<VV> 175 vs 185

[bowtieguy at cox.net]

Bob,

Thank you. Performance to me means accuracy in speedometer readings, handling, traction, ride and braking. 

Bob
bowtieguy at cox.net
64 Monza with DB 175/80/13 1" WW tires
  ----- Original Message ----- 
  From: BobHelt at aol.com 
  To: bowtieguy at cox.net ; virtualvairs at corvair.org 
  Sent: Friday, September 01, 2006 11:56 AM
  Subject: Re: <VV> 175 vs 185 


  In a message dated 9/1/2006 9:29:33 AM US Mountain Standard Time, bowtieguy at cox.net writes:
    I thought the 175 was closest in size diameter to the 650:13 from past discussions for speedometer accuracy. What did I miss?

    Bob Vukas

  Hi Bob,
  As with all things in life, one must define his terms. Otherwise we start comparing apples and oranges.

  First comparisons between stock (came on the car) tires and replacements can generally be based on one of two characteristics (ignoring things like ride and cornering). 
  These are 1) comparison of tire measurements of tires mounted on rims and filled with air.These wsould include diameter and circumference, etc.

  Second characteristic 2) would be how many revs per mile the tires go when mounted on the car at say, 50 mph. This would affect speedo accuracy and other things.

  These characteristics are entirely different because of the change from bias tires on the 1960s and radials of today.

  So here are the answers: 

                                                  6.50-4ply        6.50-2ply       175          185
  diameter (Unmounted)            24.3                24.3              24.1        24.6
  revs per mile (RPM)                 853                 864               863         843

  So you can see that 175 tires are similar the the 2-ply in RPM but the 185s are closer to the 4-ply 6.50s.  So the choice now becomes less distinct. Similarly, the 175s are smaller in diameter than the 6.50s and the 185s are larger. So which do you choose? This affects how the tires fill the tire well and how they "LOOK" when on the car. Most people choose the 185s for appearance and for being closest to the original 4-ply tire RPMs to keep the speedos reading close.

  Regards,
  Bob Helt.