The Tool Box - Tires
By Bob Caffee
Jan 12, 2011 - 8:30:47 AM
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Tires... are you confused yet?
How do you read a tire sidewall and what does it mean? Of course all
manufacturers are going to put their name on it, and they will also put
the model, be it numbers or letters.
Now let's look at the size: we'll use 295 80 R 22.5. The 295 is the
tread width in millimeters, 80 is the aspect ratio of the tread vs
sidewall or sidewall height is 80% of the tread width, R means this is a
radial tire, and 22.5 is the wheel size, a 22 1/2" wheel.
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Next is the DOT code. This is required by law, and is usually 12
characters after the letters DOT. The first four are the manufacturer
and plant code, next four are at the discretion of the manufacturer, and
the last four are the date code in the format of wwyy. So 2309 means
the tire was made the 23rd week of 2009. The DOT code is required, but
not on both sides of the tire, so if you look and don't see it, it
should be on the other sidewall. You can tell how old the tire is with
this code, and it is not recommended that you run tires over seven years
old by the tire manufacturers association. I check the date code on all
tires before I buy them, and while I'm waiting for tire repairs, just
for fun I look at the tires in the rack that are for sale. It may
surprise you just how old some new tires really are.
The load range is next, a simple letter B thru M less the I. Load range
is tied to ply rating with this letter, B being 2 ply and each letter
gaining a 2 ply rating up to M at 22 ply. The weight capacity of the
tire is determined by the DOT in their testing and given the rating at a
specified air pressure. There is also the load index/speed rating. You
may not know what it is by looking but it looks kind of like this:
144/141L or 161L. The first is for a single/dual 6175 lbs/5675 lbs load
index, speed rating L or 75 mph max, the second is a wide single 10,200
lbs load index, speed rating L or 75 mph.
Speed ratings are on all tires you just have to know what to look for.
Truck tires are rated from B thru N less I, B being 30 mph and N being
87 mph. Now all these ratings and indexes assume the tires are properly
inflated for the load they are carrying and conditions the tire was
designed to operate in. There are other markings, but they don't have
any real meaning to those who didn't build the tire, like me.
Which tires are your best choices? There are so many options to choose
from it can be difficult to make a good decision. Do I want the longest
wearing, the best ride, am I going for the fuel savings? How about
traction? Is a deep lug right or do I want a less aggressive tread? What
kind of road conditions will I be encountering? Ice and snow, muddy
lots, nice smooth paved highways or all of the above? Will most of my
miles be out on the open highway or city delivery type driving? What is
the needed load capacity? Will I be running duals or wide base singles
on the drive axle and or trailer? Is price going to play a major role in
my decision?
There are lots of differing opinions on this subject, some informed,
some not so much. My opinion is just that, informed as much as I can be,
but still an opinion. With that said, here it is:
I would like a tire that gave me the best ride, traction, life, aided in
fuel savings and was CHEAP. We all know that's not going to happen, so I
have to decide what is most important to me. First my tires must be the
most fuel efficient I can get in the size I run. Once I find a tire
that meets that criteria I look at the rest of its specs. Looking at the
load range ( weight rating ) it must meet or exceed the axle rating.
For example, if you have a 12,000 lb steer axle each single tire must
exceed a 6,000 lb rating as most tires do. Dual tires on a 20,000 lb
axle each tire must handle 5,000 lbs (20,000 divided by 4). A wide
single on the drive or trailer axle needs to handle at least 10,000 lbs
each.
Ok my selection passes so far; let's look at the traction rating, which
is a rating that is hard to find. It is marked on passenger vehicle
tires but you have to ask for it on truck tires. Ratings are AA, A, B,
C, with AA being the best. This tells us how easily it will spin or
slide. The wear rating is also found on passenger tires but you must ask
on truck tires. The larger the number the longer it will last. The
temperature rating is again on passenger tires but you must ask on truck
tires. Ratings are A, B, and C, and tells us how well it will dissipate
heat. Traction, wear and temp ratings are not widely available so not a
deal breaker on a tire purchase.
Back to traction. The typical tread for a drive axle is a deep
aggressive lug style that is not usually good for fuel mileage, and
since we stay mostly on interstate highways a less aggressive tread is
more acceptable. If I were to run duals I would go with an all-position
tire on the steers and the drives, and those with a lift axle here also.
We run wide singles on our drives and the choices are limited, but
there are very good mileage-enhancing designs, and they are getting
better all the time. Some think lugs are the only way to go in ice or
snow; I say use what you are comfortable with, and if it gets too bad,
pull over and wait it out - safety is most important.
Life expectancy is a variable that is what it is. Typically the deeper
the tread the longer it will last. Tires will wear less the slower you
drive. Keeping the proper inflation pressures for the load you are
carrying helps also. Driving habits can also cause premature tire wear,
shortening the life. Keeping the axles aligned lengthens life, and not
just the steer axle - do them all.
Ride is also not real a real choice, however the higher the load/ply
rating the firmer the ride. The wide singles do give a better ride than
the typical set of duals: fewer sidewalls equals less stiffness.
Price is a component we cannot overlook. If you find the perfect tire,
it meets most of your "specs", the price vs. value must be considered.
All things purchased for your truck have a ROI (return on investment) to
be considered. If you buy the higher priced more fuel efficient tires
will they save enough fuel to pay the difference over the less expensive
tires? The more fuel efficient tires will probably wear out sooner than
the deeper treaded tires as they typically start with less tread. Price
isn't the real consideration, it's value. Mileage vs. miles...
something to think about.
For most, choosing a tire is as simple as replacing what you have with
the same thing. If you're happy with them, great. If you aren't happy
with what you have this will give you something to think about. In any
case, use the right tire for the job it's going to do. All-position is
just that, it will work on the steers, drives and trailer. Steer tires
only on steer axle (not too many manufacturers make these but there are a
few). Drive tires on the drive axle and trailer although you don't need
the traction of a drive style tire on the trailer. Trailer tires must
not be used anywhere but a dead axle, as the sidewalls are not designed
to handle torque from the drive or the side loads of the steer axle,
they are ok on trailers and tag or pusher axles lift able or not. Hope
this helps. Bob
By the way did you know the Michelin man has a name? It's Bibendum. Thought you might like to know.
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