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Can someone explain to me why larger rims slow your car down?

 
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i dunno about size but usually larger rims weigh more. it will take more power to turn the wheel. that's what i think anyway. someone please correct me if i'm wrong

 
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actually larger rims weigh usually about the same or lighter than the stock steel versions.

but the main reason why you lose power with larger rims is b/c they change the gear ratio of the car by making it taller. in essence, the engine has to rotate more to make the wheel turn once. also larger wheels put more rubber to road and that means more rolling resistance=power loss.

 
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<< actually larger rims weigh usually about the same or lighter than the stock steel versions >>

not sure on that[IMG]i/expressions/face-icon-small-confused.gif[/IMG]Most larger rims weigh more then smaller rims dont they[IMG]i/expressions/face-icon-small-confused.gif[/IMG]

 
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yeah what ever Suziq said make sense. but i thought when u get bigger rims u get thinner tires, thus in order to maintain the same circumferece. thus if it's the new circumference is bigger or smaller than stock, it will affect ur speedometer and power to turn

 
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OK, the reason big rims slow down the car is because big rims usually weigh more than stockers. In some cases, big rims can weigh up to 15 lbs more than a stock wheel. All this added weight means that it takes more horsepower to turn, thus the horsepower to the ground is reduced. It is exactly the same concept as using a lightweight flywheel or a carbon fiber driveshaft. Reducing the weight of the drivetrain increases the amount of power to the ground. Hope this clears up this commonly misunderstood issue.

 
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yeah that's exactly what i meant [IMG]i/expressions/face-icon-small-smile.gif[/IMG]

 
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<< &lt;&lt; actually larger rims weigh usually about the same or lighter than the stock steel versions &gt;&gt; >>




<< not sure on thatMost larger rims weigh more then smaller rims dont they >>


larger aftermarket rims can weigh less than than the stock 15 inch steel rim cause our stock rims are heavy, about 18lbs and are only 15 inch, but you can find aftermarket 16 or 17 inch rims that weigh about the same or less.

 
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i don't totally agree with the a rim being up to 15# heavier than a stocker--especially if from a quality brand like eneki. but its 3am and i have no time to zzzzzzzzzzzzzzzzzzzzzzz [IMG]i/expressions/face-icon-small-blush.gif[/IMG]

 
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i know chrome rims can be heavy. obviously racing rims will weigh less

 
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<< Can someone explain to me why larger rims slow your car down? >>


you actually go faster
larger wheel=higher top speed and slower acceleration because you are adding more gear ratio. so it has more to do with the final tire/wheel diameter then the weight of the wheel.
if u wanted to accelerate faster rims that are a little heavier but are smaller would make you go faster than larger rims that are lighter.

 
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double post

 
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<<

<< Can someone explain to me why larger rims slow your car down? >>


you actually go faster
larger wheel=higher top speed and slower acceleration because you are adding more gear ratio. so it has more to do with the final tire/wheel diameter then the weight of the wheel.
if u wanted to accelerate faster rims that are a little heavier but are smaller would make you go faster than larger rims that are lighter. >>




Let's not forget... the heaver the wheels, the more pressure you put on your brakes to stop from going so fast.

So do you put aftermarket sport brakes on the car to help that?

And since you lose HP from heavier wheels (soon I'm going to get some 17s, and I will watch the weight), will adding an intake (say AEM CAI) and a better exhaust even out the odds? Or are the wheels that heavy?

 
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estimated loss in horespower going from stock wheels to a 17" light weight rim 15# to 19# around 5 horsepower at the wheels. Gain for adding intake header exhaust around 10hp+- . With wheels and ihe you just spent $2000+ to get around 5hp! The benefits though are crisper turn in response, better handling and better braking (as said before the braking only comes if you use a light enough wheel!) Also to add to the physics aspect, it takes more power for a car to drive a 17" wheel than a 15" wheel even if they are the same weight! the 17" wheel has more of its weight located farther away from the hub making it harder to turn. Also you would get higher gearing only if the wheels were not properly plus sized, but as stated before you can also use this to adjust for top speed or acceleration. I would suggest acceleration!!!!

 
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Actually there are only two people that are accurate in their statements.
The reason that your car goes slower, or seems as such is for this simple fact.
When you go from a 175 tire to a 205 or 215 size tire you are changing your gear ratio.
This in return lower's you gear ratio. For everyone that does not know what gear ratio is,
I will explain it to you. In my truck, I have 4.56:1 g/r. This means that my drive shaft have to
turn 4.56 time to make my wheels rotate once. Now that is not all. To get your final g/r you have
to now add your tire size in there to the equation.... Anyways to sum it up. The less rotations it takes you motor
to make to make you wheels make one complete rotation, the more hp required to make it turn. When you change to a
bigger tire/rim combo, you are lowering you g/r even more. So now you loose some of your bottom end power but gain
top speed...

I hope that this clears up any misconceptions about larger tire/rim combo's

 
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Good explination Boosted..BTW..when did you get "Moderating status"....congrats.......anyway...the physics term to discribe all your statements is rotational inertia...........a good visual I like to use for those who may still have a hard time understanding the principle....is take a 17 inch string and tie a nut at the 15 inch mark and start spinning it over your head...observing the difficulty in getting the nut swinging, then notice the effort while spinning at the circular motion(angular velocity and accelration..ie. wheel, gears, drive train all in one)...now move that same nut out to the 17 inch mark....start spinning it...... in a nut shell you'll notice that

a. To get the nut started is a little more difficult, even though the weight is the same
b. Once in angular motion, you'll notice the effort to spin that same nut is easier
c. This simple test will roughly illustrate, the harder acceleration of our cars with increases rotaitonal inertia, and the increased higher speeds with larger rims.

Its all about checks and balances....sure you give up some things, but gain others. It is just all about what makes you happy!

Peace! [IMG]i/expressions/face-icon-small-smile.gif[/IMG]

 
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Boosted, when you switch to a larger wheel, the force at the road goes down thus acceleration is adversley affected ala (f=ma) however power remains the same - power is work/time = force*distance/time for a larger wheel force is reduced, but distance covered increases and time stays the same (at a given axle rpm the wheel spins at the same rate no matter what the size) so power remains the same. acceleration still goes down.

The perceived lack of power in a bigger wheel is a combo of this, the inertia reqd, and a higher frictional force that hi pref tires give (mu-r or rolling resistance)

-m

 
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Boosted - good job - but you are all missing one very improtant thing. Inertia (simply though of in terms of weight distrubution) For the purposes of this descusion it can more or less be neglected. But just for general knowledge that is why you see rim companies try to concentrate the weight of the rim at not on the center by the axel but also the center of the tire. That combined with everything boosted said, not to mention friction, temp of tires from friction and its result on static and kinetic friction and also a couple other little things determine how your wheels roll.

 
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I want to clarify something:

For those who don't know:
a tire marked P 195 45 ZR 17 has,

-a width of 195 millimetres,
-a sidewall that is 45 percent of 195mm tall = 88mm,
-a 'ZR' speed rating over 180 Mph or something like that.
-and has an internal diameter / fits a wheel of 17 inches.

So, changing from a 175 to a 205 or 215 tire doesn't affect the car's gear ratio directly, it is the corresponding increase in the sidewall height associated with a wider tire that will change the final drive ratio. E.g: A tire marked P185 50 15 has a slighlty smaller diameter than one that is P215 50 15 only because 50 percent of the treadwidth is now larger. So, as long as the siewall height is compensated for, a switch to wider tires won'd do anything but increase friction/rolling resistance.
More obviously, changing from a 40 to a 50-series tire changes the final gear raito beacuse the diamater/circumference are increased assuming the size of the wheel and tread width are the same.

 
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thanks guys. this was very helpful