>> RE What size tyre for MGB wire wheels - Help
The original tyres from England came with the 165SR14 markings. Nearly all
passenger car tyres sold today are sized using the metric or P-metric system
of measurement which includes section width, aspect ratio, type of contruction,
rim diameter and, on many newer tyres, a load index and speed rating.
I didn't have a problem finding the 165SR14's for my old '66 B, but you can
do better than that! Let's break this down first:
165 = Section Width
The width of an inflated, unloaded tyre as measured from sidewall to sidewall,
not including protective ribs, raised designs or lettering. Section width
varies with the width of the wheel rim on which the tyre is mounted. For every
1/2 inch increase (decrease) in rim width, add (subtract) roughly 0.2 in, or
5 mm, from the section width.
S = Speed rating
The S, T, and V are speed ratings corresponding to maximum allowable speeds
as follows:
Q = 99 mph H = 130 mph
S = 112 mph V = 149 mph
T = 118 mph Z = over 149 mph (Triumphs need not be concerned)
Not all tyres sold in the USA have a speed rating (e.g., P155/80R13). Speed
ratings appear in one of two forms, depending upon the marking system used.
The ratings appear as a letter preceding contruction type (195/65VR15) or
following the load index (195/65R15 91V).
R = Construction type: R for Radial, B for bias ply.
14 = Rim Width is the distance between rim flanges in contact with
the tyre.
Now that we are all tyre sizing experts, let me say that I found the stock
rubber too thin! I currently run 175/70 14's all round and prefer the handling.
Handling is a very subjective performance parameter, and only you can decide
what "feels" best. I know a few madmen that run 185/70 14's and they look
nice and squat, but they have a way of scraping the inner wings on bumps, the
clearance is just marginal.
In this measurement system the middle figure (70 or 75) is the aspect ratio,
commonly called the tire's series. It refers to the tire's cross sectional
profile: the ratio of the tire's section height to its section width,
expressed as a percentage. A '70 series tire has an aspect ratio of 70%.
If you're considering converting your original equipment size to one of a wider,
lower profile, choose a size close in diameter and with at least the same load
carrying capacity. A tyre with a different diameter will affect vehicle
height, ground clearance, effective gearing and speedometer accuracy.
The 165SR14 can use a 4.5" to 5" rim, and will have an approx overall diameter
of 24.5". Let's say we had the very common 175/70 14's on the B. To keep
the rims and go lower profile we would want 205/60SR14. But the clearance
will kill that! The next option with increasing rim size is 205/55SR15.
Wouldn't that look good!
To sum it up, my preference for the B is 175/70SR14's. And special thanks to
my trusty Euro-tire pamphlet. It is a wonderful reference. Good Luck!!
- Skip
Cusack@gumby.msd.ray.com (508) 858-5492
'72 B roadster
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