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.|
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.
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