I went thru the calcs I could find and you will not like the answer for tire
size.
There isn't one that will work.
Assuming: Current tire (185/75x14) has a diameter of 24.93" and goes 60 MPH
with a 4.55 FDR.
To go the same speed with a 3.9 FDR you would have to have a tire that was
21.5" diameter.
The 155R14 are 23.8" in diameter, not small enough.
Closest I could find on the Coker tire store was "Coker Verdestein Spint,
145-13, Radial" @ 21.75" which would have your speedometer showing 61 mph @
60 mph actual.
Tires are not the way to get the speedometer to indicate the correct MPH in
this case. I would go with one of the other recommendations (i.e. have the
speedometer recalculated). Recalculated is better than the change the face
of the speedometer to indicate correctly since that will NOT change the
odometer, that would still read wrong.
There are mechanical speedometer gearing changers out there for the OLD hot
rods (I believe they are still available, haven't done the search).
Nowadays it is done electrically but those will not work with our mechanical
gauges.
Paul
-----Original Message-----
From: spridgets-bounces@autox.team.net
[mailto:spridgets-bounces@autox.team.net] On Behalf Of Dave KK7SS
Sent: Sunday, March 06, 2011 12:26 AM
To: spridgets_autox.team.net
Subject: [Spridgets] Tires and indicated speed question.
Sorry about the LBC content... Not! <Grin)
The Morris Minor 1000 has had the 4.55 rear end replaced with a 3.9.
It also has 185/75x14 tires.... which are a shade too fat for the rim.
We know that when the speedo indicates 55mph that it's actually travelling
at 65mph!
(proved on the highway!)
The tires are out of balance and are getting rather worn.
So, I'm thinking of putting 155R14's (Firestone from Coker) on.
If my calculationa are correct, this should at least bring it down to 60mph
at an indicated 55mph.
Comments solicited...
And, No, I don't want to put a 4.22 in !!
--
Dave G KK7SS
DN06ig
,59 Morris Minor 1000
'65 Sprite - in process
'76 Midget - shared with my #4 son.
'06 Honda Civic Hybrid
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