Howdy subey-ga,
Indeed, bearings are involved to transfer the weight on the frame of a bicycle
and a truck to the wheels.
If you will scroll to the bottom of this "Bikes Not Bombs" manual, you can see
a basic diagram of a bicycle hub and axle set.
http://www.bikesnotbombs.org/eab-pdf/eab_man_ch5.pdf
Note there is a set of bearings on both sides of the hub that handles the
transfer from the frame to the axle.
Friction is always a concern when it comes to bearings. Modern bearings are
lubricrated and sealed. New designs, like this one from Zipp, are made with
friction in mind.
http://www.zipp.com/Portals/0/Technology/Documents/A%20Note%20on%20BearingTechnology.pdf
"Most bearings utilize a brass waffle retainer within the cartridge to ensure
the balls remain evenly spaced throughout the cartridge, this also keeps the
balls from rolling against each other, but it does introduce a point of wear,
heat buildup, and friction, as the ball is forever rolling against a metallic
element. Zipp was the first company to spec a plastic retainer made from Teflon
so that each ball is properly located in the cartridge, but the balls never
have any sliding contact with any metal components."
Zipp has some very nice diagrams of bearing cartridges in the above document
that you should examine.
Bicycles use a "cup and cone" style of bearings, but the newer models use the
cartridge style, shown in "Sheldon Brown's Bicycle Glossary" as presented on
the Harris Cyclery website.
http://sheldonbrown.com/gloss_ba-n.html
"Bearings used in bicycles are usually of the cup-and-cone type, but many newer
bicycles use cartridge bearings."
There is a nice picture on the above page that illustrates the two types.
Cars, and it follows, trucks, are no different, except the sealed bearings are
just larger. Here is a diagram of the rear axle of a Porsche 944, as seen on
the AutomobileAtlanta website.
http://www.autoatlanta.com/model/944catalog/944.46-2.jpg
The part marked with a "5" is a ball bearing and the part marked with a "7" is
a cylinder roller bearing.
There are some larger images on the DRIVEWIRE website of the cylinder roller
bearing type mentioned above.
http://images1.drivewire.com/live/K800027798SKF.JPG
http://images1.drivewire.com/live/K800048842NTN.JPG
Please note that these don't use ball bearings, but rather cylinder bearings.
Timken is a large manufacturer of automobile, truck and other axle bearings.
http://www.timken.com/
They make the "Wheel Boss" wheel end system for heavy trucks.
http://www.timken.com/industries/automotive/products/wheelboss/
"The WHEEL BOSS line includes an adjusting nut, a patented HDL? grease seal,
a non-vented hub cap and Timken tapered roller bearings. Each WHEEL BOSS
component supports longer bearing life, greater fuel efficiency and reduces
maintenance costs."
Note that the above system uses a tapered roller bearing, and the above page
has an image of one of this type.
A better picture of a tapered roller bearing is shown on this Timken page.
http://www.timken.com/products/bearings/products/P900.asp
"With our P90 bearings, we?ve taken the concept of power density ? increasing
the bearing capacity-to-weight ratio ? to provide you with a lighter, more
fuel-efficient solution for your axle designs."
You should browse the Timken website in detail for more on the manufacturing
process, as it shows that with higher load demands, so the materials used to
manufacture the bearings have to improve.
http://www.timken.com/products/bearings/
Better steel and surface treatments are used to ward off the wear that is
encountered. Roller bearings are used to spread the load across a wider
surface, and tapered roller bearings are used to handle increased torque.
But, even on ball (cylindrical) roller bearings, the contact surface is an
always changing one, so the theory is that wear is spread, hopefully evenly,
across the entire surface of the bearing.
If you need any clarification, please feel free to ask.
Search strategy:
Google search on: bicycle bearings
://www.google.com/search?q=bicycle+earings
Google search on: truck bearings
://www.google.com/search?q=truck+bearings
Referenced the Timken website.
http://www.timken.com/
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