Re: 165/HR/whatever tire size comparisons

["Csank" <csank@domain.elided>]

> A new "vintage" Michelin XAS (from Coker Tires) in 165 HR 14 has an
overall diameter of 24.5 inches; a newer 185-70-14 averages around 23.7
inches, and a 195-65-14 at 23.5. A one-inch difference in rolling diameter
effectively lowers the car's gearing substantially, resulting in many more
revs per mile. Someone else is welcome to do the math to calculate how many
for a particular car. Hope this clears it up.
> Cheers,
> Paul Mitchell

Hi all,

I like all the explanations, but there have been a couple of minor
inaccuracies about tires (tyres for our UK friends).  I don't know where
Paul got his sizing on the XAS in 165-14, but I don't think it's right.
Everything that I have seen (other than his entry) states that the 165-14
diameter is most closely matched by 185/70-14, or 215/60-14...etc. There are
a bunch of places where you can find a calculator to help you determine what
tires to use to replicate the diameter of a 165-14 tire.  The best one that
I know of is on the Swedish Roundtail site run by our Alfisti friend, Wille
Roos (go to www.veloce.nu and hit the button on the left about Rims and
Tires, then check the "article about tires").  Incidentally, he also has a
page about Rims that different auto manufacturers produced that will fit any
Alfa (4X108, 4X98, 5X98, etc.), and the site includes the offset too!

In any event, one should always remember that there are lots of things to
consider when selecting to change the tires to a larger/ wider/ lower
profile sizing.  More rubber usually means more unsprung weight, stiffer
sidewalls, harder steering, possible rubbing...and the shocks, springs,
bushings (bushes), anti-roll bars, chassis, etc. are all affected when you
change sizes.  Another thing to consider is the added stress on important
front end and steering parts (like the now very old and getting weakened 105
steering boxes).

I am not saying that anybody should avoid getting wider, better performing,
more modern tires (heck, my '69 Spider has 185/70HR-14 Pirelli P400s, my '78
Alfetta SV has 205/50ZR-15s, and my Milano has 195/50-15s), I am just saying
that these issues should be considered carefully.  In my view, a
conservatively increased tread width (with a similar diameter to stock) tire
mounted on a set of lighter than stock rims is the way to go.  That would
mean a 185/70-14, where a 165-14 size was original, or a 215/60-14 where a
185/70-14 was original would be my choice (IMHO/ YMMV/ etc.).

Cheers to you all,
Alex Csank
Norfolk, VA

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