Re: Tire Sizes and how to calculate

["MO ( Steve Mick)" <micher@xxxxxxxxxxxxxxx>]

Herb, Once in a great while I am wrong, so this may be the time. :-) 
Taller-wider tires make more of a footprint on the road which gives more 
traction  Lower gears ( higher numerically) accelerate quicker. . It's a 
balance act between  acceleration,  traction , and cruising speed. 
Personally , I think about 29" tall tire is probably the limit unless the 
rear is jacked way up. With 3:91 reart gears, I think you will just have to 
live with a little higher cruising RPM. I am now debating on a gearset in 
the 3;50 or 3:70 range with a 29" tall 
tire....................MO.............sw  iowa
----- Original Message ----- 
From: "Herb" zephyr9900@xxxxxxxxxxx
To: <1962to1965mopars@xxxxxxxxxx>
Sent: Wednesday, June 10, 2009 11:32 AM
Subject: Re: Tire Sizes and how to calculate




When your replacing tires on your car you need to get tires the same height
as were installed from the factory such as a 27 inch tall tire was the
average for our B body's.  Rim diameter dosen't matter or the width of the
tire other than rubbing on the inner or outer fenders.  If the 3:91s were
stock and you change your tires to a taller tire you will throw your
speedometer off and on new cars with a computer a Lot More.  If the 3:91s
were not stock and you installed them you are completely defeating the
purpose of installing 3:91s and your wasting all the money you spent on them
going with a bigger tire!   You should have thought about RPMs & MPH before
the gear change and not in your tire choice!!  If the tire shop your dealing
with cant help you with a 27 inch tall tire in any width or rim size they
are idiots that you need to run away from them ASAP!!  Their are several out
their that haven't got a clue as to how to properly fit a tire to a car
other than what the book/computer says.  Was looking for tires for my
Durango last week and was told by a tire shop that I had to buy new rims &
tires for it because no one makes tires for that size rim on Durango's
anymore.  Stunned I asked if they don't make 285/50 R20s anymore?  They said
yes but not for a Durango!  They need to close their doors and go away in
embarrassment.  Now if you are trying to get better gas mileage the best
thing to do is change your 3:91s to something more streetable such as a 3:23
or 2:73s but that is not always affordable & don't forget your tranny gear.
The other problem other than your spedo is if you go to too tall of a tire
to make a difference in offsetting the 3:91s, your going to have to invest
in air shocks to keep things from rubbing and remember the taller the tire
the narrower it will have to be to keep from rubbing the outer fender well
making your Polara look goofy driving down the road.  What area do you live
in I have a 3:23 & a 2:73 sure grip that we can work out a trade for your
3:91 or something.  Sorry for such a long winded reply but their is a point
that form over function dictates the avenue followed but, it is your car!!

        
Herb

1956 Plymouth Belvedere 361
1959 Coronet 326 Poly
1963 Fury 2D/HT 6.1
1963 Sport Fury Convertible 361
1970 Challenger RT 440
1999 Durango SLT 5.9
2006 300-C Heritage 5.7
2008 SRT-8 Magnum 6.1
St. Louis, MO.

http://1962to1965mopar.ornocar.com/mmo42009.html




-------Original Message-------

From: Layne Grissman
Date: 6/9/2009 10:58:41 PM
To: 1962to1965mopars@xxxxxxxxxx
Subject: Tire Sizes and how to calculate

Does anyone know how to calculate final tire size when trying to keep
the RPM's down?  What is the typical RPM range I should try to keep it
in and at what speeds?  I was figuring about 2800 RPM at about 60-65
mph.....We have a 3.91 Sure Grip rear...Want to get the right tires
the first time....  :)  Is there a formula?

Also was the typical final gear on the A727 1.00??

Thanks all!

Layne
'64 Polara 500
'08 Charger
'08 Ram (yeah it's got a Hemi)
[Non-text portions of this message have been removed]


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Please address private mail -- mail of interest to only one person -- directly to that person.  I.e., send parts/car transactions and negotiations as well as other personal messages only to the intended recipient, not to the Clubhouse public address. This practice will protect your privacy, reduce the total volume of mail and fine tune the content signal to Mopar topic.  Thanks!

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