20's weigh less????

[morcheez]

just in case anyone was worried about weight issues with bigger rims i found out something interesting today
alright i have some numbers for u ...using the same scale one right after the other.

stock rim with bridgestones 58lb
american racing rebel w/ 255/35 56.5 lb
and just b/c i have a tire laying around brand new 28lb

needless to say i am surprised the 20's weigh less

 

[bartkwan]

thanx for the info

 

[DOGO X]

Will depend on the wheels and tire combo tho.

 

[morcheez]

Will depend on the wheels and tire combo tho.

this is tru...its just that i didnt think of my rims as "light"

 

[CBRBob]

It may weigh the same or less but its WHERE the weight is. The farther out you put the RIM, the harder it will be to change the speed of the rim. So your truck will accelerate and decelerate more slowly. Hence your truck will performe worse as far as speed changes go. Typically when going + on wheel diameters, you should ALWAYS upgrade the braking systems. From 18" to 20", perhaps at min. a more agressive pad. Up to 22", most likely will need a bbk!

Think of holding 2 gallons of something against your chest, spin and stop. Then hold those gallons at arms reach, try spin and stop at the same rate you did before. You will be slower even though you have the same weight.

 

[Jonathan]

your rims weigh 33 lbs (per AR). must be in the tires?


edit- also on my scale, the stock combo weighted a tick under 60 lbs.

 

[Xacto]

It may weigh the same or less but its WHERE the weight is. The farther out you put the RIM, the harder it will be to change the speed of the rim. So your truck will accelerate and decelerate more slowly. Hence your truck will performe worse as far as speed changes go. Typically when going + on wheel diameters, you should ALWAYS upgrade the braking systems. From 18" to 20", perhaps at min. a more agressive pad. Up to 22", most likely will need a bbk!

Think of holding 2 gallons of something against your chest, spin and stop. Then hold those gallons at arms reach, try spin and stop at the same rate you did before. You will be slower even though you have the same weight.

yea, but in cheez' case i think it's only like maybe 2-4 more pounds that are spread out over 2 inch farther from the center than stock. maybe not even that much.

 

[CBRBob]

I coach people on the racetrack racing motorcycles as well as teaching people to ride on the street(MSF classes). On one particualrly fast track (VIR-full), I noticed through the esses how much effort it took to change direction. Since current bike tech makes things so light as it is, it is tough to lighten up bikes without some SERIOUS cash. Barring carbon fiber wheels (3 to 5K for TWO of them), I went with what they call 'wave' rotors. They are the same dia., but like slotted rotors on 4wheeled vehicles, they actually remove some of the material from the outside dia.(hence waves) and cutting teardrop slots in both directions completely through the disc.
I weighed these when they came in and measured the thickness. They were thicker by .5mm and weight about the same, DAMN! I though it wouldnt do much. The 1st time I rode it hard after breaking in the new pads/rotors I thought I left a bolt loose. The bike steered from side to side so quickly it almost felt wrong. I checked it all over and realized that my investment paid off!
Not long after, one of the bike magazines did a wheel weight AND inertia comparison. So whats this mean? Inertia tests=energy required to change speed of the wheel. What they found out was some of the wheels were inexpensive, $1800/pr and some were $6000/pr. The full carbon wheels (6K) weighed maybe 2-3lbs less but since a lot of that was at the outside of the wheel, it came in the BEST in the inertia tests. Some other aluminum wheels were tested against the stock wheels. Although the aftermarket wheels were a full pound lighter, the design did not lighten the wheels at the rim, only in the hub and spoke area. In fact they were slightly heavier at the rim area. The outcome.... they were almost identical in testing. In other words, $1,800 out the door(unless you just wanted looks). What made the test valid was all the wheels were the same size so it proved not just how much weight, but WHERE the weight is. So 2-4lbs may not seem like much, but spin it up and you will see it is. Just think about how much inertia that 1oz. balancing weight has in it. If it wasnt there, you could feel it.

 

[morcheez]

It may weigh the same or less but its WHERE the weight is. The farther out you put the RIM, the harder it will be to change the speed of the rim. So your truck will accelerate and decelerate more slowly. Hence your truck will performe worse as far as speed changes go. Typically when going + on wheel diameters, you should ALWAYS upgrade the braking systems. From 18" to 20", perhaps at min. a more agressive pad. Up to 22", most likely will need a bbk!

Think of holding 2 gallons of something against your chest, spin and stop. Then hold those gallons at arms reach, try spin and stop at the same rate you did before. You will be slower even though you have the same weight.

would this apply even the the 18 and 20 w/ a tire were the same diameter

 

[shook]

cant go wrong with lightweight 18s !! :top:

 

[CBRBob]

would this apply even the the 18 and 20 w/ a tire were the same diameter

YES! The RIM diameter is farther out(read more metal farther out). Picture a 18" wheel with a tall sidewall and lets say a 28" tire dia. Now make a 24" wheel with an ultra short sidewall and the same 28" tire dia. look at how much more metal it takes to make just the rim(nevermind how much longer the spokes are to reach the rim).

Now I am not sure is the math is 100% and I am making this very general but lets say we are only talking about the actual rim, not the spokes. If you consider the metal to be the same across the wheel with, an 18" wheel has 56" of rim legnth. A 24" wheel has 75" of rim legnth. So thats 33% more metal not even accounting for the extra metal for the spokes to reach the rim. Again the farther out the weight, the worse the truck will handle, speed up, slow down, respond to bumps etc.

Anyone in the performance motorcycling community can attest, the rim diameters moved around to find a good balance of stability and handling. For almost 20 years, the 17" diameter has been found to be the best. In racing they have gone DOWN to a 16.5" dia. So bigger is not always better.

 

[Xacto]

YES! The RIM diameter is farther out(read more metal farther out). Picture a 18" wheel with a tall sidewall and lets say a 28" tire dia. Now make a 24" wheel with an ultra short sidewall and the same 28" tire dia. look at how much more metal it takes to make just the rim(nevermind how much longer the spokes are to reach the rim).

Now I am not sure is the math is 100% and I am making this very general but lets say we are only talking about the actual rim, not the spokes. If you consider the metal to be the same across the wheel with, an 18" wheel has 56" of rim legnth. A 24" wheel has 75" of rim legnth. So thats 33% more metal not even accounting for the extra metal for the spokes to reach the rim. Again the farther out the weight, the worse the truck will handle, speed up, slow down, respond to bumps etc.

Anyone in the performance motorcycling community can attest, the rim diameters moved around to find a good balance of stability and handling. For almost 20 years, the 17" diameter has been found to be the best. In racing they have gone DOWN to a 16.5" dia. So bigger is not always better.

didnt someone say that the rim weighed almost the same as the tire, or maybe they said the tire weighed even more?

 

[Jonathan]

if his OD is the same, and the tire is 3-4 lbs lighter, than that would be a postive thing, not a negative cbrbob. that would mean since they basically are the same weight and height, the 20 will carry its weight closer to the inside. on the pig of an XR it shouldnt be noticeable anyways. its not a streetbike or race car, plain and simple :laugh:

 

[morcheez]

yeah i get it ...wait no i dont haha....my rim weighs 28.5 pounds and the tires weighs 28 pounds(according to my scale) so why do all the problems have to do with the rim ?:dontknow:

 

[CBRBob]

yeah i get it ...wait no i dont haha....my rim weighs 28.5 pounds and the tires weighs 28 pounds(according to my scale) so why do all the problems have to do with the rim ?:dontknow:

Remember, if the tire is the same dia and the wheels are the diff sizes the sidewall will be shorter (all else being equal) so the tire may weight less. Fine, but WHERE MOST the weight of the wheel is now farther out. Not just on the outer dia. of the tire but the wheel. Its the ability to change the speed of that weight that will be affected. Yep, the truck is 3,600lbs and what we are talking about may not seem like much but it really does affect how the ride of the truck is. With that much inertia spinning, how it reacts to the road is worse. People typically blame the extra harshness of a larger wheel/tire combo to the short sidewall, to an extent, its true. Some of it is also contributed to the inability of the tire to react fast enough to the roadway.

 

[Xacto]

Remember, if the tire is the same dia and the wheels are the diff sizes the sidewall will be shorter (all else being equal) so the tire may weight less. Fine, but WHERE MOST the weight of the wheel is now farther out. Not just on the outer dia. of the tire but the wheel. Its the ability to change the speed of that weight that will be affected. Yep, the truck is 3,600lbs and what we are talking about may not seem like much but it really does affect how the ride of the truck is. With that much inertia spinning, how it reacts to the road is worse. People typically blame the extra harshness of a larger wheel/tire combo to the short sidewall, to an extent, its true. Some of it is also contributed to the inability of the tire to react fast enough to the roadway.

you came mentioning the actual rim...correct me if im wrong...but wouldnt your point be far more valid if we were talking about the width of the rim rather than the overall diameter? wouldnt that make the largest change in outer weight? plus we dont really know for sure if it's the rim part that is so heavy. i mean for all we know the outer part of the rim could be light than the outer part of the stock rim.

 

[CBRBob]

you came mentioning the actual rim...correct me if im wrong...but wouldnt your point be far more valid if we were talking about the width of the rim rather than the overall diameter? wouldnt that make the largest change in outer weight? plus we dont really know for sure if it's the rim part that is so heavy. i mean for all we know the outer part of the rim could be light than the outer part of the stock rim.

Thats why I said all else being equal.

Again, you have a set of 5lb weights? Hold one in each hand against your chest, spin around quickly and stop quickly. Now hold them at arms legnth, try it again, you will see how much longer it will take to do the same thing.

Someone here or at CT widened stock rims. Yes it will do the same thing as you are adding weight at the outside of the rim.


OK, I found something that might explain it for ya......

So take it the same way, an 8" wide 18" and a 20" The 18" will perform better as far as changes in inertia is concerned.

I found something that might explain it for you....
http://www.sportrider.com/features/146_0402_motorcycle_wheel_comparison/moment_inertia.html

 

[Xacto]

Thats why I said all else being equal.

Again, you have a set of 5lb weights? Hold one in each hand against your chest, spin around quickly and stop quickly. Now hold them at arms legnth, try it again, you will see how much longer it will take to do the same thing.

Someone here or at CT widened stock rims. Yes it will do the same thing as you are adding weight at the outside of the rim.


OK, I found something that might explain it for ya......

So take it the same way, an 8" wide 18" and a 20" The 18" will perform better as far as changes in inertia is concerned.

I found something that might explain it for you....
http://www.sportrider.com/features/146_0402_motorcycle_wheel_comparison/moment_inertia.html

yea i understand, but when you bring 5 lbs out, you're bringing it out a good two and a half feet+ and you're moving at about 5 mph and there's alot of variables like friction, zero torque, you're basically just in constant motion and you provide a change in the moment of inertia etc. In the case of the rim it's maybe 4 lbs spread out over an extra 1.5 inches if that. Also there's a differnece between a slowing object while changing the moment of interia compared to an object that receives torque at the center, rather than from a lever arm, so it changes the whole moment of inertia concept. So i mean what you're saying is a simplified version of it and what you're saying is true, but it's not nearly that dramatic.

What i mean is....your example, that of a bike, will have much more drastic results from a few pound rim difference than a car. a car is a hell of alot heavier and a hell of alot more powerful. If you put a 100 pound subwoofer box in a minicooper, you will definitely feel the difference. if you put a 100 subwoofer box in a semi, you probably wont feel the difference.

 

[morcheez]

im still scratching my head over here :hmmmm2:

 

[Xacto]

well the twenties have a larger diameter, therefore there is more weight spread out away from the center of the wheel, which, by Newton's law, would make the wheel harder to spin. The thing is, the tire is lower profile, and the tire and wheel weigh about the same whereas i THINK the XR stock tires were heavier than the stock wheels. So, the fact that your twenties with lower profile wheels are in total 1 inch bigger in total diameter than the stockers and are 2 pounds lighter leads me to believe this moment of inertia is changing so slightly it really should not be that effective...at all. In fact id consider it possible that the moment of inertia changing in your benefit. there's just so many variable it's hard to determine.

basically id keep in mind that it's basically the same as stock right now lol