Will bigger rims slow me down?

[EBUCKS]

mx3man83 I didn't say anything about rotational mass. I was merely speaking of tire diametres. I know that the mass of the rim will affect your take off speed. However, I wasn't speaking of that. <BR>Now how is it that you're going to call me an idiot? You seem to be the idiot who got all bent out of shape, because you can't phuckin' read. I've already taken physics and passed it (10 phuckin' years ago). Since you still need the phuckin' course, maybe you should take English as a second language to help you understand what the phuck is going on.<BR>A guy tries to be helpful, and he gets some beeeyatch up his a$$. <P>Freq I got size 12 shoes. So the cushion is good so ya don't get a bendy. [img]shrug.gif"%20border="0[/img] <P>one

[ProtegeSTS]

Both of you people are retarded...<P>Tires weigh more than Wheels...<P>Typical lightweight wheel =13lbs<BR>typical 15" tire =20lbs<P>think...<p>[ September 27, 2002: Message edited by: ProtegeSTS ]

[voltaire]

I agree with ProtegeSTS, but I'm wondering what the exact proportion of tire to wheel weight is.<P>The 2 questions are: What's the typical weight of 1" of tire sidewall? What's the typical weight of 1" of rim?<P>Tires may typically weigh more than rims, but the only thing really increasing/decreasing on tires is the sidewall. I imagine the tread and steel belt are the heaviest parts of a tire.

[Freq2002]

This is why I really dislike this BBS, the kiddies (of all ages) who cant be constructive in thier criticism, but have to throw a b---- fit.<P>OK, so now that everyone is all bent, do ANY of you have concrete proof that a larger rim, (EXCLUDING the 1-ton chrome plated behemoths) will take more to turn than a stocker? Not he said she said, which is all I've seen so far, but concrete proof, in writing. I can claim anything I like & if I get all technical I could even get people to eblieve my line of s---, but does that make it right?<BR>I'm talkin about the GOOD race rims too, not the cheap a-- wanna be's. If ya do, I'd love to see it. It would probably be of great interest to all the professional rally race teams that run the 16-17" rims to save WEIGHT (extra emphasis on 'save WEIGHT'), & increase lateral stability by decreasing sidewall roll.<BR>Also take into account that while a 17" rim may weigh more than a 14" of the same style, when you look at tires of the same outer diameter, the rubber weighs less.<P>But hey, yanno what? Maybe I'm just an idiot, & I never learned anything in all the school I've had, the nearly 20 years of being a mechanic on cars, bikes, trucks, tractors, & aircraft. Never learned s--- racing drag cars & off-road,... Yeah, thats it, I AM a retard,... <BR>Two words for the haters, 1st one is "bite", you figgure out the 2nd.<P>Volt> It would be hard to get a typical weight on rims as it depends greatly on the material used & the wheel pattern. A race duty mag-alloy rim will weight alot less than any aluminum wheel. Tires also vary depending on tread type, what the belts are made of & number of layers of each material.<p>[ September 27, 2002: Message edited by: Freq2002 ]

[voltaire]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Freq2002:<BR><STRONG><BR>Volt> It would be hard to get a typical weight on rims as it depends greatly on the material used & the wheel pattern. A race duty mag-alloy rim will weight alot less than any aluminum wheel. Tires also vary depending on tread type, what the belts are made of & number of layers of each material.<BR></STRONG><HR></BLOCKQUOTE><P>Yeah, I didn't figure it would be easy. I was thinking more along the lines of an average or maybe a few random samples. Not that I expect anybody to have exact the weights of different size but otherwise indentical tires and wheels laying around, but I'll see what I can do in a reasonable amount of time when I get a chance. If someone already has this, feel free to beat me to the punch (please!).<P>Everyone needs to keep in mind that there are 3 (or 4 depending on the way you look at things) basic considerations when choosing the tire and wheel size/weight combination. Those are handling, top speed, & acceleration. The fourth is appearance, but that's better left out of it for the sake of science.<P>You also have to consider the limits of the particular vehicle. On top of that you've got weather/season choices, braking characteristics, speed-rating, durability, dependability, and safety concerns. To top it all off cost is a major factor as well. That's all I can think of off the top of my head, but I'm sure I left something out!<P>As is apparent, tire & wheel size/weight combination is complicated to say the least. It's not surprising that there's so much disagreement on the subject. That said, everyone needs to COOL IT!!! Let's discuss this with facts. Imagine how cool it would be if everyone could do a little bit of research on their own and have a discussion here based on what they found.<P>Not that I'm all that optimistic that we'll come to an agreement.....<p>[ September 27, 2002: Message edited by: voltaire ]

[mx3man83]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by ProtegeSTS:<BR><STRONG>Both of you people are retarded...<P>Tires weigh more than Wheels...<P>Typical lightweight wheel =13lbs<BR>typical 15" tire =20lbs<P>think...<P>[ September 27, 2002: Message edited by: ProtegeSTS ]</STRONG><HR></BLOCKQUOTE><P><BR>your going to sit here and try to tell me that a rubber tire weighs more than a metal rim?? Maybe the tires for an earth mover...but definitely not an mx3.

[voltaire]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by mx3man83:<BR><STRONG><P><BR>your going to sit here and try to tell me that a rubber tire weighs more than a metal rim?? Maybe the tires for an earth mover...but definitely not an mx3.</STRONG><HR></BLOCKQUOTE><P>The two *are* usually about the same weight. He was comparing a typical tire to a "lightweight wheel".<P>Tires are heavy, pick one up. Remember they're not just rubber, there's also a steel belt. And rubber isn't exactly light, it's pretty dense stuff.

[ProtegeSTS]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by mx3man83:<BR><STRONG><P><BR>your going to sit here and try to tell me that a rubber tire weighs more than a metal rim?? Maybe the tires for an earth mover...but definitely not an mx3.</STRONG><HR></BLOCKQUOTE><P>go read the tire comparison in Grassroots Motorsports this month. They list weights of several high performance tires in a 15" size, aka MX3 size. Being that ive got 8 Falkens sitting in my living room, 4 mounted on Kosei K1s (13lbs each), and 4 alone, i can attest to fact that tires are heavy. Steel belts are not light. And aluminum alloy (what they make wheels out of) IS light.<P>Please READ and do research before you determine what your correct answer is. It solves little "debates" like this before they even start.<P>Stock MX-3 GS SE wheels will run ~15lbs. OEM Miata wheels are 11-16 lbs depending on model. You wont find tires that light.

[Sean Mandell]

what tire is the the lightest?

[Sean Mandell]

also anyone that buys heavy 17" wheels will notice that braking is a more important issue than acceleration and upgrading the brakes is essential (pads,rotors and brake lines)When ever you see civics at import shows with 19" rims you will notice that the brakes are upgraded too. this is not just for looks but trying to stop fast with 19" with stock brakes could be a scary situation.

[Freq2002]

You NEED to upgrade your braking capacity if you're driving much higher speeds or in the case of rally or road racing, you do a LOT of consistant hard braking. Larger diameter discs will give more stopping power, but the size/weight of the tire isn't an issue so long as the wheel fits over the caliper.<BR>The weight difference of the wheels in respect to braking is like saying you need bigger brakes coz you filled up your gas tank,... Also take into account that upgrading to larger discs & multi piston calipers will ADD wieght. More rotational mass that you have to spin, blah, blah, fewkin blah.<BR>Braking & accelertion are two totaly differnt schools of thought.<P>Bottom line. Only reason the street geeks get big rims & big brakes is to look cool. The REAL reason to do it is for increased lateral stability for hard cornering. The larger rim gives room for larger brakes for increased braking ability so you can scream up to a corner & brake to a safe entry speed just before the turn. Doin this with stock brakes isn't the best idea. So, unless you're doing real racing, the point is moot. Truth is it's a waste of money just to look cool, just like everyone else. But it's up to you whatya wanna do with your bones.<BR>For drag racing (the legal kind), stock brakes are plenty as they have the overun area on the track to slow down. Find some light 14's & run a good street/strip rubber. It'll cost ya a LOT less on tires & if a couple pounds is making that much differnce to you at the strip, maybe you need to drop that 3-4000 bones that wheels & brakes will cost & do somethin with that pig under the hood.<P>But thats just me & most people think I'm wierd,...

[Sean Mandell]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Freq2002:<BR><STRONG><BR>The weight difference of the wheels in respect to braking is like saying you need bigger brakes coz you filled up your gas tank<P>But thats just me & most people think I'm wierd,... </STRONG><HR></BLOCKQUOTE><P>I always though that tha brakes slow the wheels down and the tires stop the car. If wheel is bigger and heavier therefor adding pressure on caliper. big brake kits are not neccesarily better then oem with green stuff pads and X rotors unless the size of the wheel is double the stock weight. For 17" wheels close to or lighter than stock weight, brakes won't be a facter. <BR> <BR> [img]shrug.gif"%20border="0[/img]

[tk1138]

‘Rotational mass’??? Do you mean moment of inertia? Inertia is given by mass times radius squared, so although the rim might way more or not, the rubber on it will generally dominate the inertia.<P>Moment of Inertia:<BR>The work required to accelerate an object from zero angular velocity by a given angular velocity (RPM) is equal to the moment of inertia times one half the angular velocity squared.<BR>Work=(1/2) *I*w^2 (^ means ‘to the power of‘, w should be omega)<BR>I=(1/2)*M*(Ri^2+Ro^2) this is for a hollow cylinder, but is analogous to rims where Ri is approximately the radius at which the material gets thicker & Ro is the radius to the outside<BR>Power=Work/time=(1/4)*M*(Ri^2+Ro^2)*w^2<P>If we use Tire assemblies that have the same mass, but have larger rims, then we see that the moment of inertia increases, and it takes more power to spin the wheels up.<BR>DP/dRi=(1/2)*M*w^2*Ri<P>If you get bigger rims, and want the same power, then the overall mass of the wheels should be reduced by the same factor.<P>Here are some sample calculations of inertia and the difference between hypothetically crappy tires and hypothetically great tires. <BR> <BR>The moment of inertia of a tire is very complex to calculate (I=the integral of radius squared with respect to mass), so we’ll use an estimate that should yield similar or slightly higher results (hollow cylinder).<BR>I=(1/2)*M*(Ri^2+Ro^2)<P>For the inside radius we’ll use 17/2” =. 2159 Meters and for the outside we’ll use 23/2” = .2921 Meters for the mass we’ll a somewhat heavy amount of 10Kg which is about 21 Lbs. For the angular velocity in radians per second well take 100Mph=44.7sec, and divide by the radius to get 153 rad/s.<BR>I=. 660 kg*m^2<BR>Work=7722 joules<BR>Now divide this over the time it took you to go this fast, and you see that while not insignificant, the energy used in accelerating the rotating (crappy) wheels isn’t a lot.<BR>772 watts=1.03 Horsepower<BR>*4 wheels= 4 Horses<P><BR>If we make some arbitrarily high performance rims with light tires on them then M=5kg, evenly distributed… I=.2133 kg*m^2, …Work=2496 joules. Divide this by the time it took you to get there and…<BR>250 watts=1/3 Horsepower<BR>*4wheels=1.33 Horses<P>REALLY good wheel assemblies will seem to free up about 3 more horse power than really bad tires at about 100 MPH. At lower speeds the differences are less pronounced, and at higher speeds the differences are more pronounced.<P>dP/dv=(1/4)*M*(Ri^2+Ro^2)*2*w (v=velocity=k*angular velocity)<P>Unless you increased the overall radius of your tire, or filled it with silicone, you don’t need bigger brakes just from changing rims. Getting better rims will reduce the need for brakes by a small amount. The acceleration difference, and brake difference will be the same (although the engine cannot apply power evenly over the RPM range.)<P>In summary: If you race, it’s probably worth it to get ‘light’ rims & tires (as long as you don’t sacrifice traction). If you don’t, looks are probably more important than inertia.<P>You cannot tell the inertia just by weight, or rim size, although weight is a better indicator.<P>If you want to compare two tire assemblies, you can:<BR>1. jack up the rear of your car.<BR>2. put one wheel on the one of the back wheels of your car.<BR>3. spin it up to a constant speed. <BR>4. time how long it takes to spin down.<BR>5. put the other assembly on the SAME side in the back.<BR>6. spin it up to the SAME constant speed.<BR>7. time how long it takes to spin down.<BR>8. the ‘better or quicker’ tire will take a shorter period to spin down.<BR>How you spin them up is up to you, but be careful!!! In addition, be consistent. The moment of inertia will be roughly proportional to the time it took to spin down.<P>I’d do it myself, except I don’t have any rims ;-(<P>This doesn’t take into account handling or other factors.<P>Sorry for the long post, but I doubt anyone on this board will do a proper test and account for all the variables, and even if they do they probably won’t test all the possible combinations.

[Freq2002]

Uhhhhh, yeah, what he said,...<BR>LMAO :p <P>Good s--- there tho meng. Unfortuanately I failed algebra, lest not get into trig. <BR>Given all of this info, the proper formulae along with correct data on the wheels & tires in question I could build a calculator on MS Excell to figure the variations in moment & tourqe requirments, etc. Already have a killer one for figuring out displacement, comression, deck, head vol. And one that will tell you your speeds at shift point given the gear ratios & tire OD.<BR>If anyone has a clue what I'm talkin about & would like a copy I can send.

[OsoSlo z28]

freq, hook a brotha up.