[alfa] Re: alfa-digest V10 #209 - Tyres (sic) Again

[AlfaNeely@xxxxxxx]

In a message dated 7/11/2004 7:26:55 PM Central Daylight Time, 
owner-alfa-digest@domain.elided writes:
Date: Sun, 11 Jul 2004 15:16:23 -0700
From: alfacybersite <acs@domain.elided>
Subject: [alfa] Tyres (sic) Again


<snip>

This is a general question to all, but gear ratios and final drive 
ratios have always been a huge mystery to me. Sorry to have to admit it 
in print, but...: So's if I go taller (tyres / tires wise) than original 
on the '69 Round-Tail am I in even bigger trouble or am I correct that 
the Duetto, which has just been determined to have the same final drive 
as the '69 Round-Tail (and using Beatle's figure) "should" have a tire 
with the circumference of 77.8" and since this is a "shorter" final 
drive, it's okay to go a bit taller? Got that?
----------------------

    Yes, the Duetto had tall 155/15 tires and the same 41/9 or 4.56 rear axle 
ratio as later spiders.  The 1750 round tail had shorter 165/14 tires, a 
bigger engine and the same gear ratio.  Thus going to a taller tire will make 
acceleration slower, may increase gas mileage and will change the speedometer 
error slightly.  It will not cause the car to fall apart or blow up or cause the 
end of the world.  You will probably never notice the difference, other than 
having to recalebrate your brain to a different speedometer error.
    Alfa went to a 41/10 ring and pinion for a 4.10 ratio in 1982.  They used 
a 185/70/14 tire, which is approximately the same diameter / circumference as 
the 165/14.  In 1985, the Quadrifoglio came with that same axle ratio with 
195/60/15 tires.
    In the USA, we never did get the 43/10 or 4.30 rear gear ratio in the 105 
/115 Alfas.  Too bad as that might have been a nice gear ratio for certain 
applications.

    I would suggest that you stay away from 195/70/14 and taller tires.  I 
have found it is very hard to get stiff side walls on such a tall tire.  Even my 
ex wife noticed years ago when I put 195/70/14 tires on our Alfetta.  I was 
pleased when I discovered 205/60/14 tires.
    Or play with some of the 16 / 17 inch rims now available.  The problem 
there is pot holes can damage a rim due to not enough rubber in the side wall.

Ciao,
Russ Neely
Oklahoma City
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