Ok, I want from my 16" LS Sport Chrome rims to 17" RPM 502's. MY acceleration just sucks now, like when i press down i dont really go anywhere like i used to. do the bigger size really make this huge of a difference? If so, is there anyway i can increase the get go on the rims anyway?
its only a cavalier do think to much in to it. the bigger the rims the more the engine has to work to get it moving
More mass will always turn slower. How heavy are the wheels? My 17's should be a bit lighter than stock, we will see when I get some tires. Every 10 lbs of rotational mass is about .10 in the 1/4. So if the wheels are 20 lbs heavier than stock, your car would be about .2 slower. What size tires are you running, that could be a problem as well if they are not sized right.
2012 HD VRSCF
2010 Ford Explorer
2006 Ford Ranger
2004 Chevy Cavalier
it shouldnt make that much of a difference
Fire Fighter wrote:More mass will always turn slower. How heavy are the wheels? My 17's should be a bit lighter than stock, we will see when I get some tires. Every 10 lbs of rotational mass is about .10 in the 1/4. So if the wheels are 20 lbs heavier than stock, your car would be about .2 slower. What size tires are you running, that could be a problem as well if they are not sized right.
It's not that simple, and yes, it can make a huge difference.
My 18's are boat anchors and definitely hurt the performance.
It's not just the weight that matters, but how far that mass is from the center of rotation. Most of the mass of a wheel is in the outer rim, so a bigger wheel is heavier and has the mass centered further from the hub.
Someone with more of a physics background will have to clarify this, but I believe the work needed to turn the mass increases exponentially as the distance from the center increases.
So basically, it's a huge difference if they're a lot heavier. More than you'd expect it to be.
Now consider this... your car is feeling more sluggish because you need more power to get those wheels turning. This weight difference has just as much of an effect when you're braking as when you're accelerating. Since the stock brakes suck ass on a stock car, imagine what effect your new wheels are having on your stopping power. I highly recommend at least upgrading your rotors and pads to something with more biting power and fade resistance.
Wild Weasel wrote:Fire Fighter wrote:More mass will always turn slower. How heavy are the wheels? My 17's should be a bit lighter than stock, we will see when I get some tires. Every 10 lbs of rotational mass is about .10 in the 1/4. So if the wheels are 20 lbs heavier than stock, your car would be about .2 slower. What size tires are you running, that could be a problem as well if they are not sized right.
It's not that simple, and yes, it can make a huge difference.
My 18's are boat anchors and definitely hurt the performance.
It's not just the weight that matters, but how far that mass is from the center of rotation. Most of the mass of a wheel is in the outer rim, so a bigger wheel is heavier and has the mass centered further from the hub.
Someone with more of a physics background will have to clarify this, but I believe the work needed to turn the mass increases exponentially as the distance from the center increases.
So basically, it's a huge difference if they're a lot heavier. More than you'd expect it to be.
Now consider this... your car is feeling more sluggish because you need more power to get those wheels turning. This weight difference has just as much of an effect when you're braking as when you're accelerating. Since the stock brakes suck ass on a stock car, imagine what effect your new wheels are having on your stopping power. I highly recommend at least upgrading your rotors and pads to something with more biting power and fade resistance.
Mostly correct. The angular acceleration (alpha) of the wheels is determined by the torque acting on the wheels (t) divided by the moment of intertia (I). Alpha = t/I. As you increase the moment of inertia (I) and keep the torque (t) from the engine the same (in this case as in the same engine power, not a static torque), your angular acelleration (alpha) will decrease. Think of the moment of inertia as how hard is is to turn something...
The Moment of inertia for a disk = Mass x (Radius squared). The moment of inertia for a solid cylinder is 1/2 x Mass x (Radius squared). I assume that the moment of inertia for a wheel is somewhere in between. What this means is that an increase of 1" (2.54cm) while keeping the mass the same would yeild a larger I. The value for I isn't fully exponential, but each additional inch does add more and more.
For example, lets assume a wheel weighs 12 kg and that the moment of inertia for that wheel is given by the equation 3/4 x Mass x (Radius squared). A 16" wheel would then have an I value of .372 The same mass in an 18" wheel would have an I value of .470, an increase of about .1. This increase of .1 tranlates into (roughly) a 21% reduced value for the angular acelleration of the wheel.
Now, in no way are these figures considered to be accurate representations of real world scenerios. They are only examples of basic principles that come into effect when you increase the wheel size. Other factors may come into play, such as reduced tire size, etc., however, that is a general and basic explanation of the physics behind your wheel.
god damn, that was impressive... better than i could ever have attempted.
so basically, it doesnt matter so much how light your rim is, it is the placement of the weight (which is obviously on the outside edge of the rim) that plays the biggest factor.
torque = force applied * distance
so that would mean...
force applied = torque / distance
increase the distance and the force applied will decrease. the force NEEDED to move a mass is constant. now since that is true, the farther we move the weight to the outside (increasing the size of the rim by inches) the less force is applied to that rim at the same torque.
so to move that bigger rim, we need to increase the force applied. to increase the force applied we either need to decrease the distance, the weight, or increase the torque.
getting the lightest possible tire and rim combo will help. the weight of the rim is usually given when you are shopping them around. the weight of the tire is available in the spec charts. make it as light as possible, or produce more torque seem to be your only options.
i dont know if this further explains what pork chop said, or if it just further confuses people. basically, if you dont know what you are doing, ask some one who does. now you know why your fuel economy went down when you put those big fancy rims on, and why i still only want a 15" alloy
Injection is nice but id rather be BLOWN!
whitegoose wrote:god damn, that was impressive... better than i could ever have attempted.
so basically, it doesnt matter so much how light your rim is, it is the placement of the weight (which is obviously on the outside edge of the rim) that plays the biggest factor.
torque = force applied * distance
so that would mean...
force applied = torque / distance
increase the distance and the force applied will decrease. the force NEEDED to move a mass is constant. now since that is true, the farther we move the weight to the outside (increasing the size of the rim by inches) the less force is applied to that rim at the same torque.
so to move that bigger rim, we need to increase the force applied. to increase the force applied we either need to decrease the distance, the weight, or increase the torque.
getting the lightest possible tire and rim combo will help. the weight of the rim is usually given when you are shopping them around. the weight of the tire is available in the spec charts. make it as light as possible, or produce more torque seem to be your only options.
i dont know if this further explains what pork chop said, or if it just further confuses people. basically, if you dont know what you are doing, ask some one who does. now you know why your fuel economy went down when you put those big fancy rims on, and why i still only want a 15" alloy
The problem there is that you can't use that equation for any useful purpose here. You are correct that torque = force x distance, however, the distance in that equation is the distance from the center of mass the force is being applied. In this case, this will be identical in all circumstances because the lug nuts will be in the exact same spot with respect to the center of mass (center of the wheel).
You are also correct that weight (and since gravity is constant, mass) and radius of the wheel effects acelleration. However, that would be due to their effect on the moment of inertia of the wheels, not the torque being applied upon them.
cant let me feel smart can you porkchop....
just had to go and burst my buble...
*goes and hides in a deep dark hole*
Injection is nice but id rather be BLOWN!
Its good to see we have some real educated people in here. Seems like people know a lot more than just cars. Sounds like everyones got some engineering education in this forum. Good old kinematics and dynamics, applied to the real world.
Do you guys have Albert Einstein or Erico Fermi, on your staff to help you out!
j/k - Excellent explanation...a sticky on that would be nice...IMHO...most people probably don't know the consequences of going from there 15" rims to 19"+...Ouch! All they see is the cool factor....anyway...good food for thought!
Thanks for the info.......
Silver Stripey makes your Day!
yea many dont and i sure didn't.
oh yea i have 17"x7 rpm 502's. I need to figure out how much they weigh still though
well i might as well ask this.... can not properly tighting your lug nugs do anything as far as performance wise?
DcM wrote:well i might as well ask this.... can not properly tighting your lug nugs do anything as far as performance wise?
yeah, when a wheel breaks off, it usually hurts performance
not to mention, the wheel will wobble, and that hurts performance too
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Quote:
DcM
Thursday, April 06, 2006 6:17 PM
Ok, I want from my 16" LS Sport Chrome rims to 17" RPM 502's. MY acceleration just sucks now, like when i press down i dont really go anywhere like i used to. do the bigger size really make this huge of a difference?
Its called unsprung weight and it is detrimental to performance. Design of the wheel, construction methods, size, etc all determine how much it weighs. The bigger the weight difference, well.. you know.
Man I really wanted to input somethign smart here...
But I can give a good example of a past experience...
My old 92 Chevy Lumina Z34 ran a 14.9 1/4 mile on the stock 16x6.5 wheels with 225/60R16's... those weighed in at a nice 51lbs each (wheels and tires +air, yes air adds a small amount of weight)... when I switched to my 17x8's with 245/45ZR17's the weight of each wheel/tire decreased to 49lbs each... That's a total of -8lbs unsprung weight. When I ran again with the new wheels / more traction I only got a 15.4... and the wheels were LIGHTER.
They already talked about inertia and all the formulas. Basically the majority of the mass is the rim of the wheel (the flat part the tire mounts over). The further you move it out, the harder it is to get it moving... that's why a lot of good drag racers run small diameter wheels.
But with bigger / wider wheels, you sure do handle better!
And unsprung weight can make a huge difference in handling, as well as performance, sir above me.
Pork Chop Sandwiches!!! wrote:Wild Weasel wrote:Fire Fighter wrote:More mass will always turn slower. How heavy are the wheels? My 17's should be a bit lighter than stock, we will see when I get some tires. Every 10 lbs of rotational mass is about .10 in the 1/4. So if the wheels are 20 lbs heavier than stock, your car would be about .2 slower. What size tires are you running, that could be a problem as well if they are not sized right.
It's not that simple, and yes, it can make a huge difference.
My 18's are boat anchors and definitely hurt the performance.
It's not just the weight that matters, but how far that mass is from the center of rotation. Most of the mass of a wheel is in the outer rim, so a bigger wheel is heavier and has the mass centered further from the hub.
Someone with more of a physics background will have to clarify this, but I believe the work needed to turn the mass increases exponentially as the distance from the center increases.
So basically, it's a huge difference if they're a lot heavier. More than you'd expect it to be.
Now consider this... your car is feeling more sluggish because you need more power to get those wheels turning. This weight difference has just as much of an effect when you're braking as when you're accelerating. Since the stock brakes suck ass on a stock car, imagine what effect your new wheels are having on your stopping power. I highly recommend at least upgrading your rotors and pads to something with more biting power and fade resistance.
Mostly correct. The angular acceleration (alpha) of the wheels is determined by the torque acting on the wheels (t) divided by the moment of intertia (I). Alpha = t/I. As you increase the moment of inertia (I) and keep the torque (t) from the engine the same (in this case as in the same engine power, not a static torque), your angular acelleration (alpha) will decrease. Think of the moment of inertia as how hard is is to turn something...
The Moment of inertia for a disk = Mass x (Radius squared). The moment of inertia for a solid cylinder is 1/2 x Mass x (Radius squared). I assume that the moment of inertia for a wheel is somewhere in between. What this means is that an increase of 1" (2.54cm) while keeping the mass the same would yeild a larger I. The value for I isn't fully exponential, but each additional inch does add more and more.
For example, lets assume a wheel weighs 12 kg and that the moment of inertia for that wheel is given by the equation 3/4 x Mass x (Radius squared). A 16" wheel would then have an I value of .372 The same mass in an 18" wheel would have an I value of .470, an increase of about .1. This increase of .1 tranlates into (roughly) a 21% reduced value for the angular acelleration of the wheel.
Now, in no way are these figures considered to be accurate representations of real world scenerios. They are only examples of basic principles that come into effect when you increase the wheel size. Other factors may come into play, such as reduced tire size, etc., however, that is a general and basic explanation of the physics behind your wheel.
My head hurts now, good post tho
so how much performane will i lose when i go and get my enkei evo 5's put on, that is kinda scary, my car is slow as it is
fully built 2200-TO4E T3/T4-HP tuners-373hp @18psi
they are 18x 7.5 by the way, wrapped in BFG KDW 2's
fully built 2200-TO4E T3/T4-HP tuners-373hp @18psi
what is the best rim size for acceleration? when i was over in germany i used to see BMWs and VWs with 15's and under...i wanted to get 16's or 17's.which one would be better to have?
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young_Z95 wrote:what is the best rim size for acceleration? when i was over in germany i used to see BMWs and VWs with 15's and under...i wanted to get 16's or 17's.which one would be better to have?
In general? The smallest and lightest wheel you can find.
