barry@fountain.net wrote:
> So, I've finally got the money for five new Pirelli tires, and it
>seems
> like the P600M+S 185/14R are the way to go. But what's the diference in
> aspect ratio mean for a '78 MGB? The choices I've seen from the various
> posts range from 60 to 70, and the options for the P600 are either 55,
> 60 or 65. Does it make a difference whether I get the 60 or 65 tires?
Can't say enough good about Pirelli P600 tires. And the company has an
awful lot going for it too. Just check out their home page:
http://www.pirelli.com/
I'm sure you will agree that these guys are 'car guys'.
Anyway, tire sizes. The first number is always supposed to be the width
of the contact patch in millimeters. As their are 25.4 millimeters per
inch, then a 185 series tire should always be about 7 1/4 inches wide.
The second number is the aspect ratio and is thought of as a percentage
and means the tire sidewall is 'aspect ratio' percent high as it is
wide. Thus the 185 series tire should have a sidewall height of
aspect 65 = 4 3/4
aspect 60 = 4 3/8
aspect 55 = 4
If you double that number (top and bottom of tire) and add the rim
diameter (14 inches for a 'B') you should be pretty close on the height
of the tire. I say pretty close as the 'standards' can be +/- 15%. You
care about the height of the tire to keep the speedometer equally
inaccurate after the swap. Also, as it effects gearing, different tire
sizes can effect acceleration and top speed -- shorter tires quicker;
taller tires faster.
Pirelli lists the 65 series tires for 14 inch wheels in only 185 and 195
series when buying P600's.
If you can find someone who sells or can order the Pirelli P6 tires, you
can get them in anything from 175 to 205 by 70 sizes (T-speed rated).
According to Pirelli, they are still available. The P6s are the
predessors to the P600s and it is still a fine tire.
It's a pity that the performance tire folks are ignoring the 13 and 14
inch tire sizes. To have much of a choice you have to back all the way
down to the Pirelli P400 Touring tire. The P300 tire is the cheapest of
the lot but I am not all that impressed with their handling quite yet. I
put them on the TR6 based on price and, so far, I am not thrilled with
the handling. But I haven't quite gotten used to the car yet, either.
Anyway, do the math of your original tire size and your desired tire
size then ask the list if anyone is running a tire that size on a 'B'.
You can do some great comparison shopping at
http://www.tirerack.com/tires/tirebran.htm
Bob Allen, Kansas City, '69CGT (Pirelli P6s), '75TR6 (Pirelli P300s)
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