robert weeks wrote:
> While perusing my dog eared copy of Robert Bentley's "The Complete Official
> Sprite / Midget 1967-1974" I noticed that the specified tire size for
> radials on these cars are 145SR-13. The PO had mounted 155SR-13. I know
> that this throws the speedo off, but in which direction? Am I going faster
> than the speedo says or slower? Im guessing slower, but math was never my
> strongest area
Well, assuming the world is perfect, you are going slightly
faster.
The rule is supposed to be that tires with no aspect ratio
markings have an 80 aspect ratio.
If the world was perfect, that would mean your slightly-wider
tires have a slight-taller profile as well. This means that each
turn of the tire goes a little farther than your car would
normally go. Therefore, same RPM, same speedo reading as before,
but you are going a little faster.
But in reality, tire diameters between makers and models
and so on are rather loose. You may find your tire diameter
is more, less, or the same as the original. All in all,
it's not likely to be very far off at all for such a small
difference.
> Are there other advantages/disadvantages to running larger tires? Better
> gas milage? Worse gas milage? Smoother ride?
Well, if your tires were large enough to make a difference,
think of it as having a lower ratio rear end (or a very mild
overdrive). So in theory you get slightly better mileage
and lower revs-at-speed but at the expense of acceleration.
> I just checked British Wire Wheel and they
> don't even carry them, the 155's are the smallest they stock.
I still have 145s on my Midget, but hardly any midgets
I see still do. I wouldn't worry. Many people I know are
running 185s without modification, with 165s and 155s
being the norm.
--
Trevor Boicey
Ottawa, Canada
tboicey@brit.ca
http://www.brit.ca/~tboicey/
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