The new size will be just fine as far as the speedometer goes (speedo will
read about 2% too slow), but the new tires are 3/4" wider. That's NOT a
good thing in winter, and will negate some of the advantage of the winter
Actually, 0.7% too slow. The circumference of a tire is based on its
radius, not its sidewall alone. At 60mph, the nominal difference would be
Recall that the rim is 15", so its radius is 7.5" or 190.5mm.
Yep. My bad, as they say these days. I must have hit the wrong keys on my
calculator, then not bothered to double-check.
The correct arithmetic:
(15" wheel = 381mm diameter.)
215 * .60 * 2 = 258mm
195 * .65 * 2 = 253.5mm
258 + 381 = 639mm tire diameter
639 * 3.14159 = 2007.4mm rolling circumference
253.5 + 381 = 634.5mm tire diameter
634.5 * 3.14159 = 1993.3mm rolling circumference
2007.4 / 1993.3 = 100.7%
Therefore, the 215 is 0.7% larger than the 195.
As far as the speedometer and odometer go, the tires are the same.
Yeah, but you can find the percentage difference from the radius of the tire
directly. The percentage difference should be less than 3% either way,
with practical considerations factored in. Most people do not even know
what the numbers on their tires mean!
actually,going from a 65 profile to a 60 will make the speedo read HIGH;
the smaller tire circumference means you are travelling LESS distance over
the same time/RPM,and thus the car will be slower than INDICATED speed,and
actual miles driver will be lower than indicated miles.
a 60 profile tire has a smaller circumference than a 65 profile tire.
of course,that adds in with whatever OTHER errors your speedometer/odometer
yeah,but your speedometer/odometer will be off,not reading accurately.
Not by much,though. it will read higher than actual speed,and odometer
miles will be less,because of the slightly smaller circumference.
I suppose you could measure them both to find the difference,and calculate
you might have wheelwell clearance problems with the wider tread.
Sure you can. The difference in circumference is about 1/2 inch and as
Tegger noted...your speedo reading will be off only a miniscule amount. The
difference in height is about 3/10 of an inch so clearance in that plane
shouldn't be a concern. The difference in width is about ,8 of an inch.
However, as Tegger pointed out, the wider tire will not perform as well in
winter conditions as the narrower tire, given all other factors are
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