RE: [alfa] Formula for calculating correct tire size

["Jeff Greenfield" <alfaguy@xxxxxxxxxxxx>]

Biba -

Here is a basic primer on tire nomenclature which might be of interest to
you and others ...

The 'SR' that you refer to in the 165SR14 means that the tire has a speed
rating of S (Slow, max of 113MPH if I remember correctly). In the old days
there was also, H and V each having an incrementally higher rating.

Now there are many more, T, W, Z, etc. I'm sure a search of tire speed
ratings on google would turn up a chart describing all of them.

'R' stands for radial, so these two have nothing to do with size.

Modern tires are labeled in the form of 185/70/14 excluding the speed
ratings. This relates to a tread width of 165mm, and ID of 14" (equal to the
wheel diameter, why one dimension is in mm and the other in inches I'll
never understand).

The '70' refers to the sidewall height as a percentage of the tread width.
This is how you can change wheel diameters and tire widths and still keep
the OD of the combination close to what it was originally.

Hence a 165/14 is roughly equivalent to a 185/70/14. So if you enter an
original tire size into any of the calculators that were mentioned, it
should spit out all the variations that are roughly the same overall OD.

HTH,

Jeff

-----Original Message-----
From: owner-alfa@domain.elided [mailto:owner-alfa@domain.elided] On Behalf Of
alfacybersite
Sent: Thursday, July 08, 2004 4:40 PM
To: AD
Subject: [alfa] Formula for calculating correct tire size

I want to thank everyone who sent me the various sites for doing just
what I asked. Sure couldn't figure out the Miata one. There sits three,
three digit numbers - all looking like variations on the sidewall
height. Ummm...

While I couldn't quite get it to do everything I wanted,
http://ejelta.com/tiresize/  sent to me by Benjamin Kaupp was the most
helpful. The main thing is an important page appears when you first go
to the site. If one starts putting in the information it  logically asks
for (rim width from - to, etc) this page then disappears from the face
of the earth.

However, rebooting and clicking on 15" I  got about seventy jillion (+
or -) tire sizes along with their diameters - which was the main point.

Before I get to my other questions, I have a question. How does one know
exactly how tall a Particular tire is before purchasing? I forget if
TireRack gives that info. Right now I'm thinking of cheating big time -
195/65-15. The diameter (theoretically) is 24.98. I figure I can get a
25" tire in the spare tire well. You can see my concern. Yeah, I know,
get a smaller one for the spare.

The inside 69's glove box decal shows the size as 165/S-14. What the
hell size is S? The  calculator indicates 165/70-14 as being 23.09". I
have a Bridgestone 165/ SR-14 in the shop which measures 24" with about
half tread. What size is SR?

Should I go up approximately 2" in diameter, will I have to get out and
give it a push just to get it off the line every time I come to a stop?
Yeah, yeah, I know the speedo will also be off a might.

A 185/70-14 (which I see frequently on '69 Alfa Spiders) is 24.20"
(theoretically).

What's the tallest you 15" Duetto guys (yes, you can take that as a
compliment) have gone and what were your (driving) experiences?

One other tiny little question. I'm also thinking of installing some
used lower / shorter springs all around. Might I have a bit of a
conflict, rubbing wise? I do have the opportunity to make my own offset
though.

Okay, just one last question: While not the best of revues, I sure liked
the looks and especially the name of the Pirelli P6000 Sport Veloce
195/65-15 tire. Anyone tried them?

Thanking you all in advance for answering each and every one of my
questions,

Biba
Irwindale, CA USA
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