By Roger Marble
If a tire is being designed for a specific vehicle manufacturer such
as Ford, Chevy, Toyota, or BMW, there will be a number of tires
submitted by competing tire companies all trying to deliver the best
overall compromise in performance characteristics. Please note that all
original equipment ("OE") vehicle manufacturers have slightly different
requirements but all make similar requests for performance improvements
in many areas. In the future I will use the term "OE" to include these
car and pickup manufacturers.
is a good time to talk about some of the various trade-offs the engineer
is faced with when trying to meet conflicting goals and customer wants.
I am sure we would all like an RV that has all the interior space and
amenities of a 40’ diesel pusher but gets 25 mpg and can be driven down
crowded city streets without knocking off our mirrors. Oh yes, it should
also cost under $30k. Well, Bunkie, that just ain’t gonna happen in real
The same goes for a tire that handles like an
Indy tire, is as quiet as the proverbial mouse, has great off-road
traction, is good for 100k miles, and costs $25. One thing few people
realize is that most if not all performance characteristics are a
compromise. For example, if you improve wet traction you probably hurt
fuel economy unless you use a special type of rubber that costs double
per pound and is more difficult to process. If you improve handling you
might hurt ride and noise. When you improve noise you can significantly
increase the cost of making the molds used in manufacturing. The cost of
a tire mold can be as low as $10,000 and can approach $100,000 each.
Depending on the production volume needs, a tire manufacturer could need
30 or more molds. The list of trade-offs goes on and on.
competition for a tire application might start three or more years
before scheduled start of delivery with two to five tire manufacturers
competing for the contract, knowing that only one or two will end up
being selected to actually provide tires. The costs associated with
building and testing special prototype tires can run in the hundreds of
thousands of dollars and are absorbed by the tire company. The only way a
tire company can afford this type of activity is by landing a contract
for a few hundred thousand tires so the costs can be spread out.
“OE,” an RV manufacturer may only need a couple thousand tires, so a
custom tire designed for a specific RV would be cost prohibitive. Since
the RV manufacturer won’t be trying to get custom tires, it doesn’t
have staff engineers working on developing specifications for such
tires. The RV company will in all likelihood either take what comes
already on the cut-away chassis or the bare chassis for Class-C or A
vehicles, and in the case of trailers, may buy the tire with the lowest
cost that can meet tire size requirements and expected delivery
For RV applications the one thing that is in
the control of the manufacturer is “Reserve Load.” This is the
difference between the load placed on each tire with the RV normally
loaded and the load capability of the tires at specified inflation.