Hi Listers -
Well with all of this brew-hahahaha about tyre sizes I guess that I'll have
to put my two cents worth into the word stew. I used to work in tyres (damn
uncomfortable it was, it was!). While not exactly an oracle, I've bead
pinched enough fingers to know enough to make an educated opinion.
Contrary to the beliefs of many rodders and racers, the factory pays REAL
engineers lots of money to calculate the best way to do things. Now I know
that many will argue that the factory folks are into cost cutting and will
include only the barest minimum equipment that will do the job, BUT that is
usually only true with loss leader economodels. The missunderstanding seems
to come from the criteria used to do the original calculations. The MGB had
a number of aspects for the engineers to consider when these cars were
designed. Ride heigth, clearence in motion, ride smoothness, steering ease,
sound level, unsprung weight, as well as handling. Very early MGBs came
with cross-ply tyres that translate to 155X14 in radial terms though in
reality they were still taller and narrower than that. Thems Morris Minor
size and they can't effectively keep a Minor on the road let alone a
heavier and much more powerful MG. The factory upgrade was 165X14 usually
Dunlop SP4 radials.
We used to fit Michelin XAS asemetrical 165s to Bs with great results and
their effective road holding and standard size would allow the owner to
lower the car by an inch or two and fit sway bars and Koli shock kits.
American Racing 14X5 1/2 eight spoke mags were the correct offset and only
slightly wider than stock and the cars were greatly improved yet lost
little of the characteristics that were designed in at the factory. We
also used this same combination on Datsun 1600/2000 roadsters with simular
results. That was then and this is now!
When 70 series tyres became available in a bunch of sizes we started to
experiment. The best MGB combination seemed to be using standard Datsun
240Z rims or stock spec aftermarket mags and 185/70X14 tyres. 70 series
tyres are easy to calculate. Go down two sizes, 185/70X14s are the same
height as 165X14 only as wide as 185X14s would be. If you had enough
fenderwell clearence and your rims were wide enough, these would work
better than the originals without much loss to the other criteria. Early
MGB wheels weren't wide enough and "pinched" the 185/70s so they weren't
totally on the ground flat but 185/70s seem to be alright on later Rostyle
wheels. The Datsun roadsters taper at the rear and provide less fenderwell
clearence so this upgrade required raising the rear suspension or cutting
out the wheel arches - not good. The only thing that seemed to change was
an increased steering wheel effort, and this didn't seem to bother other
people as much as it did me.
Today the sizes have changed again. I understand that the closest thing
that you can buy from the corner tyre store is a 175/75X14 though these
still appear to be slightly taller and narrower than the old 165X14s.
My best advise: instead of spending lots of money and screwing around with
re-engineering your car (unless you are REALLY into that) buy the best
quality high performance standard sized tyres and install the best shock
kits you can find and afford. The car will be much nicer to drive in
day-to-day use and you can spend your savings on paint and interior or
taking your sig. other on wicker basket, wine and cheese weekends.
Rick Feibusch
Automotive Journalist/Appraiser
Venice Beach, California
310-393-6605
Fax:396-1933
1959 Morris Minor Convertible
1960 Morris Minor Saloon
1961 Morris Minor Pickup
1969 Chevy Malibu Sport Coupe
1969 Chevy Malibu Convertible
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