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Thread: big rimz small tires/small rimz big tires theory?

  1. #1
    707dog
    not to clear on the way this all works but some have said that a truck with small rims but big tires doesnt mess with the trans and breaking as much as a truck with big rims and small tires and vise versa(when towing or not towing?)...i have 24's(up from 22's) on my denali and i notice the difference in the trans shifting but not much with breaking while towing..also the stress on the truck itself?..any out takes on this???

  2. #2
    YeLLowBoaT
    Wheels are lighter then tires...up to a point, by going to a larger wheel you will have less rotating mass...

  3. #3
    curtis73
    That is a common misconception ^^^ Hate to disagree, but there are several factors involved.
    First of all, its true that tire typically weighs more than wheel, but the moment of inertia is further out the radius with larger wheels. If you swing a string with a weight on it, it takes more energy to overcome inertia if you move the weight further out the string even though you haven't changed the overall weight.
    Also, for any given tire wheel package, you add weight going to a larger wheel (and although it sounds backwards) you ALSO add weight going to the smaller sidewall tire. A tire with a shorter sidewall requires more/stronger material to prevent distortion of the tire at speed. If you compare for instance a 255-65/17 to a 255-60/18, (both the same diameter) the 18" tire weighs more despite the fact that there is less "tire." You've also concentrated that weight more toward the outside of the radius which changes the moment of inertia.
    Careful selection of wheel brand and type can net you an overall weight reduction, but bigger wheels almost always adds weight and adds it near the circumference. Even if the wheels weighed the same and the tires weighed the same, you'd be concentrating more tire near the outside which is harder inertia to overcome.
    The transmission hunting should be a very mild effect if at all. Bigger wheels slow down acceleration, but wouldn't change shift points, and once you're at speed it doesn't require any extra energy to maintain that speed regardless of wheel weight. Did you add overall diameter? If so you could have placed the engine in a lugging state at a different point than your previous combo causing hunting.
    Huge wheels look killer, but have almost no benefits. Handling, braking, acceleration, and weight capacity all suffer. At-limit tire grip qualities are sharpened with lower profile tires; that is to say the difference between grip and "oh crap" is very little. They become very sensitive to camber changes which (especially in GM trucks) is optimized for comfort, not handling. Tall skinny tires give up peak grip, but you can just keep turning the wheel and slip rates are very progressive and forgiving. Most vehicles have a range of wheels where handling is best. Any less and you have too much tire flex and any more you have skittish tires that give up bite and become unpredictable. For instance, I turned down 16" wheels for free for my E30 BMW. The 15s turn consistently better times at the autocross than 16s. My Impala SS seems to like 17-18, but 19 and 20 are just bling; no handling, stiff ride, bent wheels, slower accelleration, yadda yadda.

  4. #4
    lilrick
    That is a common misconception ^^^ Hate to disagree, but there are several factors involved.
    First of all, its true that tire typically weighs more than wheel, but the moment of inertia is further out the radius with larger wheels. If you swing a string with a weight on it, it takes more energy to overcome inertia if you move the weight further out the string even though you haven't changed the overall weight.
    Also, for any given tire wheel package, you add weight going to a larger wheel (and although it sounds backwards) you ALSO add weight going to the smaller sidewall tire. A tire with a shorter sidewall requires more/stronger material to prevent distortion of the tire at speed. If you compare for instance a 255-65/17 to a 255-60/18, (both the same diameter) the 18" tire weighs more despite the fact that there is less "tire." You've also concentrated that weight more toward the outside of the radius which changes the moment of inertia.
    Careful selection of wheel brand and type can net you an overall weight reduction, but bigger wheels almost always adds weight and adds it near the circumference. Even if the wheels weighed the same and the tires weighed the same, you'd be concentrating more tire near the outside which is harder inertia to overcome.
    The transmission hunting should be a very mild effect if at all. Bigger wheels slow down acceleration, but wouldn't change shift points, and once you're at speed it doesn't require any extra energy to maintain that speed regardless of wheel weight. Did you add overall diameter? If so you could have placed the engine in a lugging state at a different point than your previous combo causing hunting.
    Huge wheels look killer, but have almost no benefits. Handling, braking, acceleration, and weight capacity all suffer. At-limit tire grip qualities are sharpened with lower profile tires; that is to say the difference between grip and "oh crap" is very little. They become very sensitive to camber changes which (especially in GM trucks) is optimized for comfort, not handling. Tall skinny tires give up peak grip, but you can just keep turning the wheel and slip rates are very progressive and forgiving. Most vehicles have a range of wheels where handling is best. Any less and you have too much tire flex and any more you have skittish tires that give up bite and become unpredictable. For instance, I turned down 16" wheels for free for my E30 BMW. The 15s turn consistently better times at the autocross than 16s. My Impala SS seems to like 17-18, but 19 and 20 are just bling; no handling, stiff ride, bent wheels, slower accelleration, yadda yadda.
    Hmmm. well put.

  5. #5
    curtis73
    I learned it from racing as well as some "light" reading I did. "Race car vehicle dynamics" by Milliken. Its a nice little 900-page engineering textbook that I somehow felt compelled to read. I'm an auto customizer so it was important to me to know how to fulfill my customer's requests
    I had a webpage published on this exact topic but I turned it over to another racer to host and I can't seem to retrieve it. I think he may have let it slip away.

  6. #6
    707dog
    thanks for the detailed offering..i was always wondering cause if i took my 22's with tires on them they where the same size as my stocks with terrain tires. now as for my 24's they are a little bit taller alot wider (305 or 325/45/24) if i put them next to my stocks there is only about a 1"-1"1/2 difference at a glance and about 2"'s wider with the 24's on the truck i do notice the take off lag...will the bigger wheels plus towing run hell on my trans or rear wheel bearings? or will they still remain as strong as with stocks on?? the reason so many ?'s is i like my big wheels its my 5th set but i tow alot and sure everbody wants a clean azz towing set up but i also dont want to destroy my ride either......

  7. #7
    Brian
    It has been my experience that the low profile tires really don't work very well off road. My EX came with 20s on it when I bought it. Next tire change will be going back to 18s.

  8. #8
    Beer-30
    Bigger rims with shorter tire, to equal ORIGINAL overall diameter will typically increase handling. Due to less tire height, there is less tire roll. As you corner, the tires on the outside of the turn try to roll under the car. The less tire height means less tire roll, and thus, better handling. Additionally, lower profile tires usually end up being wider - which means more tire footprint and thus, better handling. Typically, there is no adverse wear on the rest of the car, other than harsher ride for the occupants. Less tire also means less absorbancy for bumps and whatnot.
    Taller tires than factory puts additional load on all components that work with it. Lug nuts tend to break after time from the added leverage against them. The taller the wheel/tire assembly, the longer the "arm" is trying to bend everything attached. Ultimately, wheel bearings will fail - usually the front(s) - from the added side-side load during turns and bumps. All of the stock components (rotors, lugs, spindles, bearings, ball joints, tie rod ends) were designed to handle hits from the leverage that the stock 29-32 (or so) inch wheel/tire assemblies can produce. Going to the larger of the spectrum (35, 38, 40-up) is just borrowed time on now "test" components. They were not engineered for such leverage and rotating mass.
    This is not to say that lowered vehicles with shorter tires are any better. Nothing is free, and there are several problems to that side also.
    Getting back to taller overall diameter. It will change shift points and in some cases, tranny "hunting". This is caused by the torque curve being changed - as the tranny sees it. Where the vehicle in question used to be able to still pull OD on a slight incline will now not have the torque to the ground that it used to. So, now it is on the edge of having the torque to do it or not. Now it bumps out of OD, catches up in speed, and shifts back into OD - so on and so forth. The engine is still putting out the same amount of torque, but the overall drive ratio has now been changed by the taller tire. This is why people generally end up changing gears with taller tires. To bring the overall drive ratio back to square. 3.73s get changed to 4.10s. 4.10s go to 4.56s and so forth, depending on how out of control the tire size gets. Some end up with 5.13s.
    Lowered or raised, taller or shorter wheel/tire combos all have their negatives. Once again, nothing is free.

  9. #9
    curtis73
    Bigger rims with shorter tire, to equal ORIGINAL overall diameter will typically increase handling. Due to less tire height, there is less tire roll. As you corner, the tires on the outside of the turn try to roll under the car. The less tire height means less tire roll, and thus, better handling. Additionally, lower profile tires usually end up being wider - which means more tire footprint and thus, better handling.
    While this has been the traditional thought for a long time, we're finding that this also is not always the case. You're right, more wheel and less tire will improve peak lateral Gs up to a point. The problem is going TOO big takes away too much sidewall flex and the tire can't conform to camber changes, road imperfections, and bumps and they get skittish which reduces overall grip and lateral Gs. I could typically pull .92Gs steady state in my E30 BMW on 15s or 16s, but 17s with the same tire type, compound, and width could only muster .90Gs. That's actually a pretty big difference. All the tires tested were Toyo Proxes T1R in 205mm width. (uncle works for Tire Rack and we used my autocross car for some testing) Suffice it to say that most people are giving up serious lateral handling because they are going too big.
    Also wider tires does not always increase the amount of rubber that touches the road. Skinny tires have a long contact patch front to rear, wide tires have a wide contact patch side to side, but there is no more rubber touching the road. That is one of the reasons why going wider can reduce acceleration traction. Even if you DID increase the square inches of rubber touching the road, you aren't increasing the weight of the car, meaning you would be reducing psi and therefore the coefficient of friction as well.
    The stability associated with wider tires doesn't come from a larger contact patch, it comes from a different contact patch.

  10. #10
    TollyWally
    " Lug nuts tend to break after time from the added leverage against them"
    I'm not picking on you or your comment, (well maybe just a little bit), but I've beat the hell out of quite a few cars back in the day and I never broke a lug nut due to over leveraged stress. Lots of other stuff but never a lug nut. My .02

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