Dismiss Notice

Welcome To CK5!

Registering is free and easy! Hope to see you on the forums soon.

Score a FREE t-shirt and membership sticker when you sign up for a Premium Membership and choose the recurring plan.

figuring out RPMs with new tires

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by 85GMCJimmy, Aug 3, 2002.

  1. 85GMCJimmy

    85GMCJimmy Registered Member

    Joined:
    Feb 21, 2000
    Posts:
    83
    Likes Received:
    0
    Location:
    South Carolina
    I am about to get a set of 33's, but when doing calculations when going at 45 mph, i would only be turing 1000 RPM. Did i do something wrong?? Which gear ratios do you use for your transmission? as far as first, second, third, and etc??? can someone please help me??
     
  2. tackettb

    tackettb Registered Member

    Joined:
    Jul 18, 2002
    Posts:
    49
    Likes Received:
    0
    Location:
    Tacoma, Wa
  3. POWERMAD

    POWERMAD 1/2 ton status

    Joined:
    Mar 4, 2001
    Posts:
    3,466
    Likes Received:
    0
    Location:
    Oregon
    336 X axle ratio X mph divided by tire size.
    Take a tape measure and measure the tire, don't go by what is stamped on the tire, most tires are up to 2 inches smaller than what they are stamped.
    my 33's are actualy 31".
    so my formula would be 336 x 4.1 x70 div by 31= 3110 rpm's at 70mph.
     
  4. Pure Insanity

    Pure Insanity 1/2 ton status

    Joined:
    Mar 17, 2001
    Posts:
    4,579
    Likes Received:
    0
    Location:
    Dade City, Florida
    Or the easy way........ 4lo.com They have a gear calculator at the top of the page. /forums/images/icons/grin.gif
     
  5. Grim-Reaper

    Grim-Reaper 3/4 ton status Author

    Joined:
    Feb 17, 2000
    Posts:
    7,385
    Likes Received:
    0
    Location:
    Atlanta
    Randy's has a really nice one here.
    http://www.randysringandpinion.com/calculators.shtml
    I alway's put 1 inch less than the tire is marked.
    For 3.08 in 3rd you would be turning 1494 and in OD 1019.
    With 33's and a 700 R4 4.10 would be a good gear choice. Less stress on the tranny. 4.56 would not be a bad choice either. would let you go to 35's in the future.
     
  6. Pure Insanity

    Pure Insanity 1/2 ton status

    Joined:
    Mar 17, 2001
    Posts:
    4,579
    Likes Received:
    0
    Location:
    Dade City, Florida
    Good one Grim. Its now in my favorites list. /forums/images/icons/cool.gif
     

Share This Page