*** Does My 2 Cents Add Up ? ***

    OK, I have been thinking about this and I think I got it.


    Before I start, I'm not trying to tell everyone somthing they already know, I'm trying to work this out and in the proses, maybe some other members might get a better understanding of how this works as well as me.


    If you were to take two tires with the same width and weight but different heights and apply them to the same gears, the difference in the equations would be revolution of tire per axle turn. Isn't that what ratios are all about. Picking your tire size and then selecting the correct gears to effectively put your motor in the proper power band to operate your vehicle. Keeping everything else relatively the same except height (weight and friction changes this a little and contributes some) your ratio changes from lets say 3.73-1 to 4.10-1 due to the longer revolution of the taller tire. This effectively changes the ratio without changing the gears and puts the motor out of it's power band. This is why it performs sluggishly and gives poor gas mileage.
    As 2000Sahara said...

    Quote

    Adding Bigger tires without regearing takes the engine out of its optimal power range. For example, you will have to bring your rpm's up a bit more to get the tire moving from a dead stop due to its larger diameter and weight. By bringing the rpm up you are taking the engine above its power band, causing it to feel sluggish. On the other hand once you are moving down the highway at speed your engine may be running at a lower rpm which would usually mean better mileage however, because of the larger diameter and weight and improper gearing you need a bit more throttle to get moving...Hence poor gas mileage and wear and tear.


    I think I'm starting to understand this now. Rolling resistance/friction and additional tire weight does play a small part and only makes this worse, but is not the main culprit.


    How am I doing so far?

    There is nothing that can't be fixed if you throw enough money at it,

    With that said, I bought the 4 banger for it's fuel mileage. A get to work and back rig that I can enjoy driving. I want to keep my fuel economy and don't want to regear at this time so I guess I'll down size one tire size from what I have now (235/75/R15) and get a 2.5" lift instead of a 4" lift. I'm now thinking of ....


    2.5 RC lift on 215/75/R15's


    This will give me a little better stance and still keep my 5Th gear and fuel economy for my highway driving to work. I read that any thing over a 3% diameter change in tire size is when you will notice a difference in performance. This will keep me under that threshold. I think eventually this will become a toy and will be built that way but for now it's a highway rig.


    Now I need to pick out a tire, which should be easy in that size range. Again, a good beefy tire but good on the highway.


    Recommendations ?


    John

    There is nothing that can't be fixed if you throw enough money at it,

    I have to replace my leaf springs due to bad sag and wanted to go a little taller. I posted in an earlier thread that I liked Yankee19934"s jeep before he put on his 33's


    It was Yankee19934's 92YJ / 4"lift on 31" tires that I liked. The taller stance off the "stock" look.
    Mine being a 92 YJ also, this is the look I'm trying to achieve.


    Yankee's 4" on 31's
    Mine would be 2" on 28s


    Here is a shot of Yankee's 92 YJ and the look I'm trying to achieve


    There is nothing that can't be fixed if you throw enough money at it,

    If I was you I would do the 4" and 31s.....you should still get around ok with the 4 banger. Its a good platform if you end up wanting to do more. If it was me after the 2" and whatever 215/75/R15's are :doh: lets just say it would probably be a wast of time :bang:
    Good luck with it, just dont do things twice like a lot of people :up:

    Just when I thought I had my mind made up, you threw that in. LOL
    I guess I have a decision to make. Very Good Advice. If I intend to eventually build this into a toy, Why do things twice. I really do like the 4" on 31's. Damn ! Decisions Decisions.

    There is nothing that can't be fixed if you throw enough money at it,

    my thoughts on explaining taller tire vs power loss is this.... think of riding a 10 speed bicycle. bigger gear= less pedal rotations for the speed, but harder to pedal. am i making any sense here? i had 33's on my 89 4 banger. not AS bad on the yj for the simple fact that it does have 4.10's in the rear. i had 33-12.50's, the motor has plenty of juice to move them. u just lose 5th gear. but because of the tires being larger, u ride in 4th and do 60-65 pretty easily. uphill climbs (like bridges and such) are a little disappointing, but i dealt with it until i did a motor swap.
    hope that helps...


    I was trying to teach you a little bit about gearing/ tire size / power loss without getting too technical, as your question was worded as if you had no prior experience with the subject. Seems to me that someone who has owned so many lifted vehicles would understand this topic by now..... :shrug: Hows that for an honest answer?

    2000 Sahara, All custom...
    2000 Cherokee Police package, Beater....


    I may be slowest and the stupidest

    Sorry for sounding so strong yesterday. I was having a bad day. Forgive me.


    I have always accepted the answer and knew the basic principals behind what to do. Larger tires = regearing due to power loss. I followed the charts and regeared accordingly. This time I wanted to know why and how it works specifically and the cause and effect of the tire/lift swap so I could make a compromise I was willing to live with. After your explanation yesterday, it put things in perspective for me. I now have a better understanding of the ( Whole ) concept.


    Thanks for your input,


    John

    There is nothing that can't be fixed if you throw enough money at it,

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