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By Kelvin Dodd
If concours-quality restoration is
your thing, or you believe that what
the factory offered is sacrosanct, then
this article is not for you. If, however,
you are open to change and are
interested in improving the looks and
handling of your car, then read on.
There are two primary reasons
to upgrade wheels from their original
sizes: increased performance and
visual impact. Obviously, the intent
of any change is to get the most out of
your car without breaking your budget
or creating more problems than you
already have. As in any modification,
a balance between cost, performance,
and drivability must be determined,
based on each individual’s needs. This
article will broadly cover some of the
positive and negative aspects of wheel
and tire changes.
Let’s Put Some Rubber On The Road!
When most of our classic cars were
new, the factory wheels and tires were
sufficient for the vehicles’ anticipated
performance and to defi ne their
looks. Nowadays, that original look
may be dated, and the performance
expectations have increased to keep
up with current trends of high-speed
stability and cornering. I’m a firm
believer in skinny tires sliding around
mountain curves: For me, the “new”
sport of sport-compact “drifting” was
pioneered by the MGs, Triumphs,
and Healeys during the street races
and rallies of the ’50s. But this type of excitement at low speeds may not be
everybody’s cup of tea, particularly
during rush hour.
Today, the many available wheel
and tire options offer increased
stability and safety for performanceminded
drivers, or the choices may
be merely adequate for those keeping
up with modern iron on American
freeways. Changing to a wider wheel
allows the use of wider, lower-profile
tires, which generally have far superior
handling characteristics compared
to the original-sized tires. Typically,
increasing the original rim width by
1” will allow the use of a slightly wider
70- or 65-series tire, the closest sizes
to the original 82-series (which were
the only factory-offered tires with any
kind of performance pretensions).
Note that the TR6 and MGB Limited
Edition were both equipped with
more modern wider wheels from the
factory.
A Quick Note On Tire Sizing
 Modern tires are listed in Metric sizes.
The first group indicates the nominal
width of the tire, called the section
width. The second group is the aspect
ratio, which gives the height of the
sidewall as a percentage of the width;
this is also referred to as the profile of
the tire. So, 70-series tires have taller
sidewalls than 50-series sizes. Modern
performance tires are generally only
available in low-profile 70-series and
lower aspect ratios.
Even these minor upgrades can
cause fi t problems with the limited
clearance in narrow wheelwells.
Correct-offset wheels must be used to
ensure that the tire is centered in the
wheelwell. Generic wheels and older
American “Mag” wheels often have
the incorrect offset and will cause
fitment problems, even with stock
tire sizes.
How To Measure Wheel Offset
- Find the overall width of the
wheel. Divide this width in two to
give the centerline depth.
- Lay a straightedge across the
inner rim of the wheel. Measure
from the straightedge to the
mounting rim of the wheel.
- Subtract the centerline depth
from the mounting rim depth.
This gives the offset, which is now
usually designated in millimeters.
Positive offset indicates that the
hub center (mounting surface) is
toward the outside of the car; negative
offset indicates that the hub center is
closer to the brake drum.
Here are some typical offsets
necessary to keep the wheel centered
for popular British sportscars:
Sprite/Midget: +20mm
MGA/MGB: +22mm
TR2-TR6: +6mm
TR7-TR8: +15mm
Spitfire: +20mm
By keeping the wheel centered
in the wheelwell, there is less chance
of the wider tires fouling the inner
fender, suspension components, or
outer fender—this is most important
with the narrow rear fenderwells of
most British cars. For street driving
where there is likely to be a lot of
suspension and body movement, it
is a good idea to stay conservative
on width. Otherwise, the smell of
burning rubber and the sounds of
tire-rub are going to accompany any
spirited driving. Make it a point to do
your test-driving with your spouse or
significant other in the car. This way,
you won’t experience the unpleasant
surprise of their added weight
causing the tires to rub.
If you want that maximum rubber,
road-racer look, be aware
that most racecars have had some
radical surgery and are often fitted
with stiffer springs and panhard rods
or other axle locators to ensure that
suspension movement is limited.
You can’t have the same look and
performance without making the
same sacrifices.
What Are Some Of The Pitfalls?
 Sprite/Midget: The square-arch
rear-fender cars have very restricted
wheelwells. Even a 165-section tire
is probably going to rub on the back
under hard cornering. The round
wheel-arch cars have much less of a
problem, and 5.5” wheels can be fi tted
with wide tires as long as the springs
do not allow the tire to contact the
fender lip. This led to many a Bugeye
that looked like it got mated to a
steamroller. Perhaps Austin moved to
the square wheel arches specifically
to prevent Americans from fitting
Chevy Vega wheels with fat, wide-oval
tires to their cars.
Austin-Healey: Big Healeys’
wheelwells on the BN2 onward are
wide open. Their rear suspension
has limited movement, which allows
fi tting wider wheels and tires without
major rubbing problems. However,
overly wide tires can spoil the clean
lines of the car when negative-offset
wheels are installed, which push the
tire edge past the fender lip. BN1
fenders are very tight, so wider tires
are not advised. On all models, check
fender clearance.
MGA: Like the Healey, the rear wheel
arches are open and can accommodate
tires up to 195 cross-section without
problems.
MGB: The rear fender lip on early
cars and lowered late cars is at the
widest point of the tire, so tire bulge
can be an issue. Raising or lowering
the suspension may allow extra
clearance, but suspension travel can
cause clearance issues, particularly
on the left-hand side of the car.
The inner bumpstop structure and
front swaybar can cause clearance
issues for wheels that have too much
positive offset. Under hard cornering,
the rear axle will move sideways,
aggravating clearance problems. On
this car it is very important to have
the wheel centered in the well, as
suspension travel and axle movement
can be major problems. Minor fender
clearance issues can be addressed by
rolling or grinding the rear fender lip.
TR2-TR4A: Fender clearance is an
issue, and a wheel with less positive
offset is required to clear the front
brake calipers. This restricts the
maximum wheel width.
TR250-TR6: Again, a less positive offset
wheel is required to clear the
front brake caliper; fender clearance
is improved and tires up to 205 cross-section
can be installed as long as the
car is not significantly lowered. Rear fender
clearance can be a problem on
lowered cars.
TR7/TR8: A positive-offset wheel is
required, but the wheelwells are quite
spacious. 205/60-13 tires will fit on the
original factory alloy wheels without
any clearance problems.
Spitfire: Open wheelwells allow
the use of 5.5” wheels. These can be
mounted with 185/70 series tires, but
they may stick out beyond the fenders.
Plus-Size Wheel Options
One way to increase the availability
of high-performance tires is to
increase the diameter of the wheel,
which allows the use of lower profile tires while still maintaining
the correct overall tire diameter.
Only baseline modern vehicles are
equipped with 13" and 14" wheels,
so high-performance tire availability
in these sizes is very limited. By
increasing rim diameter one inch
(+1) or even two inches (+2), the
availability of lower-profile highperformance
tires becomes much
greater. In some cases, larger diameter
wheels allow the use
of wider tires because the tires’
sidewalls don’t flex as much, so
clearance under load may be greater.
MGB: An inch-larger wheel allows
the use of high-performance lowprofile tires without compromising
looks and performance. A popular
performance option for the 14” wheel
is the 195/60-14 tire, which has a
much smaller diameter than stock.
This reduces the overall gear ratio
and does not fi ll the wheelwell from
front to rear.
MGB Plus Sizing
STOCK WHEEL DIAMATER: 14”
Typical Tires: 165/80-14 (diameter 619.6 mm)
185/70-14 (diameter 614.6 mm)
+1 WHEEL DIAMETER: 15”
Tire Choices: 185/65-15 (diameter 621.5 mm
195/60-15 (diameter 615.0 mm)
There may be clearance problems with this width of tire on some wheels.
+2 WHEEL DIAMETER: 16”
Tire Choices: 195/55-16 (diameter 620.9 mm)
205/50-16 (diameter 611.4 mm)
This width of tire could only be fitted to a car modified rear fenders and some type of axle location device such as a panhard rod.
TR6: Moving up an inch in diameter
allows the use of a wider wheel due
to increased suspension clearance.
Note that the only available 15”
performance tire has a much smaller
diameter than stock.
TR6 Plus Sizing
STOCK WHEEL DIAMETER: 15”
Typical Tire: 185/80-15
(diameter 677 mm)
Performance Alternative: 195/65-15
(diameter 634.5 mm)
+1 WHEEL DIAMETER: 16”
Tire Choice: 205/60-16
(diameter 652 mm)
TR7/TR8: The look of the “wedge” is
really improved with more modern
tire and wheel combinations. This
“shape of things to come” really was
ahead of its time and looks dated
mainly due to the small 13”-diameter
wheels. A number of sticky 205/60-13
tires are on the market, but increasing
wheel diameter gives the car a whole
new image.
TR7/TR8 Plus Sizing
STOCK WHEEL DIAMETER: 13”
Original Tire: 185/70-13
(diameter 589.2 mm)
Performance Alternative: 205/60-13
(diameter 576.2 mm)
+1 WHEEL DIAMETER: 14”
Tire Choices: 185/60-14
(diameter 577.6 mm)
195/60-14 (diameter 589.6 mm)
RECOMMENDED +1
205/55-14 (diameter 586 mm)
Not many tire options available
+2 WHEEL DIAMETER: 15”
Tire Choices: 185/55-15
(diameter 584.5 mm)
195/50-15 (diameter 576.0 mm)
205/50-15 (diameter 586 mm)
Recommended +2 size
What If I Have Wire Wheels?
Although the classic wire-wheel crowd
doesn’t have as many performance
options, they shouldn’t feel left out.
Here are some suggestions that will
get you going with even more style.
Spline-Drive Alloy Wheels: An
expensive option, but the best alternative
to converting to bolt-on wheels
for maximum strength and a look that
shouts CLASSIC PERFORMANCE!
Clearance is a major issue as
the 13”, 14”, and 15” spline-drive
wheels are 5.5” wide and there must
be enough clearance to the outer
fender for the wheel to be removed.
Just because a tire fits the rim doesn’t
mean you won’t need a body hammer
and cutting torch to remove the wheel.
A very tasty combination for the
MGB is a +1 package of a 15” splinedrive
wheel and a 185/65-15 tire. This
will clear on most cars; the larger
195/60-15 will likely rub under hard
cornering.
Wire Wheel Options: The first option
is to look at the factory racing history
and see if a wider wheel was available
as an option. In the case of the MGB,
the factory offered a 5.5” 72-spoke
wire wheel, which has the correct
offset to handle larger rubber without
clearance problems.
Most early cars originally
equipped with 48-spoke 15x4 wheels
can be easily upgraded to 60-spoke
15x4.5 wheels or even the 15x5 72-
spoke wheel originally specifi ed for
the MGC. The exception is the Austin-
Healey, with front 2” drum brakes:
Where 60-spoke wheels foul the brake
drum, the wider MGC wheels will fit
without a problem.
The 72-spoke 15x5.5 wire wheel
was originally fi tted to the TR6 and
the necessary reduced offset may
cause tire-rubbing on the outer fender
of cars originally fi tted with 48- and
60-spoke wheels.
Center-lace wheels are available in
15x5.5 for the small sportscar hub and
also for the larger Jaguar hub. These
wheels look stunning, but also have a
much-reduced offset. So, outer fender
clearance must be carefully checked.
The unobstructed rim was a highlight
of the AC Cobra, so these wheels are
often called “Cobra” wheels and look
stunning on a TR250 or TR6.
Tires and wheels are one of the
most popular topics for discussion,
and I hope that this article may
clear up some of the questions about
possible fitments. Each car is different,
so always check clearance before
allowing a tire to become damaged
and unsafe. If you are looking for the
ultimate in wide rubber, be ready to
do some body modifications; if in
doubt, stay conservative and minimize
headaches. The difference in handling
between one tire size to the next may
be insignificant compared to the
problems caused by tire-rub when
cornering. |
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