Gear Ratio Chart for Different Tire Sizes...

Discussion in 'Tires / Wheels' started by Dave, Aug 22, 2011.

  1. Dave

    Dave Administrator Administrator Moderator

    Messages:
    15,590
    Likes Received:
    6
    Joined:
    Feb 22, 2006
    Location:
    on here
  2. J-Thompson

    J-Thompson Full Access Member

    Messages:
    2,048
    Likes Received:
    0
    Joined:
    Jul 10, 2007
    Location:
    just south of doucheville
    It should be noted for the sake of this site that the KJ
    came stock with 29" tall tires and with the auto it had
    3.73 gears 6 speeds came with 3.55's
     
  3. tommudd

    tommudd Moderator Staff Member Moderator

    Messages:
    17,862
    Likes Received:
    456
    Joined:
    Jul 14, 2005
    Location:
    Southeastern Ohio
    Plus just so some know its not the RPM you would see driving down the road in overdrive
     
  4. ridenby

    ridenby Gold Supporter

    Messages:
    4,288
    Likes Received:
    0
    Joined:
    Apr 19, 2009
    Location:
    Kentucky
    Very informative,Thanks Dave.
     
  5. tjkj2002

    tjkj2002 Full Access Member

    Messages:
    10,612
    Likes Received:
    8
    Joined:
    Dec 17, 2006
    Location:
    Somewhere between being sane and insane!
  6. Conorren

    Conorren New Member

    Messages:
    4
    Likes Received:
    0
    Joined:
    Sep 22, 2012
    Location:
    new york
    It is important to have gears according to the type and size of the tiers. you can get different gears based on different types of tires as to improve the flexibility of your vehicle.
     
  7. reflection

    reflection Full Access Member

    Messages:
    33
    Likes Received:
    0
    Joined:
    May 7, 2015
    Location:
    istanbul
    how much does the gear ratio effect mpg in real life? (not theory) can anyone give an example?

    thanks

    caner
     
  8. tommudd

    tommudd Moderator Staff Member Moderator

    Messages:
    17,862
    Likes Received:
    456
    Joined:
    Jul 14, 2005
    Location:
    Southeastern Ohio
    Installed 265-75-16s on mine after running 245-75s and 265-70s for quite q while
    after installing them had to wait a week before I could regear
    HATED driving the KJ, couldn't use over drive if I did mileage was 15 or so overall down from 20-21.
    After regear went back up to 20-21 average with highs of 23 on long trips, could use over drive like it was stock. Around town way more fun light to light
    Best single thing besides getting rid of the crappy suspension there is
     
  9. twowings

    twowings Full Access Member

    Messages:
    802
    Likes Received:
    0
    Joined:
    Nov 23, 2014
    Location:
    Tulsa, OK
    Mileage is a function of RPM, not speed...so spinning the engine faster at any given speed is going to use more fuel and vice-versa...
     
  10. tommudd

    tommudd Moderator Staff Member Moderator

    Messages:
    17,862
    Likes Received:
    456
    Joined:
    Jul 14, 2005
    Location:
    Southeastern Ohio
    :shrug:
    Depends on how you look at that
    Given we are talking about Jeeps and installing taller tires etc then above could be taken the wrong way
    For example with a fully loaded trailer in tow, using OD mine gets about 14-15, kick off the over drive which lets the RPMs go up and I now get 17-18
     
  11. twowings

    twowings Full Access Member

    Messages:
    802
    Likes Received:
    0
    Joined:
    Nov 23, 2014
    Location:
    Tulsa, OK
    I agree...I should have added the caveat "as long as the engine is in its natural powerband"...
    otherwise all bets are off...:gr_grin:
     
  12. Jbergun

    Jbergun Full Access Member

    Messages:
    1,009
    Likes Received:
    0
    Joined:
    Jun 4, 2015
    Location:
    Chicago
    I got a question what if i put 4.10 gears in there with my stock sized 235-70-16 general grabber at2
     
  13. tommudd

    tommudd Moderator Staff Member Moderator

    Messages:
    17,862
    Likes Received:
    456
    Joined:
    Jul 14, 2005
    Location:
    Southeastern Ohio
    Fun at the stop lights!
     
  14. Jbergun

    Jbergun Full Access Member

    Messages:
    1,009
    Likes Received:
    0
    Joined:
    Jun 4, 2015
    Location:
    Chicago
    Why is that better acceleration? cause i wouldnt mind that and for the cost its not outrageous
     
  15. Jbergun

    Jbergun Full Access Member

    Messages:
    1,009
    Likes Received:
    0
    Joined:
    Jun 4, 2015
    Location:
    Chicago
    I just dont understand it
     
  16. twowings

    twowings Full Access Member

    Messages:
    802
    Likes Received:
    0
    Joined:
    Nov 23, 2014
    Location:
    Tulsa, OK
    Do you have access to a multi-speed bicycle? Accelerate from a dead stop to a quick pace and note the effort expended...now change gears to engage a larger-diameter gear on the rear wheel and perform the same test...notice the difference in effort and time-to-speed?

    That's the miracle of gear ratios....:gr_grin:
     
  17. Jbergun

    Jbergun Full Access Member

    Messages:
    1,009
    Likes Received:
    0
    Joined:
    Jun 4, 2015
    Location:
    Chicago
    Thank you for the analogy as i have experienced this first hand so my current gears is which i would be willing to do this now if i wouldnt lose alot of mpgs as sure as i wouldnt hurt my engine or trans i want a lift one day when i need new tires probably a year or two from now but can i do this now what will be the pros and cons
     
  18. twowings

    twowings Full Access Member

    Messages:
    802
    Likes Received:
    0
    Joined:
    Nov 23, 2014
    Location:
    Tulsa, OK
    Well, once you regear and move the engine out of its powerband, then you've wasted your money and time...every engine has a rev range where it makes power (torque)...the factory engineers calculated the gear ratio that would give you the best compromise of power, economy, drivability (very important!), and reliability (VERY important!)...this calculation included tire size....if you study a gear ratio chart that lists speed and rpms at a given speed (say, 65 mph), you will see how different gear ratios in the differentials affect engine speed...old-time work trucks like pickups and farm trucks had gearing that let the engine make power at lower speeds which makes sense when you consider the kinds of work they were tasked with: heavy loads, bad roads, bad weather, etc...if you take one of those trucks on the highway, you would be hard-pressed to exceed 50 mph because of the very 'tall' gearing (like 4.88-5.13:1 or even higher) which had the engine screaming at high rpms at that speed...now let's look at race cars (not dragsters...they need higher ratios for quick acceleration)....they need very high speeds and have the luxury of great distances to reach high speeds...a race car is very hard to get rolling from a dead stop (lke a multi-geared bicycle in the highest gear) because their gear ratios are 'short' to enable taking advantage of high rpms (where race engines are tuned to make power) but once you get them rolling they are wicked fast...but their engines are tempermental (comparatively) to your street car and not suited for everyday driving, starting in all temperatures, conserving fuel, etc...all the things your street car does relatively well....you can modify your Jeep to your liking with bigger tires and higher gear ratios and all the toys we like to have but you have to make modifications in concert because changing one thing may cause needed changes in other areas...and you can reach a point where you don't really want to drive it every day because it no longer is suited to the street while being lots of fun on the trail....sorry for the long post....HTH
     
  19. Jbergun

    Jbergun Full Access Member

    Messages:
    1,009
    Likes Received:
    0
    Joined:
    Jun 4, 2015
    Location:
    Chicago
    Never be sorry for providing someone with information thank you for taking the time to explain it in words i understand now i get it she is my daily driver for now one day she might be my toy but thanks again for helping me wrap my mind around that
     
  20. YP047

    YP047 New Member

    Messages:
    2
    Likes Received:
    0
    Joined:
    Jun 18, 2016
    Location:
    Idaho
    So is it better to push the Over drive button in every time you highway drive or pushing it in (on an Automatic) does that shut it off?..my 02 seems to have a stall/flat spot if you stomp on the Gas..anyone else?Thanks