18 inch wheels vs 16 - Rotating mass

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Thread: 18 inch wheels vs 16 - Rotating mass

  1. #1
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    18 inch wheels vs 16 - Rotating mass

    I've got 18" rims on my car right now and drove a buddy's that has the stock GE 16" rims on. Both of our cars are NA and slow. Well, I noticed his accelerated so much quicker and smoother than mine did. I figured it was because he has smaller rims on so there isn't as much of a rotating mass. These NAs are so slow that with 18s on it feels like I'm having to floor it just to get to 60 mph.

    For a car making 180 rwhp, what difference is there if I downgrade rim and tire size from 18s to 16s? I'm just tired of not being able to accelerate comfortably. This car can't even get out of it's own way. It's also not comforting when like, minivans are passing you in traffic. Are my wheels too big for the NA?

    I'm not going turbo for a while now and am just looking to make my ride more comfortable to drive and accelerate faster in the meantime. Also seems like these bigger wheels are killing my gas mileage.

    Who knows a lot about this? Not looking to get flamed or ragged on, just lookin' for some advice.

    2JZ-GE | Turbonetics T66 | AEM

  2. #2
    Is it turbo? Is it stick? TROLL's Avatar
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    rotating mass will have a huge affect on accelleration (and braking, and turning)... and the farther from the center of rotation the more detrimental the extra weight will be.
    however, consider this... you've got 18" of wheel and 3" of tire... he's got 16" of wheel and 5" of tire. the extra aluminum in your wheel is most likely heavier than the extra tire in his, but by how much? hard to say without weighing them.

    other places where you have rotating mass are brake rotors, axles, driveshaft, clutch/flywheel, etc... reducing weight in any of these will have a much large impact than static weight reduction.

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    OG Rich B's Avatar
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    SInce you are asking th e RR&A forum, the standard line on optimum rims for a SUpra (turbo, though) would be to add one size up from stock for big brakes, and then keep the 17's in the rear for that very reason - to reduce rotating inertia.

    However, The other component of interest to the road racers is trying to maximize the contact patch area, which is enhanced by bigger sizes.
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    SupraForums Member
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    Is the outside diameter of your 18" about the same as his 16"? If yours are larger diameter, that would in effect lower your drive ratio which will cause more sluggish acceleration. Give us the sizes here so we can evaluate magnitude.

    As far as power loss attributed to heavier larger wheels, has anybody ever heard numbers more than about 5whp for such losses?

  5. #5
    Exiled Supra Owner FLZ_Boy's Avatar
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    I love my 16", but wish there was a larger size tires for the rims (very limited). Here are the stats for the 16":

    Size:

    225/50/16x8 Fronts
    245/45/16x9 Rears

    Weight:

    19 lbs. front

    21 lbs rear

    The TT 17" has more tire selections available, but weights are:

    21 lbs. front

    23 lbs. rear (I think it was 23........or was it 24..........)
    Last edited by FLZ_Boy; 06-23-2008 at 05:44 PM.
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    wow. i have the moda r8. i believe they are 31 lbs per rim. so that's roughly 124 lbs. compared to your 16" at 80 lbs. There is a 44 lb difference in rims here. How does this affect rotation mass and drive ratio?

    The tires I have on right now are 265x35 in rear and 235x40 in front. That is for 18" rims.

    If I go to stock MKIII turbo rims I believe my tires would be about 225? These are the rims I have laying around the garage. They're the JDM ones and they're mint. I think they'd make for a clean, not so attention-drawing, look to the car while i save on gas mileage and regain comfort. Meanwhile I'll be saving for some Work Equips and the turbo build lol.

    These are the rims I'm wanting to put on in the meantime....


    So, am I losing out on acceleration or what? how much extra weight am i dragging with these 18s on?

    This is all from the previous owner. I'm looking to get new tires soon so this is why I'm wondering about rim sizes and stuff.

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    ESE CULO RemixPinoY's Avatar
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    I know how you feel, I have 19's and I know their not light either just cheapo TSW's. Kinda disappointed in acceleration, friends prelude thats stock can take me off the line, takes me awhile to catch him.

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    not to mention, my braking is awful. i will brake like i do normally and the car will just slow down. to get it to actually stop i have to really add some pressure.

    and my mpg is suffering!!!

  9. #9
    SupraForums Member Supra GTR's Avatar
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    Are you road racing your vehicle or is this for street racing?

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    Moderator SideWinderGX's Avatar
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    Quote Originally Posted by Nick 95 6sp View Post
    Is the outside diameter of your 18" about the same as his 16"? If yours are larger diameter, that would in effect lower your drive ratio which will cause more sluggish acceleration. Give us the sizes here so we can evaluate magnitude.

    As far as power loss attributed to heavier larger wheels, has anybody ever heard numbers more than about 5whp for such losses?
    The amount of power you necessarily 'lose' from having a greater amount of rotational mass, isnt the same as how much power/acceleration you will gain. a dyno will measure how much power you have, it wont put into perspective how quickly it will accelerate on the street

    im assuming thats what you meant though.

    as im on the stock sawblades, im not looking for anything but 5 spoke, lightweight 16" rims. itll keep my speedometer measuring correctly and reduce rotating mass, along with a steel 1 piece drive shaft ill (eventually) get. it is SO much more gratifying to fly by people with bigger rims, rather than putting more 'show' into my car

  11. #11
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    i'm not racing this car at all. it's an na. lol racing an na.

    i just want the damn thing to drive comfortably.

  12. #12
    Exiled Supra Owner FLZ_Boy's Avatar
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    Nothing wrong with racing a NA, it's one of my most dependable track cars (large road courses with straightaways I get killed).

  13. #13
    SupraForums Member Supra GTR's Avatar
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    Quote Originally Posted by kaos View Post
    i'm not racing this car at all. it's an na. lol racing an na.
    NA's have been successfully raced in SCCA Club Racing for several years.

    Quote Originally Posted by kaos View Post
    i just want the damn thing to drive comfortably.
    What is comfortable for you? Turning better? Softer ride?

    Most people in the road race section get aftermarket wheels because they wanted wider tires and as wide a track as possible for better handling through the corners/sweepers.

    IMO, the picture you posted would not be comfortable. It's under-tired and the track is way too narrow, like riding on space savers.

  14. #14
    SupraForums Member Wiisass's Avatar
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    I think the trick is to not buy wheels that weigh 30lbs no matter what size they are. You can get decent 18s that are not too expensive that are in the low 20lb range and if you want to spend more, you can save even more weight.

    But 30+lbs for the wheel alone is a lot of weight. And don't forget to factor in tire weight to the whole thing as well. 18" and 16" tires weigh different amounts.

    And then the difference in height, as Nick pointed out, is a big factor. It's going to affect the final drive and how the engine puts down the power. Shorter tires will make the car feel like it's accelerating a little faster and taller tires will make it feel a little slower but you'll have a higher top speed and spend more time in each gear.

  15. #15
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    Quote Originally Posted by Wiisass View Post
    I think the trick is to not buy wheels that weigh 30lbs no matter what size they are. You can get decent 18s that are not too expensive that are in the low 20lb range and if you want to spend more, you can save even more weight.

    But 30+lbs for the wheel alone is a lot of weight. And don't forget to factor in tire weight to the whole thing as well. 18" and 16" tires weigh different amounts.

    And then the difference in height, as Nick pointed out, is a big factor. It's going to affect the final drive and how the engine puts down the power. Shorter tires will make the car feel like it's accelerating a little faster and taller tires will make it feel a little slower but you'll have a higher top speed and spend more time in each gear.
    this sounds comforting to hear. i was under the impression that bigger tires on a car that isn't so fast would mean twice as much wear on the engine since it's technically having to constantly lug more weight around and rev a little higher in the rpms. plus bad gas mileage??

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