Im no expert, but the xB can only fot what a 17'?
i want to save up and put like some crazy 25's on it hahahahaa! :twisted: :twisted:

25's are not a practical size. the xB can fit a nice 18" or 19" rim. if can hold a 20", but that is not practical also.

personally I think anything over 18 inches is way to much rolling mass for this type of car....your really screwing up braking with those bigger rims

personally I think anything over 18 inches is way to much rolling mass for this type of car....your really screwing up braking with those bigger rims

Please explain if you are for real. What is the difference, if any between a 215/45r17 and a 215/35r19. You stated above that anything over 18" has too much rolling mass. Doesn't rolling mass have to do with overall height and weight? Don't wafflle and disappear from this forum and pretend you don't follow up on your own posts'. Thank you for your reply!! Dubbox

Rolling mass deals with anything pertaining to the wheels tires and breaks....as you go to a larger rim it which tends to be heavier it takes alot more breaking power to stop the automobile that is using that large rim....and also accelerating it takes power to get your car rolling which this car doesnt have to get adequate acceleration off the line....so thats why talking to someone that deals with large rims they will always recommend upgrading to large rotors to counteract the crappier breaking distance

Rolling mass deals with anything pertaining to the wheels tires and breaks....as you go to a larger rim it which tends to be heavier it takes alot more breaking power to stop the automobile that is using that large rim....and also accelerating it takes power to get your car rolling which this car doesnt have to get adequate acceleration off the line....so thats why talking to someone that deals with large rims they will always recommend upgrading to large rotors to counteract the crappier breaking distance

1. spelling

breaks=brakes
it which=it
breaking=braking

2. salespeople

if you are buying big rims, an easy add on sale would be big brakes especially, if the person being sold is ignorant. They do fill the wheels better, but mainly makes the salesperson more money.

3. engineering

rolling mass is something important on BMX bikes and motorcycles where the wheel weight represents a significant part of the overall vehicle weight. Not a negligible factor on a 100hp 2400lb vehicle. Also take into consideration stock steel wheels weigh more than larger aftermarket alloys

4. proof

something you did not provide to back up your opinions.

I decided to refresh my Physics and came up with the following conclusion: from the point of view of acceleration, an increase of X in wheel or tire weight is no worse than an increase of 2X in passenger weight. Not 6x, not 8x, just 2x worst case. This is why.

At any given speed/gear combination there is maximum torque T available at the wheels. The torque does two things: (1) opposes the rolling resistance and the aerodynamic drag and (2) accelerates the car. The equation that describes the equilibrium is:

T = I*u + M*r*a + D*r

*: denotes multiplication
T: torque at the wheels
I: total moment of inertia of the rotating parts
u: angular accelaration of the rotating parts
M: total mass of the vehicle
r: external radius of the tires
a: linear acceleration
D: total drag and rolling resistance

The first term, I*u, is the torque used in making the wheels rotate faster. The second, M*r*a, is the torque used to accelerate everything (wheels included) in the direction of movement. The third is the torque used to cancel the drag and rolling resistance.

Another way of writing the equation above is:

T/r = I*u/r + M*a + D

Now the terms are forces. The left side is the force available at the contact patch.

If the tires are not slipping, the angular acceleration and the linear acceleration are related in the following way:

a = u*r

Replacing in the equation and moving things around, we get

T/r - D = (I/r^2 + M)*a

^: denotes exponentiation (r^2 means "r squared")

We can say that the left side is the force available for acceleration. Such force accelerates an "non-rotating equivalent mass" E,

E = I/r^2 + M

Now suppose that we increase the weight of the wheels and tires by an amount X. Both the total mass and the moment of inertia will increase; let's call the new mass M' and the new moment of inertia I'. Obviously,

M' = M + X

What about I'? Well, the moment of inertia of a "punctual mass" [m] (a mass concentrated in a point) at a distance [r] from the axis of rotation is [m*r^2]. That is, the moment of inertia depends critically on the distance between the mass and the axis of rotation.

In a real wheel + tire combination the mass is distributed in different amounts at different distances from the center. In order to compute the total moment of inertia we would need to know the mass distribution and use integral calculus. We can do a simpler thing though. We can make the pessimistic assumption that all of the mass increment is located on the periphery of the tire, that is, at a distance [r] from the center. This assumption is pessimistic because in a real wheel some of the weight will be located closer that [r] and will contribute less to the total momentum (it is not too pessimistic though: most of the weight is located pretty far from the center, if not at the periphery). So now we can compute I',

I' = I + X*r^2

The new "equivalent mass" is,

E' = I'/r^2 + M' = I/r^2 + M + 2*X

In other words, from the acceleration point of view, the equivalent non-rotating mass increment corresponding to an increment X in rotating mass is - at worst - 2X.

NOTE: After doing some approximations and assumptions about weight distribution in a typical wheel + tire combo, I believe that 1.7X is a better approximation. A 10lb/wheel weight increase would not hurt acceleration worse than carrying RinTinTin.

Comments anyone?

holy crap ... :shock: ... my brain glazed over about halfway through that.

Sorry,

Did not mean to glaze over any brains..... 8) Just hate to see ignorance spread like wildfire. I was in rare form last night after being up 48 hours straight working :oops: .

Although your grasp of mathematics is VERY impressive, my non scientific butt dyno disagrees with you. I am not straight out calling bull____ on you or looking for a fight. I dont sell upgraded brake packages so I don't have alterior motives. I just disagree!!

damn, feel like i just took a math course. i follow it though, i get what he's saying about it and it makes sense. :wink:

I thought trd was for toyota racing division ...

apparently it refers to Torque divided by Radius minus Drag! :lol:

good post lavabox ...

thanks for getting my back tbblizzard. been out of school a long time now, but math never changes. :)

i have seen first hand a dyno testing out this rotational mass exercise.

late model ford mustang 4.6l, did base line runs.

went +2 on the wheels and BBK redid the dyno runs

overall it lost 2.1 hp and 2.3 lb/ft

now in my book thats not a lot to lose sleep over.

I'll tread lightly through this thread... but my understanding is that so long as the weight/mass does not increase, the larger wheel will not degrade performance in a measurable way. So if the stock steel wheels are swapped for larger yet lighter wheels the end result should be negligable. Or you could get some 13" alloys and make that car rock with all the extra power! :P

Ok then, If it has been proven that acceleration is'nt considerably affected, how about braking distances??

Lavabox, great analysis! Glad to see that there are folks here who actually think about how things work!

I'd say that the effect of the wheel mass is closer to 1X than 2X. since the moment of inertia of 1 kg of mass about the wheel axis is exactly the same as the moment of intertial of 1KG of body mass about the instantaneous pivot of the tire/ground interface. The radii are the same, so the moments of inertia are the same as well.

Unless you markedly change the rolling radius of the wheel, there will be little effect on acceleration or braking. However, going to wheels that would require body modifications implies that the rolling radius will be changed. If somebody's bucks-up enough to handle the extensive body mods, a brake and final drive change won't distress that person too much.

Rolling mass deals with anything pertaining to the wheels tires and breaks....as you go to a larger rim it which tends to be heavier it takes alot more breaking power to stop the automobile that is using that large rim....and also accelerating it takes power to get your car rolling which this car doesnt have to get adequate acceleration off the line....so thats why talking to someone that deals with large rims they will always recommend upgrading to large rotors to counteract the crappier breaking distance

1. spelling

breaks=brakes
it which=it
breaking=braking

2. salespeople

if you are buying big rims, an easy add on sale would be big brakes especially, if the person being sold is ignorant. They do fill the wheels better, but mainly makes the salesperson more money.

Comments anyone?

Oh yeah. First off if you want to disagree with someone's post, then disagree and post up some facts to back your statement up. There is no reason to make fun of his spelling or anything else for that matter. Normally I would watch and laugh, but he happens to be joining my club, so I decided to step in and put my 2 cents in.

First, you posted "spelling" and pointed out all of his mistakes, why? I don't know, maybe you're insecure or something. BUT "it which" is NOT a spelling mistake, it is a grammar mistake, he didn't spell either word, he just used them wrong. So before you go into trying to sound like a Rhodes Scholar with everyone, check yourself.

Second, almost his entire post was pertaining to stopping power when going to a bigger rim. Which is true, when you step up to bigger rims and tires you aren't required to upgrade your brakes, BUT it is a very smart thing to do. He posted 1 sentence in his entire post about acceleration and that caused you to "explain" it with a post that was longer than the Bible. Also, it looked like a cut and paste that you threw together.

Third, sales people will make a suggestion on brakes when someone buys larger rims and tires. Sure they get more money, but as I said before it is a valid point. They don't pull this ____ out of the air, maybe if you went in somewhere and bought new rims and tires and they suggested adding a new seat cover or an air freshener, then you would have a point. When going with bigger rims and tires you almost always gain added weight, added weight spinning around is harder to stop with the same brakes on a car. Upgrading brakes with larger/heavier rims and tires is a universal rule, everyone knows this. When you upgrade your brakes it shortens stopping distance, when you add weight to a vehicle or to the wheels it lengthens stopping distance. By upgrading you are balancing out the equation.

Fourth, I'm glad to see you have a groupie, maybe you 2 can talk math.

Peace,

-Z

I've seen an xB with 20' rims on it and as cool as it looked, I really would'nt see anyone actually driving it on the road. But it looked cool non-the-less.

E=mc^2

There!

A stock wheel weights about 17.5 ibs, now you can compair the weight to your aftermarket wheels... When I was switching from wheel to wheel, and i can definately tell a difference in acceleration from a stock wheel to a cast wheel to a forged wheel. I also know big brakes on a scion kills the acceleration. Talk to anyone with a big brake set up on their scion, i can assure you that they will tell you there is a difference in acceleration but does help in braking.

anything above a 20 is recommened to increase the brakes.

the mass is not the major factor, but the diameter of the wheel, Larger wheel takes more power to start and stop.

E=mc^2
There!

Ah, the physics formula that everyone can quote, but that 95% of folks cannot explain! :)

Much more important to the present discussion are:

F=ma

I=mr^2

τ=Iα

τ=Fl

Rolling mass deals with anything pertaining to the wheels tires and breaks....as you go to a larger rim it which tends to be heavier it takes alot more breaking power to stop the automobile that is using that large rim....and also accelerating it takes power to get your car rolling which this car doesnt have to get adequate acceleration off the line....so thats why talking to someone that deals with large rims they will always recommend upgrading to large rotors to counteract the crappier breaking distance

1. spelling

breaks=brakes
it which=it
breaking=braking

2. salespeople

if you are buying big rims, an easy add on sale would be big brakes especially, if the person being sold is ignorant. They do fill the wheels better, but mainly makes the salesperson more money.

Comments anyone?

Oh yeah. First off if you want to disagree with someone's post, then disagree and post up some facts to back your statement up. There is no reason to make fun of his spelling or anything else for that matter. Normally I would watch and laugh, but he happens to be joining my club, so I decided to step in and put my 2 cents in.

First, you posted "spelling" and pointed out all of his mistakes, why?

Perhaps because the reader might learn something? After all, if a writer wants to sound like he knows something about what he is talking about, it would be helpful to be able to spell the words correctly. If he has misspelled "Onomatopoeia" it would be understandable, but if he is talking as someone knowledgeable about brakes shouldn't he be able to spell "brake"?

Second, almost his entire post was pertaining to stopping power when going to a bigger rim. Which is true, when you step up to bigger rims and tires you aren't required to upgrade your brakes, BUT it is a very smart thing to do.

Now there is the mother of all broad statements! The vast majority of people "stepping up" to larger wheels won't be able to tell any difference at all, and the chances of screwing up the brake balance and ABS system makes altering the brake system a very dicy situation on an xB unless you _really_ know what you are doing. By this I mean that you should be qualified (or willing to pay someone who is qualified) to do the _engineering_, not just swap parts.

The person "upgrading" to large wheels is unlikely to actually be using the car for any sort of high performance application. The car will simply be driven or trailered to various meets for others to gawk at. Folks who will be doing track time won't be doing it on wheels that are markedly different in diameter from stock.

He posted 1 sentence in his entire post about acceleration and that caused you to "explain" it with a post that was longer than the Bible. Also, it looked like a cut and paste that you threw together.

Y'know, any time that someone is thorough, someone complains about the length of the post. I'm sorry that it didn't meet your "7 second sound bite" rule, but sometimes it just takes longer than that to explain the concepts. Engage your brain! :)

Third, sales people will make a suggestion on brakes when someone buys larger rims and tires. Sure they get more money, but as I said before it is a valid point. They don't pull this ____ out of the air,

They don't? As soon as they show me their engineering degree (or even a high school diploma!) I might be more inclined to believe them. Heck, even if they could give a rational explanation I'd love it. Unfortunately, almost every salesman's spiel boils down to "such and such magazine said", "such and such aftermarket manufacturer recommends" or the catch-all "everybody knows".

The bad thing about gaining understanding of how automobiles work is that you realize how many people are spewing pure BS for others to lap up.

When going with bigger rims and tires you almost always gain added weight, added weight spinning around is harder to stop with the same brakes on a car. Upgrading brakes with larger/heavier rims and tires is a universal rule, everyone knows this.

Who is this "everyone" and who made him an expert?

Your statement about added wheel weight being the reason for larger brakes shows that you haven't examined the situation very well. Even if you doubled the rotational inertia of the wheels it would have a trivial effect on braking. The real justification for increasing the size of the brakes is that the increased rolling radius demands an increased amount of torque from the brakes. Increased torque demands increased pad pressure and therefore increased pedal effort.

Oddly enough, this increased pedal effort and pad pressure does not mean that the brakes are going to be absorbing more energy or getting any hotter. Since the friction surface is moving more slowly the greater friction force is applied over a smaller distance and therefore generates the same heat.

When you upgrade your brakes it shortens stopping distance, when you add weight to a vehicle or to the wheels it lengthens stopping distance. By upgrading you are balancing out the equation.

Really? If the brakes are capable of taking the wheels to the point of lockup then larger brakes won't have any effect at all on stopping distance. The only reason to go to larger brakes is if repeated high-effort braking is anticipated, as in racing use. For normal street use big brakes are a waste of money and might even make the vehicle more dangerous if they are not engineered correctly.

Fourth, I'm glad to see you have a groupie, maybe you 2 can talk math.

The math isn't that difficult. Simple algebra. Perhaps you might give it a try. You might even learn something! :shock:

George

People people people,

In the words of that famous campaigner for peace and equality, Mr. King, "Why can't we all just get along?"

A) Lighten up, Francis.

B) As a professional writer, ain't none of ya gotten all your spelling and grammar write.

C) That was a colloquialism. I can use colloquialisms because I can spell colloquialism.

D) Good grammar and good writing ain't always the same thing.

E) Less ego, more team play please? I come here to enjoy and learn, not to watch ____ing matches.

F) Please review A) once more.

Tank ewe fur yore s'port.

M.e.

Wow George is the smartest guy on the entire forum I wish everyone could be as intelligent as he is :roll:

I would go on and point out all your flaws in your personality and your attempt at being a member of the human race, but I'm more focused on some punk ___ kid who tried to start something and wouldn't finish it. But I will say that I know the kind of person you are and it's pathetic.

-Z

People people people,

In the words of that famous campaigner for peace and equality, Mr. King, "Why can't we all just get along?"

A) Lighten up, Francis.

B) As a professional writer, ain't none of ya gotten all your spelling and grammar write.

C) That was a colloquialism. I can use colloquialisms because I can spell colloquialism.

D) Good grammar and good writing ain't always the same thing.

No, but bad grammar and spelling isn't a positive indicator. As a professional writer you can break the rules as you did above to achieve the effect you wish. Non-pros break the rules at random, achieving no effect beyond showing lack of understanding of the rules. If you had entered your thoughts about brakes into this thread I doubt that you would have used incorrect grammar or spelling in that post.

E) Less ego, more team play please? I come here to enjoy and learn, not to watch ____ing matches.

What better example of team play than to inform 95% of the team members that they don't need to waste money on unneeded brake upgrades?

To me "team play" does not translate to "hype the products". It means "provide information so that others can make informed decisions." Informed give-and-take is what makes discussion groups so valuable. With so much hype out there these days, a voice of restraint is sorely needed.

George <--not into B*rney-style behavior

Although your grasp of mathematics is VERY impressive, my non scientific butt dyno disagrees with you. I am not straight out calling bull____ on you or looking for a fight. I dont sell upgraded brake packages so I don't have alterior motives. I just disagree!!

i have seen first hand a dyno testing out this rotational mass exercise.

late model ford mustang 4.6l, did base line runs.
went +2 on the wheels and BBK redid the dyno runs
overall it lost 2.1 hp and 2.3 lb/ft
now in my book thats not a lot to lose sleep over.

Guys,

A dyno is designed to test torque and horsepower not acceleration or deceleration capacity. In the mustang example, there was less than a 1% loss in hp/torque. This is to be expected but is not the complete picture. What you are not calculating into the equasion is that the wheel may have a larger diameter. If the diameter of the tire did not stay EXACTLY the same your numbers could go up or down. Also the rubber compound on lower profile tires is usually much stickier, creating more drag which would also lower your numbers. If the tire diameter was larger, that would translate into more movement or speed, and therefore a wash. If the compound was stickier, that would translate into less wheelspin and again a wash or maybe an improvement in acceleration. There are three things to remember,

1. Toyota offers a factory upgrade with 18" wheels, they will be safe with regards to braking.

2. I have not yet seen a thread that states, " I got bigger wheels and damn, my car is slow now."

3. If this stuff was easy to calculate, we would not need drag strips!!

nuff said!

Rolling mass deals with anything pertaining to the wheels tires and breaks....as you go to a larger rim it which tends to be heavier it takes alot more breaking power to stop the automobile that is using that large rim....and also accelerating it takes power to get your car rolling which this car doesnt have to get adequate acceleration off the line....so thats why talking to someone that deals with large rims they will always recommend upgrading to large rotors to counteract the crappier breaking distance

1. spelling

breaks=brakes
it which=it
breaking=braking

2. salespeople

if you are buying big rims, an easy add on sale would be big brakes especially, if the person being sold is ignorant. They do fill the wheels better, but mainly makes the salesperson more money.

Comments anyone?

Oh yeah. First off if you want to disagree with someone's post, then disagree and post up some facts to back your statement up. There is no reason to make fun of his spelling or anything else for that matter. Normally I would watch and laugh, but he happens to be joining my club, so I decided to step in and put my 2 cents in.

First, you posted "spelling" and pointed out all of his mistakes, why? I don't know, maybe you're insecure or something. BUT "it which" is NOT a spelling mistake, it is a grammar mistake, he didn't spell either word, he just used them wrong. So before you go into trying to sound like a Rhodes Scholar with everyone, check yourself.

Second, almost his entire post was pertaining to stopping power when going to a bigger rim. Which is true, when you step up to bigger rims and tires you aren't required to upgrade your brakes, BUT it is a very smart thing to do. He posted 1 sentence in his entire post about acceleration and that caused you to "explain" it with a post that was longer than the Bible. Also, it looked like a cut and paste that you threw together.

Third, sales people will make a suggestion on brakes when someone buys larger rims and tires. Sure they get more money, but as I said before it is a valid point. They don't pull this ____ out of the air, maybe if you went in somewhere and bought new rims and tires and they suggested adding a new seat cover or an air freshener, then you would have a point. When going with bigger rims and tires you almost always gain added weight, added weight spinning around is harder to stop with the same brakes on a car. Upgrading brakes with larger/heavier rims and tires is a universal rule, everyone knows this. When you upgrade your brakes it shortens stopping distance, when you add weight to a vehicle or to the wheels it lengthens stopping distance. By upgrading you are balancing out the equation.

Fourth, I'm glad to see you have a groupie, maybe you 2 can talk math.

Peace,

-Z



LOL :D :D :D

George is my idol and mentor, not my groupie!
Also my deepest apologies to dinkjs, no harm meant.

1. spelling
equasion = equation

2. kharma's a _____

3. I was never talking about upgrading the brakes on a Scion. I was talking about other applications, such as the people with the SUVs that go from stock 16" rims to 22" or bigger.

"nuff said!"

-Z

Wow George is the smartest guy on the entire forum I wish everyone could be as intelligent as he is :roll:

I would go on and point out all your flaws in your personality and your attempt at being a member of the human race, but I'm more focused on some punk ___ kid who tried to start something and wouldn't finish it. But I will say that I know the kind of person you are and it's pathetic.

-Z


Flaws? Pathetic? Isn't that the kettle calling the pot black?

Wow.. you guys' knowledge of physics and math is impressive.

But I like to keep all of my mental capacity focused on three things:

1. Gettin booty

2. Gettin more booty

3. Gettin a wider variety of booty


:twisted:

1. spelling
equasion = equation

2. kharma's a _____

3. I was never talking about upgrading the brakes on a Scion. I was talking about other applications, such as the people with the SUVs that go from stock 16" rims to 22" or bigger.

"nuff said!"

-Z


1. you got me
2. ???
3. Where did you indicate you were talking about SUV's?
4. Isn't this thread about scions?
5. You jumped into this thread _____ing about protecting your girlfriend, why can't he stand up for himself and defend his own thread

1. you got me
2. ???
3. Where did you indicate you were talking about SUV's?
4. Isn't this thread about scions?
5. You jumped into this thread _____ing about protecting your girlfriend, why can't he stand up for himself and defend his own thread

3. When did I indicate I was talking about Scions?

The whole thing started when someone brought up a brake uprgade when going to larger wheels. You came in and claimed that it's BS and that going to larger rims/tires does not affect stopping distance. Which maybe in the magical land of douche bags that you live in it doesn't affect stopping distance, but in the real world it does. We stopped talking about Scions when you posted up the copy and pasted equations to show everyone how smart you were. Those weren't Scion equations.

5. Why can't you defend your thread without the help of your ___ clown partner?
-Z

1. you got me
2. ???
3. Where did you indicate you were talking about SUV's?
4. Isn't this thread about scions?
5. You jumped into this thread _____ing about protecting your girlfriend, why can't he stand up for himself and defend his own thread

3. When did I indicate I was talking about Scions?

The whole thing started when someone brought up a brake uprgade when going to larger wheels. You came in and claimed that it's BS and that going to larger rims/tires does not affect stopping distance. Which maybe in the magical land of douche bags that you live in it doesn't affect stopping distance, but in the real world it does. We stopped talking about Scions when you posted up the copy and pasted equations to show everyone how smart you were. Those weren't Scion equations.

5. Why can't you defend your thread without the help of your ___ clown partner?
-Z

1. you got me
2. ???
3. Where did you indicate you were talking about SUV's?
4. Isn't this thread about scions?
5. You jumped into this thread _____ing about protecting your girlfriend, why can't he stand up for himself and defend his own thread

3. When did I indicate I was talking about Scions?

The whole thing started when someone brought up a brake uprgade when going to larger wheels. You came in and claimed that it's BS and that going to larger rims/tires does not affect stopping distance. Which maybe in the magical land of douche bags that you live in it doesn't affect stopping distance, but in the real world it does. We stopped talking about Scions when you posted up the copy and pasted equations to show everyone how smart you were. Those weren't Scion equations.

5. Why can't you defend your thread without the help of your ___ clown partner?
-Z


Well, I guess you are right. You are so mature for your age. Your intelligence is superior. Everything you say is right. It is obvious that nobody here knows what they are talking about. I must just be jealous that you won't be my ___ clown partner. I guess I will go off with my current ___ clown partner and play in the magical land of douche bags. Maybe some day you will come and visit? The herbal scents are quite beautiful this time of year.