would then be "stiffer," effecting shock absorber function, and decreasing overall comfort, creating a jarring ride.  As such, increasing the leaf spring capacity with helper springs would help maintain ground clearance, but would also detract from overall ride quality and handling.

This leads to addressing the issue at the shock absorbers.  Stock shock absorbers on most lowered-floor minivans are a fluid-filled, dampened cylinder, where they extend and compress as the wheels travel up and down.  Of course, because shock absorbers connect from the axle to the chassis, weight in the vehicle alone can compress them, lowering the minivan - and the weight of a powerchair and passengers can compress them to an almost non-functional level.  And, this is where a solution comes in.

As a substitute to traditional standalone shock absorbers, companies like Monroe make "load adjusting shock absorbers (as with Monroe's Sensa-Trac Load Adjusting series), in that it's an advanced shock absorber with a secondary variable rate spring around it, specifically designed to dramatically improve heavy load characteristics, without detracting from overall handling.  Specifically, the variable rate spring helps support the load, while the leaf springs and shock absorbers perform optimally.  In fact, Monroe states that its Sensa-Track Load Adjusting shock absorbers can support a cargo load up to 1,200lbs. while maintaining original ride height.  And, at under $300 installed at most auto service centers, load adjusting shock absorbers are a very economic way to increase the practicality and usability of a lowered-floor minivan.

On lowered-floor minivans, consumers and manufacturers alike use load adjusting shocks as an upgrage toward dramatically improving loaded vehicle ground clearance when a heavy powerchair and passengers compresses the stock suspension.  No, load-adjusting shock absorbers won't increase a maximum ride height of 5" or so, but they can come close to maintaining it under heavy loads, notably reducing the likelihood of bottoming out, as well as increasing overall handling - making for an all-around more usable, comfortable vehicle.  

Published 3/07, Copyright 2007, WheelchairJunkie.com