Re: [Chrysler300] 300 L wheels & tires

[Edward Mills Antique Tractors <millserat@xxxxxxxxxxxxx>]

Gary Barker wrote:
> I have always put a small dap of Grease on the tire and then role the 
> car at least one turn  of the wheel and then Measure the  distance 
> between the grease spots.    Gary Barker
>
> --------------------------------------------------
> From: "Michael Reed" <mrreed@xxxxxxxxx>
> Sent: Thursday, January 01, 2009 4:29 AM
> To: "Edward Mills Antique Tractors" <millserat@xxxxxxxxxxxxx>; "300 
> Club Server" <Chrysler300@xxxxxxxxxxxxxxx>
> Subject: Re: [Chrysler300] 300 L wheels & tires
>
>> The Web site mentioned (Car / SUV / Van / Light Truck Tire 
>> Calculator) can be very useful. I would like to caution readers, 
>> however, regarding the "Wheel Circumference" value returned. The 
>> number is accurate, based on the "Overall Wheel Diameter" provided, 
>> and is valid for a wheel/tire carrying no weight and inflated. The 
>> page calculates the circumference mathematically.
>>
>> However, mounted on a vehicle, unjacked, the tire has a "rolling 
>> circumference" -- and it is not the same value as can be calculated. 
>> The "flat" at the bottom, where the weight rests, creates a tire that 
>> is not round. I don't believe the actual circumference of a tire can 
>> be calculated accurately, as the "flat" on a tire with weight on it 
>> varies according to a number of factors. Back in my racing days, we 
>> had to physically measure the circumference using a tape measure to 
>> get an accurate circumference value. Due to the larger 'flat' on 
>> today's radial tires the difference between actual and calculated is 
>> even greater.
>>
>> As the "Wheel revolutions per mile" and "Wheel revolutions per second 
>> @ 65MPH" are derived from the calculated circumference, those values 
>> are inaccurate also.
>>
>> Mike Reed in flooded Lake Odessa, Michigan -- but the "F" is high and 
>> dry across the street....
>>
>>  ----- Original Message -----  From: Edward Mills Antique Tractors
>>  To: Larry Nirenberg
>>  Cc: rselby41@xxxxxxxxx ; 300 Club Server
>>  Sent: Wednesday, December 31, 2008 10:25 PM
>>  Subject: Re: [Chrysler300] 300 L wheels & tires
>>
>>
>>  Larry Nirenberg wrote:
>>  >
>>  > Before I guessed I would go to this web site and figure out an
>>  > equivalent to the OEM radius tire in a 15" size. If you do this the
>>  > tire will definitely fit-
>>  >
>>  > http://www.net-comber.com/tirecalc.html
>>  > <http://www.net-comber.com/tirecalc.html>
>>  >
>>  > ________________________________
>>  >
>>  > From: Chrysler300@xxxxxxxxxxxxxxx
>>  > <mailto:Chrysler300%40yahoogroups.com>
>>  > [mailto:Chrysler300@xxxxxxxxxxxxxxx
>>  > <mailto:Chrysler300%40yahoogroups.com>]
>>  > On Behalf Of Roger Selby
>>  > Sent: Tuesday, December 30, 2008 9:29 PM
>>  > To: 300 Club Server
>>  > Subject: [Chrysler300] 300 L wheels & tires
>>  >
>>  > Hi 300 Friends,
>>  > I was driving my 300 L to the Sparks/Reno 300 Meet, last June, when a
>>  > gal
>>  > ran a RED light and took out my cars front end. A new clip, 
>> sub-frame &
>>  > 6
>>  > months later, it is out of the body shop. Arbogast Body & Paint, 
>> Auburn,
>>  > Ca. did a great job & are super people.
>>  >
>>  > I am now looking to put on Magnum 500 wheels 15X7 inch & 235/75/15
>>  > tires.
>>  > Will I have the clearance to run these larger, 15 inch tires?
>>  >
>>  > If anyone knows, please advise.
>>  >
>>  > Thank you, Roger Selby
>>  > Placerville, Ca.
>>  > 530-622-1020
>>  >
>>  > [Non-text portions of this message have been removed]
>>  >
>>  >
>>  Diameter is only part of the problem - and don't for a minute believe
>>  that all the same size tires are the same size. check the referenced
>>  site for starters, but check vendor info on tire dimensions - 
>> especially
>>  tread width. On several 235/75R15 I looked at there was more than an
>>  inch difference in tread width - from 5.9 inches to 7.4 inches. If your
>>  OE tire was 9.00-14 - BFG tread width was only 4.8 inches.
>>
>>  Don't know about your application and wheel offset will also be
>>  important - but on a non-letter 67 300, the 7.25 inch tread width on
>>  15x6 with 0.5 inch inboard offset, they rub at both front and rear
>>  inboard edges at extremes of steering. Factory offset for the 67's was
>>  0.25 inch inboard and I think the 15x7 are 0.25 inch inboard so they
>>  should be better than 15x6 with 0.5 inch inboard, but rub was at static
>>  condition - tires will deflect inboard a bit under hard cornering.
>>
>>
>>
>>
>> [Non-text portions of this message have been removed]
>>
>>
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>>
>>
>
hey guys don't get too hung up on circumference. The only thing that 
circumference affects is speedometer error. And a paper tape measure of 
circumference is probably fine for a belted radial which will not grow 
significantly due to the belt stiffness. The older bias ply tires and 
especially race tires grew with inflation - typical cold pressures were 
in the low 20's and operating temperatures were typically 32-35 psi hot 
- and especially race tires on a hot day at 230F pyro temp would 
increase enough that you could feel it if you changed a rear on one side 
til it warmed up - but not to worry much about street belted tires on an 
antique.

The 5 items you want to know are 1. diameter as it affects clearance; 2. 
static loaded radius as it affects car height and radials are lower than 
old bias tires at same diameter or circumference; 3. tread width as it 
and diameter affect clearance at steering extremes; 4. section width 
which is a function of tire and wheel - as this affects clearance to 
struts and other hardware; and 5. offset which is a function of wheel 
geometry only but will affect all lateral clearance issues.

If  you are really concerned with speedo error, consider most 
speedometers are off by a percent frequently more as speedometer pinions 
offer about a +/-2% calibration per tooth change - and a difference of 1 
inch in circumference on a 90 inch circumference is only 1.1% or 60.6 
mph vs 60 mph.

best, Ed

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