Feature -
Understanding Tires...
by Byron R. Daugherty
Tires are a complete mystery.
First of all, Its difficult to imagine what sort of tire will fit the needs of your
driving habits. Sure, you can tell my dry weather driving habits by the scraps on the door
handles (No, my Fiero doesn't lean in corners that badly, I'm exaggerating!) But I require a
lot of good rain and snow traction as well. Getting a good answer about what is truly the
best tire for a Fiero is like searching for the Holy Grail--everyone has an answer but it
seems to come up lacking.
Writing on the (Side)Wall
To get closer to this answer, we
need to under stand a little more about the shoes were going to saddle our Fieros up with.
First, lets examine how to read a tire. A tire can give you a lot of information in all
those letter and number combinations. Check figure 1 to follow along.
Tire Size Designation
- This gives you the dimensions of the tire. In figure 1 the tire is 225/50-R-16.
225 is the tire tread width in millimeters, 50 is the profile or aspect ratio (ratio of
the sidewall height to the tread width), R denotes its a radial, and 16 is the rim
diameter in inches. See. Confusing, they use both inches and millimeters.
Speed Rating Index - The
speed at which the tire is designed to maintain proper dissipation of friction generated
heat. Some examples, H-Rated is up to 130 MPH the tire can resist temperature buildup,
which in turn avoid overheating of the tires which causes failure. Z rated is 149+. Some
people mistakenly believe that a Z rated tire has more traction than an H. This is no
always true as the rating is based solely on heat dissipation. It is true that a lower
speed rating can mean less road noise and a little more comfort.
Speed ratings: S=112 MPH / 160
KPH, T=118/190, U=124/200, H=130/210, V149/240, W=168/270, Y=186/300, Z=149+/240+
UTQG Marking - Uniform
Tire Quality Grading, a rating of tread wear, traction, and temperature resistance of a
tire.
- Tread wear is
specified by the manufacturers and, therefore, is most accurate in comparing tires of the
same brand. It is graded on percent, ex. a 150 grade tire is 1.5 times longer lasting than
a 100 grade tire (given same driving habits, etc.)
- Traction is
represented by a grade of A, B, or C with A being the highest. This is tested on the tires
ability to stop on a straight-ahead braking test on asphalt and concrete, no wet cornering
is tested. A means the tires performed well on both asphalt and concrete--B means
performed well on at least one and C means the tire performed badly on at least one
surface.
- Temperature Resistance
is also A, B, or C. It measures the tires ability to dissipate heat at high speeds. Grade
C is minimum for a passenger car under Federal Motor Vehicle Safety Standards. Temperature
Resistance ratings are not required on winter and light truck tires.
Original Equipment Code - Optionally on tires, this specifies of this tire meets the design and
construction specifications for car companies to be original equipment on certain cars.
Usually Porsche and Ferrari cars have these codes on their original equipment tires.
Now, you've understood some of the
markings and what they mean, and how that can show you a clearer path to understanding a
tire, you step into the muddy path of wanting to get slightly larger wheels with lower
profile tires for looks and handling. Does it cause a problem? Well, yes. Not only can you
risk damaging your car by placing improper sized or offset wheels on it, but if the wheel
and tire clears everything, you still might be messing up your speedometer and odometer.
Plus One
The "Plus 1" concept
fixes this problem. Looking at figure 2, we can see that if you add 1 inch to rim
size, you can obtain a close outer tire dimension if your go with a lower profile tire.
Remember the profile number from above? The percentage of the height of the sidewall of
the tire to tread width. If you set your sights on keeping that outer dimension the same,
you can put a larger rim on your Fiero with a wider, lower profile tire, and still come
within +/- 2 tenths of an inch difference in diameter, or +/- 4 tenths of a MPH
speedometer difference. Warning! Some 16" and 17" and above rims REQUIRE
suspension modification on the Fiero!
Tire Categories
Now lets get into specifics. You
are looking for a certain type of tire but are wondering what tires are closer to your
needs. Here are some tire "buzz words" you can use when shopping for the tire
for your needs and their qualifications.
Competition -
Autocross, Solo II or track DOT street legal tires. S, H, V, or Z speed rated and
12-17" rim diameter.
Ultra High Performance
- You want killer dry road performance, and have your snow tires in the garage. These
tires are going to be V or Z rated and a profile of 55 or lower.
Ultra High Performance
All-Season - Great performance in the sun, and enough to get you past rain and
snow without changing tires. These tires are M&S (mud & snow) rated, and are V or
Z speed rated, and profile of 55 or lower.
High Performance -
Great performance, but a little less noise and slightly smoother ride. Look for U or H
speed rating and profile of 60 or lower.
High Performance
All-Season - Same as above except for light snow & rain. M&S rated, U or
H speed rated, and profile of 60 or lower.
Performance All-Season
- Good performance, appearance and price. M&S rated, S or T speed rated. Profile of
60, 65, or 70.
Touring -
Performance, but comfort and low noise is important. M&S, speed rating of S, H or V,
and profile of 60, 65 or 70.
All-Season -
Basic tires to get you to work and back. M&S, speed of none or S, and profile of 80,
75 or 70.
More Information
Now, lets throw some more
information into the mix. Compounds. Recently, large strides in rubber compounds have been
made that make a huge difference in tire longevity and performance. Yes, you think, the
stock Fiero tires were an unimaginable leap far beyond the old bias-plys of the 60s. But,
strides have been made in the past couple of years that far eclipse even that difference
in terms of traction and heat dissipation. Currently, Pirrelli and Continental tire
companies have developed compounds that not only give their high end tires incredible
traction in summer that rivals summer only tires, but whose wet and snow traction can
rival the best all-season tires today. These tires also have an incredible tread life.
Unfortunately, they also carry an unforgettable price as well!
Lets go shopping!
You're probably thinking to
yourself, "That's a lot of information, will I remember it when Im shopping for
tires?" Well, yes. Heres how. Keep this article handy, and call either the Tire Rack,
or Discount Tires Direct. Tell them your habits and information, and they will recommend
tires in your price range. Get a quote from them, then you can see if you can beat it
elsewhere, but you wont find the knowledge anywhere else as good. In fact, the Tire Rack
sends their employees 10 days a year to training for wheels and tires. You most likely to
get a good answer there first, before you hit the local K-MARTs auto department to buy the
generic specials.
Personal Testimony
When I first bought my '86 GT, it
needed tires. I took it to a tire place in Downers Grove, and told them what tires I
wanted put on. I had heard that Bridgestone Potenza HP41s, all-season high-performance
tires were good. Having lived with those crummy Eagle GTs and then GT+4s in the winter
before, I wasn't going to make that mistake again! My HP41s have lasted over 50,000 miles
and were incredible in the rain, great in the snow, and did well on the autocross course.
But now, they are too noisy (always had a lot of noise) and not much traction. We re-shod
our '87 with Pirelli P4000 Super Touring, a Touring tire, and man, you can roll down your
windows, and you still cant hear these tires on the road! They're more comfortable too, and
have great traction in rain. Unfortunately, you also cant hear these tires squeal when you
are sliding, rain or dry. Great tires for the "cruiser", not the
"bruiser". Our '88 has Eagle GTs in front and Dunlops on back. The previous
owner couldn't find all of one tire in stock where he had them put on at. They seem OK, but
the suspension is too different for me to voice a clear comparison. The Mercedes is the
best comparison of speed ratings. It came stock with Z rated Pirellis that seemed harsh,
but we replaced them with the same tire, only in a H rating. The car did not have any loss
in traction, dry, snow, or rain, yet the ride was less noisy and less sharp on bumps. My
choice for my '86. I'm going to go with a Pirelli High Performance All-Season tire, staying
with my H speed rating.
References
The Tire Racks Inside Track On-Line, Road & Track Magazine
(various issues), Discount Tire Direct. |