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Tire & Wheel
Plus Sizing
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![](3D"Tyres&wheels,plussizing_fichiers/image003.jpg")
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Upgrading Wheels And Tires For Fashion And Perform=
ance
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![](3D"Tyres&wheels,plussizing_fichiers/image004.jpg")
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By Kelvin Dodd
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Moss Motors offers Panasport wheels for
classic style and performance.
Plus-size fitments are available for many MG and TR applications (TR6=
+2
shown).
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I=
f concours-quality restoration is your thing, or you b=
elieve
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 improv=
ing
the looks and handling of your car, then read on.
There are two p=
rimary
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 Rubbe=
r
On The Road!
When most of our
classic cars were new, the factory wheels and tires were sufficient f=
or
the vehicles’ anticipated performance and to define their looks.
Nowadays, that original look may be dated, and the performance
expectations have increased to keep up with current trends of high-sp=
eed
stability and cornering. I’m a firm believer in skinny tires sli=
ding
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
performance-minded 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
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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.
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Some Popular First-Step
Performance Upgrades
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CAR
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ORIG.
WHEEL
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ORIG. TIRE
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UPGRADE WHEEL
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UPGRADE TIRE
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Spitfire/Midget
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4"
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155-13
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5"
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175/70/13
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MGB
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4.5-5"
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165-14
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5.5"
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185/70-14
195/65-14
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MGA,
TR4,
A-H
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4"
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165-15
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5.5"
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195/65-15
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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 ra=
tio,
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 h=
ave
taller sidewalls than 50-series sizes. Modern performance tires are
generally only available in low-profile 70-series and lower aspect
ratios.
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Even these mi=
nor
upgrades can cause
fit problems with the limited clearance in narrow wheelwells.
Correct-offset wheels must be used to ensure that the tire is cente=
red
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.=
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How To Measure
Wheel Offset
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1. Find the overall wi=
dth of
the wheel. Divide this width in two to give the centerline depth.=
2. Lay a straightedge across the inner rim of the wheel.
Measure from the straightedge to the mounting rim of the wheel.
3. Subtract the centerline depth from the mounting rim dep=
th.
This gives the offset, which is now usually designated in
millimeters.
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Positive offset
indicates that the hub center (mounting surface) is toward the outsid=
e of
the car; negative offset indicates that the hub center is closer to t=
he
brake drum.
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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
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Here are some typical
offsets necessary to keep the wheel centered for popular British
sportscars:
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Typical Wheel Offsets=
Sprite/Midget: +20mm
MGA/MGB: +22mm
TR2-TR6: +6mm
TR7-TR8: +15mm
Spitfire: +20mm
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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 movemen=
t is
limited. You can’t have the same look and performance without ma=
king
the same sacrifices.
What Are Some Of
The Pitfalls?
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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 mu=
ch
less of a problem, and 5.5” wheels can be fitted with wide tir=
es
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 wi=
th
fat, wide-oval tires to their cars.
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Austin-Healey: Big Healeys’ wheelwells on the BN2 onward a=
re
wide open. Their rear suspension has limited movement, which allows
fitting wider wheels and tires without major rubbing problems. Howe=
ver,
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 advi=
sed.
On all models, check fender clearance.
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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 loweri=
ng
the suspension may allow extra clearance, but suspension travel can
cause clearance issues, particularly on the left-hand side of the c=
ar.
The inner bumpstop structure and front swaybar can cause clearance
issues for wheels that have too much positive offset. Under hard co=
rnering,
the rear axle will move sideways, aggravating clearance problems. On
this car it is very important to have the wheel centered in the wel=
l,
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.
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MGA: Like
the Healey, the rear wheel arches are open and can accommodate tire=
s up
to 195 cross-section without problems.
TR2-TR4=
A: Fender clearance is an
issue, and a wheel with less positive offset is required to clear t=
he
front brake calipers. This restricts the maximum wheel width.
TR250-T=
R6: 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-fen=
der
clearance can be a problem on lowered cars.
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TR7/TR8: A positive-offset wheel is required, but the
wheelwells are quite spacious. 205/60-13 tires will fit on the orig=
inal
factory alloy wheels without any clearance problems.
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Spitfire: Open wheelwells allow the use of 5.5” wheel=
s.
These can be mounted with 185/70 series tires, but they may stick o=
ut
beyond the fenders.
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P<=
/b>lus-Size Wheel Options=
One way to in=
crease
the availability of high-performance tires is to increase the diame=
ter
of the wheel, which allows the use of lower-profile tires while sti=
ll
maintaining the correct overall tire diameter. Only baseline modern
vehicles are equipped with 13" and 14" wheels, so high-pe=
rformance
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 high-performance 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 l=
oad
may be greater.
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![](3D"Tyres&wheels,plussizing_fichiers/image005.jpg")
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MGB:
An inch-larger wheel allows the use of high-performance low-profile
tires without compromising looks and performance. A popular perform=
ance
option for the 14” wheel is the 195/60-14 tire, which has a mu=
ch
smaller diameter than stock. This reduces the overall gear ratio and
does not fill the wheelwell from front to rear.
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MGB Plus Sizing
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STOCK WHEEL DIAMETER: 14”
Typical Tires: 165/80-14
(diameter 619.6 mm)
185/70-14 (diameter 614.6 mm)
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+1 WHEEL DIAMETER: 15”<=
span
style=3D'font-size:10.0pt;font-family:Arial'>
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.
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+2 WHEEL DIAMETER: 16”<=
span
style=3D'font-size:10.0pt;font-family:Arial'>
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
with modified rear fenders and some type of axle
location device such as a panhard rod.
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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=
8;
performance tire has a much smaller diameter than stock.
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TR6 Plus Sizing
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STOCK WHEEL DIAMETER: 15”
Typical Tires: 185/80-15
(diameter 677 mm)
Performance Alternative: 195/65-15
(diameter 634.5 mm)
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+1 WHEEL DIAMETER: 16”
Tire Choice: 205/60-16
(diameter 652 mm)
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TR7/TR8:
The look of the “wedge” is really improved with more mode=
rn
tire and wheel combinations. This “shape of things to come=
8;
really was ahead of its time and looks dated mainly due to the smal=
l 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.
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TR7/TR8 Plus Sizing
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STOCK WHEEL DIAMETER: 13”
Typical Tires: 185/70-13
(diameter 589.2 mm)
Performance Alternative: 205/60-13
(diameter 576.2 mm)
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+1 WHEEL DIAMETER: 14”<=
span
style=3D'font-size:10.0pt;font-family:Arial'>
Tire Choices: 185/60-14
(diameter 577.6 mm)
195/60-14 (diameter 589.6 mm)
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RECOMMENDED +1
205/55-14 (diameter 586 mm)
Not=
many
tire options available
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+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)
Rec=
ommended
+2 size
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What If I Have Wire Wheel=
s?
Although the cl=
assic
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 alter-native to converting to bolt-on
wheels for maximum strength and a look that shouts CLASSIC PERFORMANC=
E!
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&#=
148;
spline-drive 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 wi=
der
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
specified for the MGC. The exception is the Austin-Healey, with front
2” drum brakes: Where 60-spoke wheels foul the brake drum, the w=
ider
MGC wheels will fit without a problem.
The 72-spoke 15=
x5.5
wire wheel was originally fitted to the TR6 and the necessary reduced
offset may cause tire-rubbing on the outer fender of cars originally
fitted with 48- and 60-spoke wheels.
Center-lace whe=
els
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 the=
se
wheels are often called “Cobra” wheels and look stunning on=
a
TR250 or TR6.
Tires and wheel=
s 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. E=
ach
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 betwe=
en
one tire size to the next may be insignificant compared to the proble=
ms
caused by tire-rub when cornering.
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![](3D"Tyres&wheels,plussizing_fichiers/image001.gif")
![](3D"Tyres&wheels,plussizing_fichiers/image002.jpg")