Results 1 to 2 of 2

Thread: 2001 V70XC - 235/60R18 on 7.5" x 18" rim

  1. #1
    Join Date
    Oct 2011
    Location
    Northshore - Great Lakes
    Posts
    768

    Default 2001 V70XC - 235/60R18 on 7.5" x 18" rim

    Volvo specification recommends 235/50R18 tire for 7.5" x 18" rim, but I found 235/60R18 new Pirelli set for $130 (shipped). Is there a fitment, fender rub and safe driving issue?

    Thank you.
    2001 V70XC - Nautic Blue/ 2-tone Sand/ Premium/ Instant MPG 12 - 63/ Pirelli P4 12/32" - 740/ Duracell 48/ MOBIL-3309/ Pennzoil EURO 5W-40/ Zimmerman Z-coated/ Akebono/ 190K-mi/ Great Lakes

  2. #2
    Join Date
    Aug 2017
    Location
    Pleasanton CA USA
    Posts
    177

    Default

    The "50" in the tire spec refers to the tire height (rim to road) as a % of the tire width 235mm.

    Comparing a 50% vs. a 60% height:

    .50 x 235 = 117.5mm ( 4.6 " )

    .60 x 235 = 141mm ( 5.55" )

    There's the strong possibility that the 235/60 tire will rub against the front wheel housing during turns.

    There are other considerations:
    You'd be increasing the rolling wheel radius by 0.95".

    radius 1: 18/2" + 4.6" = 13.6" circumference = 2pi x r1 = 85.45"

    radius 2 : 18/2" + 5.55" = 14.55" circumference = 2pi x r2 = 91.42"

    Your speedometer will under-report the true speed by 7%, which could lead to speeding tickets.

    The torque delivered to the road will be 7% lower, a noticeable decrease in acceleration and braking decelleration. The transmission shift points would not know that that you've put larger tires on, as the shift points are determined by shaft speed measurements.

    It doesn't sound like a good plan. Tire height is a key design parameter of the drivetrain physics design. That's why the tires are spec'ed for height as well as width.
    Last edited by pbierre; 10-05-2018 at 12:16 PM. Reason: radius correction

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •